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This is to certify that the
thesis entitled

INTERACTION EVALUATION OF GLYPHOSATE,
GLUFOSINATE, CHLORIMURON AND
THIFENSULFURON COMBINATIONS

presented by

Rachel Kaye Bethke

has been accepted towards fulfillment
of the requirements for the

MS. degree in CROP AND SOIL SCIENCE

 

 

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INTERACTION EVALUATION OF GLYPHOSATE, GLUFOSINATE,
CHLORIMURON AND THIFENSULFURON COMBINATIONS

By

Rachel Kaye Bethke

A THESIS
Submitted to
Michigan State University
In partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Crop and Soil Science

2010

ABSTRACT

INTERACTION EVALUATION OF GLYPHOSATE, GLUFOSINATE,
CHLORIMURON AND THIFENSULFURON COMBINATIONS

By
Rachel Kaye Bethke
The stacking of genes to provide resistance to several herbicides
previously injurious to a crop provides new opportunities for control of a larger
range of species and herbicide resistant weeds. Studies were conducted in the
field in 2008 and 2009 and in the greenhouse from 2008 to 2010 to evaluate the
combination of glyphosate and glufosinate and the sulfonylurea herbicides,
chlorimuron and thifensulfuron on four weeds prevalent in Michigan cropping
systems; common lambsquarters, velvetleaf, giant foxtail and Canada thistle.
Antagonism was observed with combinations of glyphosate and glufOsinate,
glyphosate and chlorimuron and glufosinate and both sulfonylureas.
Fluorescence measurements of leaves of the treated plants were taken in the
greenhouse at 2, 4, 6, 8, 24, 48 and 72 hours after treatment to determine the
time of herbicides injury to the plant photosynthetic system. Fluorescence
parameters showed glufosinate acted within 2 hours after treatment and
glyphosate within 24 hours after treatment. Absorption and translocation of 14C-
glyphosate and 14C-chlorimuron was examined in the greenhouse to. determine
the basis for the observed interactions. The addition of chlorimuron increased
absorption and translocation of 14C-glyphosate and the addition of glyphosate to
14C-chlorimuron also increased absorption and either decreased or had no effect

on translocation out of the treated leaf.

Dedication Page

This thesis is dedicated to my father, John Carl Bethke. Whom instilled in me a
love of plants and agriculture. I am ever grateful to be your daughter.

ACKNOWLEDGEMENTS

I wish to thank Dr. Donald Penner for serving as my major professor and mentor
for my masters studies at Michigan State University. His dedication and professionalism
brought me to enjoy and understand the act of research first as an undergraduate at
Michigan State and throughout my masters. I would also like to thank Dr. Wesley
Everman, Dr. Christy Sprague and Dr. Daniel Brainard for serving on my guidance
committee and sharing their experience and guidance with me. I would like to extend a
special thank you to Jan Michael for technical, statistical and emotional support
throughout my program. Her dedication, attention to detail and wonderful personality has
been a welcome joy in my research. I would also like to thank Gary Powell, Andy
Chomas and Erin Taylor for their assistance in field and lab research. I am very
appreciative to everyone who has helped me with my field studies and the use of the

Sprague lab. I would especially like to thank William Molin at the USDA-ARS research
station in Stoneville, MS for his assistance with my fluorescence research, thank you for
sharing your time, equipment and knowledge throughout my project.
Many graduate students have been integral to my research. Kate Withers, Tim
Boring, Kelly Barnett, Calvin Glaspie, Molly Buckham, Alex Lindsey, Laura Bast, and
Stephanie Peck have been the best of friends and the greatest colleagues I could ever
ask for. I could not thank my undergraduate workers enough for their assistance in the
grind of my project. Demitria Gavit, Allison Wielfart, Adam Wentworth and Lauryn
Schroeder have all been eager students to learn and devote their time to research.
Finally I wish to thank my family, John, Ruth, Norma and Nick for being a constant
source of encouragement during my studies. I am eternally grateful for all of their love,
support and positive attitude shared with me during my time at Michigan State

University.

TABLE OF CONTENTS

LIST OF TABLES vii

LIST OF FIGURES ............................................................................... xi

CHAPTER 1

LITERATURE REVIEW
INTRODUCTION ..................................................................... 1
THE IMPACT OF HERBICIDE RESISTANT WEEDS ........................ 2
WEEDS OF INTEREST .............................................................. 4
HERBICIDES OF INTEREST ......................................................... 8
TANK-MIX INTERACTIONS OF HERBICIDES ................................. 15
ABSORPTION AND TRANSLOCATION OF HERBICIDES .......... 21
LITERATURE CITED ................................................................. 24

CHAPTER 2

EARLY DETECTION OF HERBICIDE INTERACTION WITH FLUORESCENCE
MEASURMENTS

ABSTRACT ............................................................................ 35
INTRODUCTION ..................................................................... 36
MATERIALS AND METHODS .................................................... 39
RESULTS AND DISCUSSION ................................................... 41
LITERATURE CITED .......... 54
CHAPTER 3 '

EVALUATION OF THE INTERACTION BETWEEN GLYPHOSATE AN
GLUFOSINATE

ABSTRACT ............................................................................ 55

INTRODUCTION ..................................................................... 56

MATERIALS AND METHODS .................................................... 61

RESULTS AND DISCUSSION ......... 67

LITERATURE CITED ............ 79
CHAPTER4

EVALUATION OF THE INTERACTION BETWEEN GLYPHOSATE AND THE
SULFONYLUREA HERBICIDES, CHLORIMURON AND THIFENSULFURON

ABSTRACT ............................................................................ 83
INTRODUCTION ..................................................................... 84
MATERIALS AND METHODS .................................................... 87
RESULTS AND DISCUSSION .................................................... 95
LITERATURE CITED ............................................................... 115

CHAPTER 5

EVALUATION OF THE INTERACTION BETWEEN GLUFOSINATE AND THE
SULFONYLUREA HERBICIDES, CHLORIMURON AND THIFENSULFURON

ABSTRACT ........ 118
INTRODUCTION ..................................................................... 119
MATERIALS AND METHODS ................................................... 121
RESULTS AND DISCUSSION .................................................... 127
LITERATURE CITED ............................................................... 141
APPENDIX ...................................................................................... 144

vi

LIST OF TABLES
Table 1. Herbicide combinations applied in fluorescence studies ......... 47

Table 2. Herbicide combinations applied in field studies 2008 and
2009 ........................................................................................ 72

Table 3. Herbicide combinations applied in fluorescence studies .......... 73

Table 4. Visual control 7 and 28 days after treatment of velvetleaf,
common lambsquarters and giant foxtail when applied with combinations

of glyphosate and glufosinate in 2009 field study ............................... 74
Table 5. Herbicide combinations applied in field studies 2008 and

2009 ....................................................................................... 103
Table 6. Herbicide combinations applied in fluorescence studies ......... 104

Table 7. Herbicide treatments for 14C absorption and translocation
studies .................................................................................... 105

Table 8. Visual control 7 and 28 days after treatment of velvetleaf,
common lambsquarters and giant foxtail when applied with combinations
of glyphosate and glufosinate in 2009 field study .............................. 106

Table 9 Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on giant foxtail 7, 14, 21 and 28 days after
treatment ................................................................................. 107

Table 10. Herbicide combinations applied in field studies 2008 and
2009 ....................................................................................... 133

Table 11. Herbicide combinations applied in fluorescence studies ....... 134

Table 12. Visual control 7 and 28 days after treatment of velvetleaf,
common lambsquarters and giant foxtail when applied with combinations
of glufosinate and chlorimuron in 2009 field study.................... ......... 135

Table 13. Visual control 7 and 28 days after treatment of velvetleaf,
common lambsquarters and giant foxtail when applied with combinations
of glyphosate, glufosinate and chlorimuron in 2009 field study.. ........ 144

Table 14. Percent control compared to the untreated for combinations of

glyphosate and glufosinate on Canada thistle 5, 7, 14, 21 and 28 days
after treatment ......................................................................... 145

vii

Table 15. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of glyphosate and
glufosinate for canada thistle and velvetleaf ................................. 146

Table 16. Percent control compared to the untreated for combinations of
glyphosate and glufosinate on velvetleaf7, 14,21 and 28 days after
treatment ............................................................................... 147

Table 17. Percent control compared to the untreated for combinations of
glyphosate and glufosinate on common lambsquarters 5, 7, 14, 21 and 28
days after treatment ...... 148

Table 18. Percent control compared to the untreated for combinations of
glyphosate and glufosinate on giant foxtail 5, 7, 14, 21 and 28 days after
treatment ................................................................................ 149

Table 19. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of glyphosate and
glufosinate for common lambsquarters and giant foxtail. . . . . . . . . . .. ........ 150

Table 20. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on Canada thistle 7, 14, 21 and 28 days after
treatment ................................................................................ 151

Table 21. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of chlorimuron and
glyphosate for canada thistle and velvetleaf ................................... 152

Table 22. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on velvetleaf 7, 14, 21 and 28 days after
treatment ................................................................................. 153

Table 23. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on common lambsquarters 7, 14, 21 and 28
days after treatment ......................................................... . ......... 154

Table 24. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of chlorimuron and
glyphosate for common lambsquarters and giant foxtail ..................... 155

Table 25. Percent control compared to the untreated for combinations of

glyphosate and chlorimuron on giant foxtail 7, 14, 21 and 28 days after
treatment ................................................................................. 156

viii

Table 26. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on Canada thistle 7, 14, 21 and 28 days after
treatment ................................................................................ 157

Table 27. Fresh weight and height reduction compared to the Untreated
control 28 days after treatment for combinations of chlorimuron and
glufosinate for canada thistle and velvetleaf ................................... 158

Table 28. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on velvetleaf 7, 14, 21 and 28 days after
treatment ................................................................................. 159

Table 29. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on common lambsquarters 7, 14, 21 and 28
days after treatment ................................................................... 160

Table 30. Fresh weight and height reduction compared to the Untreated
control 28 days after treatment for combinations of chlorimuron and
glufosinate for common lambsquarters and giant foxtail ..................... 161

Table 31. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on giant foxtail 7, 14, 21 and 28 days after
treatment ................................................................................. 162

Table 32. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on Canada thistle 7, 14,21 and 28 days
after treatment .......................................................................... 163

Table 33. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of thifensulfuron and
glufosinate for canada thistle and velvetleaf ................................... 164

Table 34. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on velvetleaf 7, 14, 21 and 28 days after
treatment ................................................................................. 165

Table 35. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on common lambsquarters 7, 14, 21 and 28
days after treatment ......................................................... . ......... 166

Table 36. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of thifensulfuron and
glufosinate for common lambsquarters and giant foxtail ..................... 167

Table 37. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on giant foxtail 7, 14, 21 and 28 days after
treatment .......... 168

Table 38. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on Canada thistle 7, 14, 21 and 28 days
after treatment ......................................................................... 169

Table 39. Fresh weight and height reduction compared to the Untreated
control 28 days after treatment for combinations of glyphosate and
thifensulfuron on Canada thistle and velvetleaf ............................... 170

Table 40. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on velvetleaf 7, 14,21 and 28 days after
treatment ................................................................................. 1 71

Table 41. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on common lambsquarters 7, 14, 21 and 28
days after treatment ................................................................... 172

Table 42. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of glyphosate and
thifensulfuron on common lambsquarters and giant foxtail ................. 173

Table 43. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on giant foxtail 7, 14, 21 and 28 days after
treatment ......... 174
Table 44. Fv/Fm values of Canada thistle in fluorescence studies ........ 175

Table 45. Fv/Fm values of common lambsquarters in fluorescence
studies .................................................................................. 176

LIST OF FIGURES

Figure 1. Chlorophyll fluorescence induction curve (Kautsky/OJIP curve)
of a 15 minute dark adapted healthy Canada thistle leaf ...................... 48

Figure 2. Species differences in Fv/Fm by herbicide mode of action (a)
glyphosate (b) glufosinate (c) chlorimuron on (0) giant foxtail, (I)
velvetleaf, (A) Canada thistle, and (x) common lambsquarters ............. 49

Figure 3. Species differences in ij by herbicide mode of action (a)
glyphosate (b) glufosinate (c) chlorimuron on (9) giant foxtail, (I)
velvetleaf, (A) Canada thistle, and (x) common lambsquarters ............ 50

Figure 4. Species differences in OJIP curve by herbicide mode of action
48 hours after treatment (a) glyphosate (b) glufosinate (c) chlorimuron on
(0) giant foxtail, (I) velvetleaf, (A) Canada thistle, and (x) common
lambsquarters .......................................................................... 51

Figure 5. Fv/Fm differences in mode of action by species (a) Canada
thistle (b) common lambsquarters on (9) control, (I) 1X glyphosate, (A)
1X glufosinate, and (x) 1X chlorimuron. Vertical bars represent Fisher's
protected LSD at p=0.05 significance level, when not present = Not
significant ................................................................................. 52

Figure 6. OJIP curve differences in mode of action by species 48 hours
after treatment (a) Canada thistle (b) common lambsquarters on (9)
control, (I) 1X glyphosate, (A) 1X glufosinate, and (x) 1X chlorimuron...53

Figure 7. Glyphosate(GLY) and glufosinate(GLU) on Canada thistle (a)
and velvetleaf (b) visual observations in the greenhouse 28 days after
treatment. Antagonism by Colby's method indicated by a (-). LSD = 15 (a)
and 10 (b) .................................................................................. 75

Figure 8. Glyphosate(GLY) and glufosinate(GLU) on giant foxtail visual
observations in the greenhouse 5 DAT (a) and 28 DAT(b). Antagonism
and synergism by Colby's method indicated by a (-) or (+) respectively.
LSD = 8 .................................................................................... 76

Figure 9. Fv/Fm of glyphosate(GLY) and glufosinate(GLU) on Canada
thistle. Where a (* ) indicates the combination is significantly different from
glyphosate applied alone and a (0) indicates significantly different from
glufosinate applied alone .............................................................. 77

Figure 10. Fv/Fm of glyphosate and glufosinate on Canada thistle at (a) 2

hours after treatment and (b) 72 hours after treatment. Where a (*)
indicates the combination is significantly different from the control ......... 78

xi

Figure 11. Chlorimuron(CHL) and glyphosate(GLY) (a) and
thifensulfuron(THl) and glyphosate (b) on common lambsquarters °/o
height reduction from the control in the greenhouse 28 days after
treatment. Synergism by Colby' s method indicated by a (+). LSD: 5 for 7
DAT and LSD: 8 for 28 DAT ....................................................... 108

Figure 12. Chlorimuron(CHL) and glyphosate(GLY) on velvetleaf(ABUTH)
and common lambsquarters(CHEAL) % height reduction in the ,
greenhouse 28 days after treatment. Antagonism and synergism by
Colby's method indicated by a (-) or (+) respectively. LSD = 9 for ABUTH
and LSD = 17 for CHEAL ............................................................ 109

Figure 13. Fv/Fm of glyphosate(GLY) and Chlorimuron(CHL) on Canada
thistle at (a) 2 hours after treatment and (b) 72 hours after treatment.
Where a * indicates significant difference from the control. (a) LSD =
0.0356 and (b) LSD =0.1795 ........................................................ 110

Figure 14. 14C-glyphosate absorption in (a) Canada thistle, (b) common
lambsquarters and (0) giant foxtail. A (*) indicates significantly different
from herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT,
days after treatment; GLY, glyphosate ............................................ 111

Figure 15. 14C-glyphosate translocation out of the treated leaf by (a)
Canada thistle, (b) common lambsquarters and (c) giant foxtail. A (*)
indicates significantly different from herbicide alone at that time.
Abbreviations: CHL, chlorimuron; DAT, days after treatment; GLY,
glyphosate ............................................................................... 1 12

Figure 16. 14C-chlorimuron absorption in (a) Canada thistle, (b) common
lambsquarters and (0) giant foxtail. A (*) indicates significantly different
from herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT,
days after treatment; GLY, glyphosate ........................................... 113

Figure 17. 14C-chlorimuron translocation out of the treated leaf by (a)
Canada thistle, (b) common lambsquarters and (c) giant foxtail. A (*)
indicates significantly different from herbicide alone at that time.
Abbreviations: CHL, chlorimuron; DAT, days after treatment; GLY,
glyphosate ............................................................................... 1 14

Figure 18. Chlorimuron(CHL) and glufosinate(GLU) on common
lambsquarters visual observations in the greenhouse (a) 7 days after
treatment and (b) 28 days after treatment. Synergism by Colby's method
indicated by a (+). LSD = 5 for 7 DAT and LSD = 12 for 28 DAT .......... 136

xii

Figure 19. Chlorimuron(CHL) and glufosinate(GLU) on giant foxtail visual
observations in the greenhouse (a) 7 days after treatment and (b) 28 days
after treatment. Antagonism and synergism by Colby's method indicated
by a ( ) or (+) respectively. LSD: 5 for 7 DAT and LSD: 8 for 28

DAT ........................................................................................ 137

Figure 20. Thifensulfuron(THl) and glufosinate(GLU) on velvetleaf visual
observations in the greenhouse (a) 7 days after treatment and (b) 28 days
after treatment. Antagonism and synergism by Colby's method indicated
by a (-) or (+) respectively. LSD = 5 for 7 DAT and LSD : 8 for 28

DAT ........................................................................................ 138

Figure 21. Fv/Fm of glufosinate(GLU) and Chlorimuron(CHL) combinations
on Canada thistle. Where a (*) indicates the combination is significantly
different from glufosinate applied alone .......................................... 139

Figure 22. Fv/Fm of glufosinate(GLU) and Chlorimuron(CHL) on Canada
thistle at (a) 2 hours after treatment and (b) 72 hours after treatment.
Where a (*) indicates the combination is significantly different from the
control ..................................................................................... 140

xiii

CHAPTER 1
LITERATURE REVIEW

Genetically modified crops resistant to glyphosate, glufosinate, and the
sulfonylurea herbicides, will soon be commercially available. Hybrids already on
the market include glyphosate and glufosinate stacked resistance under the trade
name HerculexT'“ by Dow Agrosciences (Anonymous 2010a). Dow Agrosciences
has also released SmartStaxTM corn hybrids with Monsanto for the 2010 growing
season. It is the first eight-gene stacked corn hybrid, with herbicide resistance to
both glyphosate and glufosinate (Anonymous 2008). Du-Pont Pioneer is currently
developing Optimum®GAT® (356043) soybean which will be resistant to
glyphosate and the sulfonylurea herbicides. This new trait has been under field
test since 2003 and is set to release in 2013 or 2014 (Willits 2009). The GAT®
gene (glyphosate acetyltransferase) catalyzes the acetylation of glyphosate to
the inactive N-acetyl glyphosate (NAG) form (Siehl et al. 2007). Pioneer is also
developing a corn hybrid (98140) with Optimum®GAT® technology ineluding
resistance to glufosinate still pending approval (W illits 2009). Resistance to these
herbicides will give producers new opportunities for herbicide management
systems. However, the tank-mixing of these herbicides could result in
unexpected interactions such as reduced, improved, or similar weed control

compared to the herbicides applied alone.

THE IMPACT OF HERBICIDE RESISTANT WEEDS

Plants can generally react in one of three ways to the application of an
herbicide; susceptibility, tolerance or resistance (LeBaron and Gressel 1982).
Susceptibility occurs when a plant is treated with a herbicide and becomes
injured. Generally, tolerance and resistance refer to conditions where the plants
withstand herbicide applications (Gressel 1985). Tolerance is referred to as the
natural occurring non-phytotoxic response of a weed species or crop to a specific
herbicide (Holt and Lebaron 1990). Resistance often involves the concept of
selection of a physiological mechanism in a weed after repeated exposure to an
herbicide. Herbicide resistance was first reported by Switzer for 2,4-D in wild
carrot (Switzer 1952).

To date there are 347 herbicide resistant biotypes in 195 species occurring in
over 340,000 fields across the world (Heap 2009a). Prior to development of
herbicide resistance, many of these weed species were difficult to control, and
present an even greater challenge for economically sound management.
Worldwide, 108 weed species have been confirmed resistant to ALS-inhibiting
herbicides, and eighteen species have been confirmed resistant to glyphosate
(Heap 2009a). The newest weed in the United States with confirmed resistance
to glyphosate is giant ragweed (Ambrosia trifida L.), found in a population in
Tennessee (Norsworthy et al. 2010).

The normal variability in response of weeds to a herbicide can allow

populations of weeds with enhanced tolerance to increase with increased use of
2

the herbicide even though the weed can still be controlled at a higher rate (Owen
and Zelaya 2005). Shifts in weed populations; either to resistant populations, or
other tolerant species, due to overuse of one mode of action (MOA) have been
observed in a few studies (Davis et al. 2009; Heard et al. 2003; Hugh and
Reboud 2009; Wilson et al. 2009). Repeated use of glyphosate over 6 years led
to a population shift from populations of kochia (Kochia scoparia L. Schrad.) and
wild proso millet (Panicum miliaceum L. ) to populations of common
lambsquarters (Chenopodium album L. ) (Wilson et al. 2009). After four years of
non-glyphosate postemergence herbicide use, the ratio of glyphosate resistant
horseweed (Conyza Canadensis L. Cronq.) to glyphosate susceptible biotypes
shifted from 3:1 to a ratio of 1:6 (Davis et al. 2009). A four year experiment in
Canada showed that applying ALS inhibiting herbicides increased the occurrence
of the resistant weed biotypes (Hugh and Reboud 2009).

Resistance to multiple herbicides is also becoming a large problem in several
areas. Common waterhemp (Amaranthus rudis Sauer) resistant to both
glyphosate and thifensulfuron has been confirmed in Missouri (Legleiter and
Bradley 2008). Common waterhemp also has been confirmed resistant to the
protoporphyrinogen oxidase (PPO) - inhibiting herbicides such as lactofen,
fomesafen and acifluorfen (Legleiter and Bradley 2008; Patzoldt et al. 2005). To
control weeds that are resistant to multiple herbicides it is important to use
different herbicide chemistries to achieve complete control so the resistant genes

will not persist in the seedbank.

WEEDS OF INTEREST

Weeds are a problem in all cropping situations. Producers work diligently to
protect their investment by using methods of weed control such as applying
herbicides to control competitive weeds that can be detrimental to cr0p yields.
Knowledge of herbicide programs specific to a farmers weed problem is
necessary to ensure adequate control and protect the environment. Michigan
producers are generally confronted with weeds adapted to the Michigan
environment. lnforrnation on weed density thresholds for specific species and
optimum height for control is valuable when developing an herbicide program.
The weeds studied for this research were chosen because they are common
weeds in Michigan agronomic systems. Two annual broadleaves; common
lambsquarters (Chenopodium album L.) and velvetleaf (Abutilon theophrasti
Medik.); an annual grass species; giant foxtail (Setaria faberi Herrm.), and the
perennial; Canada thistle (Cirsium arvense L. Scop.), were chosen to be the

focus of this study.

Common Lambsquarters (Chenopodium album L.) Common lambsquarters
is a summer annual broadleaf weed which belongs to the goosefoot
(Chenopodiacea) family. It is a worldwide problem and considered one of
the most important weeds in agriculture (Heap 2009a). It is native to
Europe and Asia, and is one of the five most widely distributed weeds
(Holm et al. 1977). Common lambsquarters is a problem due to the

species high fecundity; producing over 70,000 seeds per plant Which can

persist up to 78 years in the soil. The dimorphic characteristics of common
lambsquarters seed results in a relatively germinable thin-walled brown
seed that will germinate the next year and a darker seed that exhibits
primary dormancy (Harper et al. 1970). Common lambsquarters also may
hybridize with the other Chenopodium species, opening the door for new
genetic populations and subsequently a variety of subspecies, varieties

and forms (Abrams 1944).

Common lambsquarters has populations that are resistant to a variety of
herbicide Modes of Action across the country and the world. The first report of
triazine (photosystem II (PSII) inhibitor) resistance was common lambsquarters in
1975 in Michigan; since that time 18 countries have reported PSll inhibitor
resistance (Heap 2009a). Common lambsquarters has also exhibited resistance
to the ALS-inhibitors; thifensulfuron and imazamox in Michigan, Ohio, and
Ontario (Heap 2009a).

Resistance to glyphosate has not been reported for common lambsquarters.
However, producers and extension agents have reported problems with
controlling common lambsquarters with glyphosate in the Midwest (Owen and
Zelaya 2005; Wilson et al. 2009). These studies attributed the shift of weed
population to glyphosate tolerant biotypes of common lambsquarters to the
natural variability in tolerance and repeated use of low rates of glyphosate.
However, this study also found that weed populations shifted to common
lambsquarters even when no glyphosate was applied, telling that common

lambsquarters is a very competitive weed even without herbicide resistance.

5

Velvetleaf (Abutilon theaphrasti Medik.) Velvetleaf is a summer annual
which belongs to the Malva (Malvacea) family. Velvetleaf is a very
competitive weed and is especially a problem in soybean production
(Eaton et al. 1976; Hagood et al. 1980). Velvetleaf was introduced from
China in the 1700’s as a fiber crop (Spencer 1984). However, due to the
lack of good fiber quality velvetleaf was not readily used. It became a
successful weed due to the lack of control, seed dormancy, high
germination depths, and tolerance to herbicides (Spencer 1984). Until
glyphosate was introduced, velvetleaf was one of the most common weed
problems in corn, soybean, and cotton in the United States due to the low
efficacy of the preplant and preemergence herbicide options (Harvey et al.
1977; Herr and Stroube 1970).

Velvetleaf has been confirmed resistant to the triazines, which was first
reported in 1984 in Maryland and reported in 2004 in Michigan (Heap 2009a).
The mechanism for resistance is increased herbicide metabolism due to
enhanced glutathione s-transferase activity (Anderson and Gronwald 1991).

Velvetleaf has also been reported to have differential tolerance to glyphosate but

no known resistance has been reported (Kapusta et al. 1994).

Giant Foxtail (Setaria faberi Herrm.) Giant foxtail is a summer annIIal grass

in the grass (Poacea) family which reproduces by seed. It is a native of

eastern Asia (Wang et al. 19953; Wang et al. 1995 b) and has expanded
due to human influence (Haflinger and Scholz 1980). It is an economically
important weed and is considered a nearly monomorphic species (Wang et
al. 1995a; Wang et al. 1995 b) having only slight biotype differentiations in
adaxial leaf blade pubescence (Pohl 1962). It is a C4 plant and Competes
efficiently because of its plastic growth (Dekker 2003). Giant foxtail is
extremely competitive in corn reducing yields 13-14% with only three
plants per foot of a row in Michigan (Anonymous 2005). Allelopathic effects
of giant foxtail have been found to reduce corn growth (Bell and Koeppe
1972)

Resistance to the triazine herbicides in giant foxtail was first confirmed in
1984 in Maryland and most currently with resistance to the ALS inhibitors in 2006
in Michigan (Heap 2009a). Giant foxtail has also been found with resistance to

the ACCase inhibitors in Wisconsin and Iowa (Heap 2009a). There is no

confirmed glyphosate resistance in giant foxtail.

Canada thistle (Cirsium arvense L. Scop.) Canada thistle, a member of the
Aster (Asteraceae) family, is a perennial weed that grows from seed and
underground roots. It is considered a potential model weed due to the
weedy characteristics, small genome, cDNA library, adaptability to a wide
range of conditions, distribution, and economic impact (Chao et al. 2005).
This species has significant ecotype differences depending on location of

root stock source with differences in leaf, seed and flower morphology,

7

which can lead to differential response of herbicides (Hodgson 1964).
Proper control and management of Canada thistle requires that the roots
of the plant be killed or somehow removed. Shoot elongation and flowering
are induced with a 16h photoperiod. Without this photoperiod they remain
low growing rosettes (Hunter and Smith 1972). The physiological stage of
growth has been important for translocation of systemic herbicides to the
roots; more glyphosate is translocated to the roots when applied at the
rosette stage than the bud stage (Hunter 1995).

The only reports of herbicide resistance in Canada thistle were to the

synthetic auxins in 1979 and 1985 in Sweden and Hungary, respectively (Heap

2009a).

HERBICIDES OF INTEREST

Glyphosate. Glyphosate (N-(phosphonomethyl)-glycine) is a broad-
spectrum organophosphorus postemergence herbicide that inhibits the 5-
enolpyruvylshikimate-3—phosphate synthase enzyme (EPSP). This enzyme
is involved in the synthesis of the aromatic amino acids phenylalanine,
tyrosine, and tryptophan as well as secondary plant products (Amrhein et
al. 1980; Jaworski 1972). Inhibition of EPSP synthase is competitive with
respect to phosphoenolyruvate and uncompetitive with respect to
shikimate-3-phosphate (Boocock and Coggins 1983). This inhibition leads

to an accumulation of shikimate in the primary vacuole of glyphosate-

treated tissue (Hollander-Czytko and Amrhein 1983). Observed glyphosate
phytotoxicity in plants is not only due to the inhibition of aromatic amino
acids (Duke 1985), but also inhibits the accumulation of a chlorophyll
precursor; 5-aminolevulinic acid (ALA), which results in reduced
chlorophyll synthesis (Kitchen et al. 1981) and a decrease in all porphyrin
enzymes (Hoagland and Duke 1982). The cause of this reduced ALA
accumulation is thought to be due to a reduction of q-ketoglutarate
production by glyphosate (Hoagland and Duke 1982). Glyphosate has a
general effect on all plant cellular structures with which it comes in contact.
These general effects include; swelling of the chloroplast envelope and
thylakoids, and swelling of the endoplasmic reticulum (Pihankaski and
Pihankaski 1980). Glyphosate also has a feed-back inhibition on
phenylalanine ammonia—lyase (PAL), an enzyme in the synthesis of the
amino acids phenylalanine and tyrosine. Glyphosate decreases their
synthesis, which leads to decreased synthesis of phenolic compounds
resulting in decreased feed-back inhibition of PAL synthesis (Duke and
Hoagland 1984).

Glyphosate sensitive weeds exhibit early symptomology of chlorosis followed
by necrosis usually from 2 to 10 days after application (Baird et al. 1971). Injury
symptoms generally appear first on immature leaves and at growing pOints (Baird

et al. 1971 ). Glyphosate gives a wide range of control of annual and perennial

weeds and generally is considered very phytotoxic to annual grasses (Sprankle

9

1974). After what seems like complete necrosis and leaf drop, compensatory
growth of the weeds can occur. This positive response of plants to injury is found
commonly in perennial and woody species but also is exhibited as witch’s broom
in grasses and meristematic regrowth in dicots. This can result in greater than
expected dry weights than controls (Belsky 1986). Glyphosate resistant crops
allow selected glyphosate formulations to be used postemergence throughout the
growing season.

Glyphosate efficacy on weeds of interest. Glyphosate is a non-selective
herbicide; however certain weed species are inherently tolerant to glyphosate.
Velvetleaf exhibits a low level of tolerance to glyphosate (Kapusta et al. 1994),
whereas the Poacea species like giant foxtail, are susceptible (Sprankle 1974).
Velvetleaf’s tolerance to glyphosate has been attributed to an elevated EPSP
, synthase level in many species that will compensate for the glyphosate induced
reduction of EPSP synthase (Amrhein et al. 1983). Common lambsquarters has
been shown to have differential susceptibility to glyphosate application, the
reason is not entirely known. Some have reported differences in control based on
growth stage (Jaworski 1972; Lich et al. 1997; Ziska et al. 1999) and others have
reported no differences between growth stages in response (Sikkema et al. 2004;
Tharp et al. 1999). These differences have been attributed to different biotypes at
these locations (Schuster et al. 2007). Glyphosate efficacy on Canada thistle is
dependent upon the stage of growth, with more injury occurring when controlled

in the rosette stage than at bud initiation (Hunter 1995, 1996).

10

Glufosinate. Glufosinate (2—Amino-4-(hydroxy-methyl-phosphoryl)butanoic acid)
is a broad-spectrum, postemergence herbicide that results in necrosis of the
plant tissue on contact. Glufosinate is a glutamine synthetase (GS) enzyme
inhibitor in sensitive species inhibiting the production of glutamine (Hoagland
1983; Lea et al. 1984). Glutamine synthetase converts glutamate and ammonia
to gluatamine. Inhibition causes accumulation of toxic ammonia in the cells
(Manderscheid and Wild 1986; Wild et al. 1987). However this ammonia build up
is not what is directly responsible for glufosinate toxicity, the ammonia has been
thought to directly affect photosynthesis (Ridley 1989) but when ammonia alone
is added, photosynthesis is not inhibited (Wild et al. 1987). Alternative evidence
shows that photosynthesis is inhibited by an accumulation of glyoxylate inhibiting
ribulose-1,5 bis-phospate carboxylase/oxygenase (rubisco) (Wendler 1992; Wild
1993). Glufosinate has no herbicidal activity unless applied directly to the foliage,
increasing the spray carrier volume helps increase coverage (Smith 1988a,
1988b). The FINALE formulation of glufosinate was introduced by Bayer Crop
Sciences in 1994 and discovered in 1981 (Sensemen 2007). The herbicide was
primarily used as a bum-down herbicide before crop planting in reduced tillage
systems and for weeds in right-of-ways and other non-crop areas (Smith 1988b).
Sensitive species exhibit chlorosis and wilting occurs within 3-5 days after
application with necrosis developing after 1-2 weeks. The symptomology is
similar to that of the PS" inhibitors and will not occur unless light is present (Hess
2000; Hoagland 1983). Rate of symptomology after application increases with

bright sunlight, high humidity, and moist soil conditions. Under these conditions

11

injury can be seen by 2 days after treatment (Al-Khatib et al. 2003) The contact
herbicide has little movement in the xylem and phloem although greater
translocation is found in the grass species than broadleaf herbicides (Steckel et
al. 1997a). Translocation of glufosinate can be increased if applied at high
relative humidity (Coetzer et al. 2001 ).

Glufosinate efficacy on weeds of interest. Glufosinate has been shown to
have differential efficacy among weed species. Common lambsquarters
(Chenopodium album L. ) has been shown to have a low level of tolerance to
glufosinate (Steckel eta. 1997c). Other research has shown that glufosinate at
similar rates is more effective on common lambsquarters than glyphosate
(Higgins et al. 1991; Tharp et al. 1999).Giant foxtail requires less than half the
rate of glufosinate to achieve 50% control as compared to velvetleaf or common
lambsquarters (Steckel et al. 1997b). Velvetleaf and giant foxtail control were
100% from one application at the 400 g/ha rate, while more was required for
control of common lambsquarters (Krausz et al. 1999). Glufosinate has low long
term efficacy on perennial weeds like Canada thistle due to the small amount of
translocation causing regrowth from the roots (Pline et al. 2000) Glufosinate
resistance is rumored to have been reported on two species; rigid rye grass
(Lolium rigidum Gaudin.) and goosegrass (Eleusine indica L. Gaertn.), although

not yet published (Ian Heap, personal communication, October 13, 2009).

Chlorimuron-ethyl. Chlorimuron-ethyl (2-[[[[(4-chloro-6-methoxy-2-

pyrimidinyl)amino]carbonyl]amino]sulfonyl] benzoic acid) is a selective

12

sulfonylurea herbicide used preemergence and postemergence primarily for
broadleaf weed control in soybean (Claus 1987). Chlorimuron was intrbduced in
1986 as CLASSIC© by DuPont, the appeal of chlorimuron was its control of
broadleaf weeds at significantly low application rates and the tolerance that
soybean exhibits to the herbicide (Claus 1987). Chlorimuron inhibits acetolactate
synthase (ALS), inhibiting the branched chain amino acids, valine and isoleucine
(La Rossa and Schloss 1984). Soybean is tolerant to chlorimuron and can be
applied over the top at labeled rates with minimal crop injury (Krausz et al. 1992).
Chlorimuron also exhibits residual weed control which could be beneficial for
longer term control in the field. It persists longer in soils with high pH and has an
average field half-life of 40 days (Wauchope 1992).

Susceptible weeds show rapid inhibition of growth when chlorimuron is
applied (Claus 1987). Chlorosis is observable to the naked eye 3 to 5 days after
application followed by necrosis of the apical meristem. Complete control is
exhibited within 7 to 21 days on susceptible plants. Some species will never
exhibit the necrosis and will remain green but stunted. Chlorimuron is readily
absorbed in sensitive species and translocated to the meristems of roots and
shoots (Claus 1987).

Chlorimuron efficacy on weeds of interest. Control of velvetleaf by the full rate
of chlorimuron is 75% (Claus 1987). Chlorimuron has very little efficacy on
common lambsquarters with over 50 g/ha required for complete control (Lich et
al. 1997). Chlorimuron does not control grass species (Jordan et al. 1997).

Control of Canada thistle by chlorimuron was 43% when the adjuvants crop oil

13

concentrate (COC) and 28% urea ammonium nitrate (UAN) were used, control
was increased to 77% when non-ionic surfactant (NIS) was used (Sprague et al.

1999)

Thifensulfuron-methyl. Thifensulfuron-methyl (methyl 3—[[[[(4-methoxy-6-
methyl-1 ,3—5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2-thiophenecarboxylate),
a sulfonylurea, is an ALS inhibitor, applied postemergence. It was first
introduced and sold as PINNACLE by Du Pont in 1987 for use in wheat and
soybean.

Symptoms in sensitive plants are similar to those exhibited with chlorimuron
injury, growth is inhibited within hours of application while injury symptoms
appear 1-2 wk later (Sensemen 2007). It is readily absorbed by foliage and roots
and is translocated through the xylem and phloem with accumulation in
meristematic areas. lts persistence in the soil can be up to 6 d under aerobic
conditions and 28 d in anaerobic conditions.

Thifensulfuron efficacy on weeds of interest. Thifensulfu ron generally has
good efficacy on velvetleaf and common lambsquarters when applied at labeled
rates with adjuvants (Fielding and Stoller 1990). Research on thifensulfuron

activity in Canada thistle and giant foxtail has not completed to date.

Adjuvants. The addition of ammonium sulfate (AMS) increases the Control of
many weeds with weakly acidic herbicides such as glufosinate (MasChhoff et al.
2000; Pline et al. 2000; Young et al. 2003); and glyphosate (Donald 1988;

Salisbury 1991; Turner and Loader 1975; Wills and McWhorIer 1985).

14

The addition of AMS to glufosinate has been shown to increase the uptake by
23% (Maschoff et al. 2000). However, the addition of AMS to glufosinate has
also been reported to decrease glufosinate absorption in common lambsquarters
(Pline et al. 1999). The addition of AMS to glyphosate failed to increase
glyphosate efficacy on common lambsquarters (Young et al. 2003). Ammonium
sulfate addition increased absorption translocation of the herbicides in the plant.
The addition of AMS to glyphosate has been shown by numerous studies to be
advantageous, with a two-fold increase in glyphosate rate required to meet the
equivalent control of the addition of AMS (Young et al. 2003). Glyphosate
benefits more from the addition of AMS when applied at lower rates than at

higher rates (Young et al. 2003).

TANK-MIX INTERACTIONS OF HERBICIDES

Combining herbicides is a tool producers can use to increase the range of
control. By combining herbicides with different modes of action and different
target weeds, a farmer can potentially increase the spectrum of weed control in
his field with less application cost. Tank-mixtures, much like herbicide rotation,
are also used to prevent the development of herbicide resistant weeds by altering
selection pressures. Tank-mixing has been shown to be more effective in
reducing resistance evolution than using herbicides in a rotation (Hugh and
Reboud 2009). Much research and review has been done on the joint action of
herbicides in a tank-mix (Colby 1967; Hatzios and Penner 1985; Streibig et al.
1998). Information on the potential effects of reduced rate dosage due to

environmental factors like rain could be determined from studying the joint action

15

of herbicides at a range of rates (Streibig et al. 1998). Common terminology used
to report results of combinations and interactions are; synergistic, antagonistic
and additive (Morse 1978). There are many differential definitions for these terms
used across the science disciplines. Synergism is defined as “The combined
action of two or more agents that is greater than the sum of the action (sic) of
one of the agents used alone.” (Anonymous 2010). Antagonism is defined as the
interaction between two or more chemical substances that diminishes the effect
that each of them has individually (Anonymous 1989). These definitions are
similar to those found in the herbicide handbook and are the official definitions of
the WSSA (Sensement 2007). Much controversy is raised around the issue
classifying a combination as synergistic or antagonistic. This is due to the
contrasting definitions and the confusion of the word sum in the definition of
synergism (Morse 1978).

A large number of herbicide combinations have resulted in herbicide
antagonism (Hatzios and Penner 1985; Zhang et al. 1995). The mechanisms of
herbicide antagonism are classified as being either biochemical, competitive,
physiological or chemical (Morse 1978). Biochemical antagonism occurs when
the antagonist interacts with the other herbicide to decrease the amount available
at the site of action, usually the result of reduced herbicide absorption, altered
transport and increased biotransforrnation (Hatzios and Penner 1985).
Competitive antagonism occurs when herbicides with the same site of action are
applied and is a function of the concentration as well as affinity for site of action

(Hatzios and Penner 1985). Physiological antagonism occurs when two

16

herbicides affect two different modes of action that produce opposite effects of
the physiological process (Hatzios and Penner 1985). Chemical antagonism
occurs when the two herbicides mixed interact in the mixture to form some type
of inactive chemical complex (Hatzios and Penner 1985).

As different weed species react differently to the application of one
herbicide, they also react differently to a tank-mixed herbicide. A review by
Zhang et al. (1995) found there was little difference in the amount of synergism
and antagonism in monocot species but that there were significantly more results
of antagonism on monocot species. Differences in injury were also seen between
weed families. In 12 studies on the Chenopodiaceae family only one resulted in a
synergistic response. The Compositae, Gramineae and Leguminosae families
showed more antagonistic interactions than synergistic. Zhang inferred that the
genetic, physiological, morphological and biological differences between species
and families are what may be responsible for the differential response.

Tank mix interactions can occur between selective herbicides Such as the
ALS inhibitors in this study and non-selective herbicides such as glyphosate and
glufosinate. It is a common practice to mix slow acting systemic and fast acting
burn down herbicides for a broad spectrum of control (Green 1989). The most
commonly seen interaction between these herbicides is antagonism, especially
at reduced rates (Hydrick and Shaw 1994). Research has indicated that with an
increase in the rate of the non-selective herbicide, antagonism can be overcome
while still keeping the rate of the selective herbicide (Hydrick and Shaw 1994;

Rhodes Jr. and Coble 1984). A rate response has been observed with many tank

17

mix interactions. One example was that increasing a glyphosate rate in
combination with acifluorfen eliminated antagonism (Jordan et al. 1997).
Reduced rates of many herbicides can still have the same efficacy as the full
recommended rate and using these rates in combination with other herbicides is

a common practice (Green 1991 ).

Tank-mixing glyphosate and the sulfonylureas. The Herbicide Handbook
states that chlorimuron may have reduced efficacy when tank-mixing With other
herbicides (Sensemen 2007). One study found that chlorimuron and glyphosate
were either additive or antagonistic depending on rates applied and species
applied to (Starke and Oliver 1998). A recent study found that glyphosate tank-
mixed with one- half label rates of chlorimuron gave the highest percent control
(80%) of the combinations studied on common lambsquarters (Knezevic et al.
2009). The addition of chlorimuron to glyphosate did not reduce the efficacy of
glyphosate in velvetleaf (Jordan et al. 1997). Variation between years Was found
in 1996 and 1997 field studies. In 1996 Vidrine et al. 2002 found that at all rates
of chlorimuron plus glyphosate had greater control than glyphosate applied
alone, however this was not observed in 1997 (Vidrine et al. 2002). These
studies were not subjected to Colby’s analysis of interaction and thus mixed
results could have been observed. Tank-mixing glyphosate plus chlorimuron and
thifensulfuron resulted in lower soybean yields compared with glyphoSate alone

but with no significant differences in weed control (Corrigan and Harven 2000).

18

Tank-mixing glufosinate and the sulfonylureas. Research on tank mixtures of
glufosinate and the sulfonylureas is limited to a few studies. Glufosinate
combined with chlorimuron and metribuzin resulted in an additive effect in
sicklepod (Senna obtusifolia L. H.S. lriwn & Bameby ), antagonism at low
glufosinate rates in entireleaf morningglory (Ipomoea hederacea var.
integn'uscula) and antagonism at high glufosinate rates in johnsongrass
(Sorghum halepense L. Pers.) (Hydrick and Shaw 1994, 1995). The authors
determined that the addition of a selective foliar herbicide to the non-selective
glufosinate normally resulted in antagonism but could usually be overcome when
glufosinate was applied at higher rates. As the results show this was not always
true but was true for the broadleaf weeds studied. No known studies have

completed looking at the interaction between glufosinate and thifensulfuron.

Tank-mixing glyphosate and glufosinate. Recent reports have documented
the interaction between glyphosate and glufosinate (Chuah et al. 2008; Everman
et al. 2009; Kudsk and Mathiassen 2004; Whitaker 2010). One study observed
antagonism between the two herbicides in goosegrass (Eleusine indica) at all
rates (Chuah et al. 2008). They attributed this observed antagonism to the fast
acting nature of glufosinate injuring the plant before the slower acting systemic
glyphosate can act (Chuah et al. 2008). Another study that observed antagonism
between glyphosate and glufosinate also observed synergism (Kudsk and
Mathiassen 2004). Although little research to date has been published on the

interaction of glyphosate and glufosinate, antagonism has been reported

19

between glyphosate and other contact herbicides (Appleby and Somabhi 1978;
Hayward et al. 1988; Hydrick and Shaw 1994; Lich et al. 1997; Wehtje et al.
2008). Glufosinate acts faster than glyphosate to injure the plant, much like
diquat, a bipyridilum contact herbicide. In diquat plus glyphosate treatments,
early synergism was observed between the chemicals (4 DAT), but later
antagonism was observed due to increased regrowth (Wehtje et al. 2008). Higher
glyphosate rates were needed to compensate for the inhibition of glyphosate
activity caused by the rapid plant death and retention of glyphosate in the treated
leaf. An example of synergism of fast acting herbicides is diuron and paraquat.
Diuron quickly inhibits photosynthesis before paraquat can cause cell destruction
and allows limited paraquat translocation to unsprayed portions of the plant

(Hayward et al. 1988).

Evaluation of the interactions. Interactions could be deemed antagonistic,
synergistic or an additive effect based upon the statistical methodologies used to
compare them. Two models are commonly used to determine the joint action of
herbicides; the Additive Dose Model (ADM) and the Multiplicative Survival Model
(MSM) (Morse 1978; Streibig et al. 1998). The ADM is used when looking at the
joint action of herbicides of the same mode of action and assumes that the effect
of each herbicide dose could interchange with each other and not affect efficacy
(Streibig eta. 1998). The MSM assumes that each herbicide has a different
mode of action and acts independently on the plant resulting in a multiplicative

effect (Streibig et al. 1998). The fundamental difference is that the MSM

20

considers effects while ADM considers dose rates. MSM is the most commonly
used method in weed science in the form of Colby’s equation (Colby 1967),
which does not require estimation of dose-response cunres (Morse 1978). There
is no agreement on which of these models is the best to use, however it has
been argued that conceptually ADM has more advantages than MSM and so
MSM should only be used when looking at mixtures of herbicides with different
modes of action (Streibig and Jensen 2000). It is for that reason that the MSM

was used for this research.

ABSORPTION AND TRANSLOCATION OF HERBICIDES

Absorption and translocation of herbicides varies dependent upon the
herbicide applied, weed species and the environment. For herbicides to be
effective they must come into contact with the living tissue. The effectiveness of
the herbicide is directly related to its absorption in the plant and for systemic
herbicides, movement throughout the plant. The reason for the interaction
between herbicides can be observed through absorption and translocation
studies. The interaction between glyphosate and glufosinate has been studied
through absorption and translocation studies at MSU and resulted in antagonism
of the two herbicides on giant foxtail due to reduced absorption and translocation

out of the treated leaf (Everman et al. 2009).

14C-glyphosate. Glyphosate is absorbed across the cuticle when applied

postemergence (Boerboom and Wyse 1988). Glyphosate is a non-polar herbicide

21

and of the non-polar herbicides has the slowest transport across plasmalemma
(Jachetta et al. 1986)

Translocation of glyphosate is primarily in the symplast with accumulation
of glyphosate occurring in the immature leaves, meristems and underground
tissues (Martin and Edgington 1981). There is little evidence of apoplastic
movement but it has been observed (Sprankle et al. 1975).

Absorption of 14C-glyphosate increases over time. Foliar absorption of
glyphosate commonly ranges between 25 and 50% (Sprankle et al. 1975; Wyrill
and Burnside 1976; Young et al. 2003). Sandberg et al. (1980) reported that
glyphosate translocation was 3 to 20% of 14C applied at 72HAT in five species.
Translocation of 14C glyphosate to the roots of Canada thistle was greater when
applied at the rosette than the bud-stage (Hunter 1996).

Growth stage and plant stress before herbicide application reduce the
absorption and translocation of glyphosate in many species (Ahmadi et al. 1980,
Pline et al. 2001). The addition of adjuvants increases absorption which
increases overall translocation throughout the plant (Sherrick et al. 1986,

Sprankle et al. 1975).

14C-chlorimuron. Chlorimuron is a systemic herbicide that is readily taken up by

both roots and shoots and is translocated to the meristematic regions (Claus
1987). Adding glyphosate to the tank mix increased the absorption of 14C-

chlorimuron in Palmer amaranth and velvetleaf, this increase was attributed to

the addition of AMS when glyphosate was added (Starke and Oliver 1998).

22

However, translocation by sulfonylureas out of the treated leaf is generally
limited. Chlorimuron absorption was less than 53% after 96 hours and
translocation was 30% out of the treated leaf in yellow nutsedge (Cyperus
esculentus L.). Only 4% of the translocated herbicide was found in the
underground tubers (Troxler et al. 2003).

The objective of these studies was to evaluate the interaction between
glyphosate, glufosinate and the sulfonylurea herbicides chlorimuron and
thifensulfuron in a matrix combination of all rates studied. By determining if any
interactions exist we can conclude that herbicide programs in stacked gene traits
and field with herbicide resistant weeds need to be adjusted. To determine the
basis of the interaction we will look at absorption and translocation of glyphosate
and chlorimuron alone and in combination and will use fluorescence
measurements to determine how quickly the interaction takes place before it is

visually observable.

23

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34

CHAPTER 2

EARLY DETECTION OF HERBICIDE INTERACTIONS WITH
FLUORESCENCE MEASUREMENTS

Abstract: Tank-mixing of herbicides with different chemistries provides the
opportunity to control a wider range of weed species and herbicide resistant
weeds. Interactions between glyphosate, glufosinate, and chlorimuron have been
observed in the greenhouse and the field. The objective of this study was to
evaluate the combinations of glyphosate, glufosinate and chlorimuron on three
annual weeds; giant foxtail, common lambsquarters, and velvetleaf and the
perennial weed, Canada thistle using fluorescence. Fast acting herbicides like
glufosinate cause rapid inhibition of photosynthesis which is observable through
fluorescence measurements before injury may be visible. When applied alone or
in combination with these herbicides, glufosinate caused a rapid decrease in the
maximum capacity for photochemical quenching evident by the parameters
derived from the OJIP curve; Fv/Fm (maximum quantum efficiency of
photosystem II), ij (relative changes in the J step) and changes in the
Kautsky/OJIP curve. Changes in Fv/Fm-were observable within 2 hours after
treatment (HAT) when glufosinate was applied alone or in combinatiOn, indicative
of the rapid breakdown of the plants protective non-photochemical photosynthetic
systems. Changes in Fv/Fm were observable within 24 HAT with glyphosate
applied alone and in combination with chlorimuron, whereas application of
chlorimuron alone produced no observable changes until 72 HAT. The fast action
of glufosinate on the photosynthetic system may limit translocation and

expression of the activity of glyphosate and chlorimuron and results indicate that

35

the combinations of glufosinate with glyphosate and chlorimuron can be
antagonistic.

Nomenclature: Canada thistle (Cirsium arvense), chlorimuron, common
lambsquarters (Chenopodium album), giant foxtail (Setaria faberi),
glufosinate, glyphosate.

Key words: fluorescence, FvlFm, Kautsky induction curve, OJIP curve

Early detection of herbicide injUIy is an important means for detection of
misapplication in the field and for research on herbicide mode of action. Early
detection refers to using other modes of determining plant response to herbicide
injury prior to the observation of .visual injury. Early detection of herbicide injury
by fluorescence measurements has been used successfully in many stUdies
(Barbagallo et al., 2003).

Glyphosate, glufosinate, and the sulfonylurea herbicides, although not
primarily Photosystem ll (PS II) inhibitors, do ultimately cause cellular death
resulting in a weakened ability to use or disperse light energy. Changes in
fluorescence induction (Kautsky curve) have been used extensively in
photosynthesis and herbicide research and are the basis for all fluoresCence
parameters (Abbaspoor and Streibig, 2005; Christensen et al., 2003; Percival
and Baker, 1991). The benefits of using fluorescence include its non-invasive
procedure, sensitivity to many biotic and abiotic stressors, ease and efficiency
and numerous parameters to measure the status of the photosynthetic apparatus
(Abbaspoor and Streibig, 2005; Barbagallo et al., 2003; Frankart et al., 2003;

Strasser et al., 2000).

36

Several parameters are used to measure the fluorescence signal. The most
important are those parameters that can be used to elucidate differences in
changes to the PS II system. Illumination of dark-adapted unstressed leaves
produces a rise in chlorophyll fluorescence emission from the ground state (F0)
to its maximum value (Fm) within one second (Figure 1). Within that second
other parameters are also observed. One such parameter is the JlP-test. Based
on the Kautsky curve the polyphasic rise of OJIP is observed in all plant species.
The shape of this curve is very sensitive to stressors (Percival and Baker, 1991;
Strasser et al., 2000). OJIP has three distinct phases associated with events in

PSII (Govindjee, 1995). The three phases are as follows: (1) (O to J) phase

corresponds with the complete reduction of QA of PS ll, (2) (J to I) phase

correspOnds to the transfer of electrons, from GA to 03, this phase is Controlled

by the PS ll donor side which is responsible for water splitting activity, (3) (l to P)
phase which corresponds to the release of fluorescence quenching by the
oxidized plastoquinone pool (Figure 1). The J to I phase is of particular interest
because it is an indicator of the water-splitting activity of PS II. The relative
changes at the J step [ij: (Fm-Fj)/Fm] can be indicative of a reduction of the
activity of PS ll. Reductions in the rise of these phases correspond to the
destruction of the particular photochemical mechanism, therefore it may be
possible to pin-point exactly when and where these non PS II mode of action
inhibitory herbicides act on the PS II system by looking at where the curve

flaflens.

37

Another important parameter is the Fv/Fm [Fv/Fm = (Fm-Fo)/Fm] (Figure 1)

parameter (Butler, 1978). The dark adaptation of a leaf allows PSII to be fully
reduced at OA and when illuminated the maximum quantum efficiency of the PS

ll photochemistry can be determined by Fv/Fm. This parameter is used most
often in the literature to indicate plant health with a value of 0.83 indicating no
stress to the plant. Fv/Fm has been used to measure the effect of glyphosate on
fluorescence in previous studies. Kirkwood et al. 2000 used this parameter and
detected some differences from the control one day after treatment while neither
Olesen and Cedergreen, 2010 or Ralph 2000 found any effect of glyphosate on
Fv/Fm. Changes in the ij parameter derived from Kautsky curve were observed
4 hours after glyphosate application when applied on sugar beet (Beta vulgaris
L.) and at 24 hours after application in white mustard (Sinapis alba L.)
(Christensen et al. 2003).

The objectives of this study were to determine if fluorescence measurements
of herbicide treated plants were different among species and determine if there
were fluorescence differences among herbicide modes of action. We hypothesize
that there will be differences in how species respond to herbicides indicated by
fluorescence parameters. Secondly, there will be mode of action differences in
fluorescence parameters, that the different parameters; Fv/Fm, ij and OJIP
curves will show similar to herbicide applications, and fluorescence parameters
will indicate injury to the photosynthetic system much earlier than visually

observed.

38

MATERIALS AND METHODS

Plant material. Common lambsquarters (Chenopodium album L.), velvetleaf
(Abutilon theophrasti Medik.) and giant foxtail (Setaria faberi Herrm.) were grown

from seed in the greenhouse. Approximately 10 seeds each were sown into soil

mediaa in 900 mL black plastic pots. Plants were thinned to one per pot upon

emergence. Canada thistle (Cirsium arvense L. Scop.) plants were grown from

root stockb obtained in May of 2008 and transplanted into soil media in” 900 mL

black plastic pots. These plants were genetically similar. Tillers from stock plants
were transplanted into fresh media and pots. Canada thistle plants were selected
for treatment 2 weeks after transplant.

All plants were grown in greenhouses at Michigan State University campus in
East Lansing, MI and experiments took place in May of 2009. Natural light was

supplemented by high-pressure sodium lamps that produced a photoSynthetic

photon flux density of 200 mol m'2 s". The photoperiod was 16/8 h light/dark,
and the temperature was 23:-3°C. Plants were fertilized with 50 ml of fertilizer
solution containing 6 mg/L of 20% nitrogen, 20% P205 and 20% K20 as needed.

Plants were 10-12 cm tall at time of treatment and were randomly assigned to
herbicide treatments. Treatments were replicated three times and the experiment
repeated three times with common lambsquarters and Canada thistle.
Treatments were replicated three times and the experiment conducted one time

with velvetleaf and giant foxtail.

39

Herbicide treatments. Herbicide treatments consisted of glyphosate,
glufosinate and chlorimuron alone and in combinations at the rates seen in Table
1. Ammonium sulfate (AMS) at 2% v/v was used as an adjuvant when
glyphosate or glufosinate were applied alone or in combination with chlorimuron.
Crop oil concentrate was used at 1% v/v when chlorimuron was used alone.

Treatments were applied using a single-tip track sprayer using a TP8001 flat fan

nozzlec delivering 187 L ha‘1 at a pressure of 207 kPA. Treatments were based

on preliminary studies which showed these rates had the highest observable
interaction and were also the most economically interesting, such as, a high and
a low rate combined, low rates combined and high rates combined.
Fluorescence measurements. After herbicide application the plants were
immediately returned to the greenhouse and prepared for fluorescenCe reading.
Fluorescence readings were taken at 2, 4, 6, 8, 24, 48 and 72 hours after
treatment (HAT). The second set of fully emerged leaves above the cotyledons,

with at least one more set of fully emerged leaves above were selected for

fluorescence evaluation. Leafclipsd were placed in the middle of the selected leaf

directly next to the midvein with the least amount of contact with any major veins.
The clip has a small shutter plate that must be closed over the leaf once the clip
is attached so that light is excluded and dark adaptation begins to take place.
The process of dark adaptation varied depending on plant species, ambient light
history and whether the plant was stressed. The average time required for dark

adaptation in this study was 15 minutes. Once dark adapted, the Handy Pocket

PEAe optical interface is attached to the clip around the shutter plate, the shutter

40

was opened and high intensity LED light passed through a NIR filter, onto the
leaf. Then a highly sensitive PIN photodiode detects the fluorescence Signal at
tops intervals for 1 second. The data obtained in the 1 second period was, saved
in the Handy Pocket PEA and later downloaded into a computer. The Kautsky
curves for different doses and time intervals were visually examined to determine
the effect of time and dose. Parameters from the Kautsky curve were obtained

using the Handy Pocket PEA software. Data were subjected to ANOVA using

PROC MIXED in SASf and treatment means for Fv/Fm and ij with species were

compared using Fisher’s Protected LSD at the p : 0.05 significance level. Among
species comparisons were done by creating contrast statements anaIyZing

differences between species with a chosen LSD = 0.1.

RESULTS AND DISCUSSION

Species differences. Data from the application of the 1X rate of each mode of
action on all four species was analyzed to test the hypothesis that there would be
differences in response to herbicides among species (Figure 2 and 3). Multiple
parameters were chosen for comparison; Fv/Fm and ij characterizes species
response to herbicide application. The Fv/Fm of a healthy plant is 0.83, a value
smaller than 0.83 is an indication of the inability of the plant, due to injury, to
efficiently photosynthesize. ij is indicative of the flattening of the OJIP curve at

the J to I phase. Both a lower ij and the flattening of the OJIP curve at the J to I

phase indicates that the plant is unable to effectively transfer electrons from GA

41

to 03. Observed flattening of the OJIP curve at the other phases can Indicate

stress on other photosynthetic processes outlined in the introduction.

The following are observations based on the data obtained from the
fluorescence experiments. The Fv/Fm at 2 HAT of the 1X glyphosate rate on
Canada thistle were significantly higher than all other species except giant foxtail.
The Fv/Fm values for glyphosate at 48 HAT were lowest in Canada thistle and
highest in giant foxtail though not significantly different (Figure 2a). ij values for
the glyphosate treatment followed the same trend as Fv/Fm (Figure 33). There
were no species differences following the 1X glufosinate treatment at 2 HAT, but
at 4 HAT Fv/Fm of giant foxtail were significantly lower than for common
lambsquarters. Fv/Fm values for glufosinate treatments were lowest in Canada
thistle and highest in giant foxtail at 48 HAT (Figure 2b). ij values for
glufosinate treatments responded similarly as Fv/Fm but at 48 HAT ij were
highest for common lambsquarters (Figure 3b). The Fv/Fm following the 1X
chlorimuron applications to Canada thistle were significantly higher than for all
other species at 2 HAT. The Fv/Fm for common lambsquarters had the lowest
Fv/Fm at this time (Figure 2c). The Fv/Fm for giant foxtail at 48 HAT was higher
than all other species. The Fv/Fm for Canada thistle was significantly lower than
common lambsquarters at 72 HAT. The ij for chlorimuron showed less
significant differences but were still apparent (Figure 3c). The ij and Fv/Fm
showed similar trends for differences among species. Induction curves showed
that there were differences among species OJIP readings, and F0 and Fm

readings at 48 HAT (Figure 4). Following glyphosate application the OJIP curve

42

for common lambsquarters was the most like the normal OJIP curve while the l
peak was no longer observable in any species (Figure 2, 4a). Glufosinate
application resulted in a larger reduction in Fv/Fm observable by the extreme
flattening of the OJIP curve in all species (Figure 4b). The curve for common
lambsquarters was the only one to still show the P peak while the curve for
Canada thistle showed no peaks. Chlorimuron application resulted in less
changes in the OJIP curve than was observed for the other herbicides but the I
peak in the curve was still not observable (Figure 4c). The OJIP curve for
common lambsquarters differed the most from the others and was the ‘most

similar to the curve for the control (Figure 1, 4c).

Mode of action. The mode of action differences for the Fv/Fm were c0mpared
for the1X rate of each herbicide applied alone. Analysis of Fv/Fm data facilitated
comparison of species differences between Canada thistle and common
lambsquarters (Figure 5). Mode of action differences were observable for Fv/Fm
values of Canada thistle at 2 HAT. Fv/Fm following application of IX glufosinate
was significantly lower than the control from 2 HAT to 72 HAT (Figure 5a). The
Fv/Fm for plants receiving application of 1X glyphosate also were significantly
lower than the control at 24 HAT. The Fv/Fm for those sprayed with glufosinate
were always significantly lower than Fv/Fm for glyphosate except at the 72 HAT
reading (Figure 5a). Fv/Fm values for Canada thistle that were sprayed with
chlorimuron were never significantly different from the control. Mode of action
differences in Fv/Fm values among herbicides were observed in common

lambsquarters beginning at 6 HAT. The Fv/Fm values following application of IX

43

glufosinate were significantly different from the control and other herbicides at 6
HAT (Figure 5b). Fv/Fm values after glufosinate application remained
significantly different from the control and other herbicide treatments until 48
HAT. Fv/Fm values at 48 HAT following glufosinate application at 1X Were no
different from those following glyphosate at 1X but both were significantly lower
than the control and following the 1X chlorimuron application (Figure 5b). Fv/Fm
values at 72 HAT after glufosinate application were significantly lower than
following glyphosate application however; they are both significantly different
from the control and following chlorimuron application. Fv/Fm values for common
lambsquarters receiving chlorimuron were not significantly different from the
control during the course of observation (Figure 5b). OJIP curves at 48 HAT
showed differences between species and herbicide mode of action (Figure 6).
Canada thistle had lower Fm values than common lambsquarters regardless of
herbicide modes of action (Figure 6). Glufosinate application to Canada thistle
caused a complete collapse of all OJIP peaks whereas for common
lambsquarters this curve still had the P peak. In Canada thistle the collapse of
the glyphosate curve was more obvious than in common lambsquarters (Figure
6). Plants receiving chlorimuron treatments responded similarly to the control for

both species (Figure 6).

This study showed that there were differences in fluorescence values
within species and from herbicides with different modes of action. Species
differences were characterized with Fv/Fm and ij parameters. These

parameters presented similar data trends to one another. Comparison of OJIP

44

curves among species showed species dependent responses to herbicide modes
of action. Modes of action differences for herbicides were evident with
fluorescence patterns like Fv/Fm. This parameter showed glufosinate action
rapidly (2 HAT) resulted in a breakdown of the photosynthetic apparatUs. OJIP
curves of all species responded to glufosinate application with complete
flattening of all phases except the I to P phase in common lambsquarters.
Glyphosate application resulted in a flattening of the OJIP curve and a reduction
in Fv/Fm beginning at 24 HAT. Whereas chlorimuron application did net result in
flattening the OJIP curve. Thus, fluorescence measurements indicated'injury to
the photosynthetic system much earlier than was visually observable. With
glufosinate we saw reductions in fluorescence parameters evident at 2 HAT
following glufosinate application and at 24 HAT with glyphosate. Visible injury
was not viewable until 3 to 5 days after treatment and 7 to 10 days after

treatment, respectively.

45

SOURCE OF MATERIALS

alBaccto® High Porosity Professional Potting Mix, Michigan Peat 00., Houston,
TX.

bDon Penner’s Farm Williamston, MI. pennerd@msu.edu.
CTeeJet®, Spraying Systems Co., PO. Box 7900, Wheaton, IL 60189.

dLeaf Clips, Handy Pocket PEA, Hansatech Instruments, Narborough Road,
King’s Lynn, Norfolk, UK.

eHandy Pocket PEA, Hansatech Instruments, Narborough Road, Kings Lynn
Norfolk, UK.

fThe SAS System for Windows, Version 9.2, SAS Institute Inc., 100 SAS
Campus Dr., Cary, NC 27513.

46

Table 1. Herbicide combinations applied in fluorescence
studiesa

 

 

 

 

Herbicides Applied bLSpecies - Fluorescence Studies
CIRAR + CHEAL ABUTH + SETFA
Control Control
0.25X GLYb 0.25x GLY
0.5x GLY 1X GLY
1X GLY 0.25X GLU
0.25X GLU 0.5x GLU
0.5x GLU 1X GLU
1X GLU 1X CHL
0.25X CHL 0.25X GLY + 1X CHL
0.5X CHL 0.25X GLU + 1X CHL
1X CHL 0.25X GLU + 1X GLY
0.25X GLU + 1X GLY
0.5X GLU + 0.5X GLY
1X GLU + 0.25X GLY
0.25X GLU + 0.25X CHL
0.25X GLU + 1X CHL
0.5x GLU + 0.5X CHL
1X GLU + 0.25X CHL
1X GLU + 0.5X CHL
1X GLU + 1X CHL
0.25X GLY + 0.25X CHL
0.25X GLY + 1X CHL
0.5X GLY + 0.5X CHL
1X GLY + 0.25X CHL
1X GLY + 0.5x CHL
1X GLY + 1X CHL

 

 

 

a Where 1X : the labeled rate; glyphosate applied as Roundup
WeatherMAX 1X : 840 g ae/ha; glufosinate applied as

LIBERTY 1X : 420 g ai/ha; chlorimuron applied as CLASSIC
1X:889mma

b Abbreviations: GLY, glyphosate; GLU, glufosinate; CHL,
chlorimuron.

47

 

   

 

 

3000'-
7 """""""" T; """"""""
: w.-
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8 I u: I 5'
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.‘E I
0’ I
m I
1000‘ I
I
O
0 I I I l I I l
0-01 0.10 1.00 10.00 100.00 1000 10000

Time (ms)
Figure 1. Chlorophyll fluorescence induction curve (Kautsky/OJIP curve) of
a 15 minute dark adapted healthy Canada thistle leaf.

48

Fv/Fm

 

 

O T I T I I 1
2 4 48 72

 

6 8 24
Hours After Treatment (HAT)
(b) 0 9 _ Species Differences - 840 g ailha Glufosinate

Fv/Fm

 

 

 

6 8 24
Hours After Treatment (HAT)
(C) 0 9 Species Differences - 8.8 g ailha Chlorimuron

0.8
0.7
0.6
0.5 a
0.4 a
0.3 -
0.2 ~
0.1 ~
0 r r r r r r
2 4 48 72

 

Fv/Fm

 

 

6 8 24
Hours After Treatment (HAT)

Figure 2. Species differences in Fv/Fm by herbicide mode of action (a)
glyphosate (b) glufosinate (c) chlorimuron on (0) giant foxtail, (I) velvetleaf,
(A) Canada thistle, and (x) common lambsquarters

49

 

 

 

6 8 24 48 72
Hours After Treatment (HAT)

(b) 0.6 Species Differences - 840 g ailha Glufosinate

ij

 

 

Hours After Treatment (HAT)
0.6 _ Species Differences - 8.8 g ailha Chlorimuron

 

 

0 T I I I T I

2 4 6 8 24 48 72
Hours After Treatment (HAT)

Figure 3. Species differences in ij by herbicide mode of action (a)
glyphosate (b) glufosinate (c) chlorimuron on (9) giant foxtail, (I) velvetleaf,
(A) Canada thistle, and (x) common lambsquarters

 

50

3000 (a)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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932000 _,..- 2" . .. (I
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500
0 ..
0.01 0.10 1.00 10.00 100.00 1000.00
3000 Time (ms)
(b)
@2500
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8
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93
§1500 .-.. ““33“ng
g *_"-¢MJW (x) “.1" i =::0 _ 1’
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0 01 0.10 1.00 10.00 100.00 1009.00
3000 TTme (ms)
- 2......“ (X
2500 (C) a"
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rfr’ ,. ”3% 2"“
500 gf‘ #‘f
rd” A.,...”
0. 31 0.10 . 1.00 10.00 100.00 1000.00
limetms) ,

Figure 4. Species differences in OJIP curve by herbicide mode of action 48
hours after treatment (a) glyphosate (b) glufosinate (c) chlorimuron on (0)
giant foxtail, (I) velvetleaf, (A) Canada thistle, and (x) common
lambsquarters

51

0-9 Fva on CIRAR

 

 

 

 

 

 

 

Figure 5. Fv/Fm differences in mode of action by species (a) Canada thistle
(b) common lambsquarters on (9) control, (I) 1X glyphosate, (A) 1X
glufosinate, and (x) 1X chlorimuron. Vertical bars represent Fisher's
protected LSD at p=0.05 significance level, when not present: Not

significant.

52

3000

2500

O
O
0

Relative f_lpores,gence
O 01
o o

 

 

 

 

 

(b)

 

 

0.10 1.00 10.00 100.00 1000.00
Time (ms)
(x
«th!
-ve- —- P/ g

 

0.01

0.10 1.00 10.00 100.00

Time (ms)

1000.00

Figure 6. OJIP curve differences in mode of action by species 48 hours after
treatment (a) Canada thistle (b) common lambsquarters on (9) control, (I)
1X glyphosate, (A) 1X glufosinate, and (x) 1X chlorimuron.

53

LITERATURE CITED

Abbaspoor, M., and J.C. Streibig. 2005. Clodinafop changes the chlorophyll
fluorescence induction curve. Weed Sci. 53: 1-9.

Barbagallo, R.P., K. Oxborough, K.E. Pallet, and NR. Baker. 2003. Rapid, non-
invasive screening for perturbations of metabolism and plant growth using
chlorophyll fluorescence imaging. Plant Physiol. 132: 485-493.

Butler, W. L., 1978. Energy distribution in the photochemical apparatus of
photosynthesis. Annual Review of Plant Physiology, 29, 345-378.

Christensen, M.G., H.B.Teicher and J.C. Streibig 2003. Linking fluorescence
induction curve and biomass in herbicide screening. Pest Manag Sci
59:1303-1310.

Frankart, C., P. Eullaffroy, and G. Vemet. 2003. Comparative effects of four
herbicides on non-photochemical fluorescence quenching in Lemna minor.
Environ. Exp. Bot. 49: 159-168.

Govindjee, A. 1995. Kautsky-chlorophyll-a fluorescence. Aust. J. Plant Physiol.
22: 131-160.

Kirkwood, R.C., R. Hetherington, T.L. Reynolds, and G. Marshall , AbSorption,
localization, translocation and activity of glyphosate in bamyardgrass
(Echinochloa crus-galli (L) Beauv): influence of herbicide and surfactant
concentration. Pest Manag Sci 562359-367 (2000).

Olesen, OF, N. Cedergreen. 2010. Glyphosate uncouples gas exchange and
chlorophyll fluorescence. Pest Manag Sci 66:536-542.

Percival, MP, and NR. Baker. 1991. Herbicides and photosynthesis. Pages 1-
26in N.R. Baker and MP. Percival, eds. Herbicides. London: Elsevier.

Ralph, P.J., Herbicide toxicity of Halophi/a ova/is assessed by chlorophyll A
fluorescence. Aquat Bot 662141 -1 52 (2000).

Strasser, R.J., A. Sirivastava, and M. Tsimilli-Michael. 2000. The fluorescence
transient as a tool to characterize and screen photosynthetic samples.
Pages 445-483 in M. Yunus, U. Pathre, and P. Mohanty, eds. Probing
Photosynthesis: Mechanisms, Regulation and Adaptation. London: Taylor
8 Francis.

54

CHAPTER 3

EVALUATION OF THE INTERACTION BETWEEN GLYPHOSATE AND
GLUFOSINATE

Abstract. The stacking of genes to provide resistance to several
herbicides previously injurious to a crop provides new opportunities for control of
herbicide resistant weeds. Specifically the opportunity may exist to control
glyphosate resistant weeds with glufosinate. The combination of the non-
selective foliar herbicides, glyphosate and glufosinate, in a tank mix has the
potential to cause unexpected interactions. The objectives of this study were to
evaluate the combination of glyphosate and glufosinate on three annual weeds
prevalent in Michigan cropping systems; giant foxtail, common lambsquarters,
velvetleaf and the perennial weed, Canada thistle and to determine if
fluorescence parameters would be indicative of the combined herbicide injury
before being visually observable. Field and greenhouse studies showed
differential results for the combination of glyphosate and glufosinate on the weed
species studied. Early synergism was observed in the greenhouse for giant
foxtail and in the field for common lambsquarters, velvetleaf and Canada thistle.
This early synergism was not observed in the other species. Field studies to
determine herbicide interactions may result in more erratic data due to the effect
of environment on herbicide absorption and translocation. FluorescenCe
measurements in the greenhouse show that although glufosinate does rapidly act
to break down the PSII system of photosynthesis, it does affect how the

herbicides act in combination on these systems.

55

Nomenclature: Canada thistle, Cirsium arvense L. Scop; common .
lambsquarters, Chenopodium album L.; giant foxtail, Setaria faberi Herrm.;
velvetleaf, Abutilon theophrasti Medik; glufosinate, 2-amino—4-(hydroxy-methyl-
phosphoryl)butanoic acid; glyphosate, N-(phosphonomethyl)-glycine

Key words: Additive effect, antagonism, Colby’s, herbicide interaction, reduced
rates, synergism, tank-mixing.

Combining herbicides is a tool producers can use to increase the range of
weed control. By combining herbicides with different modes of action and
different target weeds, a farmer can potentially increase the spectrum of weed
control in his field with less application cost. Tank-mixtures, much like herbicide
rotation, are also used to prevent the development of herbicide resistant weeds
by altering selection pressures. Tank-mixing has been shown to be more
effective in reducing resistance evolution than using herbicides in a rotation
(Hugh and Reboud 2009). However tank-mixing can also result in uneXpected
interactions between herbicides, such as antagonism.

The stacking of traits for multiple herbicide resistance including those
resistant to both glyphosate and glufosinate will give producers the option to
apply tank-mixtures of these two broad spectrum, postemergence herbicides
potentially allowing for more weed species controlled with one herbicide
application.

While studying the interaction of these chemicals it is important to understand
their chemistry to determine how they may or may not work together. Glyphosate
(N-(phosphonomethyl)-glycine) is an organophosphorus herbicide that inhibits

the 5-enolpyruvylshikimate-3-phosphate synthase enzyme (EPSP) stopping the

synthesis of the aromatic amino acids, secondary plant metabolites and inhibiting

56

production of a chlorophyll precursor resulting in reduced chlorophyll synthesis
(Amrhein et al. 1980; Jaworski 1972; Kitchen et al. 1981). Glyphosate sensitive
weeds exhibit early symptomology of chlorosis followed by necrosis usUally from
2 to 10 days after application (Baird et al. 1971).

Glyphosate is a non-selective herbicide; however certain weed species are
inherently tolerant to glyphosate. Velvetleaf exhibits a low level of tolerance
(Kapusta et al. 1994) whereas the Poacea species like giant foxtail, are
susceptible (Sprankle 1974). Common lambsquarters has been shown to have
differential susceptibility to glyphosate application, which is thought to be based
on growth stage (Jaworski 1972; Lich et al. 1997; Ziska et al. 1999) and others
have reported no differences between herbicide responses by growth stage
(Sikkema et al. 2004; Tharp et al. 1999). These differences have been attributed
to different biotypes at the locations studied at (Schuster et al. 2007). Glyphosate
efficacy on Canada thistle is dependent upon the stage of growth, with more
injury occurring when controlled in the rosette stage than at bud initiation (Hunter
1995,1996)

Glufosinate (2-amino-4-(hydroxy-methyl-phosphoryl)butanoic acid) inhibits the
production of glutamine synthetase in sensitive species resulting in the buildup of
toxic ammonia and an inhibition of photosynthesis causing eventual necrosis of
the plant tissue (Hoagland 1983; Lea et al. 1984, Manderscheid and Wild 1986,
Ridley 1989, Wild at al. 1987).

Glufosinate sensitive species exhibit symptomology that is similar to that

of the PSII inhibitors and only occurs in the presence of light (Hess 2000;

57

Hoagland 1983). Rate of symptomology after application increases With bright
sunlight, high humidity, and moist soil conditions. Under these conditi0ns injury
can be seen by 2 days after treatment (Al-Khatib et al. 2003). Glufosinate has
been shown to have differential efficacy among weed species. Comm0n
lambsquarters has a low level of tolerance to glufosinate (Steckel et al. 1997).
Other research has shown that glufosinate at similar rates is more effective on
common lambsquarters than glyphosate (Higgins et al. 1991; Tharp et al. 1999).
Giant foxtail requires less than half the rate of glufosinate for 50% control than
velvetleaf or common lambsquarters (Steckel et al. 1997b). Velvetleaf and giant
foxtail control was 100% from one application at the 1X application rate, while
more was required for control of common lambsquarters (Krausz et al. 1999).
Glufosinate has low long term efficacy on perennial weeds like Canada thistle
due to the small amount of translocation causing regrowth from the roots (Pline
et al. 2000)

Recent reports have documented the interaction between glyphosate and
glufosinate (Chuah et al. 2008; Everrnan et al. 2009; Kudsk and Mathiassen
2004; Whitaker 2010). Antagonism was observed between the two herbicides in
goosegrass (Eleusine indica L. Gaertn.) at all studied rates (Chuah et al. 2008).
They attributed this observed antagonism to the fast acting nature of glufosinate
injuring the plant before the slower acting systemic glyphosate can act (Chuah et
al. 2008). Another study that observed antagonism between glyphosate and
glufosinate also observed synergism (Kudsk and Mathiassen 2004). Although

little research to date has been published on the interaction of glyphosate and

58

glufosinate, antagonism has been reported between glyphosate and other
contact herbicides (Appleby and Somabhi 1978; Hayward et al. 1988; Hydrick
and Shaw 1994; Lich et al. 1997; Wehtje et al. 2008). Glufosinate acts faster than
glyphosate to injure the plant, much like diquat, a bipyridilum contact herbicide. In
diquat plus glyphosate treatments, early synergism was observed betWeen the
chemicals (4 DAT), but later antagonism was observed due to increaSed
regrowth (Wehtje et al. 2008). Higher glyphosate rates were needed to
compensate for the inhibition of glyphosate activity caused by the rapid plant
death and retention of glyphosate in the treated leaf. An example of synergism of
fast acting herbicides is diuron and paraquat. Diuron quickly inhibits
photosynthesis before paraquat can cause cell destruction and allows limited
paraquat translocation to unsprayed portions of the plant (Hayward et al. 1988).

The interaction between glyphosate and glufosinate has been studied through
absorption and translocation studies at MSU and resulted in antagonism of the
two herbicides on giant foxtail due to reduced absorption and translocation out of
the treated leaf (Everman et al. 2009).

Glyphosate and glufosinate, although not primarily Photosystem ll (PS ll)
inhibitors, do ultimately cause cellular death resulting in a weakened ability to use
or disperse light energy. Changes in fluorescence induction (Kautsky curve) have
been used extensively in photosynthesis and herbicide research and are the
basis for all fluorescence parameters (Abbaspoor and Streibig, 2005;
Christensen et al., 2003; Percival and Baker, 1991). The benefits of uSing

fluorescence include its non-invasive procedure, sensitivity to many biotic and

59

abiotic stressors, ease and efficiency and numerous parameters to measure the
status of the photosynthetic apparatus (Abbaspoor and Streibig, 2005;
Barbagallo et al., 2003; Frankart et al., 2003; Strasser et al., 2000). Illumination

of dark-adapted unstressed leaves produces a rise in chlorophyll fluorescence
emission from the ground state (F0) to its maximum value (Fm) within one

second. An important parameter used in fluorescence research is the Fv/Fm

[Fv/Fm : (Fm-Fo)/Fm] parameter (Butler, 1978). The dark adaptation of a leaf

allows PSII to be fully reduced at QA and when illuminated the maximum

quantum efficiency of the PS ll photochemistry can be determined by Fv/Fm.
This parameter is used most often in the literature to indicate plant health with a
value of 0.83 indicating no stress to the plant. Fv/Fm has been used to measure
the effect of glyphosate on fluorescence in previous studies. Kirkwood et al 2000
used this parameter and detected some differences from the control one day
after treatment while neither Olesen and Cedergreen 2010 or Ralph 2000 found
any effect of glyphosate on Fv/Fm.

The objectives of this research were to evaluate potential interactions among
four rate matrix combinations of glyphosate and glufosinate in the field and
greenhouse, determine if the interactions were significant for antagonism and
synergism or just additive, determine if results in the greenhouse were consistent
with observations in the field, determine if there were differences between visual
control and quantitative measurements, determine if there were different
fluorescence responses among species and determine if fluorescence

measurements were indicative of early herbicide injury. We hypothesized that

60

weed control with combinations including low rates of glufosinate and the range
of glyphosate will be antagonistic while glufosinate at higher rates will be so fast
acting that antagonism will no longer be observed when combined with
glyphosate, early synergism between glyphosate and glufosinate would be
evident in some species, but by 28 DAT the synergism may no longer be evident
and fluorescence measurements would be indicative of the interaction much

earlier than visually observed.

MATERIALS AND METHODS

Field Trial. Field trials were conducted in 2008 at the Michigan State University
Agronomy Research Farm (42°42’42” N, 84°28’1 3” W) and 2009 at the Michigan
State University Plant Pathology Research Center (42°40‘59” N, 84°29’5” W) in
East Lansing, MI. The soil at the Agronomy Research Farm was a sandy clay
loam with 2.6% organic matter and a pH of 6.3. The soil at the Plant Pathology
Research Center was a fine sandy loam with a 2 to 6% slope, a pH of 6.9 and
2.5% organic matter. Fields preparation included fall-plowing followed by
cultivation in the spring to obtain maximum weed emergence. The experimental
design was a randomized complete block in 2008 and 2009. Treatments differed
between years and therefore were separated by year and summarized in Table
2.

Herbicide applications were made using a tractor-mounted compressed-air

sprayer calibrated to deliver 178 L / ha at 207 kPa through AirMix 11003

nozzlesa. Common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon

61

theophrasti Medik.) and giant foxtail (Setaria faberi Herrm.) were the predominant
weed species in both years and were the focus in this study. Other weed species
present included; redroot pigweed (Amaranthus retroflexus L.), Powell amaranth
(Amaranthus powellii S. Watson), common ragweed (Ambrosia artemisiifolia L.)
and large crabgrass (Digitaria sanguine/is L. Scop.) in 2008. Weed species in
2009 were similar to those in 2008 but also included a large population of wild
mustard (Sinapsis arvensis L.).

Visual estimates of weed control were made at 7, 14, 21 and 28 days after
treatment (DAT) in 2008 and 7, 14 and 21 DAT in 2009 on a scale of 0% (no

control) to 100% (complete control) based on injury compared to the untreated

control.

Greenhouse studies.

Plant material. Common lambsquarters, giant foxtail, and velvetleaf from

seed, and Canada thistle (Cirsium arvense L. Scop.) from root stockb were

grown In 9-cm pots contalnlng a commerCIal pottlng medlum In a greenhouse

with temperature maintained at 23 i 3°C. Natural light was supplemented by

high-pressure sodium lamps producing a photosynthetic photon flux density of

200 mol m'2 s.1 with a photoperiod of 16/8 h light/dark. Pots were watered daily

to maintain adequate soil conditions for optimum plant growth. Plants Were

fertilized with 50 ml of fertilizer solution containing 6 mg/L of 20% nitr09en, 20%

P205 and 20% K20 as needed. Weeds were sprayed at 10-12 cm which is

considered larger than optimum size which was done to accentuate differences

62

 

be
su
lhi
re;

lar

glu

Hel

E'Jej

VISU

thaj

between herbicide treatments. Greenhouse grown plants are typically more
susceptible to herbicides, however, spraying larger plants can compenSate for
this. There were four replications per experiment and each experiment was
repeated four times. When experiments were conducted on common
lambsquarters they were repeated six times because of the susceptibility to
pythium (Pythium spp.) and fusarium (Fusarium spp.) after glyphosate or

glufosinate application.

Herbicide treatments. Herbicides were applied in a matrix format so a range

of possible combinations of each herbicide at each rate were combined.

Herbicides were applied as follows; glyphosated at rates of 0, 210, 280, 420, and

840 g ae/ha and glufosinatee at rates of 0, 118, 157, 235, and 470 g ai/ha. These

rates are representative of 0.0x, 0.25X, 0.33X, 0.5X, and 1X of the label-
recommended rate (Anonymous, 2007a; Anonymous, 2007b). Ammonium sulfate
was included at 2% v/v in all treatments.

Applications were made using a single-nozzle track sprayer with an 8001

even flat fan nozzlef calibrated to deliver 187 Uha at a pressure of 207 kPa.

Visual estimates of weed control were taken at 5, 7, 14, 21 and 28 days after
treatment (DAT) on a scale of 0% (no control) to 100% (complete control) based
on injury compared with the untreated control. Plant height data was Collected
and above ground biomass was harvested and immediately weighed at 28 DAT.

Plant samples were oven-dried at 50 C for 48 hr and dry weights were recorded.

63

Data analysis. The data analysis was conducted using ANOVA uSi‘n‘g PROC

MIXED in SAS 9.29. Normality of the residuals was evaluated using normal

probability and box plots and arc sine data transformations were condUcted when
there were significant deviations from normality. Homogeneity of variances was
evaluated using Levene’s test. Herbicide combinations were determined to be
antagonistic, synergistic, or additive by comparing the observed plant responses
with the expected response when the herbicides are combined. Expected values
were calculated using Colby’s equation; E: X + Y— X Y/100 (Colby, 1967). In the
equation, X and Y is the percent growth inhibition by herbicide A and B
respectively and E is the expected percent growth inhibition by herbicides A and
B combined. Expected and observed responses were compared using Fishers
Protected Least Significant Difference (LSD) at p : 0.05 significance.
Combinations were determined as antagonistic, synergistic, or additive if the
observed response was less than, greater than or similar to the expeCted

response, respectively.

Fluorescence Studies.

Plant material. Common lambsquarters (Chenopodium album L.) Were grown
from seed in the greenhouse. Approximately 10 seeds per pot were sown into
soil media in 900 mL black plastic pots. Plants were thinned to one per pot upon

emergence. Canada thistle (Cirsium arvense L. Scop.) were grown from root
stockb obtained in May of 2008 and transplanted into soil mediac in 900 mL black

plastic pots. These plants were genetically similar. Tillers from stock plants were

64

transplanted into fresh media and pots. Canada thistle plants were selected for
treatment 2 weeks after transplant.

All plants were grown in greenhouses at Michigan State University campus in
East Lansing, MI and experiments took place in May of 2009. Natural light was

supplemented by high-pressure sodium lamps that produced a photosynthetic

photon flux density of 200 mol m'2 9‘. The photoperiod was 16/8 h light/dark,

and the temperature was 23:3°C. Plants were fertilized with 50 ml of fertilizer
solution containing 6 mg/L of 20% nitrogen, 20% P205 and 20% K20 as needed.

Plants were 10-12 cm tall at time of treatment and were randomly assigned to
herbicide treatments. Treatments were replicated three times and the experiment
repeated three times.

Herbicide treatments. Herbicide treatments consisted of glyphosate and
glufosinate alone and in combinations at the rates seen in Table 3. Ammonium

sulfate (AMS) at 2% v/v was used as an adjuvant. Treatments were applied using

a single-tip track sprayer using a TP8001 flat fan nozzlef delivering 187 L ha’1 at

a pressure of 207 kPA. Treatments were based on preliminary studies Which
showed these rates had the highest observable interaction and were also the
most economically interesting, such as, a high and a low rate combined, low
rates combined and high rates combined.

Fluorescence measurements. After herbicide application the plants were
immediately returned to the greenhouse and prepared for fluorescenCe reading.

Fluorescence readings were taken at 2, 4, 6, 8, 24, 48 and 72 hours after

65

treatment (HAT). The second set of fully emerged leaves above the Cotyledons,

with at least one more set of fully emerged leaves above were selected for

fluorescence evaluation. Leafclipsh were placed in the middle of the selected leaf

directly next to the midvein with the least amount of contact with any major veins.
The clip has a small shutter plate that must be closed over the leaf once the clip
is attached so that light is excluded and dark adaptation begins to take place.
The process of dark adaptation varied depending on plant species, ambient light
history and whether the plant was stressed. The average time required for dark

adaptation in this study was 15 minutes. Once dark adapted, the Handy Pocket

PEAi optical interface is attached to the clip around the shutter plate, the shutter

was opened and high intensity LED light passed through a NIR filter, Onto the
leaf. Then a highly sensitive PIN photodiode detects the fluorescence signal at
10|.Is intervals for 1 second. The data obtained in the 1 second period Was saved
in the Handy Pocket PEA and later downloaded into a computer. Treated plants
were visually rated for control, 0 being no control and 100 being complete
control, at 7, 14, 21 and 28 days after treatment (DAT). Plant heights Were

measured at 28 DAT and were then harvested and weighed for fresh Weight
immediately. Plants harvested were dried at 50°C for 48 hr, dry weights were

then determined and samples were discarded.

Data analysis. Data were subjected to ANOVA using PROC MIXED in SAS
and treatment means for Fv/Fm within species were compared using Fisher’s
Protected LSD at the p : 0.05 significance level. Data were transformed when
necessary for analysis and back-transforrned data are presented.

66

RESULTS AND DISCUSSION

Field Studies. Field studies in 2008 resulted in only one significant interaction;
this was due to the high rate of application of herbicides. It was for this reason
that a second field study conducted in 2009 which included a greater number of
combinations of application rates of glyphosate and glufosinate. Glyphosate
combined with glufosinate produced variable results in the field in 2009 which
were species dependent. This combination applied to velvetleaf resulted in early
synergism, but at 28 DAT all combinations were additive or antagoniStic for
control (Table 4). Glyphosate and glufosinate combined on common
lambsquarters resulted in early synergism and at 28 DAT the high rate of
glyphosate with the low rate of glufosinate resulted in antagonism. Where
glufosinate was applied at higher rates the antagonism was lost which is
consistent with much of the literature (Chuah et al. 2008; Kudsk and Mathiassen
2004; Whitaker 2010). In giant foxtail no early synergism was observed but at 28
DAT antagonism was observed with the application of below labeled rates of

glufosinate.

Greenhouse Studies. It was hypothesized that combinations including low rates
of glufosinate and the range of glyphosate would be antagonistic while
combinations with glufosinate at higher rates would be so fast acting that
antagonism would no longer be observed when combined with glyphOSate. In
greenhouse experiments, glyphosate and glufosinate were found to interact

antagonistically when applied in combination (Figure 7). This antagonism was

67

observed at the less than 1X rates of glufosinate in combination with the range of
glyphosate rates on Canada thistle (Figure 7a). Results with giant foxtail and
common lambsquarters were similar to those of Canada thistle but the
combination applied to velvetleaf resulted in antagonism across all rates of
glufosinate (Figure 7b). In field experiments results were similar to those found in
the greenhouse but with less observable trends due to the complete death of
many species attributable to the young growth stage at spraying (Table 4
appendix). There was significant regrowth from combined treatments by
velvetleaf, attributed to the failure of glyphosate reaching the actively growing
fissue

A second hypothesis was that early synergism between glyphosate and
glufosinate would be evident in some species, but by 28 DAT the synergism may
no longer be evident. This was observed for the combination of the range of
glyphosate rates and the lowest glufosinate rate on giant foxtail. At the 5 DAT
observations this combination showed synergism (Figure 8a) which by 28 DAT
was no longer evident and in one case replaced with an antagonistic interaction
(Figure 8b). Canada thistle, common lambsquarters and velvetleaf had
observable early and late antagonism (data not shown). Field studies were not
similar to the greenhouse studies. Early synergism was observed in velvetleaf

and common lambsquarters but was not seen in giant foxtail (Table 4).

Fluorescence Studies. Fv/Fm for Canada thistle was chosen as the parameter

to examine for significant differences between herbicide combinations. The

68

interactions between herbicides are discussed in great detail for both Canada
thistle and common lambsquarters in Appendix B. The Fv/Fm of a healthy plant
is 0.83, a value smaller than 0.83 is an indication of the inability of the plant, due
to injury, to efficiently photosynthesize.

Fv/Fm values following glyphosate and glufosinate combinations applied
to Canada thistle were lower than those when glyphosate only and glUfosinate
only were applied (Figure 9). Differences were dependent upon the rates in the
combination and time of measurement (Figure 9). Fv/Fm values after the
application of the combination of IX glyphosate + 0.25X glufosinate were not
statistically different from Fv/Fm values following the glufosinate only application
at 2 HAT and 72 HAT but were significantly lower than the Fv/Fm values
following the glyphosate only application from 4 HAT through 72 HAT (Figure
9a). Fv/Fm values following application of the combination of 0.5X glyphosate +
0.5X glufosinate were significantly lower than the Fv/Fm values after the
glufosinate only application at 2 and 8 HAT but were significantly lower than all
Fv/Fm values at all HAT after glyphosate only applications (Figure 9b). Fv/Fm
values following the application of the combination of 0.25X glyphosate + 1X
glufosinate were never significantly different from the Fv/Fm values when
glufosinate only was applied (Figure 9c) From 2 to 48 HAT Fv/Fm values of the
combined glyphosate and glufosinate were significantly lower than thOSe of the
glyphosate only applications (Figure 9c). Fv/Fm values following glyphosate and
glufosinate combined treatments were significantly lower than the Fv/F'm values

for the control from 4 HAT onward (Figure 10).

69

Early synergism was observed in the greenhouse for giant foxtail and in
the field for common lambsquarters, velvetleaf and Canada thistle. Field studies
to determine herbicide interactions generally resulted in more erratic data,
possibly due to the effect of the environment on herbicide absorption and
translocation. Fluorescence measurements in the greenhouse showed that
although glufosinate acted rapidly to break down the PSII system of
photosynthesis, it affected herbicide response in combination on these systems.
Glufosinate alone and in combination resulted in significantly lower FV/Fm values
than the control or glyphosate alone.

The antagonistic interaction between glyphosate and glufosinate has
been observed in other studies on other species and was commonly attributed to
the rapid action of glufosinate on the photosynthetic system which reduced
glyphosate translocation through the plant (Chuah et al. 2008; Everman et al.
2009; Kudsk and Mathiassen 2004; Whitaker 2010).

The results from these studies show that the combination of glyphosate
and glufosinate are antagonistic in common lambsquarters, Canada thistle, giant
foxtail and velvetleaf, and that although not indicative of the herbicide interaction,
they do show that glufosinate rapidly acts to break down the plant before

glyphosate.

70

SOURCE OF MATERIALS

aAirMix 11003, Greenleaf Technologies, PO. Box 1767, Covington, LA 70434.
bDon Penner’s Farm Williamston, Ml. pennerd@msu.edu.

C:Baccto® High Porosity Professional Potting Mix, Michigan Peat Co., Houston,
TX.

dRoundup WeatherMAX®, Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO
63167.

eLiberty®, Bayer CropScience, Research Triangle Park, NC.
fTeeJet®, Spraying Systems Co., PO. Box 7900, Wheaton, IL 60189.

9The SAS System for Windows Version 9.2, SAS Institute Inc, 100 SAS Campus
Dr., Cary, NC 2751.

hLeaf Clips, Handy Pocket PEA, Hansatech Instruments, Narborough Road,
King’s Lynn, Norfolk, UK.

IHandy Pocket PEA, Hansatech Instruments, Narborough Road, King’s Lynn
Norfolk, UK.

71

Table 2. Herbicide combinations applied in field studies 2008

 

 

 

 

and 2009.81
Herbicides Applied b Year - Field Studies
2008 2009
Control Control
0.25X GLYb 0.25X GLY
0.33X GLY 0.5X GLY
0.5X GLY 1X GLY
1X GLY 0.25X GLU
1X GLU 0.5X GLU
0.25X GLY + 1X GLU 1X GLU
0.33X GLY + 1X GLU 0.25X GLY + 1X GLU
0.5X GLY + 1X GLU 0.5X GLY + 0.5X GLU
1X GLY + 1X GLU 1X GLY + 0.25X GLU

 

1X GLY+1X GLU

 

a Where 1X : the labeled rate; Glyphosate applied as
Roundup WeatherMAX 1X : 840 g ae/ha; Glufosinate applied

as LIBERTY 1X : 420 g ai/ha

b Abbreviations: GLY, glyphosate; GLU, Glufosinate

Thifensulfuron.

72

 

Table 3. Herbicide combinations applied in fluorescence

 

 

 

 

studiesa ,
Herbicides Applied by Species - Fluorescence Studie_'s__
CIRAR + CHEAL ABUTH + SETFA
Control Control
0.25X GLYb 0.25X GLY
0.5X GLY 1X GLY

1X GLY 0.25X GLU
0.25X GLU 0.5X GLU
0.5X GLU 1X GLU
1X GLU 0.25X GLU + 1X GLY
0.25X GLU + 1X GLY
0.5X GLU + 0.5X GLY
1X GLU + 0.25X GLY

 

 

8 Where 1X : the labeled rate; glyphosate applied as Roundup
WeatherMAX 1X : 840 g ae/ha; Glufosinate applied as
LIBERTY 1X : 420 g ai/ha

b Abbreviations: GLY, glyphosate; GLU, glufosinate.

73

 

Table 4. Visual control 7 and 28 days after treatment of velvetleaf, common
lambsquarters and giant foxtail when applied with combinations of glyphosate

and glufosinate in 2009 field study.a

 

Visual Control
ABUTH CHEAL SETFA

Herbicide Rateb’c 7 DAT 28 DAT 7 DAT 28 DAT 7 DAT 28 DAT

 

 

 

GLY GLU Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp.0bs. “Exp. Obs.

 

gae/ha gal/ha %
0 0 — 0 — 0 — 0 — 0 - 0 — 0
210 0 - 38 — 46 - 36 - 48 — 75 - 86
420 0 - 48 - 100 — 29 - 85 — 89 — 99
840 0 - 48 - 100 - 48 - 99 — 80 - 100
0 118 - 30 - 31 - 35 — 31 — 49 — 76
0 235 — 48 - 39 - 46 - 29 - 64 — 73
0 470 - 100 — 70 — 97 - 89 - 94 86

210 470 100 99 85 63 H 98 95 94 89 98 95 98 95
420 235 73 99 (+) 100100 62 95 (+) 89100(+) 96 91 100 86l-)

840 118 64 95 (+) 100 90 H 66 95 (+) 99 91 (-l 90 95 100 89H
840 470 64 90 (+) 100 100 66 93 (+) 99 100 90 90 100 100
LSD (0.05)d 3 2 2 2 2 _ 2

 

a . . . . ' .

+ and - denote a synergistic and antagonistic interaction for a given comblnatlon accordlng to
the LSD comparison of the observed and expected values calculated using Colby’s method.
Observed values without a + or - are additive.

bAbbreviations: GLY, glyphosate; GLU, glufosinate; ABUTH, velvetleaf; CHEAL, c0mmon
lam bsquarters; SETFA, giant foxtail; DAT, days after treatment; Exp., expected; Obs., observed.

CTreatments containing glyphosate and/or glufosinate also included ammonium sulfate at 2%

dLSD values may be used to compare values.

74

(b)

Control (%)

   
  

  

I Expected
‘1 8% Observed

  
  

 

1/4X 1XGLU 1/4X 1/4X

GLU GLY + GLY +
1/4X 1X GLU
GLU

Herbicide Applied

I Expected
: 22: Obsenred

1/4X 1/4X 1X GLU 1/4X 1/4X

GLY GLU GLY + GLY +
1/4X 1X GLU
GLU

Herbicide Applied

Figure 7. Glyphosate(GLY) and glufosinate(GLU) on Canada thistle (a) and
velvetleaf (b) visual observations in the greenhouse 28 days after treatment.
Antagonism by Colby's method indicated by a (-). LSD : 15 (a) and 10 (b).

75

(a) 100 -

(+) (+)

Control (%)
01
O

I Expected
38 Observed

     

 

{.51.}

1/4X GLY 1X GLY 1/4X GLU1/4X GLY1X GLY +

_ _ _ +1/4X 1/4X GLU
HerbICIde Applied GLU

(b) 100
90
80
70
60
50
4o
30
20
10 «2

I Expected
'5 Observed

Control (%)

_L_ .J._I__I__L_ __L._L ..l_.'

  

   

_T—'"_‘

1/4X GLY 1X GLY 1/4X GLU1/4X GLY1X GLY +
+ 1/4X 1/4X GLU

Herbicide Applied

Figure 8. Glyphosate(GLY) and glufosinate(GLU) on giant foxtail visual
observations in the greenhouse 5 DAT (a) and 28 DAT(b). Antagonism and
synergism by Colby's method indicated by a (-) or (+) respectively. LSD = 8.

76

+CONTROL
+1 X GLY
+0.25X GLU

. -)(-0.25X GLU + 1X
0 r r r r . . GLY

2HAT 4HAT 6HAT 8HAT 24 48 72
HAT HAT HAT

 

 

 

(b) * .
0.9 ' - ,, j *
0.8 ., ---—-
*
E 3'; \ t -0-CONTROL
E 0.5 \ XG y
- ‘ ‘7. +05 L
0.4 - »
0.3 - +0.5x GLU
0.2 r \ y
0.1 - \ -x-o.5x GLU +0.5x
0 r T I r I T GLY

 

 

2HAT 4HAT 6HAT 8HAT 24 48 72
HAT HAT HAT

(C)

 

0.9
0.8
8'; -0-CONTROL
E .
é 0-5 +0.25x GLY
u. 0.4
0-3 -I-1X GLU
0.2
0.1 —x-1x GLU + 0.25X
O T T I I r 1 GLY

 

 

2 HAT 4 HAT 6 HAT 8 HAT 24 48 72
HAT HAT HAT

Figure 9. Fv/Fm of glyphosate(GLY) and glufosinate(GLU) on Canada
thistle.Where a (*) indicates the combination is significantly different from
glyphosate applied alone and a (0) indicates significantly different from
glufosinate applied alone.

77

(a) 0.84 -

0.82 2

0.8 2
0.78
0.76
0.74
0.72

FvlFm

0.68 d
0.66 ~
0.64 4

 

 

(b) 0.7 Herbicide Applied

Fv/F m

 

 

 

 

Herbicide Applied

Figure 10. Fv/Fm of glyphosate and glufosinate on Canada thistle at (a) 2
hours after treatment and (b) 72 hours after treatment. Where a (*) indicates
the combination is significantly different from the control.

78

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Sikkema, P. H., C. Shropshire, A. S. Hamill, S. E. Weaver, and P. B. Cavers.
2004. Response of common lambsquarters (Chenopodium albtlm) to
glyphosate application timing and rate in glyphosate-resistant corn. Weed
Technol. 18: 908-916.

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Sprankle, P., W. F. Meggitt, and D. Penner. 1975. Absorption, action and
translocation of glyphosate. Weed Sci. 23: 235-240.

Strasser, R.J., A. Sirivastava, and M. TsimiIIi-Michael. 2000. The fluorescence
transient as a tool to characterize and screen photosynthetic samples.
Pages 445-483 in M. Yunus, U. Pathre, and P. Mohanty, eds. Probing
Photosynthesis: Mechanisms, Regulation and Adaptation. London: Taylor
8r Francis.

Steckel, G. J., L. M. Wax, F. W. Simmons, and W. H. Phillips II. 1997.
Glufosinate efficacy on annual weeds is influenced by rate and growth
stage. Weed Technol. 11: 484-488.

Tharp, B. E., O. Schabenberger, and J. J. Kells. 1999. Response of annual weed
species to glufosinate and glyphosate. Weed Technol. 13: 542-547.

Wehtje, G., J. E. Altland, and C. H. Gilliam. 2008. Interaction of glyphosate and
diquat in ready-to-use weed control products. Weed Technol. 22: 472-476.

Whitaker, J. 2010. Interaction of glyphosate and glufosinate: University of
Georgia/North Carolina State University.

Wild, A., H. Sauer, and W. Ruhle. 1987. The effect of phosphinothricin
(glufosinate) on photosynthesis.1.Inhibition of photosynthesis and
accumulation of ammonia. Zeitsch rift fur naturforschung C-A J‘o'Urnal of
Biosciences 42: 263-269.

Ziska, L. H., J. R. Teasdale, and J. A. Bunce. 1999. Future atmospheric carbon
dioxide may increase tolerance to glyphosate. Weed Sci. 47: 608-615.

82

CHAPTER 4

EVALUATION OF THE INTERACTION BETWEEN GLYPHOSATE AND THE
SULFONYLUREA HERBICIDES CHLORIMURON AND THIFENSULFURON

Abstract: The stacking of genes to provide resistance to several herbicides
previously injurious to a crop provides new opportunities for control of herbicide
resistant weeds. The combination of the non-selective foliar herbicides,
glyphosate with the selective sulfonylurea herbicides in a tank mix has the
potential to cause unexpected interactions. The objectives of this study were to
evaluate the combination of glyphosate and glufosinate on three annual weeds
prevalent in Michigan cropping systems; giant foxtail, common lambsquarters,
velvetleaf and the perennial weed, Canada thistle and to determine if
fluorescence parameters would be indicative of the combined herbicide injury
before being visually observable. Field and greenhouse studies shoWed

differential results for the combination of glyphosate and the sulfonylureas on the

weed species studied. 14C-chlorimuron and 14C glyphosate were uSed to

determine the basis of a visually observable interaction. The addition of
chlorimuron to radiolabeled glyphosate resulted in an increase of glyphosate
absorption and translocation in common lambsquarters and giant foxtail and a
decrease of translocation in Canada thistle. The addition of glyphosate to
radiolabeled chlorimuron caused an increase in chlorimuron absorption in all
Species while translocation was either similar or lower than when the herbicide

was applied alone.

83

Nomenclature: Canada thistle, Cirsium arvense L. Scop; common
lambsquarters, Chenopodium album L.; giant foxtail, Setaria faberi Herrm.;
velvetleaf, Abutilon theophrasti Medik; chlorimuron, 2-[[[[(4-chloro-6-m'ethoxy-2-
pyrimidinyl)amino]carbonyl]amino]sulfonyl] benzoic acid; glyphosate, N-
(phosphonomethyI)-glycine; thifensulfuron, methyl 3-[[[[(4-methoxy-6-methyl-1,3-
5-triazin-2-yl)amino]carbonyl]amino]squonyl]-2-thiophenecarboxylate.

Key words: Additive effect, antagonism, Colby’s, herbicide interaction, reduced
rates, synergism, tank-mixing.

The Herbicide Handbook states that chlorimuron may have reduced
efficacy when tank-mixing with other herbicides (Sensemen 2007). One study
found that chlorimuron and glyphosate were either additive or antagonistic
depending on rates applied and species applied to (Starke and Oliver 1998). A
recent study found that glyphosate tank-mixed with one- half label rates of
chlorimuron gave the highest percent control (80%) of the combinations studied
on common lambsquarters (Knezevic et al. 2009). The addition of chlorimuron to
glyphosate did not reduce the efficacy of glyphosate in velvetleaf (Jordan et al.
1997). Variation between years was found in a 1996 and 1997 field stildies. In
1996 Vidrine et al. 2002 found that at all rates chlorimuron plus glyphosate had
greater control than glyphosate applied alone, however this was not obsenred in
1997 (Vidrine et al. 2002). These studies were not subjected to Colby’s analysis
of interaction and thus mixed results could have been observed. Tank-mixing
glyphosate plus chlorimuron and thifensulfuron resulted in lower soybean yields
compared with glyphosate alone but with no significant differences in Weed
control (Corrigan and Harven 2000).

Tank mixtures of glyphosate and thifensulfuron at a range of rates were

additive for control of common lambsquarters (Lich et al. 1997). The basis for the

84

interaction between these two herbicides was hypothesized to be redUced
absorption and translocation of the chlorimuron in combination compared to the
chlorimuron applied alone. Absorption of non-formulated glyphosate typically
ranged from 25 to 50% while addition of adjuvants in a formulation and
ammonium sulfate (AMS) increased absorption up to 90% (Maschhoff et al.,
2000; Sprankle et al., 1975; Young et al., 2003). Absorption of glyphosate
increased over time with the majority of uptake occurring before 72 hours after
treatment, with subsequent translocation through the phloem accumulating in

young leaves, roots and meristems (Bromilow et al., 1993). Addition of

glyphosate to chlorimuron has been shown to increase the absorption of 14C-

chlorimuron (Starke and Oliver, 1998). Chlorimuron translocation is species
dependent and generally low (<50%) (Wilcut et al., 1989).

Glyphosate and chlorimuron, although not primarily Photosystem II (PS ll)
inhibitors, ultimately cause cellular death resulting in a weakened ability to use or
disperse light energy. Changes in fluorescence induction (Kautsky curve) have
been used extensively in photosynthesis and herbicide research and are the
basis for fluorescence parameters (Abbaspoor and Streibig, 2005; Christensen et
al., 2003; Percival and Baker, 1991). The benefits of using fluorescence include
its non-invasive procedure, sensitivity to many biotic and abiotic stressors, ease
and efficiency and numerous parameters to measure the status of the
photosynthetic apparatus (Abbaspoor and Streibig, 2005; Barbagallo et al., 2003;

Frankart et al., 2003; Strasser et al., 2000).

85

Illumination of dark-adapted unstressed leaves produces a rise in

chlorophyll fluorescence emission from the ground state (F0) to its maXimum

value (Fm) within one second. An important parameter used in fluoresCence

research is the Fv/Fm [Fv/Fm : (Fm-Fo)/Fm] parameter (Butler, 1978). The dark
adaptation of a leaf allows PSII to be fully reduced at 0A and when illuminated

the maximum quantum efficiency of the PS Il photochemistry can be determined
by Fv/Fm. This parameter is used most often in the literature to indicate plant
health with a value of 0.83 indicating no stress to the plant. Fv/Fm has been used
to measure the effect of glyphosate on fluorescence in previous studies.
Kirkwood et al 2000 used this parameter and detected treatment differences from
the control one day after treatment while neither Olesen and Cedergreen 2010 or
Ralph 2000 found any effect of glyphosate on Fv/Fm.

The objectives of this study were to evaluate potential interactibns among
four rate matrix combinations of glyphosate with chlorimuron and thifensulfuron in
the field and greenhouse, determine if the interactions were significant for
antagonism and synergism or just additive, determine if results in the greenhouse
were consistent with observations in the field, determine if there were differences
between visual control and quantitative measurements, determine if there were
different fluorescence responses among species and determine if fluorescence
measurements were indicative of early herbicide injury and determine the basis
for the interactions observed between glyphosate and chlorimuron with
absorption and translocation studies. The following hypothesis were proposed,

early synergism between herbicides will be observed in some species , but at 28

86

DAT synergism may no longer be evident, the interaction of the two different
sulfonlyureas with the glyphosate may be similar to each other, fluorescence
measurements would be indicative of the interaction much earlier than visually
observed and absorption and translocation studies would show that reduced

absorption and translocation was the basis for the interaction.

MATERIALS AND METHODS

Field Trial. Field trials were conducted in 2008 at the Michigan State University
Agronomy Research Farm (42°42’42” N, 84°28’1 3” W) and 2009 at the Michigan
State University Plant Pathology Research Center (42°40’59” N, 84°29’5” W) in
East Lansing, MI. The soil at the Agronomy Research Farm was a sandy clay
loam with 2.6% organic matter and a pH of 6.3. The soil at the Plant Pathology
Research Center was a fine sandy loam with a 2 to 6% slope, a pH of 6.9 and
2.5% organic matter. Fields preparation included fall-plowing followed by
cultivation in the spring to obtain maximum weed emergence. The experimental
design was a randomized complete block in 2008 and 2009. Treatments differed
between years and were therefore separated by year and summarized in Table
5.

Herbicide applications were made using a tractor-mounted compréSsed-air

sprayer calibrated to deliver 178 L / ha at 207 kPa through AirMix 11003

nozzlesa. Common lambsquarters (Chenopodium album L.), velvetleaf (Abutilon

theOphrasti Medik.) and giant foxtail (Setaria faberi Herrm.) were the predominant
weed species in both years and were the focus in this study. Other weed species

present included; redroot pigweed (Amaranthus retroflexus L.), Powell amaranth

87

(Amaranthus powellii S. Watson), common ragweed (Ambrosia artemisiifolia L.)
and large crabgrass (Digitaria sanguine/is L. Scop.) in 2008. Weed species in
2009 were similar to those in 2008 but also included a large population of wild
mustard (Sinapsis an/ensis L.).

Visual estimates of weed control were made at 7, 14, 21 and 28 days after
treatment (DAT) in 2008 and 7, 14 and 21 DAT in 2009 on a scale of 0% (no
control) to 100% (complete control) based on injury compared with the untreated

control.

Greenhouse studies.

Plant Material. Common lambsquarters, giant foxtail, and velvetleaf from

seed, and Canada thistle (Cirsium arvense L. Scop.) from root stockb were

grown In 9-cm pots contalnlng a commerCIal pottlng medium In a greenhouse

with temperature maintained at 23 :I: 3°C. Natural light was supplemented by

high-pressure sodium lamps producing a photosynthetic photon flux density of

200 moI-m'2-s-1 with a photoperiod of 16/8 h light/dark. Pots were watered daily

to maintain adequate soil conditions for optimum plant growth. Plants were

fertilized with 50 ml of fertilizer solution containing 6 mg/L of 20% nitrogen, 20%

P205 and 20% K20 as needed. Weeds were sprayed at 10-12 cm which is

considered larger than optimum size which was done to accentuate differences
between herbicide treatments. Greenhouse grown plants are typically more

susceptible to herbicides, however, spraying larger plants can compensate for

88

this. There were four replications per experiment and each experiment was
repeated four times. When experiments were conducted on common
lambsquarters they were repeated six times because of the susceptibility to
pythium (Pythium spp.) and fusarium (Fusarium spp.) after glyphosate or

glufosinate application.

Herbicide treatments. Herbicides were applied in a matrix format so all
possible combinations of each herbicide at each rate were combined, with the

exception of the tank-mixtures of chlorimuron and thifensulfuron, both ALS

inhibitors. Herbicides were applied as follows; glyphosated rates of 0, 210, 280,
420, and 840 g ae/ha, chlorimuron-ethyle (hereafter referred to as chlorimuron)

rates of 0, 2.2, 2.9, 4.4, and 8.8 g ailha and thifensulfuron-methylf (hereafter

referred to as thifensulfuron) rates of (0, 1.125, 1.5, 2.25, and 4.5 g ailha). These
rates are representative of 0.0x, 0.25X, 0.33X, 0.5X, and 1X of the label-

recommended rate (Anonymous, 2006a; Anonymous, 2006b; Anonymous,
2007). A crop oil concentrateg (COC) was included at 1% v/v in treatments
containing only chlorimuron or only thifensulfuron. Ammonium sulfate was
included at 2% v/v in all treatments containing glyphosate or glufosinate alone or

in combination.

Applications were made using a single-nozzle track sprayer with 8001 even
flat fan nozzleh calibrated to deliver 187 Uha at a pressure of 207 kPa. Visual

estimates of weed control were taken at 5, 7, 14, 21 and 28 days after treatment

89

(DAT) on a scale of 0% (no control) to 100% (complete control) based on injury
compared to the untreated control. The timing of visual injury ratings was
dependent upon the herbicide applied and the weed species. Plant height data
were collected and above ground biomass harvested and immediately weighed
at 28 DAT. Plant samples were oven-dried at 50°C for 48 hr and dry weights

were recorded.

Data analysis. The data analysis was conducted using ANOVA in PROC
MIXEDi. Normality of the residuals was evaluated using normal probability and

box plots and arc sine data transformations were conducted when there were
significant deviations from normality. Homogeneity of variances was evaluated
using Levene’s test. Herbicide combinations were determined to be antagonistic,
synergistic, or additive by comparing the observed plant responses with the
expected response when the herbicides are combined. Expected values were
calculated using Colby’s equation; E: X + Y— X Y/100 (Colby, 1967). In the
equation, X and Y is the percent growth inhibition by herbicide A and B
respectively and E is the expected percent growth inhibition by herbicides A and
B combined. Expected and observed responses were compared using Fishers
Protected least significant difference (LSD) at p : 0.05 significance.
Combinations were determined as antagonistic, synergistic, or additive if the
observed response was less than, greater than or similar to the expected

response respectively.

Fluoresence Studies.

90

Plant material. Common lambsquarters (Chenopodium album L.), were grown
from seed in the greenhouse. Approximately 10 seeds each were sown into soil
media in 900 mL black plastic pots. Plants were thinned to one per pot upon
emergence. Canada thistle (Cirsium arvense L. Scop.) were grown from root
stock obtained in May of 2008 and transplanted into soil media in 900 mL black
plastic pots. These plants were genetically similar. Tillers from stock plants were
transplanted into fresh media and pots. Canada thistle plants were selected for
treatment 2 weeks after transplant.

All plants were grown in greenhouses at Michigan State University campus in
East Lansing, MI and experiments took place in May of 2009. Natural light was

supplemented by high-pressure sodium lamps that produced a photosynthetic

photon flux density of 200 mol m'2 s'1. The photoperiod was 16/8 h light/dark,

and the temperature was 23:3°C. Plants were fertilized with 50 ml of fertilizer
solution containing 6 mg/L of 20% nitrogen, 20% P205 and 20% K20 as needed.

Plants were 10-12 cm tall at time of treatment and were randomly assigned to
herbicide treatments. Treatments were replicated three times and the experiment
repeated three times with common lambsquarters and Canada thistle.
Treatments were replicated three times and the experiment conducted one time
with velvetleaf and giant foxtail.

Herbicide treatments. Herbicide treatments consisted of glyphosate and
chlorimuron alone and in combinations at the rates seen in Table 6. Ammonium
sulfate (AMS) at 2% v/v was used as an adjuvant when glyphosate was applied

alone or in combination with chlorimuron. Crop oil concentrate was used at 1%

91

v/v when chlorimuron was used alone. Treatments were applied using a single-
tip track sprayer using a TP8001 flat fan nozzle delivering 187 L ha'1 at a
pressure of 207 kPA. Treatments were based on preliminary studies which
showed these rates had the highest observable interaction and were also the
most economically interesting, such as, a high and a low rate combined for each
herbicide respectively, low rates combined and high rates combined.
Fluorescence measurements. After herbicide application the plants were
immediately returned to the greenhouse and prepared for fluorescenCe reading.
Fluorescence readings were taken at 2, 4, 6, 8, 24, 48 and 72 hours after
treatment (HAT). The second set of fully emerged leaves above the cotyledons,

with at least one more set of fully emerged leaves above were selected for

fluorescence evaluation. LeafclipsJ were placed in the middle of the selected leaf

directly next to the midvein with the least amount of contact with any major veins.
The clip has a small shutter plate must should be closed over the leaf Once the
clip is attached so that light is excluded and dark adaptation begins to take place.
The process of dark adaptation varied depending on plant species, ambient light
history and whether the plant was stressed. The average time required for dark

adaptation in this study was 15 minutes. Once dark adapted, the Handy Pocket

PEAk optical interface is attached to the clip around the shutter plate, the shutter

was opened and high intensity LED light passed through a NIR filter, onto the
leaf. Then a highly sensitive PIN photodiode detects the fluorescence signal at
10us intervals for 1 second. The data obtained in the 1 second period was saved

in the Handy Pocket PEA and later downloaded into a computer. Treated plants

92

were visually rated for control, 0 being no control and 100 being complete
control, at 7, 14, 21 and 28 days after treatment (DAT). Plant heights were
measured at 28 DAT and were then harvested and weighed for fresh weight

immediately. Plants harvested were dried at 50°C for 48 hr, dry weights were

then determined and samples were discarded.

Data analysis. Data were subjected to ANOVA using PROC MIXED in SAS
and treatment means for Fv/Fm within species were compared using Fisher’s
Protected LSD at the p : 0.05 significance level. Data were transformed when

necessary for analysis and back-transforrned data are presented.

Absorption and Translocation of Glyphosate and Chlorimuron

Plant Material. Common lambsquarters (Chenopodium album L.) and
giant foxtail (Setaria faberi Herrm.) from seed, and Canada thistle (Cirsium
arvense L. Scop.) from root stock were grown in 9-cm pots containing a
commercial potting medium in a greenhouse with temperature maintained at

23:3°C. Natural light was supplemented by high-pressure sodium lamps

producing a photosynthetic photon flux density of 200 mol-m'Z-s'1 with a

photoperiod of 16/8 h light/dark. Weeds were sprayed at 10-12 cm which is
considered larger than optimum size which was done to accentuate differences
between herbicide treatments. Plants were randomly assigned to herbicide
treatments and harvest times. Experiments were replicated four times and

conducted twice.

93

Uptake and translocation. The first fully expanded leaf on each plant of

each species was chosen for 14C treatment. This leaf was marked and carefully

wrapped with aluminum foil before broadcast herbicide application. Herbicide
combinations of glyphosate and chlorimuron were applied to plants at the 6 to 8

leaf stage using a single-tip track sprayer with a 8001 E flat fan nozzle delivering

187 L ha'1 at a pressure of 207 kPA. After application of the herbicides, plants
were moved to the greenhouse and the aluminum foil removed. The 14C spotting
. . 14 . . . . . -1 14

solution contalned C-glyphosate mm a speCIflc actIVIty of 5 kBq mg or C-

chlorimuron with a specific activity of 2.4 kBq mg ’1 and herbicide solution to
bring the spotting solution to the combined rates (Table 7). Ten IuL drops were
then applied to the adaxial leaf surface of the second fully expanded leaf , five on
either side of the leaf midrib, to deliver a total of 10uL of 14C-labeled and
broadcast spray mix. Following treatment the treated leaves were washed off and
plants were harvested at 6, 24 and 48 hours after treatment (HAT). At each of the
harvest times treated leaves were removed and rinsed with a 1:1 methanol 2

distilled water mix with 0.25% v/v non-ionic surfactant (NIS), to remove any

unabsorbed herbicide. The rinsate was radioassayed by liquid scintillation

spectrophotometry (LSS). The quantity of 14C-glyphosate in the rinsate was

compared to the amount of 14C-glyphosate applied for each treatment. At the

time of rinsing, plants are separated into treated leaf (TL), above treated leaf

(ATL), and below treated leaf (BTL). ATL and BTL were separated at the leaf

94

axial of the TL. The portion of 1A'C-glyphosate translocated was calculated by

subtracting the amount in the treated leaf from the amount absorbed. Plants were
then put into the dryer at 50°C for 48 hours, ground using a mortar and pestle
and Ig of material per sample weighed and oxidized.

Data analysis. Data were analyzed using ANOVA in PROC MIXED in SAS
9.2. Normality of the residuals was evaluated using normal probability and box

plots. Homogeneity of variances was evaluated using Levene’s test. No
significant differences were found between the duplicate experiments. Mean
separation was achieved with Fisher’s Protected LSD Test at the p : 0.05

significance level.

RESULTS AND DISCUSSION

Field Studies. Field studies in 2008 resulted in only one significant interaction;
due to the high rate of application of herbicides. Thus a second field study was
conducted in 2009 with a greater number combination of application rates of
glyphosate and chlorimuron. Early synergism and antagonism were observed in
all species at all the rates tested. For all species studied the 7 DAT observations
resulted in more statistically significant interactions than the 28 DAT
observations. Giant foxtail was the only species to have observable interactions
at the 7 DAT observation and no significant interactions at the 28 DAT

observations (Table 8).

Greenhouse Studies.

95

The sulfonylurea herbicides combined with glyphosate applied to common
lambsquarters resulted in similar interactions as hypothesized. At 28 DAT both of
these combinations showed similar synergistic combinations (Figure 11).
However the combination with thifensulfuron showed more synergism at all times
and also had antagonism with two combinations at 28 DAT (data not shown).
Fresh weight reduction and height reduction data indicated greater weed control
was achieved with the thifensulfuron than chlorimuron combined with glyphosate,
however, the visual control observations showed exactly the opposite (data not
shown). Chlorimuron treated plants showed greater leaf desiccation; however
plant weight and height of plants receiving chlorimuron plus glyphosate were
greater than when thifensulfuron was applied with glyphosate (Figure 11).
Although there were a few examples of when the sulfonylurea herbicides acted
similarly in combination with glyphosate, there were more instances where they
were dissimilar for weed control. The combination of the sulfonylurea herbicides
and glyphosate resulted in more significant interactions in the chlorimuron
combination than the thifensulfuron combination on Canada thistle, velvetleaf
and giant foxtail (data not shown).

The third hypothesis was that the combination of glyphosate and
chlorimuron interactions would be species dependent. Antagonism was apparent
from the height reduction data for Canada thistle and velvetleaf and the visual
control data for giant foxtail (Figure 12). Visual control data from all other species
showed species dependent antagonism and synergism less than the quantitative

observations (data not shown). The combined application of glyphosate and

96

chlorimuron to common lambsquarters showed significant synergism in data
collected at 28 DAT (Figure 12). Based on these results the combination of

glyphosate and chlorimuron was chosen for absorption and translocation studies.

Fluorescence Studies. Fv/Fm for Canada thistle was chosen as the parameter
to examine for significant differences between herbicide combinations. The
interactions between herbicides are discussed in great detail for both Canada
thistle and common lambsquarters in Appendix B. The Fv/Fm of a healthy plant
is 0.83, a value smaller than 0.83 is an indication of the inability of the plant, due
to injury, to efficiently photosynthesize.

Fv/Fm for plants receiving glyphosate and chlorimuron combinations were
no different than for glyphosate alone at all HAT (data not shown). Fv/Fm values
after combined treatments were no different from those of the control treatments
at 2 HAT. However, at 72 HAT many Fv/Fm values after application of
glyphosate and chlorimuron combinations were significantly lower than the
Fv/Fm of the control and chlorimuron only treatments (Figure 13). This indicates
that although glyphosate alone reduces the photosynthetic ability of the plant (as
seen by a reduction in the Fv/Fm with glyphosate alone and in combination) the
addition of chlorimuron does not significant change the results. Glyphosate alone
is responsible for the reduced photosynthetic ability of the plant within the period

of our study (72 HAT).

Absorption and Translocation

97

14C-glyphosate. Absorption of 14C-glyphosate ranged from 53 to 75% of

the applied radioactive material increasing from 6 HAT to 48 HAT for the majority

of rates and combinations in all species (Figure 14). The addition of chlorimuron

caused a significant increase in absorption of the 14C-glyphosate in common

lambsquarters and giant foxtail (Figure 14b,c). The absorption increased with the
combination evident in common lambsquarters may explain the observed
synergism in weed control but the increase in absorption evident in giant foxtail

does not explain the observed antagonism (Figure 14).

Translocation of 14C-glyphosate out of the treated leaf ranged from 50 to

75% of the absorbed radioactive material increasing from 6 HAT to 48 HAT for

the majority of rates and combinations in all species (Figure 15). The addition of

. . . 14 .
chlorimuron Increased the translocatlon of C-glyphosate In common

lambsquarters and giant foxtail while reduced translocation was seen with one

combination in Canada thistle (Figure 15). The reduced translocation of 14C-

glyphosates in Canada thistle is consistent with the observed antagonism

between glyphosate and chlorimuron (data not shown).

14C-Chlorimuron. Absorption of 14C-chlorimuron ranged from 85 to 99%

of the applied increasing from 6 HAT to 48 HAT for the majority of rates and

combinations in all species (Figure 16).The addition of glyphosate to 14C-

chlorimuron increased absorption in all species at all HAT (Figure 16).

98

Translocation of 14C-chlorimuron out of the treated leaf ranged from 20 to

75% of the absorbed (Figure 17). Translocation was greatest in common
lambsquarters and lowest in giant foxtail (Figure 17b,c). Translocation of 14C-

chlorimuron did not increase from 6 HAT to 48 HAT but appeared evident (Figure

17b). The addition of glyphosate to 14C-chlorimuron reduced translocation in all

species, and was dependent upon time harvested (Figure 17).

Comparison with visual observations. Antagonism was observed between
chlorimuron and glyphosate on Canada thistle in previous greenhouse studies
(data not shown). Absorption and translocation of glyphosate increased with the
addition of chlorimuron, not reflective of the observed antagonism (Fi'gUre14a,
153). Although absorption of chlorimuron increased with the addition of
glyphosate, reduced translocation of chlorimuron out of the treated leaf was
observed when combined with glyphosate in Canada thistle and could be the
cause of the observed antagonism (Figure 17a). Synergism between l0w rates of
glyphosate and the range of chlorimuron rates was observed in previ00s

greenhouse studies on common lambsquarters (Chapter 2, Figure 3). Absorption

and translocation of both 1A'C-glyphosate and radio labeled 14C-chlorimuron

increased with the addition of chlorimuron and glyphosate, respectively, in
common lambsquarters (Figure 14b, 15b, 16b, 17b). The increase in absorption
and translocation was across all rates of glyphosate although synergism was
only observed at low rates of glyphosate. The synergism between chlorimuron

and glyphosate on common lambsquarters may be due to the increaSed

99

absorption and translocation of both herbicides in combination. Antagonism was
observed between glyphosate and chlorimuron in previous greenhouse studies
on giant foxtail (Table 9). Absorption and translocation of glyphosate combined
with chlorimuron was greater than glyphosate applied alone in giant fDXIail
(Figure 14c, 15c). Although absorption of chlorimuron was greater when
glyphosate was added, translocation out of the treated leaf did not inorease,
possibly the basis of the observed antagonism in weed control (Figure 16c, 17c).
In the greenhouse studies, the two sulfonylurea herbicides responded
similarly in combinations with glyphosate but this was species dependent.
Synergism was observed in combinations with glyphosate; however, the
thifensulfuron combination provided greater weed control than the chlorimuron. In
field studies early synergism or antagonism was observed in all species except
giant foxtail. Results for some combinations were similar in field and greenhouse
studies but due to the differential environment in the field, correlation between
the two was not possible. Fluorescence measurements of glyphosate and
chlorimuron combined did not indicate an interaction prior to 72 HAT; however
glyphosate reduced the fluorescence beginning at 24 HAT. Fluorescence of
plants treated with chlorimuron indicated no injury to the photosynthetic system

prior to 72 HAT.

Absorption and translocation data for both 1A'C-glyphosate and 14C-

chlorimuron showed that increased absorption was evident with the addition of

the other herbicide. The increase in absorption could have been due to the

addition of AMS when glyphosate was paired with 14C-chlorimuron and the

100

formulation effect of chlorimuron when paired with 14C-glyphosate. Interactions

between glyphosate and chlorimuron were apparent in absorption and
translocation data for some species but the basis for all the visually observed
symptoms of interactions was not fully explained by this study. Additional studies
should be completed to further look at the effect of adjuvant additions and
formulations on these species.

The interaction of glyphosate and the sulfonylurea herbicides although not
always, generally resulted in antagonistic interactions in the species studied.
Fluorescence measurements did not indicate an early interaction but Were

indicative of glyphosate injury. Absorption and translocation studies With both

14C-glyphosate and 14C-chlorimuron applied alone and in combination were

insufficient to explain the basis of the observed interaction.

101

SOURCES OF MATERIALS

aAirMix 11003, Greenleaf Technologies, PO. Box 1767, Covington, LA 70434.

bDon Penner’s Farm Williamston, MI. pennerd@msu.edu.

cBaccto® High Porosity Professional Potting Mix, Michigan Peat Co., Houston,
TX.

dRoundup WeatherMAX®, Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO
63167.

eCLASSIC©, DuPont Agricultural Products, Newark, DE.

fHARMONY®, DuPont Agricultural Products, Newark, DE.

gCrop oil concentrate. Loveland Products, Inc. PO Box 1286 Greely, CO 80632.
hTeeJet®, Spraying Systems Co., PO. Box 7900, Wheaton, IL 60189.

iThe SAS System for Windows Version 9.2, SAS Institute Inc, 100 SAS Campus
Dr., Cary, NC 2751.

jLeaf Clips, Handy Pocket PEA, Hansatech Instruments, Narborough Road,
King’s Lynn, Norfolk, UK.

kHandy Pocket PEA, Hansatech Instruments, Narborough Road, King’s Lynn
Norfolk, UK.

102

Table 5. Herbicide combinations applied in field studies 2008

 

 

 

and 2009a
Herbicides Applied b Year - Field Studies
2008 2009
Control Control
0.25X GLYb 0.25X GLY
0.33X GLY 0.5X GLY
0.5X GLY 1X GLY
1X GLY 0.25X CHL
1X CHL 0.5X CHL
0.25X GLY + 1X CHL 1X CHL
0.33X GLY + 1X CHL 0.25X GLY + 0.25X CHL
0.5X GLY + 1X CHL 0.25X GLY + 0.5X CHL
1X GLY + 1X CHL 0.25X GLY + 1X CHL
1X THI 0.5X GLY +0.25X CHL
1X THI + 0.25X GLY 0.5X GLY + 0.5X CHL
1X THI+ 0.33X GLY 0.5X GLY + 1X CHL
1X GLY + 0.5X CHL

1X THI +0.5X GLY
1X THI + 1X GLY

 

 

 

1XGLY + 1X CHL

 

3 Where 1X : the labeled rate; Glyphosate applied as

Roundup WeatherMAX 1X = 840 g ae/ha; Chlorimuron
applied as CLASSIC 1X : 8.8 g ai/ha; Thifensulfuron applied

as HARMONY DS 1X = 4.5 g ailha

b Abbreviations: GLY, glyphosate; CHL, Chlorimuron; THI,

Thifensulfuron.

103

Table 6. Herbicide combinations applied in fluorescence

 

 

 

 

studies.a . ,
Herbicides Applied by Species - Fluorescence Studies
CIRAR + CHEAL ABUTH + SETFA
Control Control
0.25X GLYb 0.25X GLY
0.5X GLY 1X GLY
1X GLY 1X CHL

0.25X CHL 0.25X GLY + 1X CHL
0.5X CHL
1X CHL
0.25X GLY + 0.25X CHL

0.25X GLY + 1X CHL

0.5X GLY + 0.5X CHL

1X GLY + 0.25X CHL

1X GLY + 0.5X CHL

1X GLY +1XCHL

 

 

a Where 1X : the labeled rate; glyphosate applied as RoundUp
WeatherMAX 1X : 840 g ae/ha; chlorimuron applied as

CLASSIC 1X : 8.8 g ailha.

b Abbreviations: GLY, glyphosate; CHL, chlorimuron.

104

 

Table 7. Herbicide treatments for 14C absorption and translocation studies.

 

 

14c-Chlorimuron Applied 14C-Glyphosate Applied
0.25X Chlorimuron 0.25X Glyphosate
0.5X Chlorimuron 0.5X Glyphosate
1X Chlorimuron 1X Glyphosate

0.25X Glyphosate + 1X Chlorimuron 0.25X Glyphosate + 1X Chlorimuron

1X Glyphosate + 0.25X Chlorimuron 1X Glyphosate + 0.25X Chlorimuron

0.5X Glyphosate + 0.5X Chlorimuron 0.5X Glyphosate + 0.5X Chlorimuron
1X Glyphosate + 1X Chlorimuron 1X Glyphosate + 1X Chlorimuron

 

 

For Chlorimuron X: 8.8 g ailha

 

 

For Glyphosate X: 840 g ae/ha

 

105

 

Table 8. Visual control 7 and 28 days after treatment of velvetleaf, common
lambsquarters and giant foxtail when applied with combinations of glyphosate

and chlorimuron in 2009 field studya

 

Visual Control _ _
ABUTH CH EAL SETFA

 

 

 

 

 

 

 

Herbicide Rateb'c’d 7 DAT 28 DAT 7 DAT 28 DAT 7 DAT 28 DAT
GLY CHL Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp.0bs., (Exp. Obs.
gae/ha %
0 0 — 0 - 0 - 0 - 0 — 0 - 0
210 0 - 38 — 46 - 36 - 48 - 75 - 86
420 0 — 48 — 100 - 29 - 85 - 89 - 99
840 0 - 48 - 100 - 48 - 99 - 80 — 100
0 2.2 - 43 - 29 — 16 - 30 — 6 — 35
0 4.4 — 26 - 39 - 15 — 44 - 2 - 51
0 8.8 - 39 - 38 - 23 - 25 — 25 — 46
210 2.2 64 42 H 62 78 (+) 47 36 H 63 71 (+) 77 91 (+) 91 94
210 4.4 54 26 H 67 59 H 46 37 (-) 71 72 76 86 (+) 94 94
210 8.8 61 81 (+) 68 98 (+) 51 55 61 95 (+) 81 71 (+) 93 94
420 2.2 70 92 (+) 100 90 H 40 83 (+) 89 86 90 90 99 100
420 4.4 61 29 H 100 95 39 91 (+) 92 81 (-) 89 90 99 98
420 8.8 67 38 H 100100 45 57 (+) 89 72 (+) 92 86 .‘ 99 100
840 4.4 61 61 100 99 55 36 (-) 99 83 H 81 89 (-) 100 100
840 8.8 67 92 (+) 100100 59 60 99 98 85 91 100 100
LSD (0.05)8 3 2 2 2 2 _ ‘ .. 2

 

a . . . : .
+ and — denote a synergistic and antagonistic interaction for a glven comblnatlon accordlng to

the LSD comparison of the observed and expected values calculated using Colby’s method.
Observed values without a + or - are additive.

b .
Abbreviations: GLY, glyphosate; CHL, chlorimuron; ABUTH, velvetleaf; CHEAL, common
lambsquarters; SETFA, giant foxtail; DAT, days after treatment; Exp., expected; Obs,

c
Treatments containing glyphosate and/or glufosinate also included ammonium sulfate at 2%

d
Treatments containing only chlorimuron also included crop oil concentrate at 1% WV.

6
LSD values may be used to compare values.

106

Table 9 Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on giant foxtail 7, 14, 21 and 28 days after

treatment.81

Visual Control - Giant foxtail

 

 

28 DAT

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT _21 DAT
Chlorimuron Glyphosate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
gai/ha gae/ha %
0 0 - 0 - 0 - 0 - 0
2.2 0 - 0 - 0 - 4 - 15
2.93 0 - 7 - 4 - 0 - 21
4.4 0 - 7 - 4 - 3 - 20
8.8 0 - 7 - 8 - 6 - 29
0 210 - 16 - 66 - 71 - 40
0 280 - 19 - 80 - 88 - 50
0 420 - 18 - 93 - 87 - 68
0 840 - 41 - 98 - 85 - 91
2.2 210 16 18 66 69 72 84 (+) 49 44
2.9 210 21 20 68 88 (+) 71 89 (+) 53 45
4.4 210 21 9 (-) 68 89 (+) 72 85 (+) 52 45
8.8 210 21 10 (-) 69 59 (-) 73 86 (+) 57 51
2.2 280 19 13 (-) 80 86 89 89 57 55
2.93 280 24 9 (-) 81 91 (+) 88 93 61 55
4.4 280 24 13 (-) 81 89 88 91 60 55
8.8 280 24 11 (-) 81 92 (+) 89 92 64 55
2.2 420 18 11 (-) 93 97 87 91 72 70
2.93 420 24 23 93 95 87 89 75 69
4.4 420 24 18 (-) 93 98 87 88 75 77
8.8 420 24 19 (-) 94 96 88 89 77 72
2.2 840 41 29 (-) 98 98 86 89 92 89
2.93 840 45 33 (-) 98 98 85 87 93 93
4.4 840 45 31 (-) 98 99 85 91 93 86
8.8 840 45 41 98 100 86 91 93 ; 93
LSD (0.05)e 5 9

 

a . . . . . . . . .
+ and - denote a synerglstlc and antgonlstlc Interactlon for the glven comblnatlons
according to the LSD comparison of the observed and expected values calculated using

Colbys method. Observed values without a + or - are additive.

b .
Abbreviatlons: DAT, days after treatment; Exp., expected; Obs., observed.

0 . . . .
Treatments contalnlng glyphosate also Included ammonlum sulfate at 2% WV.

(1 . . . . .
Treatments contalnlng chlorlmuron also Included crop orl concentrate at 1% v/v.

e
LSD values may be used to compare values.

107

(a) 100

 

 

   

   

 

 

 

 

:9
E’
.2
‘6
3
‘U
of}
g I Expected
'5 sObse'rved
I g
1/4X 1/4X 1XCHL 1/4X 1/4X
GLY CHL GLY+ GLY+
1/4X 1X CHL
Herbicide Applied CHL
(b) 100 3
g6 90 4 (If (+)
V 80 4 52323232 23232323
.5 70 ~
‘5' 60 -
1:: 50 4
Q)
a: 40 - _
g 30 q I Expected
'63 20 ‘ EObserVed
I 10 -
O :-2-:-2- T 422-: r
1/4X 1/4X 1XTHl 1/4X 1/4X
GLY THI GLY+ GLY+
1/4X 1X THI
THI

Herbicide Applied

Figure 11 . Chlorimuron(CHL) and glyphosate(GLY) (a) and
thifensulfuron(THl) and glyphosate (b) on common lambsquarters % height
reduction from the control in the greenhouse 28 days after treatment.
Synergism by Colby's method indicated by a (+). LSD : 5 for 7 DAT and
LSD : 8 for 28 DAT.

108

DU

0
g:
3%
630
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O.:.. 0 : z ; .§:O:O:OI

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1/4X GLY

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1/4X CHL

 

 

    
    

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(%) Iuononpau 6:9

Herbicide Applied by Species

Figure 12. Chlorimuron(CHL) and glyphosate(GLY) on velvetleaf(ABUTH) and common lambsquarters(CHEAL) %

height reduction in the greenhouse 28 days after treatment. Antagonism and synergism by Colby's method

= 9 for ABUTH and LSD = 17 for CHEAL.

indicated by a (-) or (+) respectively. LSD

(a)
0.83 NS NS NS NS NS NS NS NS NS

0.81 NS
0.79
0.77
E 0.75
§ 0.73
[L 0.71
0.69
0.67
0.65
0.63
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defied-#900,? ¢CJ:6“°3“O +0 +
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(b)
Herbicide Applied
0.8 -
0.7 ~
0'6 _ NS NS
E 0.5 ' ‘
$ 0.4 ‘l * t
IL 034
0.2 4 *
0.1 —
0 4— .

 

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O$¢+6t<t¢+é<r$+x¢§tfiz+id~
Q. xQ-OctixQqu’ CK
9793; oVOéo¢o

Herbicide Applied

Figure 13. Fv/Fm of glyphosate(GLY) and Chlorimuron(CHL) on Canada
thistle at (a) 2 hours after treatment and (b) 72 hours after treatment. Where
a * indicates significant difference from the control. (a) LSD = 0.0356 and (b)
LSD =0.1795.

110

._)
A
9.)
V

  
  
     

.‘1_.»_L-. _ 4L .4._ ._.L___.l_.

  
      

 

Absorption (% of
8 8 83%ng 8 8

 
        
     

 

226 HAT
l24 HAT
, , i348 HAT
0.25X 0.5X 1X GLY 0.25X 1X GLY 0.5X 1X GLY
GLY GLY GLY+ +0.25X GLY+ +1X
1X CHL CHL 0.5X CHL
. . . CHL
HerbiCide Applied
90 1 (b)
“_80 1 * *
o .
s70 1
V6 !
5?? H T
"‘ £2 A
gel
_‘8 ' I24 HAT
<40 1
D48 HAT
30 u. u. _TT .. .. ... ... ...
0.25X 0.5X 1X GLY 0.25X 1X GLY 0.5X 1X GLY
GLY GLY GLY+ +0.25X GLY+ +1X
1X CHL CHL 0.5X CHL
Herbicide Applied CHL
»_ 80 1' * *
° J
°\O 70 1
E30
3 % $6 HAT
o ' . .
, m.
30 1 7T 48 HAT

 

0.25X 0.5X 1X GLY 0.25X 1X GLY 0.5X 1X GLY

GLY GLY GLY + + 0.25X GLY + +1X
1X CHL CHL 0.5X CHL

H . . . CHL

erbimde Applied

Figure 14. 1lj'C-glyphosate absorption in (a) Canada thistle, (b) common

lambsquarters and (0) giant foxtail. A (*) indicates significantly different from

herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT, days after

treatment; GLY, glyphosate.

111

  
   

 

   

Translocation (% of absorbed)

     
  

    
    

  

 

  
 

  

  
  
  
   

Ac 6 HAT
: I 24 HAT
I [348 HAT
0.5X X 1X GLY
GLY GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL
E Herbicide Applied ,
‘6 * '
U)
.0
(U I
‘5 l: :l
o\° 1: :i
'5 8% 2 HAT
§ :5. 5; .24 HAT
g: :l I: i048 HAT
<3 7 '1 L Q
'— T i
0.25X 0.5X 1X GLY 0.25X 1X GLY 0.5X 1X GLY
GLY GLY GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL
Herbicide Applied CHL
3801(0) .., *1”
'9 75 '1 'k 88-,
g 65 '1
0.5 60 1 42:2:
e\° 55 1
E, 50 _‘ . .226 HAT
2% :3 1 .24 HAT
§ 35 ( 5148 HAT
(0%, 30 _ .. .,.,. ,... _g ... .._. . -...
l: 0.25X 0.5X 1X GLY 0.25X 1X GLY 0.5X 1X GLY
GLY GLY GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL
Herbicide Applied CHL

Figure 15. 14C-glyphosate translocation out of the treated leaf by (a) Canada thistle,
(b) common lambsquarters and (0) giant foxtail. A (*) indicates significantly different

from herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT, days after

treatment; GLY, glyphosate.

112

é

 

 
     

        

           

 
      
       

E 98
g 96
“5 94
\°
E’ 92 2186 HAT
O
a 90 .24 HAT
g 88 D48 HAT
< 86 .
0.25X 0.5x 1x GLY
CHL CHL GLY + + 0.25X GLY + +1X
1x CHL CHL 0.5x CHL
Herbicide Applied CHL
100 .i (b) *
E 98 ( . ~
396) i
3 94 i E
2\: 92 J 1 826 HAT
g 90 1 : .24 HAT
3‘ 88 i' 5 m8 HAT
§ 86 H. _'_... . . . . .L ,, . ... :3.-
0.25x 0.5x 1x CHL 0.25X 1x GLY 0.5x 1x GLY
CHL CHL GLY + + 0.25X GLY + +1X
1x CHL CHL 0.5x CHL
Herbicide Applied CHL
100 ‘i (C)
6‘ 98 * * , * .
.9
E 96
as 94
03’ 92 1 $15: 86 HAT
7:“ .24 HAT
e 88 1
g. 86 “_ n, .3, .._. .~.-. .u_ 4.2. n48 HAT
8 0.25X 0.5X 1x CHL 0.25X 1x GLY 0.5x 1X GLY
< CHL CHL GLY + + 0.25X GLY + +1X
1x CHL CHL 0.5x CHL
CHL

Herbicide Applied
Figure 16. 14C-chlorimuron absorption in (a) Canada thistle, (b) common
lambsquarters and (c) giant foxtail. A (‘) indicates significantly different from
herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT, days after
treatment; GLY, glyphosate.

113

6‘80 - (a)

"5 50
a 6 HAT

I24 HAT
D48 HAT

     

 

   
     

'— 0.25X 0.5X 1X CHL 0.25X 1X GLY 0.5X 1X GLY
CHL CHL GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL
Herbicide Applied CHL

    
  

as 6 HAT
I 24 HAT
n48 HAT

 
  

   

    

             

l'-

0.25X 0.5X 1X CHL 0.25X 1X GLY 0.5X 1X GLY
CHL CHL GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL

. . . CHL
HerbiCide Applied

U" 03 \l m
o O O O
2.4....-
A
0
V
I!

x 6 HAT
I 24 HAT
r348 HAT

O

    

0.25X 0.5X 1X CHL 0.25X 1X GLY 0.5X 1X GLY
CHL CHL GLY + + 0.25X GLY + + 1X
1X CHL CHL 0.5X CHL
CHL

41900
O

Translocation (°/o of absorbed)
o 8

Herbicide Applied

Figure 17 . 14C-chlorimuron translocation out of the treated leaf by (a) Canada
thistle, (b) common lambsquarters and (c) giant foxtail. A (*) indicates significantly
different from herbicide alone at that time. Abbreviations: CHL, chlorimuron; DAT,
days after treatment; GLY, glyphosate.

114

LITERATURE CITED

Abbaspoor, M., and J.C. Streibig. 2005. Clodinafop changes the chlorophyll
fluorescence induction curve. Weed Sci. 53: 1-9.

Anonymous. 2006a. CLASSlC® herbicide label. E. I. du Pont de Nemdurs and
Company. Wilmington, DE.

Anonymous 2006b. HARMONY® herbicide label. E. l. du Pont de Nemours and
Company. Wilmington, DE.

Anonymous. 2007. Roundup WeatherMAX® herbicide label. Monstanto Co. St.
Louis, MO.

Barbagallo, R.P., K. Oxborough, K.E. Pallet, and NR. Baker. 2003. Rapid, non-
invasive screening for perturbations of metabolism and plant growth using
chlorophyll fluorescence imaging. Plant Physiol. 132: 485-493.

Bromilow, R.H., K. Chamberlain, A.J. Tench, R.H. Williams. 1993. Phloem
translocation of strong acids glyphosate, substitued phosphonic and
sulfonic-acids in Ricinus communis L. Pest. Sci. 37: 39-47.

Butler, W. L., 1978. Energy distribution in the photochemical apparatus of
photosynthesis. Annual Review of Plant Physiology, 29, 345-378.

Corrigan, K. A., and R. G. Harven. 2000. Glyphosate with and without “residual
herbicides in no-till glyphosate-resistant soybean (Glycine max). Weed
Technol. 14: 569-573.

Christensen, M.G., H.B.Teicher and J.C Streibig 2003. Linking fluore‘SCence
induction curve and biomass in herbicide screening. Pest Manag Sci
59:1303-1310.

Colby, S. R. 1967. Calculating synergistic and antagonistic responses of
herbicide combinations. Weeds 15:20-22.

Frankart, C., P. Eullaffroy, and G. Vemet. 2003. Comparative effects of four
herbicides on non-photochemical fluorescence quenching in Lemna minor.
Environ. Exp. Bot. 49: 159-168.

Govindjee, A. 1995. Kautsky-chlorophyll-a fluorescence. Aust. J. Plant Physiol.
22: 131 -160.

115

Jordan, D. L., A. C. York, J. L. Griffin, P. A. Clay, P. R. Vidrine, and DB.
Reynolds. 1997. Influence of application variables on efficacy of
glyphosate. Weed Technol. 11: 354-362.

Kirkwood R.C., R. Hetherington, T.L. Reynolds, and G. Marshall. 2000.
Absorption, localization, translocation and activity of glyphosate in
bamyardgrass (Echinochloa crus-galli (L) Beauv): influence of herbicide
and surfactant concentration. Pest. Manag. Sci. 56:359-367.

Knezevic, 8.2., A. Darta, J. Scott, R.N. Klein, J. Golus. 2009. Problem. weed
control in glyphosate-resistant soybean with glyphosate tank mixes and
soil-applied herbicides. Weed Technol. 23: 507-512.

Lich, J. M., K. A. Renner, and D. Penner. 1997. Interaction of glyphosate with
postemergence soybean (Glycine max) herbicides. Weed Sci. 45: 12-21.

Maschhoff, J. R., S. E. Hart, and J. L. Baldwin. 2000. Effect of ammonium sulfate
on the efficacy, absorption, and translocation of glufosinate. Weed Sci. 48:
2-6.

Olesen, C.F., N. Cedergreen. 2010. Glyphosate uncouples gas exchange and
chlorophyll fluorescence. Pest Manag Sci 66:536-542.

Percival, MP, and NR. Baker. 1991. Herbicides and photosynthesis. Pages 1-
26 in NB. Baker and MP. Percival, eds. Herbicides. London: Elsevier.

Ralph, P.J. 2000. Herbicide toxicity of Halophila ova/is assessed by chlorophyll A
fluorescence. Aquat Bot 66:141-152.

Sensemen, S. A. 2007. Herbicide Handbook 9th Edition Lawrence, KS: WSSA.
Pp. 458. ed. S.A. Sensemen

Strasser, R.J., A. Sirivastava, and M. TsimilIi-Michael. 2000. The fluorescence
transient as a tool to characterize and screen photosynthetic samples.
Pages 445-483 in M. Yunus, U. Pathre, and P. Mohanty, eds. Probing
Photosynthesis: Mechanisms, Regulation and Adaptation. London: Taylor
& Francis.

Sprankle, P., W. F. Meggitt, and D. Penner. 1975. Absorption, action and
translocation of glyphosate. Weed Sci. 23: 235-240.

Starke, R. J., and L. R. Oliver. 1998. Interaction of glyphosate with chlorimuron,
fomesafen, imazethapyr, and sulfentrazone. Weed Sci. 46: 652-660.

116

Vidrine, P. R., J. L. Griffin, and D. C. Blouin. 2002. Evaluation of reduced rates of
glyphosate and chlorimuron in glyphosate resistant soybean (Glycine
max). Weed Technol. 16: 731-736.

Wilcut, J.W., G.R. Wehtje, M.G. Patterson, T.A. Cole, and T.V. Hicks. 1989.
Absorption, translocation, and metabolism of foliar-applied chlorimuron in
soybeans (Glycine max), peanuts (Arachis hypogaea), and selected
weeds. Weed Technol. 37: 175-180.

Young, B. G., A. W. Knepp, L. M. Wax, and S. E. Hart. 2003. Glyphosate

translocation in common lambsquarters (Chenopodium album) and
velvetleaf (Abutilon theophrasti). Weed Sci. 51: 151-156.

117

CHAPTER 5

EVALUATION OF THE COMBINATION OF GLUFOSINATE AND THE
SULFONYLUREA HERBICIDES CHLORIMURON AND THIFENSULFURON.

Abstract: The stacking of genes to provide resistance to several herbicides
previously injurious to a crop provides new opportunities for control of a larger
range of species and also herbicide resistant weeds. Specifically the opportunity
may exist to control sulfonylurea resistant weeds with glufosinate. The
combination of these herbicides in a tank mix also has the potential to Cause
unexpected interactions. Studies were conducted in the field in 2008 and 2009
and in the greenhouse from 2008 to 2010 to evaluate the combination of
glufosinate and the sulfonylurea herbicides chlorimuron and thifensulfuron on
three annual weeds prevalent in Michigan cropping systems; giant foxtail,
common lambsquarters, velvetleaf, and the perennial weed, Canada thistle. In
the greenhouse, the interaction of glufosinate with the sulfonylurea herbicide
resulted in early synergism, late antagonism and late synergism. TheSe results
were dependent upon the combination applied and the species. Similarities were
found between the two sulfonylurea herbicides in combination with glufosinate

and similarities were also found between field and greenhouse results.

Nomenclature: Canada thistle, Cirsium arvense L. Scop; common
lambsquarters, Chenopodium album L.; giant foxtail, Setaria faben' Herrm.;
velvetleaf, Abutilon theophrasti Medik; chlorimuron, 2-[[[[(4-chloro-6-methoxy-2-
pyrimidinyl)amino]carbonyl]amino]sulfonyl] benzoic acid; glufosinate,_2-amino-4-
(hydroxy-methyl-phosphoryl)butanoic acid; thifensulfuron, methyl 3-[[[[(4-
methoxy-6-methyI-1 ,3-5-tria2in-2-yl)amino]carbonyl]amino]sulfonyl]-2-
thiophenecarboxylate.

118

Key words: Additive effect, antagonism, Colby’s, herbicide interaction, reduced
rates, synergism, tank-mixing.

Tank-mixing of herbicides may provide producers the opportunity to
increase the range of species controlled by combining multiple herbicides with
different modes of action in the tank-mix. The interaction between glufosinate
and chlorimuron has been extensively studied with differential results depending
on the herbicide rate, stage of weed, method of application and species (Starke
and Oliver, 1998; Vidrine et al., 2002).

Glufosinate combined with chlorimuron and metribuzin resulted in an
additive effect in sicklepod (Senna obtusifolia L. H.S. lriwn & Bameby ),
antagonism at low glufosinate rates in entireleaf morningglory (Ipomoea
hederacea var. integriuscula) and antagonism at high glufosinate rates in
johnsongrass (Sorghum halepense L. Pers. ) (Hydrick and Shaw 1994, 1995).
The addition of a selective foliar herbicide to the non-selective glufosinate often
resulted in antagonism but could be overcome by a high application rate of
glufosinate especially for the broadleaf weeds studied. No known studies
examined the interaction between glufosinate and thifensulfuron.

Desired weed control with a combination of herbicides with one application
can be cost effective. Reduced rates can lead to reduced efficacy and can occur
in the field for a number of reasons. Accidental mixing, misapplication, a rain
event during the rain free pen'od and weather conditions can prevent a producer
from getting into the field at an optimal weed size. Also, since weeds do not

emerge at the same time, there are usually weeds at variable stages in the field

119

at time of postemergence application. Reduced rates may result in a reduction of
crop yield due to less weed control. Research is necessary to determine specific
weed species response to application of reduced rates, either accidental, or by
design.

Glufosinate and chlorimuron, although not primarily Photosystem ll (PS ll)
inhibitors, ultimately cause cellular death resulting in a weakened ability to use or
disperse light energy. Changes in fluorescence induction (Kautsky curve) have
been used extensively in photosynthesis and herbicide research and are the
basis for all fluorescence parameters (Abbaspoor and Streibig, 2005;
Christensen et al., 2003; Percival and Baker, 1991). The benefits of using
fluorescence include its non-invasive procedure, sensitivity to many biotic and
abiotic stressors, ease and efficiency and numerous parameters to measure the
status of the photosynthetic apparatus (Abbaspoor and Streibig, 2005;
Barbagallo et al., 2003; Frankart et al., 2003; Strasser et al., 2000).

Illumination of dark-adapted unstressed leaves produces a rise in
chlorophyll fluorescence emission from the ground state (F0) to its maximum
value (Fm) within one second. An important parameter used in fluorescence

research is the Fv/Fm [Fv/Fm = (Fm-Fo)/Fm] parameter (Butler, 1978). The dark
adaptation of a leaf allows PSII to be fully reduced at QA and when illuminated

the maximum quantum efficiency of the PS ll photochemistry can be determined
by Fv/Fm. This parameter is used most often in the literature to indicate plant
health with a value of 0.83 indicating no stress to the plant. Fv/Fm has been used

to measure the effect of glyphosate on fluorescence in previous studies but has

120

 

not been used to study glufosinate. Kirkwood et al 2000 used this parameter and
detected some differences from the control one day after treatment with
glyphosate. Olesen and Cedergreen 2010 and Ralph 2000 did not find any effect
of glyphosate on Fv/Fm.

The objectives of this research were to evaluate potential interactions
among four matrix rate combinations of glufosinate with chlorimuron and
thifensulfuron in the greenhouse, determine if the interactions were significant for
antagonism and synergism or just additive, determine if results in the greenhouse
were consistent with observations in the field, determine if there were differences
between visual control and quantitative measurements and, determine if there
were different responses among species.

Based on prior research it is expected that, early synergism between
herbicides will be observed in some species (14 DAT or before) but at 28 DAT
may no longer be evident, the interaction of the two different sulfonylurea
herbicides with glufosinate may be similar. Following glufosinate application to
weeds, it is expected that fluorescence parameters will indicate injury to the
photosynthetic system much earlier than visually observed and changes in
fluorescence patterns will be indicative of the interaction between glufdsinate and

chlorimuron.

MATERIALS AND METHODS

Field Trial. Field trials were conducted in 2008 at the Michigan State University

Agronomy Research Farm (42°42’42” N, 84°28’1 3” W) and 2009 at the Michigan

121

State University Plant Pathology Research Center (42°40’59” N, 84°29’5” W) in
East Lansing, MI. The soil at the Agronomy Research Farm was a sandy clay
loam with 2.6% organic matter and a pH of 6.3. The soil at the Plant Pathology
Research Center was a fine sandy loam with a 2 to 6% slope, a pH of 6.9 and
2.5% organic matter. Fields preparation included fall-plowing followed by
cultivation in the spring to obtain maximum weed emergence. The experimental
design was a randomized complete block in 2008 and 2009. Treatments differed
between years and therefore were separated by year and summarized in Table
10.

Herbicide applications were made using a tractor-mounted compressed-air

sprayer calibrated to deliver 178 L / he at 207 kPa through AirMix 11003

nozzlesa. Common lambsquarters (Chenopodium album L.), velVetleaf (Abutilon

theophrasti Medik.) and giant foxtail (Setaria faberi Herrm.) were the predominant
weed species in both years and were the focus in this study. Other weed species
present included; redroot pigweed (Amaranthus retroflexus L.), Powell amaranth
(Amaranthus powellii S. Watson), common ragweed (Ambrosia an‘emisiifolia L.)
and large crabgrass (Digitaria sanguine/is L. Scop.) in 2008. Weed species in
2009 were similar to those in 2008 but also included a large population of wild
mustard.

Visual estimates of weed control were made at 7, 14, 21 and 28 days after
treatment (DAT) in 2008 and 7, 14 and 21 DAT in 2009 on a scale of 0% (no
control) to 100% (complete control) based on injury compared with the untreated

control.

122

Greenhouse studies.

Plant material. Common lambsquarters, giant foxtail, and velvetleaf from

seed, and Canada thistle (Cirsium arvense L. Scop.) from root stockb Were

grown in 9-cm pots containing a commerCial potting medium in a greenhouse

with temperature maintained at 23 :l: 3°C. Natural light was supplemented by

high-pressure sodium lamps producing a photosynthetic photon flux density of

200 mol-m'2-s'1 with a photoperiod of 16/8 h light/dark. Pots were watered daily

to maintain adequate soil conditions for optimum plant growth. Plants were

fertilized with 50 ml of fertilizer solution containing 6 mg/L of 20% nitrogen, 20%

P205 and 20% K20 as needed. Weeds were sprayed at 10-12 cm which is

considered larger than optimum size which was done to accentuate differences
between herbicide treatments and compensate for greater sensitivity of
greenhouse grown plants. There were four replications per experiment and each
experiment was repeated four times. Studies with common lambsquarters were
repeated six times because of the increased susceptibility to pythium (Pythium
spp.) and fusarium (Fusarium spp.) after glyphosate or glufosinate application.

Herbicide treatments. Herbicides were applied in a matrix format so a range

of combinations of each herbicide at each rate were used. Glufosinated was

applied at rates of 0, 118, 157, 235, and 470 g ai/ha, chlorimuron-ether

(hereafter referred to as chlorimuron) applied at rates of O, 2.2, 2.9, 4.4, and 8.8

123

 

g ailha and thifensulfuron-methylf (hereafter referred to as thifensulfuron) applied

at rates of (O, 1.125, 1.5, 2.25, and 4.5 g ailha). These rates are representative of

0.0X, 0.25X, 0.33X, 0.5X, and 1X of the label-recommended rate (Anonymous,

2006a; Anonymous, 2006b; Anonymous, 2007). A crop oil concentrateg (COC)

was included at 1% v/v in treatments containing only chlorimuron or only
thifensulfuron. Ammonium sulfate was included at 2% v/v in all treatments
containing glufosinate alone or in combination with the sulfonylurea herbicides.

Applications were made using a single-nozzle track sprayer with 8001 even

flat fan nozzleh calibrated to deliver 187 L/ha at a pressure of 207 kPa. Visual

estimates of weed control were taken at 5, 7, 14, 21 and 28 days after treatment
(DAT) on a scale of 0% (no control) to 100% (complete control) based on injury
compared to the untreated control. Plant height data was collected and above
ground biomass harvested and immediately weighed at 28 DAT. Plant samples

were oven-dried at 50 C for 48 hr and dry weights were recorded.

Data analysis. The data analysis was conducted using ANOVA in the PROC

MIXED program in SAS 9.2. Normality of the residuals was evaluated using

normal probability and box plots and arc sine data transformations were
conducted when there were significant deviations from normality. Homogeneity of
variances was evaluated using Levene’s test. Herbicide combinations were
determined to be antagonistic, synergistic, or additive by comparing the observed
plant responses with the expected response when the herbicides are combined.
Expected values were calculated using Colby’s equation; E: X + Y — X W100

124

 

(Colby, 1967). In the equation, X and Y is the percent growth inhibition by
herbicide A and B respectively and E is the expected percent growth inhibition by
herbicides A and B combined. Expected and observed responses were
compared using Fishers Protected least significant difference (LSD) at p = 0.05
significance. Combinations were determined as antagonistic, synergistic, or
additive if the observed response was less than, greater than or similar to the

expected response respectively.

Fluorescence Studies.

Plant material. Common lambsquarters (Chenopodium album L.), were grown
from seed in the greenhouse. Approximately 10 seeds per pot were sown into
soil media in 900 mL black plastic pots. Plants were thinned to one per pot upon
emergence. Canada thistle (Cirsium arvense L. Scop.) was grown from root
stock obtained in May of 2008 and transplanted into soil media in 900 mL black
plastic pots. These plants were genetically similar. Tillers from stock plants were
transplanted into fresh media and pots. Canada thistle plants were selected for
treatment 2 weeks after transplant.

All plants were grown in greenhouses at Michigan State University campus in
East Lansing, MI and experiments took place in May of 2009. Natural light was

supplemented by high-pressure sodium lamps that produced a photosynthetic

photon flux density of 200 mol m'2 s". The photoperiod was 16/8 h light/dark,

and the temperature was 23:-3°C. Pots were watered daily to maintain adequate

soil conditions for optimum plant growth. Plants were fertilized with 50 ml of

125

 

fertilizer solution containing 6 mg/L of 20% nitrogen, 20% P205 and 20% K20 as

needed. Plants were 10 to 12 cm tall at time of treatment and were randomly
assigned to herbicide treatments. Experiments were replicated three times and
the experiment repeated three times.

Herbicide Treatments. Herbicide treatments consisted of glufosinate and
chlorimuron alone and in combinations at the rates given in Table 11.
Ammonium sulfate (AMS) at 2% v/v was used as an adjuvant when glufosinate
was applied alone or in combination with chlorimuron. Crop oil concentrate was
used at 1% v/v for chlorimuron alone. Treatments were applied using a single-tip
track sprayer using a TP8001 flat fan nozzle delivering 187 L ha'1 at a pressure
of 207 kPA. Treatments were selected based on preliminary studies to obtain the
highest observable interaction, such as, a high and a low rate combined, low
rates combined and high rates combined.

Fluorescence Measurements. After herbicide application the plants were
immediately returned to the greenhouse and prepared for fluorescence
evaluation. Fluorescence measurements were taken at 2, 4, 6, 8, 24, 48 and 72
hours after treatment (HAT). The second set of fully emerged leaves above the

cotyledons, with at least one more set of fully emerged leaves above were

selected for fluorescence evaluation. LeafclipsJ were placed in the middle of the

selected leaf directly next to the midvein with the least amount of contact with
any major veins. The clip has a small shutter plate that should be closed over the
leaf once the clip is attached so that light is excluded and dark adaptation begins

to take place. The process of dark adaptation varied depending on plant species,

126

ambient light history and whether the plant was stressed. The average time
required for dark adaptation in this study was 15 minutes. Once dark adapted,
the Handy Pocket PEA optical interface was attached to the clip around the
shutter plate, the shutter was opened and high intensity LED light passed
through a NIR filter, onto the leaf. Then a highly sensitive PIN photodiode detects

the fluorescence signal at 10us intervals for 1 second. The data obtained in the 1

second period was saved in the Handy Pocket PEAk and later downloaded into a

computer for analysis. Treated plants were visually rated for control, 0 being no
control and 100 being complete control, at 7, 14, 21 and 28 days after treatment
(DAT). Plant heights were measured at 28 DAT and were then haweSted and

weighed for fresh weight immediately. Plants harvested were dried at 50°C for 48

hr, dry weights were then determined and samples were discarded.

Data analysis. Data were subjected to ANOVA using PROC MIXED in SAS
and treatment means for Fv/Fm within species were compared using Fisher’s
Protected LSD at the p = 0.05 significance level. Data were transformed when

necessary for analysis and back-transforrned data are presented.

RESULTS AND DISCUSSION

Field Studies. Field studies in 2008 resulted in only one significant interaction;
due to the high rate of application of herbicides. Thus a second field study
conducted in 2009 included a greater combination or application rates of

glufosinate and chlorimuron. Antagonism was observed at low rates of

127

glufosinate and the range of chlorimuron rates for all species (Table 12). At high
rates of glufosinate the antagonism was no longer observed except when applied
in combination with 0.5X chlorimuron on velvetleaf 7 DAT (Table 12). Synergism
was observed between high rates of glufosinate and the range of chlorimuron

rates for all other species (Table 12).

Greenhouse Studies. The hypothesis was that early synergism between
herbicides would be evident in some species, but by 28 DAT the synergism may
no longer be evident. An example of when the interaction was synergistic early
was the combination of chlorimuron and glufosinate applied to common
lambsquarters. Visual observations 7 DAT confirmed synergism in combinations
at all rates of glufosinate with various chlorimuron rates (Figure 18a). This
synergism was apparent with only one combination at 28 DAT while other
combinations showed additive effect (Figure 18b). An example of synergism not
seen early but was evident at 28 DAT visual observations. One example of this
was the effect of the combination of chlorimuron and glufosinate on giant foxtail.
At the 1/4X rate of glufosinate combined with the range of chlorimuron rates,
either an additive effect or antagonism at 7 DAT was evident which became
synergistic later (Figure 19). Another example of synergism found at 28 DAT was
the effect of the combination of thifensulfuron and glufosinate on velvetleaf. At 7
DAT this combination showed some synergistic results along with an additive
effect and antagonism (Figure 20a), by 28 DAT however all combinations with
less than 1X glufosinate resulted in synergism (Figure 20b). The combination of

thifensulfuron and glufosinate on giant foxtail resulted in similar synergism at 28

128

DAT but was only evident in the 1/4X glufosinate combination (data not shown).
Early synergism that results in antagonism over time was not always seen
between combinations but there were examples of late antagonism (Figure 19,
20). There were combinations on some species that resulted in late synergism
(data not shown).

The hypothesis that the two sulfonylurea herbicides individually in
combination with glufosinate would act similarly was not always supported (data
not shown). Again, this was species dependent and combination dependent. An
example of when the sulfonylurea herbicides produced similar responses was in
combinations with glufosinate on giant foxtail. Although there were a few
examples of when the sulfonylurea herbicides produced similar results, more
often where they were dissimilar for weed control. The combination of the
sulfonylurea herbicides and glufosinate resulted in more significant interactions in
the thifensulfuron combination with glufosinate than the chlorimuron combination
with glufosinate on Canada thistle, velvetleaf and common lambsquarters (data

not shown).

Fluorescence Studies. Fv/Fm for Canada thistle was chosen as the parameter
to examine for significant differences between herbicide combinations. The
interactions between herbicides are discussed in great detail for both Canada
thistle and common lambsquarters in Appendix B. The Fv/Fm of a healthy plant
is 0.83, a value smaller than 0.83 is an indication of the inability of the plant, due

to injury, to efficiently photosynthesize.

129

The Fv/Fm for plants receiving the combination of 0.25X chlorimuron +
0.25X glufosinate and 1X chlorimuron + 0.25X glufosinate at 2 HAT were
significantly higher than those receiving glufosinate alone (Figure 21 a,b). This
remained consistent for all readings until 24 HAT when they no longer become
significantly different. The 1X chlorimuron + 0.25X glufosinate combination was
not significantly different from the glufosinate alone at 72 HAT but the
combination of 0.25X chlorimuron + 0.25X glufosinate was significantly lower
than of glufosinate applied alone at 72 HAT (Figure 21a). Fv/Fm values at 2 HAT
for plants sprayed with glufosinate + chlorimuron showed significant differences
from the control. (Figure 22a). The Fv/Fm values at 72 HAT following the 0.25X
glufosinate and 0.25X chlorimuron combination were significantly lower than that
of the 1X glufosinate + 1X chlorimuron combination (data not shown). Fv/Fm
values of Canada thistle following combinations of glufosinate and chlorimuron
were not significantly different from the Fv/Fm after glufosinate alone application
(Figure 22b).

In summary early synergism was observed in interactions with glufosinate
in the herbicide combination due to the earlier observable (sometimes by 3 days)
injury in comparison to combinations with the sulfonylurea herbicides (more than
7 days). After that time the interaction between the herbicides became more
apparent as synergism, antagonism or additive effect which was dependent on
species and the rate of the combination. There were similarities between field
and greenhouse studies; however, the interactions were not always the same

due to differences in the stage of weed at time of herbicide application in the

130

field. Fluorescence measurements did not show differences between glufosinate
and the combination with chlorimuron. However, glufosinate rapidly acted to
break down the photosynthetic system 2 HAT and chlorimuron activity was not

seen in fluorescence measurements taken up to 72 HAT.

131

 

SOURCE OF MATERIALS
aAirMix 11003, Greenleaf Technologies, PO. Box 1767, Covington, LA 70434.

bDon Penner’s Farm Williamston, Ml. pennerd@msu.edu.

CBaccto® High Porosity Professional Potting Mix, Michigan Peat Co., Houston,
TX.

dLiberty®, Bayer CropScience, Research Triangle Park, NC.
eCLASSlC®, DuPont Agricultural Products, Newark, DE.

fHARMONY®, DuPont Agricultural Products, Newark, DE.

gCrop oil concentrate. Loveland Products, Inc. PO Box 1286 Greely, CO 80632.
hTeeJet®, Spraying Systems Co., PO. Box 7900, Wheaton, IL 60189.

iThe SAS System for Windows Version 9.2, SAS Institute Inc, 100 SAS Campus
Dr., Cary, NC 275.

1Leaf Clips, Handy Pocket PEA, Hansatech Instruments, Narborough Road,
King’s Lynn, Norfolk, UK.

kHandy Pocket PEA, Hansatech Instruments, Narborough Road, King’s Lynn
Norfolk, UK.

132

 

Table 10. Herbicide combinations applied in field studies

 

 

 

2008 and 2009.a
Herbicides Applied b Year - Field Studies
2008 2009
Control Control
1x GLU b 0.25X GLU
1X CHL 0.5X GLU
0.5X GLU + 0.5X CHL 1X GLU
0.5X GLU + 1X CHL 0.25X CHL
1X GLU+ 0.5X CHL 0.5X CHL
1XGLU+1XCHL 1XCHL
1X THI 0.25X GLU + 0.25X CHL
0.25X GLU + 0.5X CHL
0.25X GLU + 1X CHL
0.5X GLU + 0.25X CHL

 

 

 

aWhere 1X = the labeled rate; Glufosinate applied as
LIBERTY 1X = 420 g ailha; Chlorimuron applied as CLASSIC
1X = 8.8 g ai/ha; Thifensulfuron applied as HARMONY DS 1X

= 4.5 g ai/ha.

bAbbreviations: GLU, Glufosinate; CHL, Chlorimuron; THI,

Thifensulfuron.

133

 

Table 11 . Herbicide combinations applied in fluorescence

 

 

 

 

studies.a .
Herbicides Applied by Species - Fluorescence Studies~
CIRAR + CHEAL ABUTH + SETFA
Control Control
0.25X GLUb 025" GLU
0.5X GLU 0.5X GLU
1X GLU 1X GLU
0.25X CHL 1X CHL
0.5X CHL 0.25X GLU + 1X CHL
1X CHL 0.25X GLU + 1X GLY
0.25X GLU + 0.25X CHL
0.25X GLU + 1X CHL
0.5X GLU + 0.5X CHL
1X GLU + 0.25X CHL
1X GLU + 0.5X CHL

1X GLU + 1X CHL

 

 

3 Where 1X = the labeled rate; glufosinate applied as
LIBERTY 1X = 420 g ailha; chlorimuron applied as CLASSIC

1X = 8.8 g ailha.

b Abbreviations: GLU, glufosinate; CHL, chlorimuron.

134

 

 

 

Table 12. Visual control 7 and 28 days after treatment of velvetleaf, common
lambsquarters and giant foxtail when applied with combinations of glufosinate

and chlorimuron in 2009 field study.a

 

 

 

 

 

 

 

 

 

ABUTH CHEAL SETFA
Herbicide Rateb’c'd 7 DAT 28 DAT 7 DAT 28 DAT 7 DAT 28 DAT
GLU CHL Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp.0bs. . Exp. Obs.
gai/ha %
0 0 — 0 — 0 - 0 - 0 — 0 - 0
118 0 - 30 - 31 — 35 - 31 - 49 - 76
235 0 - 48 - 39 - 46 - 29 - 64 - 73
470 0 — 100 — 70 — 97 - 89 - 94 — 86
O 2.2 - 43 — 29 — 15 - 30 - 6 - 35
O 4.4 — 26 - 3g — 15 — 44 - 2 - 51
0 8.8 — 39 - 38 - 23 - 25 - 25 - 46
118 2.2 100 44 H 80 43 H 98 32 H 92 33 (-) 94 56 H 91 78 H
118 4.4 100 29 H 80 69 H 98 36 H 93 48 H 94 58 H 93 73 H
118 8.8 100 39 H 80 83 98 21 H 91 50(-) 95 79 H 93 80 H
235 2.2 70 29 H 56 71 (+) 55 20 H 50 86 (+) 66 73 (+) 82 91 (+)
235 4.4 61 28 H 62 95 (+) 54 54 60 41 H 65 81 (+) 87 81 H
235 8.8 68 94 (+) 61.98 (+) 59 42 H 47 44 73 78 85 86
470 4.4 49 14 H 58 97 (+) 45 84(+) 61 86 (+) 50 74 (+) 88 90
470 8.8 58 93 (+) 57 95 (+) 50 48 49 84 (+) 61 89 (+) 87 93 (+)
LSD (0.05)8 3 2 2 2 2 2

 

a . . . . . . . . . . .

+ and — denote a synergistic and antagonistic interaction for a given combination according to
the LSD comparison of the observed and expected values calculated using Colby’s method.
Observed values without a + or - are additive.

bAbbreviationszGLU, glufosinate; CHL, chlorimuron; ABUTH, velvetleaf; CHEAL, common
lambsquarters; SETFA, giant foxtail; DAT, days after treatment; Exp., expected; Obs., observed.

c . . . . .
Treatments containing gluphosmate also included ammonium sulfate at 2% WV.

0 . . . . .
Treatments containing only chlorimuron also included crop cil concentrate at 1% WV.

8
LSD values may be used to compare values.

135

a) 100

I 4 I J

70

1

Control (%)
01

 

   

 

 

 

 

 

40 IExpected
. KObserved
20 1
1 ..
1/4X GLU1/2X LU 1X CHL 1X CHL+1X CHL+
1/4X GLU1/2X GLU
erbicide Applied
100 1
90 4
80 .
A 70 4
O
at 60 —
‘9 50 -
8 4O _ I Expected
0 0 _ fiObserved
20 -
10 4
0 .

 

1/4X GLU1/2X LU 1X CHL 1X CHL +1X CHL +
1/4X GLU1/2X GLU

erbicide Applied
Figure 18. Chlorimuron(CHL) and glufosinate(GLU) on common
lambsquarters visual observations in the greenhouse (a) 7 days after
treatment and (b) 28 days after treatment. Synergism by Colby's method
indicated by a (+). LSD = 5 for 7 DAT and LSD = 12 for 28 DAT. '

(a) 100 -
90 -
80 -
70 -
60 4
50 4
40 4
30 -
20 -
10 -

Control (%)

I Expected
9 Obse rved

 
 

 

1/4X GLU1/2X CHL 1XCHL 1/4X GLU1/4X GLU
+ 1/2X + 1X CHL
CHL
Herbicide Applied
(b) 100 —
90 4
80 4
70 4
60 4
50 4
40 4
30 4
20 4
10 -

I Expected
88 ObserVed

Control (%)

 

1/4X GLU1/2X CHL 1X CHL 1/4X GLU1/4X GLU

+ 1/2X + 1X CHL

CHL
Herbicide Applied

Figure 19. Chlorimuron(CHL) and glufosinate(GLU) on giant foxtail visual
observations in the greenhouse (a) 7 days after treatment and (b) 28 days
after treatment. Antagonism and synergism by Colby's method indicated by
a (-) or (+) respectively. LSD = 5 for 7 DAT and LSD = 8 for 28 DAT.

137

(a) 100

Control (%)

(b) 100
90
80
70
60
50
40
30
20
1 0

Control (%)

 

 

  

 

 

1/2X GLU 1/2X THI 1/2X THI
+ 1/3X + 1/2X
GLU GLU

Herbicide Applied

1/2X THI 1/3X GLU1/2X GLU 1/2X THI 1/2X THI

Herbicide Applied

I Expected
as Observed
+ 1/3X + 1/2X
GLU GLU
(+) (+)
I Expected
9 Observed

Figure 20. Thifensulfuron(THI) and glufosinate(GLU) on velvetleaf vis'ual
observations in the greenhouse (a) 7 days after treatment and (b) 28 days
after treatment. Antagonism and synergism by Colby's method indicated by
a (-) or (+) respectively. LSD = 5 for 7 DAT and LSD = 8 for 28 DAT.

+CONTROL
+0.25X CHL
+0.25X GLU

- -)(-0.25 GLU +
0 r r r f r 1 0.25X CHL

2 4 6 8 24 48 72
Hours After Treatment (HAT)

 

 

 

+CONTROL
-I-1x CHL

+0.25X GLU

 

-x-0.25X GLU +
1X CHL

 

 

0 T T T I ‘l
2 4 6 8 24 48 72

Hours After Treatment (HAT)

Figure 21 . Fv/Fm of glufosinate(GLU) and Chlorimuron(CHL) combinations
on Canada thistle. Where a (*) indicates the combination is significantly
different from glufosinate applied alone.

139

A
DJ
V

.o

(n

(A)
2
U)

NS NS NS
NS NS

0.78 , .
E
E 0.73

0.68 I+

0.63 ~ - , - ~

V V V V 0 0 V V V V V V
e444,,44‘9344 4444
0° Q69 061’ Q"; ,9 oq’ 9' 0"
06“ C9 + (1‘
5.120 9‘" 6‘? 09‘ "
Herbicide Applied

(b)

0.8 4

NS

0.7 4 NS

0.6 4 “S
E 0.5
E 0.4

0.3 " . e

0.2 4

0.1

0

 

 

V Ox) 0° ex)

:1 0" x x0 x 0
<3 \
0'8” 0'.» 6+ .3- d—

Herbicide Applied

Figure 22. Fv/Fm of glufosinate(GLU) and Chlorimuron(CHL) on Canada
thistle at (a) 2 hours after treatment and (b) 72 hours after treatment. Where
a (*) indicates the combination is significantly different from the control.

140

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Anonymous 2006b. HARMONY® herbicide label. E. I. du Pont de Nemours and
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Anonymous. 2007. Liberty® herbicide label. Bayer Crop Science. Research
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Barbagallo, R.P., K. Oxborough, K.E. Pallet, and NR. Baker. 2003. Rapid, non-
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Colby, S. R. 1967. Calculating synergistic and antagonistic responses of
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Christensen, M.G., H.B.Teicher and JG Streibig 2003. Linking fluorescence
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Frankart, C., P. Eullaffroy, and G. Vemet. 2003. Comparative effects cf four
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Hydrick, DE, and DR. Shaw. 1995. Non-selective and selective herbicide
combinations in stale seedbed (Glycine max). Weed Technol. 9: 158-165.

Kirkwood R.C., R. Hetherington, T.L. Reynolds, and G. Marshall. 2000.
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and surfactant concentration. Pest Manag Sci 56:359-367.

141

Olesen, C.F., N. Cedergreen. 2010. Glyphosate uncouples gas exchange and
chlorophyll fluorescence. Pest Manag Sci 66:536-542.

Percival, MP, and NR. Baker. 1991. Herbicides and photosynthesis. Pages 1-
26 in MR. Baker and MP. Percival, eds. Herbicides. London: Elsevier.

Ralph, P.J. 2000. Herbicide toxicity of Halophila ova/is assessed by chlorophyll A
fluorescence. Aquat Bot 66:141-152.

Strasser, R.J., A. Sirivastava, and M. Tsimilli-Michael. 2000. The fluorescence
transient as a tool to characterize and screen photosynthetic samples.
Pages 445-483 in M. Yunus, U. Pathre, and P. Mohanty, eds. Probing
Photosynthesis: Mechanisms, Regulation and Adaptation. London: Taylor
& Francis.

Starke, R. J., and L. R. Oliver. 1998. Interaction of glyphosate with chlorimuron,
fomesafen, imazethapyr, and sulfentrazone. Weed Sci. 46: 652-660.

Vidrine, P. R., J. L. Griffin, and D. C. Blouin. 2002. Evaluation of reduced rates of

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142

APPENDIX

143

Table 13. Visual control 7 and 28 days after treatment of velvetleaf, cOmmon
lambsquarters and giant foxtail when applied with combinations of glyphosate,

glufosinate and chlorimuron in 2009 field study.a
Visual Control
ABUTH CHEAL SETFA

Herbicide Rateb 7 DAT 28 DAT 7 DAT 28 DAT 7 DAT 28 DAT
GLY GLU CHL Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs. Exp.0bs. Exp. Obs.

,C,d

 

 

 

gae/ha gai/ha %
0 0 0 — 0 - 0 — 0 — 0 - 0 - 0
210 0 0 — 33 — 45 — 35 - 48 - 75 — 86
420 0 0 - 48 — 100 — 29 - 85 - 89 — 99
840 0 0 — 43 — 100 - 43 - 99 - 30 — 100
0 118 0 - 3o — 31 — 35 — 31 — 49 — 76
0 235 0 — 43 — 39 — 45 — 29 — 54 - 73
0 470 0 - 100 - 70 - 97 - 89 — 94 — 86
0 0 2.2 — 43 — 29 — 15 — 3O — 5 — 35
0 0 4.4 - 25 — 39 — 15 - 44 — 2 — 51
0 0 8.8 - 39 — 33 — 23 - 25 - 25 — 46
210 470 0 100 99 85 63 H 98 95 94 89 98 95 98 95
420 235 0 73 99 (+) 100 100 62 95 (+) 89 100 (+) 96 91 100 86 (-l
840 118 0 64 95 (+) 100 90 H 66 95 (+) 99 91 H 90 95 100 891-)
840 470 0 64 90 (+) 100 100 66 93 (+) 99 100 90 90 100 100
210 0 2.2 64 42 H 62 78 (+) 47 36 H 63 71 (+) 77 91 (+) 91 94
210 0 4.4 54 26 H 67 59 H 46 37 H 71 72 76 86 (+) 94 94
210 0 8.8 61 81 (+) 68 98 (+) 51 55 61 95 (+) 81 71 (+) 93 94
420 0 2.2 70 92 (+) 100 90 H 40 83 (+) 89 86 90 90 99 100
420 0 4-4 61 29 H 100 95 39 91 (+) 92 81 H 89 90 99 98
420 0 8.8 67 38 H 100100 45 57 (+) 89 72 (+) 92 86 .99 100
840 0 4.4 61 61 100 99 55 36 H 99 83 (4) 81 89 H 100100
840 0 8-8 67 92 (+) 100 100 59 60 99 98 85 91 100 100
0 118 2.2 100 44 H 80 43 H 98 32 H 92 33 (4) 94 56 H 91 78 (-)
0 118 4.4 100 29 H 80 69 H 98 36 H 93 48 H 94 58 H 93 73 (-)
0 118 8.8 100 39 (-) 80 83 98 21 H 91 50 H 95 79 (-l 93 30H
0 235 2.2 70 29 H 56 71 (+) 55 20 H 50 86 (+) 66 73 (+) 82 91 (+)
0 235 4.4 61 28 (-) 62 95 (+) 54 54 60 41 H 65 81 (+) 87 81 H
0 235 8.8 68 94 (+) 61 98 (+) 59 42 H 47 44 73 78 85 86
0 470 4.4 49 14 H 58 97 (+) 45 84 (+) 61 86 (+) 50 741+) 88 90
0 470 8.8 58 93 (+) 57 95 (+) 50 48 49 84 (+) 61 89 (+) 87 93 (+)
LSD (0.05)e 3 2 2 2 2 2

 

a . . . . . . . . . .

+ and — denote a synergistic and antagonistic interaction for a given combination according
to the LSD comparison of the observed and expected values calculated using Colby/s
method. Observed values without a + or — are additive.

b
Abbreviations: GLY, glyphosate; GLU, glufosinate; CHL, chlorimuron; ABUTH, velvetleaf;
CHEAL, common lambsquarters; SETFA, giant foxtail; DAT, days after treatment; Exp.,

0 . . . . .
Treatments containing glyphosate and/or glufosmate also included ammonium sulfate at 2%

d . . . . . .
Treatments containing only chlorimuron or thifensulfuron also included crop cil concentrate
at 1% WV.

9
LSD values may be used to compare values.

144

Table 14. Percent control compared to the untreated for
combinations of glyphosate and glufosinate on Canada

thistle 5, 7, 14, 21 and 28 days after treatmenta

 

Visual Control - Canada thistle

 

 

 

Herbicide Rate‘3 5 DAT b 7 DAT 14 DAT 21 DAT
Glyphosate Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ailha %

o o - 0 - 0 .. 0 - O
210 0 - 33 - 59 - 90 - 96
280 o - 31 - 76 - 86 - 100
420 g - 43 - 75 - 94 - 99
340 o - 51 - 75 - 95 - 100

o 113 - 50 - 58 - 34 - 39

O 157 - 63 - 71 - 83 - 90

O 235 - 64 - 79 - 83 - 86

o 470 - 68 - 75 - 94 - 98
210 113 67 55 (-) 82 60 (-) 93 45 (-) 98 58
280 115 66 55 (-) 91 58 (-) 91 49 (-) 100 64
420 113 74 45 (-) 90 54 (-) 96 56 (-) 100 62
340 113 77 44 (-) 89 59 (-) 97 64 (-) 100 74
210 157 74 48 (-) 88 55 H 99 61 (-) 100 61
230 157 73 41 (-) 94 51 (-) 99 58 (-) 100 65
420 157 78 45 (-) 93 53 (-) 99 58 (-) 100 59
340 157 82 50 (-) 93 61 (-) 99 66 (-) 100 78
210 235 77 65 H 90 69 (-) 98 77 (-) 99 72
280 235 76 65 H 96 74 (-) 99 70 (-) 100 86
420 235 81 65 (-) 95 69 (-) 99 64 (-) 100 81
340 235 84 61 (-) 95 65 (-) 99 84 (-) 100 78
210 470 77 80 89 76 (-) 99 92 100 100
280 470 76 80 94 83 (-) 99 98 100 95
420 470 81 80 94 75 (-) 100 94 100 100
340 470 85 73 (-) 94 80 (-) 100 94 100‘ 96

LSD (0.05)d 9 8 10 12

 

a . . . . . . .
+ and - denote a synergistic and antgonlstic interaction for the given

combinations according to the LSD comparison of the observed and
expected values calculated using Colby's method. Observed values

0
Abbreviations: DAT, days after treatment; Exp., expected; Obs.,

c .
Treatments containing glyphosate and/or glufosinate also included

ammonium sulfate at 2% v/v.

d
LSD values may be used to compare values.

145

Table 15 . Fresh weight and height reduction compared to the
untreated control 28 days after treatment for combinations of

glyphosate and glufosinate for canada thistle and velvetleafa

 

 

 

CIRAR” ABUTH .

Herbicide RateC FWR HR FWR HR
Glyphosate Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp.
9 ae/ha g ai/ha % Reduction ——
0 0 - 0 - 0 - 0 -
210 0 - 95 - 81 - 85 -
280 0 - 92 - 83 - 86 -
420 O - 95 - 86 - 94 -
840 0 - 97 - 86 - 93 -
0 118 - 53 - 43 - 65 -
0 157 - 86 - 83 - 80 -
0 235 - 89 - 74 - 84 -
0 470 - 83 - 88 - 94 -
210 118 98 57 (-) 89 53 (-) 95 77 (-) 92
280 118 97 74 (-) 90 55 (-) 95 84 (-) 91
420 118 98 66 (-) 91 67 (-) 98 79 (-) 94
840 118 98 64 (-) 91 64 (-) 98 84 (-) 93
210 157 99 57 (-) 96 57 (-) 97 83 (-) 95
280 157 99 62 (-) 97 58 (-) 97 71 (-) 94
420 157 99 69 (-) 98 48 (-) 99 80 (-) 96
840 157 99 74 (-) 98 67 (~) 99 67 (-) 96
210 235 99 77 (-) 94 73 (-) 97 91 96
280 235 100 78 (-) 96 64 (-) 98 80 (-) 96
420 235 100 71 (-) 96 64 (-) 99 80 (-) 97
840 235 100 87 (-) 96 62 (-) 99 80 (-) 96
210 470 99 89 98 83 (-) 99 91 98
280 470 99 97 98 89 99 80 (-) 97
420 470 99 94 98 84 (-) 100 88 (-) 98
840 470 99 92 98 80 (-) 100 89 (-) 98
LSD (0.05)d 11 12 11 12

 

 

 

 

 

a . . . . .

+ and - denote a synergistic and antgonistic interaction for the given
combinationsaccording to the LSD comparison of the observed and expected values
calculated using Colby/s method. Observed values without a + or - are additive.

bAbbreviations: CIRAR, canada thistle; ABUTH, velvetleaf; FWR, fresh weight
reduction; HR, height reduction; Exp., expected; Obs., observed.

0 . . . . .
Treatments containing glyphosate and/or glufosmate also included ammonium
sulfate at 2% v/v.

d
LSD values may be used to compare values.

146

Table 16. Percent control compared to the untreated for combinations of
glyphosate and glufosinate on velvetleaf 7, 14, 21 and 28 days after

treatment.8
Visual Control - Velvetleaf

 

 

 

 

Herbicide Ratec 7 QATb 14 _DAT 21 DAT 28 DAT
Glyphosate Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ai/ha %

O O - O - O - 0 - O
210 0 - 43 - 73 - 78 - 86
280 O - 44 - 80 - 85 - 87
420 O - 49 - 96 - 96 - 99
840 O - 54 - 98 - 100 - 100

O 118 - 58 - 13 - 10 - 30

0 157 - 75 - 41 - 23 - 38

O 235 - 81 - 44 - 28 - 53

0 470 - 85 - 95 - 94 - 81
210 118 76 68 (4) 76 35 (-) 80 36 H 91 54
280 118 76 62 1‘) 82 53 H 87 36 H 91 54
420 118 77 59 (4) 97 54 (-) 97 50 (-) 99 66
840 118 79 63 H 98 76 H 100 56 H 100 68
210 157 86 57 H 84 33 H 82 38 1') 91 56
280 157 86 56 H 88 46 H 88 39 H 91 57
420 157 86 63 H 98 60 H 97 39 H 99 60
840 157 88 64 H 98 58 H 100 53 1') 100 67
210 235 89 77 (4) 85 73 (4) 84 46 H 94 65
280 235 89 76 H 89 39 H 89 43 H 94 58
420 235 90 79 (4) 98 5O (-) 97 43 H 99 57
840 235 91 70 H 98 44 H 100 49 H 100 56
210 470 91 81 H 99 84 H 99 68 H 97 73
280 470 92 82 H 99 49 H 99 43 H 98 59
420 470 92 83 H 100 73 H 100 66 (-) 99 74
840 470 93 81 (4) 100 88 (-) 100 88 (-) 100 74

LSD (0.05)d 5 11 12 10,

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby‘s method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . . .
Treatments containing glyphosate and/or glufosmate also included ammonium sulfate
at 2% WV.

(1
LSD values may be used to compare values.

147

Table 17. Percent control compared to the untreated for
combinations of glyphosate and glufosinate on common

lambsquarters 5, 7, 14, 21 and 28 days after treatment.al

 

Herbicide RateC
Glyphosate Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.

Visual Control - Common lambsquarters

 

b

5 DAT

7 DAT

14 DAT

21 DAT

 

g ae/ha g ai/ha
0 O
210 O
280 0
420 0
840 0
0 1 18
0 1 57
0 235
O 470
21 0 1 1 8
280 1 18
420 1 18
840 1 18
210 1 57
280 1 57
420 1 57
840 1 57
210 235
280 235
420 235
840 235
210 470
280 470
420 470
840 470
LSD (0.05)d

21
48
36
39
48
65
46
48
55
7O
47
5O
57
68

16
48

35

45

50

24 (+)

24 (+)

29

36 H
0 H

49 (+)

46 H
60 (-)
65 (+)
65 (+)
64
67

9

OI.
I u

0
1 O
47
46
63
12
64
75
74
22

34 H
59
15 H
48 H
48 H
40 H
51 H
69
70 H
66 H
82
34
87
87

17

0
26
58
67
91
13
52
50
74
47
51
44 H
71 (-)
26 H
42 (-)
59 H
56 (-)
39 (-)
54 (-)
62 (-)
72 (-)
67
80
90
93

17

O
49
81
93
96
18
51
66

- 100

100
100
100
100

16

38
57
48
74
34
43
64
65
54
61
67
68
73
86
97
99

 

a . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given
combinations according to the LSD comparison of the observed and
expected values calculated using Colby's method. Observed values

b Abbreviations: DAT, days after treatment; Exp., expected; Obs.,

c . . . .
Treatments containing glyphosate and/or glufosmate also included
ammonium sulfate at 2% v/v.

d
LSD values may be used to compare values.

148

Table 18. Percent control compared to the untreated for
combinations of glyphosate and glufosinate on giant foxtail 5,

7, 14, 21 and 28 days after treatment.al
Visual Control - Giant foxtail

 

 

 

 

Herbicide Ratec 5 DAT b 7 DAT 14 DAT 21 DAT
Glyphosate Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ailha %

o o - 0 - 0 - 0 - 0
210 o - 5 - 39 - 65 - 74
230 o - 1 - 34 - 71 - 84
420 o - 9 - 66 - 78 - 99
340 o - 8 - 48 - 88 - 99

o 113 - 21 - 84 - 40 _ 33

o 157 - 48 - 88 - 64 - 65

o 235 - 53 - 83 - 80 - 70

o 470 - 61 - 96 - 96 - 78
210 113 25 46 (+) 91 95 80 73 84 66 (-)
230 113 22 38 (+) 89 95 83 54 (-) 91 60 (-)
420 113 28 43 (+) 96 93 87 55 (-) 99 65 H
340 113 27 46 (+) 90 95 93 74 (-) 99 89
210 157 50 44 92 95 88 56 (-) 91 63 (-)
230 157 48 49 92 95 89 73 H 95 64 (-)
420 157 52 46 93 88 92 58 (-) 99 60 (-)
340 157 51 46 92 95 96 76 (-) 100 80 (-)
210 235 55 63 89 95 94 81 (-) 93 74 (-)
230 235 53 63 (+) 88 96 94 85 (-) 96 79 (-)
420 235 57 53 95 95 96 83 (-) 100 71 (-)
340 235 56 48 (-) 97 94 97 79 (-) 100 76 (-)
210 470 63 54 (-) 98 96 99 98 91 91
230 470 62 63 98 95 99 90 96 94
420 470 65 65 99 95 99 94 99 93
340 470 64 68 98 99 100 95 100 99

LSD (0.05)d 8 14 9 17

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

0 . . . .
Treatments containing glyphosate and/or glufosinate also included
ammonium sulfate at 2% v/v.

d
LSD values may be used to compare values.

149

 

Table 19. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of glyphosate and

glufosinate for common lambsquarters and giant foxtaila

 

 

 

 

 

 

 

 

CHEALb SETFA
Herbicide Ratec FWR HR FWR HR
Glyphosate Glufosinate Exp. Obs. Egp. Obs. Exp. Obs. Exp. 79993
g ae/ha g ailha % Reduction ——
0 0 — 0 - 0 - 0 - 0
210 0 - 25 - 28 - 98 - 86
280 0 - 42 - 43 - 99 - 96
420 0 - 66 - 65 - 99 - 88
840 0 - 72 - 83 - 99 — 97
0 118 - 31 - 28 - 90 - 84
0 157 - 38 - 32 - 93 - 80
0 235 — 37 - 39 - 100 - 97
0 470 - 63 - 56 - 99 - 97
210 118 45 39 49 33 100 97 99 83
280 118 54 49 57 39 100 100 99 97
420 118 71 38 (-) 76 28 (-) 100 98 99 90
840 118 76 52 (-) 87 55 (-) 100100 99 95
210 157 51 271-) 48 22 (-) 100100 98 97
280 157 54 46 52 23 (-) 100 100 99 98
420 157 73 51 (-) 71 46 (-) 100 96 99 91
840 157 78 51 (-) 88 43 (-) 100 99 99 94
210 235 53 49 57 37 (-) 100 100 99 97
280 235 56 47 58 38 (-) 100 100 100 98
420 235 74 53 75 43 (-) 100 100 99 96
840 235 80 52 (-) 90 501-) 100 100 100 98
210 470 71 70 60 59 100 100 100 98
280 470 73 62 61 54 100 100 100 97
420 470 84 70 79 61 (-) 100 100 100 98
840 470 90 70 91 69 (-) 100 100 100, 98
LSD (0.05)d 12 18 5 9 .

 

a . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given _
combinationsaccording to the LSD comparison of the observed and expected values
calculated using Colby/s method. Observed values without a + or - are additive.

bAbbreviations: CHEAL, common lambsquarters; SETFA, giant foxtail; FWR, fresh

weight reduction; HR, height reduction; Exp., expected; Obs., observed.

c . . . . .
Treatments containing glyphosate and/or glufosinate also included ammonium sulfate

at 2% WV.

0
LSD values may be used to compare values.

150

Table 20. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on Canada thistle 7, 14, 21 and 28 days after

treatmenta -
Visual Control - Canada thistle

 

 

 

 

 

Herbicide Ratec'd LDATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glyphosate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ai/ha g ae/ha %

0 O - O - 0 - O - O
2.2 O - 8 - 25 - 26 - 43
2.93 0 - 26 - 50 - 45 - 53
4.4 0 - 31 - 38 - 50 - 60
8.8 O - 38 - 48 - 54 - 71

O 210 - 68 - 75 - 90 - 89

0 280 - 54 - 68 - 85 - 83

O 420 - 59 - 78 - 94 - 91

O 840 - 85 - 95 - 98 - 99
2.2 210 69 53 (-) 80 68 (-) 92 78 (-) 93 80
2.93 210 76 76 88 85 94 94 95 94
4.4 210 78 7O 85 88 95 91 96 91
8.8 210 80 71 (-) 87 90 96 95 97 96
2.2 280 57 71 (-) 75 85 (+) 88 94 (+) 89 95
2.93 280 66 83 (+) 84 93 91 100 (+) 91 100
4.4 280 68 66 80 85 92 93 93 96
8.8 280 71 69 83 85 93 90 96 96
2.2 420 62 85 (+) 83‘ 100 (+) 95 100 95 100
2.93 420 69 75 89 93 97 100 96 100
4.4 420 72 79 86 98 (+) 97 98 97 100
8.8 420 75 85 (+) 88 98 (+) 97 100 98 100
2.2 840 86 90 95 100 98 100 99 100
2.93 840 89 88 98 95 99 100 99 100
4.4 840 90 89 97 100 99 100 100 100
8.8 840 91 89 98 100 99 100 100 100

LSD (0.05)6 9 9 7 7

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
ColbYs method. Observed values without a + or - are additive.

b . .
AbbreViations: DAT, days after treatment; Exp., expected; Obs., observed.
C Treatments containing glyphosate also included ammonium sulfate at 2% WV.

0 . . . . .
Treatments containing chlorimuron also included crop cil concentrate at 1% v/v.

e
LSD values may be used to compare values.

151

Table 21 . Fresh weight and height reduction compared to the untreated control
28 days after treatment for combinations of chlorimuron and glyphosate for

canada thistle and velvetleaf.a

 

 

 

 

 

 

 

ClRARb ABUTH
Herbicide Ratec’d FWR _H_R__ _FLVB_ __._;_Lj§=_
Chlorimuron Glyphosate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ae/ha % Reduction ——

o o - o - o - o - o
2.2 o - 36 - 61 - 42 - 50
2.93 o - 59 - 79 - 66 - 62
4.4 o - 63 - 81 - 46 '- 54
8.8 o — 79 - 86 - 64 - 68

0 210 - 86 - 86 - 51 - 67

o 280 — 80 - 82 - 59 - 74

o 420 - 92 - 85 - 66 - 76

o 840 - 97 - 89 - 83 - 81
2.2 210 90 86 93 83 (-) 67 68 81 63 H
2.93 210 92 94 97 91 82 73 86 77 H
4.4 210 95 94 97 88 H 69 77 84 77
8.8 210 98 96 98 87 (-) 81 77 89 79 (-)
2.2 280 86 95 92 89 74 75 86 79
2.93 280 90 97 96 91 84 75 89 75 (~)
4.4 280 92 92 96 88 H 75 79 88 75 H
8.8 280 97 95 98 86 H 82 78 91 75 (-)
2.2 420 95 98 94 94 80 79 87 77 H
2.93 420 97 98 97 89 H 89 80 90 77 H
4.4 420 97 97 97 91 82 77 88 76 (-l
8.8 420 99 97 98 9o (-) 88 78 92 76 H
2.2 840 98 98 96 93 89 82 90 77 H
2.93 840 98 97 98 91 93 92 91 83
4.4 840 99 97 98 93 89 8o 90 77 (-l
8.8 840 99 98 98 92 93 87 93 80

Lso (0.05)6 10 8 13 9

 

a . . . . . . . . . , .
+ and - denote a synergistic and antgonistic interaction for the given combinations according

to the LSD comparison of the observed and expected values calculated using Colby/s method.
Observed values without a + or - are additive.

bAbbreviations: CIRAR, canada thistle; ABUTH, velvetleaf; FWR, fresh weight reduction; HR,
height reduction; Exp., expected; Obs., observed.

c . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.

Treatments containing chlorimuron also included crop oil concentrate at 1% WV.

9
LSD values may be used to compare values.

152

Table 22. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on velvetleaf 7, 14, 21 and 28 days after

treatment.a1

 

Visual Control - Velvetleaf

 

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glyphosate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ae/ha %

O 0 - O - O - O - O
2.2 O - 44 - 46 - 44 - 46
2.93 0 - 66 - 62 - 58 - 61
4.4 O - 51 - 51 - 48 - 50
8.8 O - 52 - 56 - 62 - 68

O 210 - 34 - 46 - 64 - 49

O 280 - 40 - 53 - 64 - 70

0 420 - 43 - 58 - 7O - 69

O 840 - 51 - 66 - 89 - 94
2.2 210 63 56 66 59 78 67 H 71 69
2.93 21 0 78 65 77 69 86 85 80 79
4.4 21 O 70 61 70 69 82 85 75 80
8.8 21 0 7O 62 73 67 88 81 85 82
2.2 280 66 59 72 68 78 80 81 85
2.93 280 79 61 (-) 79 65 H 82 78 86 77
4.4 280 71 58 73 62 H 79 82 82 81
8.8 280 71 63 76 65 84 85 88 79
2.2 420 68 63 74 76 84 89 81 87
2.93 420 80 66 H 81 74 88 88 88 87
4.4 420 72 63 75 74 84 88 83 90
8.8 420 73 57 H 77 71 89 88 89 91
2.2 840 73 68 80 74 96 90 97 93
2.93 840 84 66 H 85 86 97 96 98 98
4.4 840 78 64 H 80 72 96 88 97 88
8.8 840 78 74 82 75 98 92 98 95

LSD (0.05)e 14 11 11 11

 

a . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations according
to the LSD comparison of the observed and expected values calculated using Colby's method.
Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
d . . . . .
Treatments containing chlorimuron also included crop Oll concentrate at 1% v/v.

e
LSD values may be used to compare values.

153

Table 23. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on common lambsquarters 7, 14, 21 and 28

days after treatmenta .
Visual Control - Common lambsquarters

 

 

 

 

 

Herbicide Ratec’d 7 pATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glyphosate Exp. Obs. Exp Obs. Exp. Obs. Exp.0bs.
g ailha g ae/ha %

0 O - O - O - O - 0
2.2 O - 13 - 6 - 11 — 8
2.93 0 - 11 - 15 - 17 - 16
4.4 O - 19 - 20 - 21 - 21
8.8 O - 24 - 28 - 25 - 25

0 210 - 31 - 44 - 41 - 41

O 280 - 34 - 51 - 38 - 51

O 420 - 57 - 69 - 75 - 77 .

O 840 - 70 - 81 - 88 - 93
2.2 21 0 39 43 47 63 49 57 49 73
2.93 21 0 38 34 52 50 50 56 47 68
4.4 210 43 42 55 63 54 69 52 71
8.8 21 0 46 50 59 56 55 63 52 76
2.2 280 42 57 53 68 45 68 (+) 54 71
2.93 280 41 38 58 48 (-) 47 45 54 65
4.4 280 46 4O 61 60 51 61 59 71
8.8 280 49 55 64 68 53 73 (+) 62 81
2.2 420 62 73 7O 84 76 84 77 90
2.93 420 62 78 (+) 74 84 78 88 78 91
4.4 420 64 82 (+) 75 87 80 88 81 90
8.8 420 66 7O 78 79 82 84 83 88
2.2 840 73 76 82 84 88 91 93 96
2.93 840 73 79 84 86 89 93 93 85
4.4 840 75 82 85 88 90 94 93 97
8.8 840 76 79 87 96 91 97 95 99

LSD (0.05)e ‘5 16 15 16

 

a . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
COIbYS method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

6 . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% WV.

0 . . . . .
Treatments containing chlorimuron also included crop OII concentrate at 1% WV.

9
LSD values may be used to compare values.

154

Table 24. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of chlorimuron and

glyphosate for common lambsquarters and giant foxtail.a

 

 

 

 

 

CHEAL SETFA .

Herbicide Ratec’d FWRb HR FWR Ha
Chlorimuron Glyphosate Exp. Obs. Exp. Obs. Exp. Obs. Exp.0bs.
g ailha g ae/ha % Reduction ‘ —-
0 O - O - 0 - O - O
2.2 O - 15 - 12 - 2 - 1
2.93 O - 9 - 20 - 7 - O
4.4 O - 29 - 18 - 2 - 2
8.8 O - 22 - 15 - 10 - 3
O 210 - 4O - 33 - 13 - 13
O 280 - 42 - 36 - 32 - 37
O 420 - 65 - 73 - 69 - 45
0 840 - 83 - 83 - 93 - 69
2.2 210 50 50 43 62 (+) 14 18 14 16
2.93 210 45 49 41 48 19 26 13 14
4.4 210 54 65 44 59 14 34 (+) 15 19
8.8 210 49 60 39 63 (+) 21 22 15 8
2.2 280 52 55 44 60 34 37 38 36
2.93 280 47 49 43 51 37 29 37 24
4.4 280 56 57 45 6O 33 44 38 31
8.8 280 53 76 (+) 42 76 (+) 38 35 38 32
2.2 420 66 85 (+) 74 78 7O 81 46 48
2.93 420 67 80 75 78 7O 81 45 51
4.4 420 73 84 75 82 69 89 (+) 46 59
8.8 420 69 76 76 74 71 76 46 50
2.2 840 84 91 84 85 93 96 7O 74
2.93 840 84 91 84 84 94 96 69 69
4.4 840 87 9O 84 83 93 97 69 70
8.8 840 85 90 85 84 94 97 69 74

LSD (0.05){-3 18 17 18 17

 

a . . . . . . . . . ._

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby‘s method. Observed values without a + or - are additive.

bAbbreviations: CHEAL, common lambsquarters; SETFA, giant foxtail; FWR, fresh
weight reduction; HR, height reduction; Exp., expected; Obs., observed.

c . . . ’ .
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
d . . . . .
Treatments containing chlorimuron also included crop orl concentrate at 1% WV.

9
LSD values may be used to compare values.

155

Table 25. Percent control compared to the untreated for combinations of
glyphosate and chlorimuron on giant foxtail 7, 14, 21 and 28 days after

treatmenta

 

Herbicide Ratec’d
Chlorimuron Glyphosate Exp; Obs. Exp. Obs.

Visual Control - Giant foxtail

 

7 DATb

14 DAT

21 DAT
Exp. Obs. Exp. Obs.

28 DAT

 

 

g ailha g ae/ha %
o o - o - o - o - o
2.2 o - o - o - 4 - 15
2.93 o - 7 - 4 - o - 21
4.4 o - 7 - 4 - 3 - 20
8.8 o - 7 - 8 - 6 - 29
o 210 - 16 - 66 - 71 - 40
o 280 - 19 - 80 - 88 - 50
o 420 - 18 - 93 - 87 - 68
o 840 - 41 - 98 - 85 - 91
2.2 210 16 18 66 69 72 84 (+) 49 44
2.93 210 21 20 68 88 (+) 71 89 (+) 53 45
4.4 210 21 9 (-) 68 89 (+) 72 85 (+) 52 45
8.8 210 21 10(-) 69 59 (-) 73 86 (+) 57 51
2.2 280 19 13 (-) 80 86 89 89 57 55
2.93 280 24 9 (-) 81 91 (+) 88 93 61 55
4.4 280 24 13 (-) 81 89 88 91 60 55
8.8 280 24 11 (-) 81 92 (+) 89 92 64 55
2.2 420 18 11 (-) 93 97 87 91 72 70
2.93 420 24 23 93 95 87 89 75 69
4.4 420 24 18 (-) 93 98 87 88 75 77
8.8 420 24 19 (-) 94 96 88 89 77 72
2.2 840 41 29 (-) 98 98 86 89 92 89
2.93 840 45 33 (-) 98 98 85 87 93 93
4.4 840 45 31 (-) 98 99 85 91 93 86
8.8 840 45 41 98 100 86 91 93 93
LSD 10.059 5 9 9 ,4

 

a . . . . . . . . .
+ and - denote a synergistic and antgonistic interaction for the given combinations

according to the LSD comparison of the observed and expected values calculated using

Colby’s method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% vlv.

d . . . . .
Treatments containing chlorimuron also included crop cil concentrate at 1% WV.

9
LSD values may be used to compare values.

156

Table 26. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on Canada thistle 7, 14, 21 and 28 days

after treatment.a
Visual Control - Canada thistle

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.

 

 

g ailha g ailha %

O O - O — O - O - O
2.2 O - 28 - 50 - 59 - 73
2.93 0 - 3O - 46 - 54 - 64
4.4 O - 33 - 60 - 64 - 71
8.8 O - 38 - 60 - 64 - 71

0 118 - 49 - 39 - 41 - 46

O 157 - 73 - 43 - 53 - 63

0 235 - 74 - 6O - 56 - 58

0 470 - 90 - 91 - 83 - 81
2.2 118 63 81 (+) 69 83 (+) 76 79 86 79
2.93 1 18 64 83 (+) 67 86 (+) 73 81 81 84
4.4 118 65 91 (+) 75 95 (+) 79 90 (+) 85 91
8.8 118 68 89 (+) 76 91 (+) 79 94 (+) 84 100
2.2 1 57 80 79 74 79 82 78 90 81
2.93 157 81 85 7O 93 (+) 78 87 87 93
4.4 1 57 81 85 79 93 84 89 90 91
8.8 157 83 90 77 98 (+) 83 94 89 99
2.2 235 81 76 80 68 81 66 (-) 88 69
2.93 235 82 83 78 81 80 78 84 80
4.4 235 82 90 84 95 84 93 87 96
8.8 235 83 91 84 95 84 94 88 96
2.2 470 93 81 (-) 97 81 (-) 94 79 (-) 95 81
2.93 470 93 73 (-) 96 73 (-) 92 7o (-) 94 71
4.4 470 93 89 98 89 94 89 95 90
8.8 470 94 88 96 93 94 93 94 95

LSD (0.05)8 9 13 11

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b . .
Abbrevrations: DAT, days after treatment; Exp., expected; Obs., observed.
C Treatments containing chlorimuron also included crop oil concentrate at 1% v/v.

d . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

157

Table 27 . Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of chlorimuron and

glufosinate for canada thistle and velvetleafa

CIRARb ABUTH

 

Herbicide Ratec'd FWR HR FWR HR

 

 

 

Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ailha % Reduction ‘ ——
O O - O - 0 - 0 - 0
2.2 O - 63 - 76 - 59 - 55
2.93 O - 54 - 79 - 54 - 54
4.4 O - 65 - 76 - 68 - 68
8.8 O - 71 - 82 - 74 - 72
O 118 - 50 - 42 - 29 - 30
O 157 - 50 - 38 - 47 - 41
O 235 - 51 - 56 - 51 - 46
0 470 - 79 - 75 - 63 - 67
2.2 118 84 73 87 83 74 56 (-) 76 65
2.9 118 76 79 88 81 72 74 75 76
4.4 118 85 88 87 88 79 81 81 81
8.8 118 84 98 89 94 84 80 83 77
2.2 157 85 66 86 86 89 72 H 85 74 (—)
2.93 157 76 87 87 87 89 82 85 78
4.4 157 85 93 88 83 92 85 88 81
8.8 157 84 97 89 89 93 92 88 85
2.2 235 84 73 88 79 87 83 84 78
2.93 235 78 68 9O 68 H 86 87 84 82
4.4 235 84 91 88 90 90 82 88 82
8.8 235 85 96 92 86 91 89 88 83
2.2 470 94 84 95 82 90 87 89 82
2.93 470 92 67 (-) 95 80 90 91 89 85
4.4 470 93 94 95 84 93 92 92 84
8.8 470 94 86 95 86 94 9O 92 84

LSD (0.05)9 20 16 14 9

 

a . . . . . . . . . '

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby’s method. Observed values without a + or - are additive.

bAbbreviations: CIRAR, canada thistle; ABUTH, velvetleaf; FWR, fresh weight reduction;
HR, height reduction; Exp., expected; Obs., observed.

c . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% WV.

(1 . . . . .
Treatments containing chlorimuron also included crop onl concentrate at 1% WV.

9
LSD values may be used to compare values.

158

 

Table 28. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on velvetleaf 7, 14, 21 and 28 days after

treatmenta
Visual Control - Velvetleaf

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ailha % r
o o - o - o - o - o
2.2 o - 53 - 4 - 28 - 48
2.93 o - 56 - 8 - 31 - 51
4.4 o - 59 - 23 - 4o - 64
8.8 o - 66 - 60 - 52 - 69
o 118 - 38 - 93 - 31 -— 16
o 157 - 6O - 95 - 59 - 37
o 235 - 68 - 94 - 46 - 35
o 470 - 88 - 93 - 66 - 54
2.2 118 78 75 93 79 (-) 49 52 62 53
2.93 118 78 79 .93 85 50 68 (+) 66 69
4.4 118 79 88 (+) 94 86 56 77 (+) 73 75
8.8 118 83 86 97 88 65 78 (+) 79 82
2.2 157 93 89 95 79 73 64 82 60
2.93 157 93 84 (-) 95 90 74 76 86 76
4.4 157 93 89 96 85 (-) 79 79 99 73
8.8 157 94 89 98 93 84 89 90 89
2.2 235 92 83 (-) 94 91 61 81 (+) 78 84
2.93 235 93 88 94 88 (-) 63 85 (+) 81 84
4.4 235 93 89 95 8O 68 84 (+) 86 80
8.8 235 94 88 98 84 74 86 (+) 87 83
2.2 470 97 84 (-) 93 86 75 89 (+) 89 90
2.93 470 97 89 93 90 76 89 (+) 83 91
4.4 470 97 86 (-) 94 91 79 89 87 88
8.8 470 98 88 (-) 97 9o (-) 82 86 89 83
LSD (0.05)6 8 6 1o 12

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated Using
Colby's method. Observed values without a + or - are additive.

b . .
Abbrewations: DAT, days after treatment; Exp., expected; Obs., observed.

6 . . . . .

Treatments containing chlorimuron also included crop Oll concentrate at 1% v/v.
d

Treatments containing glufosinate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

159

Table 29. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on common lambsquarters 7, 14, 21 and 28

days after treatmenta

 

Visual Control - Common lambsquarters

 

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
gai/ha gai/ha % * '
o o - o - o - o - o
2.2 o - 36 - 28 - 22 - 8
2.93 o - 37 - 26 - 19 ~ 11
4.4 o - 35 - 28 - 18 - 12
8.8 o - 38 - 3o - 22 - 21
o 118 - 15 - 41 - 39 - 21
o 157 - 61 - 66 - 69 - 61
o 235 - 65 - 69 - 74 - 64
o 470 - 73 - 61 - 61 - 68
2.2 118 46 66 (+) 58 39 (-) 52 33 (-) 27 33
2.93 118 46 71 (+) 58 47 (-) 50 47 (-) 29 48
4.4 118 45 71 (+) 59 44(-) 50 39 (-) 31 39
8.8 118 47 66 (+) 59 44 (-) 52 43 (-) 37 43
2.2 157 75 74 74 54 (-) 76 54 (-) 67 59
2.93 157 76 74 73 61 (-) 75 64 (-) 66 66
4.4 157 75 76 73 63 (-) 74 64 (-) 68 68
8.8 157 76 81 (+) 75 74 75 73 69 70
2.2 235 78 81 77 85 (+) 80 79 76 76
2.93 235 78 81 76 87 (+) 80 74 69 74
4.4 235 77 89 (+) 77 86 (+) 79 76 71 75
8.8 235 78 84 (+) 78 68 (-) 80 63 (-) 72 61
2.2 470 82 88 (+) 70 82 (+) 70 85 (+) 72 73
2.93 470 83 88 (+) 68 86 (+) 69 86 (+) 72 81
4.4 470 82 15 (-) 69 63 68 74 73 59
8.8 470 83 25 (-) 72 63 (-) 69 7o 74 58
LSD (0.05)3 5 7 9 1 12

 

a . . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b . .

AbbreVIations: DAT, days after treatment; Exp., expected; Obs., observed.
c . . . . .

Treatments containing chlorimuron also included crop cil concentrate at 1% WV.
(1 . . . . .

Treatments containing glufosmate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

160

Table 30. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of chlorimuron and

glufosinate for common lambsquarters and giant foxtail.a

 

 

 

 

 

 

 

CHEALb SETFA

Herbicide Ratec’d FWR HR FWR _ HR
Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ailha % Reduction ——
o o - o - o - o - o
2.2 o - 11 - 23 - 10 - 5
2.93 o - 24 - 31 - 20 - 12
4.4 o - 22 - 35 - 14 - 5
8.8 o - 12 - 46 - 26 - 11
o 118 - 45 - 26 - 84 - 66
o 157 - 7o - 57 - 99 - 98
o 235 - 79 - 60 - 99 - 98
o 470 - 69 - 63 - 99 - 98
2.2 118 51 59 47 48 85 95 (+) 66 88
2.93 118 57 59 47 59 87 99 (+) 70 96
4.4 118 55 52 54 65 87 99 (+) 67 97
8.8 118 52 55 6o 61 88 98 (+) 70 91
2.2 157 72 76 73 62 99 99 98 97
2.93 157 76 75 75 73 99 99 98 98
4.4 157 76 69 79 73 99 99 98 98
8.8 157 75 84 81 77 99 99 98 98
2.2 235 81 82 73 76 99 99 98 98
2.93 235 82 71 76 74 99 99 98 98
4.4 235 82 79 80 72 99 99 98 98
8.8 235 82 66 82 73 99 99 98 98
2.2 470 71 77 76 75 99 99 98 98
2.93 470 74 86 76 84 99 99 98 98
4.4 470 74 98 (+) 81 88 99 99 98 98
8.8 470 73 98 (+) 83 89 99 99 98 98

LSD (0.05)8 16 19 6 7

 

a . . . . . . . . . ,

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b Abbreviations: CH EAL, common lambsquarters; SETFA, giant foxtail; FW R, fresh weight
reduction; HR, height reduction; Exp., expected; Obs., observed.

6 . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% v/v.

d . . . . .
Treatments containing chlorimuron also included crop cil concentrate at 1% WV.

9
LSD values may be used to compare values.

161

Table 31. Percent control compared to the untreated for combinations of
chlorimuron and glufosinate on giant foxtail 7, 14, 21 and 28 days after

treatment.al
Visual Control - Giant foxtail

 

 

28 . DAT

 

 

 

Herbicide Ratec’d 7 pm" 14 DAT 21 DAT
Chlorimuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ailha -% * -
o o - o - o - o - o
2.2 o - o - 5 - 5 - o
2.93 o - 3 - 5 - 5 o
4.4 o - 3 - 5 - 5 - o
8.8 o - 2 - 18 - 14 - 2
o 118 - 76 - 68 - 74 - - 54
o 157 - 78 - 76 - 97 - 100
o 235 - 77 - 78 - 94 - 100
o 470 - 80 - 80 - 96 - 100
2.2 118 76 77 69 79 (+) 75 93 (+) 54 83
2.93 118 77 76 69 88 (+) 75 94 (+) 54 99
4.4 118 77 7o (-) 69 93 (+) 75 96 (+) 54' 99
8.8 118 77 81 73 81 (+) 77 88 (+) 55 97
2.2 157 78 79 77 86 (+) 97 99 100 100
2.93 157 78 82 77 83 97 98 100 100
4.4 157 78 88 (+) 77 86 (+) 97 99 100 100
8.8 157 78 88 (+) 81 91 (+) 97 98 100 100
2.2 235 77 87 (+) 78 85 95 97 1‘00 100
2.93 235 77 901+) 78 79 95 99 100 100
4.4 235 77 93 (+) 79 89 (+) 95 99 160 100
8.8 235 77 88 (+) 82 88 95 98 100 99
2.2 470 80 88 (+) 81 84 96 99 160 100
2.93 470 80 89 (+) 81 86 96 98 166 100
4.4 470 80 901+) 81 86 96 99 100 100
8.8 470 80 86 (+) 84 81 96 100 109' 100
LSD (0.05)9 5 7 7 8

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b
Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . . .
Treatments containing chlorimuron also included crop cil concentrate at 1% v/v.

d . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% vlv.

e
LSD values may be used to compare values.

162

Table 32. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on Canada thistle 7, 14, 21 and 28 days after

treatmenta
Visual Control - Canada thistle

 

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Thifensulfuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
gai/ha gai/ha %

O O - O - 0 - 0 - 0
1.125 O - 4 - 5 - 8 - 10
1.5 0 - 3 - 0 - 5 - 10
2.25 O - O - 0 - 5 - 10
4.5 O - 6 - 5 - 8 - 1O

0 118 - 55 - 44 - 44 - 45

0 157 - 80 - 80 - 66 - 53

O 235 - 79 - 76 - 59 - 41

0 470 - 91 - 100 - 93 - 85
1.125 118 57 74 (+) 46 71 (+) 48 74 (+) 51 76
1.5 118 56 65 44 78 (+) 47 46 51 15
2.25 118 55 46 44 64 (+) 47 58 (+) 51 53
4.5 118 58 59 47 68 (+) 49 48 51 29
1.125 157 81 61 (-) 81 76 69 58 (-) 57 40
1.5 157 81 7O (-) 80 74 68 55 (-) 57 36
2.25 157 80 75 80 69 68 53 H 57 36
4.5 157 81 75 81 69 69 63 57 58
1.125 235 80 85 78 86 62 79 (+) 47 73
1.5 235 79 86 76 91 (+) 61 61 47 30
2.25 235 79 84 76 84 61 64 47 44
4.5 235 80 86 77 93 (+) 62 76 47 60
1.125 470 92 96 100 100 93 87 87 74
1.5 470 91 94 100 100 93 77 (-) 87 54
2.25 470 91 94 100 98 93 76 (—) 87 54
4.5 470 92 99 100 98 93 85 (-) 87 73

LSD (0.05)e 9 13 8 9

 

a . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b . .
AbbreViations: DAT, days after treatment; Exp., expected; Obs., observed.
c . .
Treatments containing thifensulfuron also included crop cil concentrate at 1% WV.

6 . . . . .
Treatments containing glufosrnate also included ammonium sulfate at 2% WV.

6
LSD values may be used to compare values.

163

Table 33. Fresh weight and height reduction compared to the untreated control
28 days after treatment for combinations of thifensulfuron and glufosinate for

canada thistle and velvetleafa

 

 

 

 

 

 

ClRARb ABUTH
Herbicide Ratec’d FWR HR __E__WB_ __l_-_|_B_
Thifensulfuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ailha g ailha % Reduction ——
0 O - 0 - O - O - 0
1.125 O - 7 - 8 - 20 - 5
1.5 O - 3 - 17 - 12 - 2
2.25 O - 0 - 12 - 17 - 1
4.5 O - 12 - 27 - 19 - 6
0 118 - 28 - 40 - 26 - 21
O 157 - 64 - 73 - 50 - 47
0 235 - 59 - 64 - 71 - 58
O 470 - 95 - 88 - 91 - 75
1 .125 1 18 33 4O 45 34 37 75 25 49 (+)
1.5 1 18 3O 48 51 56 31 41 22 39 (+)
2.25 118 28 26 48 34 36 43 22 41 (+)
4.5 1 18 36 37 57 45 35 56 25 45 (+)
1.125 157 66 39 H 75 53 H 56 65 50 50
1.5 157 65 31 H 77 40 H 53 34 H 48 39
2.25 157 64 20 H 76 55 H 55 69 47 59
4.5 157 69 40 H 80 41 H 57 72 51 59
1 .125 235 59 71 66 73 73 86 59 65
1.5 235 59 87 (+) 68 74 73 84 58 66
2.25 235 59 81 68 73 75 71 58 63
4.5 235 63 85 72 81 75 84 60 67
1 .125 470 96 96 89 88 94 93 77 79
1 .5 470 95 97 90 85 92 89 75 79
2.25 470 95 97 90 86 92 90 75 78
4.5 470 96 98 91 89 93 9O 77 77
LSD (0.05)9 24 18 20 12

 

a . . . . . . . . . .
+ and - denote a synergistic and antgonistic interaction for the given combinations according

to the LSD comparison of the observed and expected values calculated using Colby‘s method.
Observed values without a + or - are additive.

bAbbreviations: CIRAR, canada thistle; ABUTH, velvetleaf; FWR, fresh weight reduction; HR,
height reduction; Exp., expected; Obs., observed.

c . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% v/v.
Treatments containing thifensulfuron also included crop oil concentrate 1% v/v.

e
LSD values may be used to compare values.

164

Table 34. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on velvetleaf 7, 14, 21 and 28 days after

treatmenta
Visual Control - Velvetleaf

 

Herbicide Ratec'd 7 DATb 14 DAT 21 DAT 28 DAT
Thifensulfuron Glufosinate Exp. Obs. Exp. Obs. Egg. Obs. EQObs.

 

 

g ailha g ailha %
O O - O - O - O - O
1.125 0 - 3 - 1 - o - 0
1.5 0 - 8 - 9 - 6 - 1
2.25 O - 16 - 16 - 9 - 3
4.5 0 - 17 - 17 - 6 - 13
O 118 - 37 - 38 - 2O - 11
O 157 - 43 - 39 - 3O - 20
O 235 - 62 - 61 - 42 - 37
O 470 - 73 - 71 - 64 - 72
1.125 118 38 61 (+) 38 58 (+) 20 45 (+) 11 41
1.5 118 42 48 43 41 24 32 12 33
2.25 118 46 61 (+) 47 48 26 36 14 33
4.5 118 47 61 (+) 48 46 25 39 (+) 22 42
1.125 157 44 64 (+) 39 53 (+) 30 33 2O 49
1.5 157 47 47 44 44 34 33 21 36
2.25 157 51 66 (+) 49 65 (+) 36 41 22 54
4.5 157 52 68 (+) 49 68 (+) 34 41 30 50
1 .1 25 235 63 64 61 60 42 49 37 60
1 .5 235 65 61 65 62 46 53 38 58
2.25 235 67 58 (-) 67 53 (-) 47 44 39 51
4.5 235 68 62 66 67 46 71 (+) 45 59
1 .125 470 73 70 71 71 64 72 72 79
1 .5 470 75 78 74 76 69 61 72 79
2.25 470 77 77 75 76 70 68 73 83
4.5 470 77 83 74 78 66 71 76 . 79
LSD (0.05)9 7 8 1o 10

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b . .

Abbrev1ations: DAT, days after treatment; Exp., expected; Obs., observed.
6 . . . . .

Treatments containing thifensulfuron also included crop cil concentrate at 1% v/v.
d . . . . .

Treatments containing glufosmate also included ammonium sulfate at 2% vlv.

e
LSD values may be used to compare values.

165

Table 35. Percent control compared to the untreated for combinations of
thifensulfuron and glufosinate on common lambsquarters 7, 14, 21 and 28

days after treatment.a

 

Visual Control - Common lambsquarters

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 28 DAT
Thifensulfuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. EXp. Obs.

g ailha g ailha %
o o - o - 0 - o - o
1.125 0 - 24 - 23 - 3o - 49
1.5 o - 26 - 31 - 42 - 54
2.25 o - 34 - 41 - 50 - 67
4.5 o - 35 - 48 - 44 - 58
o 118 - 18 - 19 - 22 - 29
o 157 - 29 - 26 - 25 - 30
o 235 - 41 - 52 - 51 - 50
o 470 - 61 - 61 - 64 - 56
1.125 118 38 47 37 58 (+) 45 61 (+) 64 66
1.5 118 40 64 (+) 43 70 (+) 55 70 (+) 68 73
2.25 118 47 61 (+) 52 70(+) 61 71 (+) 77 71
4.5 118 47 72 (+) 57 76 (+) 55 74 (+) 67 83
1.125 157 47 69 (+) 43 75 (+) 49 74 (+) 67 75
1.5 157 49 74 (+) 49 73 (+) 57 68 (+) 70 70
2.25 157 54 69 (+) 56 74 (+) 63 7o 78 71
4.5 157 54 69 (+) 62 74 (+) 57 73 (+) 68 71
1.125 235 57 72 (+) 64 71 (+) 67 73 77 71
1.5 235 58 78 (+) 67 80 (+) 72 74 79 77
2.25 235 63 78 (+) 72 76 76 74 84 76
4.5 235 62 79 (+) 75 82 72 83 (+) 76 85
1.125 470 71 76 69 78 (+) 74 68 78 71
1.5 470 72 82 (+) 73 82 (+) 78 78 81 80
2.25 470 74 83 77 82 82 77 86 81
4.5 470 74 85 (+) 79 87 (+) 79 88 80 94
LSD @0519 9 7 9

 

a . . . . . . . . .
+ and - denote a synergistic and antgonistic interaction for the given combinations

according to the LSD comparison of the observed and expected values calculated using

Colby‘s method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . . .
Treatments containing thifensulfuron also included crop Oll concentrate at 1% v/v.

d . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

166

Table 36. Fresh weight and height reduction compared to the untreated
control 28 days after treatment for combinations of thifensulfuron and

glufosinate for common lambsquarters and giant foxtail.a

 

 

 

 

 

CHEALb SETFA
Herbicide Rate"'d _Lw_R_ _flR_ __FV1F1__ _JL
Thifensulfuron GlufosinateExp. Obs. Exp Obs. Exp. Obs. Exp. Obs.
g ailha g ailha % Reduction ——
o o - o - o - o - o
1.125 0 - 41 - 38 - 4 - o
1.5 o - 22 - 35 - 4 - o
2.25 o - 36 - 50 - 9 - 1
4.5 o - 26 - 43 - 2 - 1
o 118 - 38 - 18 - 36 ~ 22
o 157 - 35 - 20 - 85 — 74
o 235 - 45 - 38 - 94 - 88
o 470 - 50 - 44 - 96 -w 97
1.125 118 66 59 48 58 38 641+) 23 531+)
1.5 118 54 63 47 67 1+) 37 551+) 22 491+)
2.25 118 59 57 6o 65 4o 53 23 451+)
4.5 118 55 7o 51 751+) 36 65 1+) 23 391+)
1.125 157 62 67 49 651+) 86 77 74 62
1.5 157 47 53 46 621+) 86 82 74 67
2.25 157 59 63 59 63 87 81 74 71
4.5 157 48 64 53 691+) 86 84 74 71
1.125 235 72 59 62 6o 94 79 1-) 88 82
1.5 235 60 69 59 68 94 92 88 89
2.25 235 64 71 69 71 94 94 88 88
4.5 235 61 72 62 77 94 88 88 79
1.125 470 67 53 63 6O 97 94 97 98
1.5 470 59 72 63 66 97 96 97 97
2.25 470 68 67 7o 73 97 96 97 96
4.5 470 56 901+) 68 85 1+) 96 97 97 97
LSD gosf 25 15 14 16

 

a . . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations according
to the LSD comparison of the observed and expected values calculated using Colby’s
method. Observed values without a + or - are additive.

b Abbreviations: CHEAL, common lambsquarters; SETFA, giant foxtail; FWR, fresh weight
reduction; HR, height reduction; Exp., expected; Obs., observed.

c . . . . .
Treatments containing glufosmate also included ammonium sulfate at 2% vlv.

d . . . . .
Treatments containing thifensulfuron also included crop 0i| concentrate 1% vlv.

e
LSD values may be used to compare values.

167

Table 37. Percent control compared to the untreated for combinations
of thifensulfuron and glufosinate on giant foxtail 7, 14, 21 and 28 days

after treatmenta
Visual Control - Giant foxtail

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT 23 DAT

 

Thifensulfuron Glufosinate Exp. Obs. Exp. Obs. Exp. Obs. E>g)..Obs.

 

g ailha g ailha %
0 O - 0 - 0 - O - 0
1.125 O - 7 - 1 - 3 - 0
1.5 0 - 12 - 1 - 4 - 0
2.25 0 - 22 - 6 - 1 - O
4.5 O - 18 - 5 - 0 — 0
O 118 - 28 - 69 - 43 - 29
O 157 - 40 - 81 — 88 - 61
O 235 - 57 - 82 - 91 - 77
O 470 - 73 - 84 - 91 - 91
1.125 118 34 44 69 82 (+) 44 86 (+) 29 61
1.5 118 38 53 (+) 69 83 (+) 45 84 (+) 29 58
2.25 118 44 42 71 76 43 74 (+) 29 53
4.5 118 40 56 (+) 70 81 (+) 43 78 (+) 29 54
1.125 157 45 60 (+) 82 84 89 85 61 64
1.5 157 48 49 82 85 88 86 61 68
2.25 157 54 61 82 83 88 84 61 58
4.5 157 50 61 (+) 82 83 88 83 61 72
1.125 235 60 71 1+) 82 73 (-) 91 86 77 71
1.5 235 63 68 82 84 91 85 77 70
2.25 235 67 66 83 88 91 87 77 79
4.5 235 64 74 83 86 91 86 77 71
1.125 470 75 74 85 88 91 84 91 91
1.5 470 77 79 85 87 91 86 91 95
2.25 470 79 83 85 88 91 86 91 97
4.5 470 77 81 85 88 91 88 91 94
LSD (0.05)" 11 7 8 9

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated uSing
Colby's method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . . .

Treatments containing thifensulfuron also included crop cil concentrate at 1% WV.
(1 . . . . .

Treatments containing glufosmate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

168

Table 38. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on Canada thistle 7, 14, 21 and 28 days after

treatmenta

 

Visual Control - Canada thistle _

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT ADAL M
Glyphosate Thifensulfuron Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ailha % ~
0 o - o - - o — o
210 0 - 69 - 81 - 79 - 83
280 0 - 89 - 95 - 98 - 99
420 o - 81 - 98 - 98 -' 99
840 0 - 9o - 100 - 99 - 94
O 1.125 - 35 - 7 - 4 - 9
o 1.5 - 44 - 9 - 14 - 13
o 2.25 - 45 - 13 - 13 - 11
o 4.5 - 45 - 26 - 29 +‘ 6
210 1.125 76 75 82 87 79 78 83 84
210 1.5 77 73 83 83 80 73 83 78
210 2.25 77 71 83 85 8O 80 83 78
210 4.5 ' 77 74 83 84 83 83 83 84
280 1.125 89 781-) 95 9o 98 87 99 86
280 1.5 89 791-) 95 92 98 88 99 91
280 2.25 89 751-) 95 93 98 89 99 94
280 4.5 89 791-) 95 98 98 94 99 100
420 1.125 89 83 98 97 98 94 99 93
420 1.5 91 87 98 98 98 94 99 96
420 2.25 90 86 98 96 98 93 99 94
420 4.5 91 791-) 98 94 98 96 99 98
840 1.125 93 89 100 99 99 99 98 100
840 1.5 94 90 100 99 99 100 100 100
840 2.25 95 88 100 98 99 99 99 100
840 4.5 95 851-) 100 93 99 93 97 92
LSD (0.05)9 8 8 14 1 14

 

a . . . . . . . . .

+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using
Colby's method. Observed values without a + or - are additive.

b . .
Abbrev1ations: DAT, days after treatment; Exp., expected; Obs., observed.
6 Treatments containing glyphosate also included ammonium sulfate at 2% WV.

11 . . . . .
Treatments containing thifensulfuron also included crop Oil concentrate at 1% vlv.

e
LSD values may be used to compare values.

169

Table 39. Fresh weight and height reduction compared to the untreated

control 28 days after treatment for combinations of glyphosate and
thifensulfuron on Canada thistle and velvetleaf.a
CIRARb

Herbicide Ratec’d
Glyphosate Thifensulfuron Exp. Obs.

 

FWR

HR

ABUTHA
HR

FWR
Exp. Obs. Exp. Obs. Exp. Obs.

 

 

 

 

g ae/ha g ailha % Reduction ——

O 0 - 0 - O - O - O
210 O - 81 - 76 - 74 - 76
280 O - 95 - 80 - 87 - 83
420 O - 95 - 83 - 95 - 93
840 O - 96 - 83 - 97 - 91

O 1.125 - 0 - 1 - 13 - 9

O 1.5 - 2 - 4 - 27 - 12

O 2.25 - 6 - 4 - 20 - 15

O 4.5 - 7 - 7 - 31 - 23
210 1 .125 81 83 76 79 75 80 78 78
210 1.5 81 71 H 76 75 78 73 79 76
21 O 2.25 82 8O 77 73 76 73 79 75
21 O 4. 5 82 87 77 74 77 88 81 81
280 1 .125 95 91 80 78 88 89 84 85
280 1 .5 95 89 80 77 90 90 85 80
280 2.25 95 93 80 82 90 90 85 81
280 4.5 95 95 81 81 90 88 86 80
420 1 .1 25 95 93 83 80 96 93 94 90
420 1 .5 95 95 83 78 96 94 94 92
420 2.25 96 95 83 82 96 89 94 92
420 4.5 96 92 84 81 96 96 95 94
840 1 .1 25 96 95 83 83 97 95 91 93
840 1 .5 96 96 84 85 97 94 92 93
840 2.25 96 96 84 83 97 94 92 93
840 4.5 96 93 84 81 97 95 93 93

LSD (0.05)9 8 6 12 8

 

a . . . . . . . . . =
+ and - denote a synergistic and antgonistic interaction for the given combinations

according to the LSD comparison of the observed and expected values calculated uSing

Colby's method. Observed values without a + or - are additive.

bAbbreviations: CIRAR, canada thistle; ABUTH, velvetleaf; FWR, fresh weight redtJ'ction;
HR, height reduction; Exp., expected; Obs., observed.

c . . . . .
Treatments containing thifensulfuron also included crop Oll concentrate at 1% v/v.

d . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% WV.

9
LSD values may be used to compare values.

170

Table 40. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on velvetleaf 7, 14, 21 and 28 days after

treatment?

 

Herbicide Ratec’d
Glyphosate Thifensulfuron Exp. Obs.

Visual Control - Velvetleaf

 

7 DATb

14 DAT

21 DAT

21mm
Exp. Obs. Exp. Obs. EXp. Obs.

 

 

g ae/ha g ailha %

o o - o - o - o - o
210 o - 39 - 53 - 6o - 73
280 o - 44 - 74 - 80 - 88
420 o - 44 - 83 - 97 - 98
840 o - 45 - 96 - 87 - 98

o 1.125 - 19 - 5 - 5 - 9

o 1.5 - 1o - 5 - 5 - 13

o 2.25 - 2o - 18 - 9 - 17

o 4.5 - 23 - 26 - 24 - 25
21 o 1 .125 51 50 56 65 6o 67 74 77
210 1 .5 45 47 56 61 6o 69 76 71
210 2.25 51 38 1-) 62 68 63 71 76 73
210 4.5 53 54 65 76 7o 83 77 79
280 1 .125 54 45 75 75 80 79 89 89
280 1 .5 49 46 76 77 80 84 90 84
280 2.25 55 54 78 68 82 83 89 84
280 4.5 56 54 80 71 85 82 9o 89
420 1.125 55 46 1-) 84 89 97 94 98 95
420 1 .5 50 56 84 94 97 98 98 97
420 2.25 55 50 86 91 97 91 98 92
420 4.5 57 58 87 93 98 98 98 96
840 1.125 56 51 96 96 87 99 98 100
840 1 .5 51 55 96 97 87 99 98 99
840 2.25 56 50 97 94 88 97 98 98
840 4.5 57 59 97 96 9o 99 98 99

LSD (0.05)e 13 14 13

 

a . . . . . . . . . .
+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using

Colbys method. Observed values without a + or - are additive.

b
Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% WV.

(1 . . . . .
Treatments containing thifensulfuron also included crop 0il concentrate at 1% WV.

6
LSD values may be used to compare values.

171

Table 41 . Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on common lambsquarters 7, 14, 21 and 28

days after treatment.al

 

Herbicide Ratec’d
Glyphosate ThifensulfuronExp. Obs. Exp. Obs.

Visual Control - Common Lambsguarters

7 _DfiATb

14 DAT

21 DAT

28ml

 

Egg. Obs. Exp. Obs.

 

g ae/ha g ailha %
o o - o - 0 - o - o
210 o - 1o - 9 - 21 - 29
280 o - 13 - 18 - 36 - 34
420 o - 21 - 38 - 39 - 54
840 o - 48 - 64 - 63 - 49
o 1.125 - o - 6 - o - 48
o 1.5 - o - 8 - o - 33
o 2.25 - 1 - 9 - 3 - 29
o 4.5 - 3 - 11 - 5 + 41
210 1.125 9 11 15 23 21 15 57 62
210 1.5 9 291+) 16 26 21 301+) 50 58
210 2.25 9 461+) 18 481+) 24 581+) 49 58
210 4.5 18 351+) 19 511+) 26 651+) 60 69
280 1.125 13 9 23 27 36 41 63 66
280 1.5 13 13 24 33 36 43 55 59
280 2.25 13 15 26 33 38 501+) 53 61
280 4.5 21 551+) 27 471+) 40 641+) 62 61
420 1.125 20 681+) 41 671+) 39 641+) 70 51
420 1.5 20 441+) 42 54 39 641+) 67 54
420 2.25 20 431+) 43 54 4o 60 1+) 66 58
420 4.5 28 26 44 47 42 551+) 75 64
840 1.125 43 58 1+) 64 71 63 791+) 75 77
840 1.5 43 61 1+) 64 77 63 821+) 66 79
840 2.25 43 591+) 66 66 63 751+) 64 79
840 4.5 49 78 1+) 67 881+) 64 85 (+) 69 85
LSD (0.05)9 15 15 11 12

 

a . . . . . . . . .
+ and - denote a synergistic and antgonistic interaction for the given combinations
according to the LSD comparison of the observed and expected values calculated using

Colby‘s method. Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

c . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.

d . . . . .
Treatments containing thifensulfuron also included crop Oil concentrate at 1% WV.

9
LSD values may be used to compare values.

172

Table 42. Fresh weight and height reduction compared to the untreated control
28 days after treatment for combinations of glyphosate and thifensquUron on

common lambsquarters and giant foxtail.a

 

 

 

 

 

 

 

 

 

CHEALb SETFA
Herbicide Ratec’d FWR HR FWR ‘ V HR
Glyphosate Thifensulfuron Exp. Obs. Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ailha % Reduction 6 ———
0 O - O - 0 - O - 0
210 O - 1O - 46 - 95 - 94
280 O - 3O - 54 - 96 - 95
420 O - 71 - 88 - 96 -‘ 97
840 0 - 83 - 86 - 97 - 96
0 1.125 - 14 - 23 - 5 - 8
O 1.5 - 32 - 37 - 19 - 6
O 2.25 - 38 - 28 - 4 - 11
0 4.5 - 31 - 35 - 5 - 7
210 1.125 23 78 (+) 59 87 (+) 96 95 94 91
210 1.5 36 65 (+) 62 87 (+) 96 86 (-) 94 86 (-)
210 2.25 40 81 (+) 59 86 (+) 95 95 95 87 (-)
210 4.5 36 88 (+) 62 85 (+) 95 96 94 94
280 1.125 33 65 (+) 61 90 (+) 96 97 95 97
280 1.5 43 90 (+) 70 86 (+) 96 95 95 97
280 2.25 45 76 (+) 64 91 (+) 96 96 95 97
280 4.5 41 93 (+) 67 95 (+) 96 95 95 97
420 1.125 71 81 91 87 96 96 97 97
420 1.5 72 68 91 84 97 97 97 96
420 2.25 72 82 90 81 96 97 97 97
420 4.5 71 91 91 90 96 96 97 97
840 1.125 83 95 89 91 97 96 97 97
840 1.5 85 96 90 90 97 98 97 97
840 2.25 86 92 89 89 97 97 97 97
840 4.5 85 9O 89 90 97 96 97 97
LSD p.05)9 21 13 6 4

 

a . . . . . . . . . ' .
+ and - denote a synergistic and antgonistic interaction for the given combinations according to

the LSD comparison of the observed and expected values calculated using Colby's method.
Observed values without a + or - are additive.

bAbbreviations: CHEAL, common lambsquarters; SETFA, giant foxtail; FWR, fresh weight
reduction; HR, height reduction; Exp., expected; Obs., observed.

6 . . . . .

Treatments containing thifensulfuron also included crop Oil concentrate at 1% v/v.
d . . . .

Treatments containing glyphosate also included ammonium sulfate at 2% WV.

6
LSD values may be used to compare values.

173

Table 43. Percent control compared to the untreated for combinations of
glyphosate and thifensulfuron on giant foxtail 7, 14, 21 and 28 days after

treatment?

Visual Control - Giant foxtail ,

 

 

 

 

 

Herbicide Ratec’d 7 DATb 14 DAT 21 DAT .e 28 DAT
Glyphosate Thifensulfu ron Exp. Obs. Egg. Obs. Exp. Obs. . Exp. Obs.
g ae/ha g ailha °/-

0 O - O - O - O - O
210 0 - 33 - 93 - 99 - 89
280 0 - 33 - 96 - 100 - 88
420 O - 41 - 100 - 100 - 78
840 0 - 39 - 100 - 78 - 100

O 1 .125 - O - 8 - 5 - 18

O 1 .5 - 5 - 9 - 5 - 16

O 2.25 - O - 9 - 14 - 16

O 4.5 - O - 9 - 1 3 - 17
210 1 .125 33 35 93 88 99 99 100 88
210 1.5 34 41 93 98 99 100 100 100
21 0 2.25 33 36 93 88 99 99 100 98
210 4.5 33 39 93 96 99 100 100 100
280 1 .1 25 33 58 (+) 97 1 00 100 100 1 00 100
280 1 .5 34 43 97 98 1 00 100 1 00 100
280 2.25 33 36 97 94 1 00 1 00 1 00 1 00
280 4.5 33 54 (+) 97 96 1 00 100 1 00 1 00
420 1.125 41 46 100 76 (-) 100 100 90 100
420 1 .5 42 51 100 98 100 100 90 99
420 2.25 41 45 100 100 100 100 90 100
420 4.5 41 51 100 100 100 100 90 100
840 1 .125 40 59 (+) 100 100 79 100 (+) 100 100
840 1 .5 4O 60 (+) 1 00 99 79 100 (+) 100 100
840 2.25 39 70 (+) 100 100 80 100 (+) 100 100
840 4.5 39 70 (+) 100 100 80 100 (+) 100 100

LSD (0.05)9 7 13 14 13

 

a . . . . . . . . . , .

+ and - denote a synergistic and antgonistic interaction for the given combinations according
to the LSD comparison of the observed and expected values calculated using Colby‘s method.
Observed values without a + or - are additive.

b Abbreviations: DAT, days after treatment; Exp., expected; Obs., observed.

0 . . . .
Treatments containing glyphosate also included ammonium sulfate at 2% WV.

6 . . . . .
Treatments containing thifensulfuron also included crop Oil concentrate at 1% WV.

6
LSD values may be used to compare values.

174

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176