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thesis entitled

HERBICIDE AND SOIL CONSIDERATIONS IN WEED
CONTROL IN POTATO

presented by
Calvin Farrell Glaspie

has been accepted towards fulfillment
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HERBICIDE AND SOIL CONSIDERATIONS IN WEED CONTROL IN POTATO
By

Calvin Farrell Glaspie

A THESIS

Submitted to
Michigan State University
In partial fulﬁllment of the requirements
For the degree of

MASTERS OF SCIENCE
Crop and Soil Sciences

2010

ABSTRACT

HERBICIDE AND SOIL CONSIDERATIONS IN WEED CONTROL IN POTATO
By
Calvin Farrell Glaspie

The effect of soil clay content, organic matter content, and pH on ﬂumioxazin
efficacy was evaluated using a greenhouse bio-assay. Clay content was not found to
affect the control of any weed species tested. Control of weed species decreased as soil
organic matter content increased reducing initial and residual control. When soil pH was
below 6, initial weed control was reduced with ﬂumioxazin. However, soils with a pH of
7 had a greater effect on the residual control with ﬂumioxazin.

Field trials were conducted at the Montcalm Research Farm near Entrican, MI in
2008 and 2009 to evaluate the effect of herbicides labeled for potatoes on three cultivars
of potato mini-tubers. Imazosulfuron and treatments containing postemergence
applications of rimsulfuron with or without metribuzin following preemergence
applications ofS-metolachlor plus linuron reduced yields in 2008 and 2009. In 2009,
treatments of dimethenamid-p, S-metolachlor, pyrasulfatole, and pendimethalin alone
reduced yields. Results ﬁ'om this study indicate greater yield losses occur when multiple
stress factors are present. Several herbicides were observed to be safe when applied

preemergence including linuron, metribuzin, and rimsulfuron.

ACKNOWLEDGEMENTS

I would like to thank Dr. Wesley Everman for serving as my major professor. I
am very thankful to have had Dr. Everman as my major professor, but also as a friend
guiding me through my degree. I would also like to thank Dr. David Douches, Dr.
Donald Penner, and Dr. Bernard Zandstra for serving on my graduate committee and

offering assistance and their research expertise in the development of my work.

The completion of my research could not have been possible without the
assistance of Andrew Chomas and his knowledge in conducting ﬁeld research. I learned
a lot from Andrew both as an undergraduate and a graduate and will never forget what he
taught me. I would also like to thank Bruce Sackett and Chris Long for their help at the
Montcalm Research Farm in creating and maintaining my research. As well, Laura Bast,
Alexander Lindsey, and John Green for being great fellow graduate students and good
friends. Without the help of all past and present undergraduate students my work would
not have been possible. Bryce Conklin, Brad Love, Jake Gebhardt, Melissa Huck, and
Dan Tratt were vital to producing my research and were all great friends to have. I would
also like to thank the MSU weed science group including people from Crop and Soil

Science and Horticulture for their ﬁ'iendship and help during my time here.

Lastly, I would like to acknowledge my family and my wife Cassandra who gave
nothing but her love and assistance to help me complete me degree. I hope that my

experience here at Michigan State will help her complete her future degrees.

iii

TABLE OF CONTENTS

LIST OF TABLES ...................................................................................................... v
LIST OF FIGURES .................................................................................................... vi
LITERATURE REVIEW
INTRODUCTION ............................................................................................. l
SOIL APPLIED HERBIICDE EFFICACY AND PERSISTANCE .................... 1
Soil interactions ..................................................................................... 2
Persistence ............................................................................................. 3
F lumioxazin ........................................................................................... 6
MANAGEMENT OF POTATOES .................................................................... 8
Cultivar Sensitivity ................................................................................. 9
Potato mini-tubers .................................................................................. 10
LITERATURE CITED ........................................................................... 12

EFFECT OF SOIL CLAY AND ORGANIC MATTER CONTENT AND SOIL PH
ON THE EFFICACY OF F LUMIOXAZIN

ABSTRACT ...................................................................................................... 18
INTRODUCTION ............................................................................................. l 9
MATERIALS AND METHODS ....................................................................... 21

Preparation of Soil ................................................................................. 22
RESULTS AND DISCUSSION ......................................................................... 24
SOURCES OF MATERIALS ............................................................................ 28
LITERATURE CITED ...................................................................................... 34

EFFECT SOIL ORGANIC MATTER CONTENT AND SOIL PH ON RESIDUAL
CONTROL WITH FLUMIOXAZIN

ABSTRACT ...................................................................................................... 36
INTRODUCTION ............................................................................................. 37
MATERIALS AND METHODS ....................................................................... 39
Organic matter soils ............................................................................... 40
pH soils .................................................................................................. 40
Data collection and analysis ................................................................... 42
RESULTS AND DISCUSSION ......................................................................... 43
Organic soils .......................................................................................... 43
Soil pH ................................................................................................... 44
SOURCES OF MATERIALS ............................................................................ 47
LITERATURE CITED ...................................................................................... 53

TOLERANCE OF POTATO MIN I-TUBERS TO PREEMERGENCE AND
POSTEMERGENCE HERBICIDES

ABSTRACT ...................................................................................................... 56
INTRODUCTION ............................................................................................. 57
MATERIALS AND METHODS ....................................................................... 59

iv

RESULTS AND DISCUSSION ......................................................................... 61

Crop injury ............................................................................................. 6l
Crop yield .............................................................................................. 63
LITERATURE CITED ...................................................................................... 71

LIST OF TABLES
Table 1. Properties of soils used to evaluate efﬁcacy of ﬂumioxazin .................. 29

Table 2. Emergence of weed species averaged by soil and regression equation
used to model weed control for clay, OM and pH soils ...................................... 30

Table 3. Properties of lab and ﬁeld soils to evaluate ﬂumioxazin’s persistence ..48

Table 4. Emergence of weed species averaged over time, 150, and regression
equation used to model weed control for organic matter soils ............................. 49

Table 5. Emergence of weed species averaged over time, 150, and regression
equation used to model weed control for pH soils .............................................. 50

Table 6. Herbicide treatments applied preemergence or preemergence followed by
a postemergence application to potato mini-tubers ............................................. 66

Table 7. Interaction of year by percent vine emergence ﬁ‘om potato mini-tubers 1
wk after preemergence herbicide application and total tuber yield, averaged across

treatments .......................................................................................................... 67

Table 8. Vine injury 1 and 2 wks after preemergence treatment and interaction of
cultivar by treatment in 2008 ............................................................................. 68

Table 9. Effect of herbicide treatment on US #1 tuber quantity and yield by plants
grown ﬁom mini-tubers averaged across cultivars .............................................. 69

Table 10. Effect of herbicide application on total tuber quantity and yield
averaged across cultivars ................................................................................... 70

vi

LIST OF FIGURES

Figure 1. Efﬁcacy of ﬂumioxazin as affected by soil organic matter content. The
vertical bars represent the standard error of means ............................................. 31

Figure 2. Efﬁcacy of ﬂumioxazin as affected by soil organic matter content.
Fitted lines are calculated by linear regression equation for velvetleaf;
barnyardgrass and giant foxtail. The vertical bars represent the standard error of
means ................................................................................................................ 32

Figure 3. Efﬁcacy of ﬂumioxazin as affected by soil pH. Fitted lines are
calculated by the inverse ﬁrst-order regression equation for velvetleaf and giant
foxtail. The vertical bars represent the standard error of means .......................... 33

Figure 4. Weed control of velvetleaf ( A), redroot pigweed (I),common
lambsquarters (V), and giant foxtail (O), with ﬂumioxazin as affected by percent
organic matter over time for lab and ﬁeld soils. Fitted lines are calculated by
linear or logistic regression for velvetleaf , redroot pigweed ,comrnon
lambsquarters, and giant foxtail ......................................................................... 51

Figure 5. Weed control of velvetleaf ( A), redroot pigweed (I),common
lambsquarters (V), and giant foxtail (O), with ﬂumioxazin as affected by soil pH
over time for lab and ﬁeld soils. Fitted lines are calculated by linear or logistic
regression for velvetleaf, redroot pigweed, common lambsquarters, and giant
foxtail ................................................................................................................ 52

vii

CHAPTER 1
LITERATURE REVIEW

INTRODUCTION

The potato (Solanum tuberosum L.) is a staple food crop grown throughout the
world ranking fourth in global agricultural production. Potatoes play a major role not
only in the economy, but also in the diet of many Americans. Management of the potato
requires a holistic approach that addresses production efficiency, economic viability,
environmental compatibility, and social responsibility (Rowe and Powelson 2008). A
growing concern in potato production is the management of weeds with increasing
restrictions on herbicide use and the development of herbicide resistance in weeds. To
manage weeds in potatoes researchers continually evaluate new herbicides. Flumioxazin
recently has been labeled for use in potatoes and could provide growers with a highly
effective alternative to traditional herbicides. However, potatoes are grown on a wide

range of soils which could impact weed control with ﬂumioxazin.

SOIL APPLIED HERBICIDE EFFICACY AND PERSISTENCE
Herbicides can vary greatly in chemical and physical properties and can differ
despite similar functionality in plants (Kah and Brown 2006). Each property of an
herbicide contributes to a cumulative effect on its existence in the soil as a solid, liquid,
or gas, impacting herbicide sorption and persistence in the soil (Monaco et a1. 2002).
Solubility of an herbicide can greatly inﬂuence its mobility in a soil (Koskinen and
Moorman 1992). Elliott et a1. (1999) attributed differences in presence of herbicides in

tile drainage water to herbicide solubility with the less soluble diclofop found in lower

concentrations than the highly soluble dicamba. Vapor pressure of herbicides indicates

their relative tendency to volatilize from the soil. Herbicides with vapor pressure greater

-2 . . . . . .
than 10 Pa are prone to be lost from 80118 due to volatilization, contributing to

signiﬁcant amounts of herbicide transfer (Koskinen and Moorman 1992). Due to its high

vapor pressure of 1.47x10'2 Pa (Senseman 2007), triﬂuralin was reported to volatilize 60

to 71% of the initial amount applied within the ﬁrst 5 days of application when not
incorporated (Majewski et a1. 1993).

Herbicide adsorption is also dependent on the chemical structure of an herbicide,
as this determines its tendency to form chemical and physical bonds with soil particles
(Calvet 1980; Leistra 1980). Soil interactions with ionic and ionizable herbicides
generally are attributed to a multitude of bond types including high energy (>80 kJ/mol)
chemical bonds such as covalent, ionic, and ligand exchange, and low energy (<80
kJ/mol) physical bonds such as hydrogen and van der Waals forces (Calvet 1980). The
collective effect of the bonds contributes to the binding of an herbicide in soil. However,
the properties of an herbicide and effect On sorption to a soil are dependent on the

properties of the soil to which they are applied.

Soil interactions. Soils are diverse heterogeneous mixtures of particles derived from
geological weathering of parent rock material and the biological organisms, past and
present, associated with it (Hillel 1998; Havlin et a1. 2005). Clay content and type in a
soil can greatly impact its cation exchange capacity (CEC) due to negative charges
caused by isomorphic substitutions (Calvet 1980; Havlin et a1. 2005). Aluminum and

iron hydroxides can also bind herbicides by anionic exchange, but generally are only

important in highly weathered soils (Kah and Brown 2006; Koskinen and Moorman
1992). Soil organic matter (SOM) has been attributed by many researchers to be the
greatest factor in herbicide adsorption (Monaco et a1. 2002; Wauchope et a1. 2002; Weber
et a1. 2007). Depending on the organism ﬁom which the SOM was derived, soil pH,
climate, and the microbial community, the type and proportion of functional groups on
the SOM can vary affecting sorption of herbicides (Walker and Austin 2003; Benoit et
a1. 2008). Imidazolinone herbicide adsorption to organic soil was found to be correlated
with the amount of carboxylic groups in the SOM (Gennari et al. 1998).

Although not a physical property of the soil, solution pH can alter the activity of
the soil’s constitutive particles (Calvet 1980; Sposito et a1. 1999; Kah and Brown 2006).
The effect of solution pH on clay particles is minor due to changes in edge charges;

however the effect of soil pH on soil SOM can be immense (Sposito et al. 1999; Kah and

Brown 2006). At pH values above the SOM hydroxyl groups pKa (5 to 7), H+

disassociates and increases the ability of the SOM to bind cations (Stevenson 1972). At
soil pH values lower than 5, Ferreira et al. (2001) found SOM to increase in

hydrophobicity, which could increase herbicide adsorption.

Persistence. By considering the chemical properties of a herbicide and the soil to which
it is applied, a relative understanding of adsorption by the soil can be attained. Few
herbicides are permanently charged, like paraquat, and can react strongly with soil
particles depending on charge polarity (Iglesias et a1. 2009). Conversely, ionizable
herbicides can form numerous interactions with soil particles often varied by soil pH

(Kah and Brown 2006). Soil solution pH signiﬁcantly inﬂuences ionizable herbicides

because it alters the herbicide speciation in a soil. Soil clay content and SOM affect
ionizable herbicide binding by providing negative sites for cationic exchange and the
combined effect of the two fractions can explain the adsorption of the majority of
ionizable herbicides in soil (Schmidt and Pestemer 1980; Diehl et al. 1995; Monaco et al.
2002). However, non-ionizable herbicides have limited interactions with soil particles
(Calvet 1980; Kah and Brown 2006). Binding of non-ionizable herbicides are attributed
instead to hydrophobic binding which is the result of a decrease in entropy due to
partitioning of the hydrophilic herbicide in the hydrophobic regions Of soil (Calvet 1980;
Koskinen and Moorman 1992). Understanding the multitude of interactions between
herbicides and the soil allows us to study its concentration in different phases and
availability for weed control.

Once an herbicide is applied to the soil, it rapidly interfaces with soil particles and
reaches a relative equilibrium (Monaco et a1. 2002). Herbicide that is not sorbed to the
soil and is in solution is generally accepted as herbicide available for weed uptake and
control (Peter and Weber 1985; Monaco et a1. 2002). Therefore, as herbicide adsorption

increases subsequent weed control decreases. Herbicide distribution in soils is described

both by Kd and K0‘: values, a measurement of amount of herbicide in solution compared

to herbicide adsorbed to soil particles (Wauchope et a1. 2002). Distribution values are
useﬁil for describing relative binding of an herbicide in given soil; however, they do not
explain individual components of herbicide adsorption, but rather the summation.
Nonetheless, distribution values give a basic understanding of herbicide adsorption in the
soil, providing information about how transfer and degradation processes will affect its

persistence.

Weed control with soil-applied herbicides is not only a function of herbicide
adsorption, but also of its persistence in the soil. Herbicides need to persist long enough
to provide adequate weed control but not too long so as to interfere with subsequent crops
or the environment. The persistence of an herbicide in a soil is a function of its loss from
the soil system and degradation. Herbicide can be lost ﬁom a system due to
volatilization, leaching, surface runoff, and loss of soil with sorbed herbicide. Herbicide
breakdown, dependent on the compound, is due to the combination of chemical
decomposition, photodecomposition, and biological decomposition. Chemical
decomposition of herbicides is due to abiotic processes such as hydrolysis and can cause
signiﬁcant dissipation of some herbicides (Kwon et a1. 2004). Photolysis can cause rapid
breakdown of herbicides such as the dinitroanalines, and can also be responsible for
signiﬁcant loss from the soil if not properly incorporated (Monaco et a1. 2002). Lastly,
microbial metabolism is responsible for the dissipation of most organic herbicides and
can vary dependent on the microbial community, density, climate, and soil type (Hurle
and Walker 1980; Rice et a1. 2002). Soils high in organic matter are reported as having
greater microbial activity (Goyal et al. 1999; Kah and Brown 2006). However, greater
amounts of organic matter increase herbicide adsorption, making the herbicide
unavailable for microbial degradation, causing an overall conﬂicting response.
Precipitation and temperature inﬂuence microbial activity and their inﬂuence may help
explain ﬂuctuation in herbicide efficacy and carry over. Overall, the degradation and

persistence of a soil-applied herbicide is due to a myriad of factors and their interactions.

F lumioxazin. F lumioxazin is a preemergence herbicide labeled for use in many crops
including alfalfa, cotton, peanuts, potato, and soybeans. An herbicide in the
protoporphyrinogen oxidase inhibiting family of herbicides, ﬂumioxazin is used in
cropping systems to manage glyphosate and acetolactate synthase inhibiting herbicide
resistant weed species due to its unique mode of action (Clewis et a1. 2007; Everman et
a1. 2009). Westhoven et a1. (2008) found that, with the addition of ﬂumioxazin and
cloransulam-methyl, control of glyphosate-resistant common lambsquarters

(Chenopodium album L.) increased ﬁ'om 81 to 96%, compared to an early postemergence

application ofglyphosate plus 2,4-D. In a greenhouse study, ﬂumioxazin at 71 g ai ha-1

provided greater than 96% control of glyphosate-resistant marestai1(Conyza canadensis
L.) 8 wks after treatment. In juneberry, residual weed control with ﬂumioxazin 8 wks
after treatment at 140 g ai ha_1 was greater than 88% for all species with 99% control of
redroot pigweed (Amaranthus retroﬂexus L.)(Hatterman-Valenti 2005). Complete

control of redroot pigweed was reported 50 days affer treatment when ﬂumioxazin was

tank mixed with clomazone at multiple rates, however ﬂumioxazin applied alone at a rate
of 71 g ai ha.l only provided 73% control of yellow nutsedge (Cyperus esculentus L.) in
sweetpotato (Kelly et aL 2006).

Grass control with ﬂumio xazin is often variable and unacceptable. Niekamp and
Johnson (2001) reported that ﬂumioxazin at 71 and 110 g ai ha] provided only 18 and
36% control of giant foxtail (Seteriafaberi L.), respectively, compared to control at

another location of 62 and 81% for the low and high rate, respectively. The authors

attributed differences in control to higher weed population at one location compared to

the other. Flumioxazin at 53 g ai ha-1 only provided 63% control ofbarnyardgrass

(Echinochloa crus-galli L.) 4 wks after treatment and at 105 g ai ha-1 provided 68 to 78%

control of giant foxtail (Taylor-Lovell et al. 2002; Wilson et al. 2002). For this reason
additional preemergence grass herbicides are included for use with ﬂumioxazin such as
S—metolachlor which increased control ofbarnyardgrass from 63% to 97% (Wilson et al.
2002)

Weed control efﬁcacy with ﬂumioxazin could vary due to interactions with the soil

solution. Flumioxazin is a non-ionic herbicide with a water solubility of 1.79 mg L.1 and

soil half life of 5 to 19 days determined by batch equilibrium experiments (Ferrell and
Vencill 2003; Senseman 2007). Microbial degradation is an important factor determining
persistence of ﬂumioxazin in the soil (Ferrell and Vencill 2003). When soil pH is above
7 hydrolysis of ﬂumioxazin could become the major process of degradation (Kwon et al.
2004). Batch equilibrium and ﬁeld experiments have been conducted to better
understand the adsorption of ﬂumioxazin. Researchers have found the adsorption of
ﬂumioxazin to be correlated with SOM and certain types of clay particles (Ferrell et al.
2005; Alister et a1. 2008). Adsorption of ﬂumioxazin to SOM is mainly attributed to
hydrophobic binding, while its adsorption to clay particles is due to surface iron and
aluminum hydroxides attracting the electronegative region on the ﬂumioxazin molecule

(Ferrell et al. 2005).

MANAGEMENT OF POTATOES
Weed control is important in potato production to reduce competition for
nutrients, light, and water, and to eliminate potential problems at harvest. Competition

with redroot pigweed and barnyardgrass from time of planting to harvest at a density of 1

plant m-1 of row has been shown to reduce marketable yields by 22 to 33% and 19 to

21%, respectively (VanGessel and Renner 1990). Weeds not only directly reduce yields
through competition but perennial species such as quackgrass (Elymus repens (L.) Gould)
and yellow nutsedge have been reported to lower tuber quality by growing into the tuber
(Lutman 1992; Boydston et al. 2008). Weed presence also may impede harvest by
interfering with digging of tubers and soil separation, requiring additional management in
correcting these problems (Lutman 1992; Boydston et al. 2008).

Growers achieve weed control in potatoes by utilizing cultural, mechanical, and
chemical control. Cultural control of weeds is achieved by promoting early and ﬁlII
development of the crop canopy often through proper fertilization and cultivar selection
(Boydston et al. 2008; Colquhoun et al. 2009). Cultivation often is used in potato
management to manage shallow rooted weeds (Bellinder et al. 2000; Boydston et al.
2008; Felix et a1. 2009). Felix et al. (2009) demonstrated the potential of using
WeedCast, a weed emergence prediction model, to effectively time cultivation in
potatoes to maximize weed control. However, control of weeds by cultivation can be
greatly improved when combined with applications of herbicides (Renner 1992; Bellinder
et al. 2000). Control of weeds is achieved with timely applications of preemergence and

postemergence herbicides. S-metolachlor applied preemergence alone at 1.12 kg ai/ha

provided 96% control of annual grass species 56 days after application (Richardson et a1.
2004). Treatments ofS-metolachlor at 1.12 kg ai/ha plus metribuzin at 0.45 kg ai/ha
provided 89 and 94% control of common lambsquarters and common ragweed (Ambrosia
artemisiifolia L. ), respectively (Richardson et al. 2004). Eberlein et a1. (1994) found that
postemergence applications of rimsulfuron at 27 g ai/ha at one location controlled hairy
nightshade (Solanum physalifolium Rusby.) and redroot pigweed 94 and 100%,

respectively.

Cultivar Sensitivity. A challenge of using herbicides for weed control in potatoes is
avoiding crop injury. Potato cultivars have variable sensitivity to herbicides attributed to
differences in absorption, translocation, or metabolism of the herbicide (Hinks 1977;
Bailey et al. 2003). Herbicide sensitivity to metribuzin is reported to be an inheritable
trait with a relative high frequency in selected progeny making it a prevalent recurring
trait (De Jong 1983). Herbicide sensitivity is of great concern to breeders because
diploid species utilized as sources for novel genes have been shown to be sensitive to
linuron and/or metribuzin (Bradeen and Mollov 2007). Metribuzin was found by Friesen
and Wall (1984) to cause injury and yield reductions on 22 different potato cultivars.
This included yield reductions of ‘Alaska Red’ by 68% with preemergence applications
of metribuzin at 1 kg ai/ha. Hutchinson et a1. (2005) reported sensitivity of the cultivar
‘Ranger Russet’ to preemergence applications of ﬂumioxazin from 53 to 140 g ai/ha,

which caused total yield reductions of l 3 to 20%.

Potato mini-tubers. Unique to managing potatoes is the utilization of whole or cut potato
tubers as the seed source for commercial production. Potatoes grown from tuber pieces
have increased vigor as compared to plants grown from true seed and additional beneﬁts
such as production of “true-to-type” plants (Struik and Wiersema 1999). However,
potato tuber pieces may harbor harmful pathogens such as Phytophthora infestans and
potato virus Y (PVY) (Allen et al. 1992; Bus and Wustman 2007; Whitworth and
Davidson 2008). Planting infected tuber pieces may result in the spread of disease.
Depending on the pathogen’s infection cycle, the spread of disease can be inﬂuenced by
cultural practices and the incidence of insect pests. PVY can spread rapidly via aphid
vectors (Basky and Almasi 2005; Valkonen 2007), which increases the importance of
removing contaminated seed. Potato seed certiﬁcation programs were initiated to
regulate the sale and production of seed potatoes to prevent the spread of diseased seed.
Seed certiﬁcation laws were created at the national and state level requiring seed
lots to meet standards to be certiﬁed. Seed certiﬁcation standards required growers to
maintain lots with 10w pathogen incidence and the initial production of seed through
tissue culture. Technological advancements and increased availability of tissue culture
have allowed for the production of in vitro plantlets to create pathogen-ﬂee pre-nuclear
(seed planted to generate nuclear or ﬁrst generation seed) plant material (Struik and
Wiersema 1999). Over time, production of early generation material has changed and
potato plantlets are now used to produce micro- and mini-tubers as the preferred initial
seed source for commercial production. Production of potato mini-tubers has received
much attention and consideration, resulting in research with the intent to maximize

production and quality of mini-tubers (Ranalli et al. 1994; Struik and Lommen 1999).

10

Although mini-tubers are similar to cut seed pieces used in production, there are
unique difﬁculties in managing them. Researchers have observed agronomic differences
when planting mini-tubers as opposed to cut seed pieces, such as reduced stem number,
delayed emergence, and reduced canopy closure (Struik and Lommen 1999). Research
done by Ranalli et al. (1994) showed that 51 days after planting, plants grown from mini-
tubers provided only 37.8% canopy closure, 34.6% less cover than plants grown from out
seed pieces, thus reducing the crop’s ability to compete with weeds (Monaco et a1. 2002).
Mini-tubers have a lower level of carbohydrate reserves and a greater surface area to
volume ratio compared to cut seed pieces. These differences cause plants grown from
mini-tubers to emerge later (Ranalli et a1. 1994; Struik and Lommen 1999), have
generally only one stem (Ahloowalia 1994; Struik and Lommen 1999), and produce
smaller sprouts (Lommen 1994). Mini-tubers producing smaller sprouts and plants
which are less vigorous could be more susceptible to herbicide injury (Scott and Phillips

1971).

ll

LITERATURE CITED

Ahloowalia, B. S. 1994. Production and performance of potato mini-tubers. Euphytica
75:162-172.

Alister, C., S. Rojas, P. GOmez, and M. Kogan. 2008. Dissipation and movement of
ﬂumioxazin in soil at four ﬁeld sites in Chile. Pest Manag. Sci. 64:579-583.

Allen, B. J., P. J. O’Brien, and D. Firman. 1992. Seed tuber production and

management. pp 247-287 in P. Harris, 2nd ed. The potato crop: the scientiﬁc basis
for improvement. New York: Chapman & Hall.

Bailey, W. A., K. K Hatzios, K. W. Bradley, H. P. Wilson. 2003. Absorption,
translocation, and metabolism of sulfentrazone in potato and selected weed
species. Weed Sci. 51:32-36.

Basky, Z. and A. Almési. 2005. Differences in aphid transmissibility and translocation
between PVYN and PVYO isolates. J. Pest Sci. 78:67-75.

Bellinder, R. R., J. J. Kirkwyland, R. W. Wallace, and J. B. Colquhoun. 2000. Weed
control and potato (Solanum tuberosum) yield with banded herbicides and
cultivation. Weed Technol. 14:30-35.

Benoit, P., I. Madrigal, C. M. Preston, C. Chenu, and E. Barriuso. 2008. Sorption and
desorption of non-ionic herbicides onto particulate organic matter from the
surface soils under different land uses. Eur. J. Soil Sci. 59:178-189.

Boydston, R. A., P. J. S. Hutchinson, and R. R. Bellinder. 2008. Managing weeds. pp

223-234 in D. A. Johnson, 2nd ed. Potato health management. St. Paul, MN: The
American Phytopathological Society.

Bradeen, J. M. and D. S. Mollov. 2007. Herbicide tolerance in primitive diploid potato
species comprising superseries Stellata: toward establishment of seedling
cultivation conditions for ﬁeld evaluations. Am. J. Potato Res. 84:415-424.

Bus, C. B. and R. Wustman. 2007. Seed tubers. Potato Res. 50:319-322.

Calvet, R. 1980. Adsorption-desorption phenomena. pp 1-30 in R.J. Hance, ed.
Interactions between herbicides and the soil. New York: Academic Press.

Clewis, S. B., W. J. Everman, D. L. Jordan, and J. W. Wilcut. 2007. Weed management
in North Carolina peanuts (Arachis hyogaea) with S-metoalchlor, diclosulam,
ﬂumioxazin, and sulfentrazone systems. Weed Technol. 21 1629-635.

12

Colquhoun, J. B., C. M. Konieczka, and R. A. Rittmeyer. 2009. Ability of potato
cultivars to tolerate and suppress weeds. Weed Technol. 23:287-291.

De Jong, H. 1983. Inheritance of sensitivity to the herbicide metribuzin in cultivated
diploid potatoes. Euphytica 32:41-48

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between spin-label 5-sasl and humic acid as revealed by esr spectroscopy.
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15

Senseman, S. A, ed. 2007. Herbicide Handbook. 9th ed. Kansas: Weed Sci. Society of
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property effects of three herbicides and three soils on herbicide mobility in ﬁeld
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health management. St. Paul, MN: The American Phytopathological Society.

16

Wilson, D. E., S. J. Nissen, and A. Thompson. 2002. Potato (Solanum tuberosum)
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16:567-574.

17

CHAPTER 2

EFFECT OF SOIL CLAY AND ORGANIC MATTER CONTENT AND SOIL PH
ON THE EFFICACY OF FLUMIOXAZIN

Abstract: The effect of soil clay content, organic matter content, and pH on ﬂumioxazin
efficacy was evaluated using a greenhouse bio-assay. Clay soils used in the study were 0,
10, 20, 30, 40, 50, 60 and 70% clay by mass adjusted by adding kaolin clay to sand.
Organic soils used in the study were 0, 0.5, 1, 2, 4, 8, 16, and 32% organic matter by

mass adjusted by adding organic soil (82% organic matter) to sand. Varying soil pH

values were achieved by acidifying (H3PO4) or neutralizing (N aOH) a control soil (pH Of

4.76) to a pH of 4, 5, 6, 7, 8 and 9. Seeds ofbarnyardgrass (Echinochloa crus-galli L.),
giant foxtail (Seteriafaberz' Herrm), redroot pigweed (Amaranthus retroﬂexus L.), and
velvetleaf (Abutilon theophrasti L.) were incorporated into the top 1.3 cm of each soil at
a density of 100 seeds per pot. Emerged plants were counted and removed in both treated
and not-treated pots 2 wks after planting, and each following wk for 6 wks. Efﬁcacy of
ﬂumioxazin was evaluated by calculating percent emergence of weeds in treated soils
compared to emergence of weeds in non-treated soils. Clay content was not found to
affect ﬂumioxazin control of any weed species tested. Control ofbarnyardgrass, giant
foxtail, and velvetleaf was reduced as soil organic matter content increased. Control of
redroot pigweed was not affected by organic matter. Soil pH below 6 reduced
ﬂumioxazin control of giant foxtail and velvetleaf but did not affect control Of
barnyardgrass or redroot pigweed. Results indicated herbicide use rate needs to be

adjusted depending on soil characteristics and targeted weed species.

18

 

Nomenclature: Bamyardgrass, Echinochloa crus-galli L.; ﬂumioxazin; giant foxtail,
Seteriafaberi Hermr.; redroot pigweed, Amaranthus retroﬂexus L.; velvetleaf Abutilon
theophrasti L.

Key words: kaolinite, adsorption, hydrophobic binding.

INTRODUCTION
Interactions between a soil-applied herbicide and the soil medium are complex. A
relative equilibrium is reached soon after application of an herbicide to the soil
(Wauchope et al. 2002; Ferrell et al. 2005). The portion of herbicide not sorbed to the
soil particle surface is generally considered as herbicide available for weed control
(Walker 1980; Peter and Weber 1985). Therefore, if herbicide adsorption increases,
subsequent weed control decreases. However, the amount and types of particles in a soil

and the soil pH can greatly affect herbicide adsorption.

Herbicide adsorption in a soil is often evaluated experimentally by deriving a Kd

value, a measure of the amount of herbicide in solution to herbicide adsorbed to soil

particles (Wauchope et a1. 2002). A Kd value is often adjusted for soil organic matter

(SOM) due to the magnitude of its role in herbicide binding (Monaco et al. 2002;
Wauchope et al. 2002; Weber et a1. 2007). SOM can differ greatly in ﬁrnctional group
type and abundance, depending on the origin of the SOM, soil pH, climate, and the
microbial community, altering sorption herbicides (Walker and Austin 2003; Benoit et al.
2008). SOM is not the sole sorbent for many herbicides. Soil clay particles due to their
net negative charge can interact with herbicides in many ways. They are reported as the

major adsorption surface for certain herbicides (Monaco et al. 2002).

19

 

Flumioxazin, a non-ionic protoporphyrinogen oxidase inhibitor, is labeled for
preemergence use in many crops including alfalfa, cotton, peanuts, potato, and soybeans
(N iekamp 2001; Wilson et al. 2002; Ferrell et al. 2005). Flumioxazin has been used
widely in cropping systems to manage glyphosate and acetolactate synthase resistant
weed species due to its unique mode of action (Clewis et a1. 2007; Westhoven et a1. 2008;
Everman et a1. 2009). F lumioxazin efﬁcacy has been shown to vary between and within
studies on different weed species (Taylor-Lovell et al. 2002; Grey and Wehtje 2005;
Norsworthy et al. 2009). Observed differences in weed control with ﬂumioxazin could
be due to variations in the chemical and physical properties of the soil to which it is
applied.

Non-ionizable herbicides such as ﬂumioxazin form relatively few associations
with soil particles (Calvet 1980; Koskinen and Moorman 1992). Adsorption of non-
ionizable herbicides to soil particles is mainly attributed to hydrophobic binding, which is
the result of a decrease in entropy due to partitioning of the hydrophilic herbicide in the
hydrophobic regions of soil (Calvet 1980; Kah and Brown 2006). SOM and the
interlayer of clays provide conditions necessary to adsorb ﬂumioxazin due to the
hydrophobicity of the particles. However, SOM and clay particles to some degree are
subject to alterations in chemical and physical structure due to solution pH. Soil pH,

depending on clay type can affect clay edge charges or binding of base cations by

replacement with H+ the pH effect on SOM can be diverse and is due to affects on

speciation of SOM ﬁrnctional groups (Sposito et al. 1999; Kah and Brown 2006).
Ferreira et al. (2001) found SOM to increase in hydrophobicity at soil pH values lower

than 5. This could increase ﬂumioxazin adsorption.

20

Batch equilibrium and ﬁeld experiments have been conducted to evaluate
adsorption of ﬂumioxazin. Researchers found the adsorption of ﬂumioxazin to be
correlated with SOM and certain types of clay particles (Ferrell et al. 2005; Alister et al.
2008). However, these experiments focused extensively on herbicide adsorption, with
effects on weed control only implied. Field studies are often conducted To determine the
effect of soil type on weed control, , but are complicated due to soil variations within a
plot, differences in weather, spatial variation in weed population and density, and a lack
in range of soil parameters tested (Walker 1980; Kah and Brown 2006; Price et a1. 2008).
Therefore, a greenhouse study was conducted to evaluate the effect of clay content, SOM

and soil pH to determine their effect on the efficacy of ﬂumioxazin.

MATERIALS AND METHODS

Three separate greenhouse studies were conducted in 2008 at Michigan State
University to investigate the effect of clay content, SOM or soil pH on ﬂumioxazin
residual control. The studies were arranged utilizing a randomized complete block
design with a factorial arrangement of treatments, four replications, and were repeated in
time. Factors included: three soil characteristics, four weed species, and two herbicide
treatments. Base soil components utilized in the study were collected from the top 13 cm
of respective soils in uniform areas with no history of ﬂumioxazin application. Soil
components were autoclaved prior to use to ensure soil sterility as ﬂumioxazin is
susceptible to rapid microbial degradation. Soil particle size distribution, pH, CBC, and

SOM content were determined for each soil used (Table 1).

21

Preparation of Soil. A kaolin clay1 hereafter referred to as clay, was added to sand2 on a

dry weight to weight basis to achieve a titration of soils. Soils ranged from 0% clay to
70% clay with interpolated soils varying 10% for 8 total test soils. Organic soil was
obtained from the Michigan State University Muck Farm in Laingsburg and is described
as a Houghton muck soil derived ﬁom reed sedge plant materials containing 82% organic
matter by mass. The organic soil was passed through a 2-mm sieve to remove large
debris prior to mixing and was added to sand on a dry weight to weight basis to achieve
0.5, 1, 2, 4, 8, 16, and 32% SOM. A base soil opr 4.76 from a blueberry ﬁeld

consisting of a Pipestone-Kingsville soil (complex, sandy, mixed, mesic Typic
Endoaquods) was adjusted to desired pH values of 4, 5, 6, and 7 using NaOH and H3PO4.

As with the organic soil, the base soil was passed through a 2-mm sieve prior to acid or
base treatment to remove debris and large particles. Calculated amounts of acid and base
were dissolved in 3 L of deionized water and added to 8 kg of soil to make a soil
solution. The soil solution was mixed thoroughly and spread over a large surface area to
allow for rapid drying to prevent prolonged anaerobic conditions. Soil was mixed every
3 hours until gravimetric water had evaporated. Soils adjusted with NaOH were

subjected to salinity analysis by determining electrical conductivity using a 1:1 soil to

. . . . -l .
water ratro. Conductrvrty of 50118 ranged from 0.4 to 0.7 mmhos cm , this was

considered to be non-saline for a soil type of loamy sand and able to support normal crop
production (Whitney 1998). Soil pH was tested after completion of the experiment to

determine pH stability and was found to vary for all soils by 0.02 to 0.16.

22

Weed species evaluated consisted of velvetleaf (Abutilon theOphrasti Medik.),
barnyardgrass (Echinochloa crus-galli (L.) Beauv.), and giant foxtail (Setariafaberi
Herrm.). These were collected ﬁom local populations in corn and soybean ﬁelds at the

Michigan State University Agronomy Farm. The redroot pigweed seed (Amaranthus
retroﬂexus L.) was obtained from a commercial source3. Seeds of each species were
planted at a density of 100 seeds per pot to obtain a target population of 50 seedlings.

Soil was added to 7 by 7 by 6.4 cm pots with the top 1.3 cm of soil being added after

mixing with one of the four weed species. After planting soil was brought to ﬁeld

. . . . . 4
capacrty and then either left non-treated or was treated wrth formulated ﬂumroxazrn at

71 g ai ha.1 with a track sprayer delivering 187 L ha-l. Pots were kept in a greenhouse

maintained at 25 i 5 C° with a 16 hour photoperiod of natural sunlight supplemented

with high-pressure sodium lighting to provide 1,000 umol rn-2 photosynthetic photon

ﬂux. The day after application, 0.64 cm of water was added over the top of all pots to
simulate incorporation by rainfall with subsequent moisture provided by sub-irrigation
and weekly topical watering of 0.64 cm.

Emerged weeds were counted and removed from pots 2 wks after planting using
forceps, carefully removing the growing point to minimize soil mixing. Seedling counts
were taken for an additional seven wks after initial removal with 96% of weed emergence
taking place between planting and the ﬁrst two seedling counts. Weed control was

calculated using the equation:

y = 100 — ((3100)

23

where y is percent control, t is number of weeds that emerged in treated soil and n is the

average emergence of weeds in the respective non-treated soil. Weed control was

analyzed with SAS5 using PROC MIXED to test for signiﬁcant interactions between

experiments, weed species, and soil characteristic (P<0.05). NO signiﬁcant differences
were found between runs, therefore data were pooled. Due to signiﬁcant species by soil
interactions, and the large main effect of soil characteristic, weed control was evaluated

separately by soil characteristic with comparisons amongst species. Weed control for

species as affected by soil differences was ﬁt with trend lines using Sigma Plot software5

and was modeled using either linear or inverse ﬁrst-order regression. Inverse ﬁrst-order

regression ﬁt to data is described as:
-b+a
y — x
. . -1 .
where y rs weed control achieved at level a x wrth asymptote b.

RESULTS AND DISCUSSION
Weed control with ﬂumioxazin varied by soil characteristic and weed species
(Table 2). Control of weeds with ﬂumioxazin as affected by SOM was best modeled by
linear regression while the effect of pH on control was best modeled by inverse ﬁrst-

Order regression with coefficient Of determination values ranging from 0.31 to 0.78.

24

-m‘ ‘0'. ’

Comparing weed control at different clay contents, no signiﬁcant differences were r
observed for control of any weed species (Figure 1). F lumioxazin has been shown to
form relatively weak associations with clay particles. Weak adsorption of ﬂumioxazin by
clay particles has been suggested to be due to an electronegative region on the molecule
causing repulsion with negative surfaces like clay particles (Ferrell et a1. 2005).
Therefore, due to low adsorption by clay particles, ﬂumioxazin availability is dependent
on soil water content (Ferrell et al. 2005). Since soils were maintained at or near ﬁeld
capacity in our study, 100% weed control was observed for all species.

SOM content effect on weed control varied by species with control decreasing as
SOM content increased (Figure 2). Increasing SOM content reduced control of all
species except redroot pigweed and was signiﬁcantly different by species due to
sensitivity to ﬂumioxazin (P<0.05). Decrease in weed control as SOM increased, as
determined from the slope of the regression equations, were 1.06, 0.89 and 0.69 for
barnyard grass, giant foxtail and velvetleaf, respectively. Control ofbarnyardgrass, giant
foxtail, and velvetleaf at 3% SOM, common to soils in Michigan, would be 93, 89, and
93%, respectively. Conversely, redroot pigweed was effectively controlled across the
SOM contents tested. Differences in control of weed species because of SOM content is
likely due to increased adsorption by hydrophobic bonding onto SOM, decreasing
herbicide concentration in solution available for control (Peter and Weber 1985;
Koskinen and Moorman 1992; Kah and Brown 2006).

Relative control of weed species by ﬂumioxazin is as follows, from greatest to
least control: redroot pigweed, velvetleaf; giant foxtail, barnyardgrass. These results are

similar to reports by others; however, the level of control they observed at varying SOM

25

contents differed from ours. Wilson et a1. (2002) found that ﬂumioxazin applied at 53 g

ai ha.l to SOM content of 0.8% provided 90 and 56% control ofredroot pigweed and

barnyardgrass, respectively, 4 WAT. At 0.8% SOM we observed 100 and 95% control of

redroot pigweed and barnyardgrass, respectively. Niekamp and Johnson (2001) observed

that ﬂumioxazin at a rate of 71 g ai ha.1 applied to soil containing 2.5% SOM provided

82 and 63% control of velvetleaf and giant foxtail, respectively, 7 WAT. At 2.5% SOM

we observed 93 and 90% control ofvelvetleaf and giant foxtail, respectively. Lastly,

Taylor-Lovell et al. (2002) found 99% control of velvetleaf at 105 g ai ha.1 of

ﬂumioxazin while only 74 to 78% control of giant foxtail when SOM was 5.6%. At
5.6% SOM we observed 91 and 87% control of velvetleaf and giant foxtail respectively.
Observed control reported in ﬁeld studies was generally lower than what we observed
suggesting that differences in control could be due to continual emergence of weeds in
ﬁeld studies whereas weed emergence in our study was during a small period of time.
Differences between studies also could be due to environmental effects including rain and
soil moisture which has a large impact on ﬂumioxazin efﬁcacy (Ferrell et a12005.)

The effect of soil pH on weed control varied by species, but all decreased as pH
decreased (Figure 3). Control of giant foxtail and velvetleaf was signiﬁcantly decreased
when soil pH was lowered below 6, with control reduced to 76.3 and 75.2%, respectively,
at a soil pH of 4. Ferreira et al. (2001) demonstrated at a pH of 5.5 or lower, SOM
increased in hydrophobicity which potentially could cause increased herbicide
adsorption, which explains the reduction in control of giant foxtail and velvetleaf. In

contrast, control of redroot pigweed and barnyardgrass was not affected by soil pH.

26

Control of redroot pigweed was 100% at pHs lower than 6 because it is susceptible to
ﬂumioxazin despite lower concentrations being available for control, which is similar to
the results Observed for varying levels of SOM. However, barnyardgrass was controlled
at pHs less than 6, regardless of observations of its relative tolerance to ﬂumioxazin at
higher SOM. Barnyardgrass emergence being unaffected in the non-treated soil, could be
due to a reduction in vigor leading to greater susceptibility to herbicide phytotoxicity
causing a signiﬁcant reduction in biomass at lower pH (data not shown).

Control of weed species in ﬁeld studies was generally lower than that observed in

our greenhouse study. Taylor-Lovell et al. (2002) found at 105 g ai ha.1 of ﬂumioxazin

and a soil pH of 6, 99% control ofvelvetleaf similar to our ﬁndings of 97%. However,

they observed 74 to 78% control of giant foxtail while we observed 93% control.

Niekamp and Jomson (2000) observed that ﬂumioxazin at a rate of 71 g ai ha-1 to soil

with a pH of 6.5 provided 82 and 63% control of velvetleaf and giant foxtail,
respectively, 7 wks after treatment. At pH of 6.5 we observed 100% and 96% control of
velvetleaf and giant foxtail, respectively.

Our results indicate that SOM content and pH can adversely impact the efficacy
of a ﬁeld dose rate of ﬂumioxazin on weed species, while clay content does not.
Although, as reported by Alister et al. (2008), the type of clay may be more important
than the amount on ﬂumioxazin adsorption, indicating our results may only apply to soils
that contain predominantly kaolitic clay. However, ﬂumioxazin has a partial
electronegative charge and may form cationic bridge bonds or anionic bonds with
aluminum and iron hydroxides which are common to highly weathered soils such as the

soils Alister et al. (2008) studied in Chile potentially explaining the differences in their

27

frndings with ours and Ferrell et al. (2005). Understanding the effect of different soil
characteristics on adsorption of ﬂumioxazin will allow researchers to make soil and weed

species speciﬁc herbicide recommendations. If the prevalent weed species is redroot

pigweed a use rate of 71 g ai ha.1 will provide 100% control regardless of SOM content

and soil pH. However, if the species of concern is giant foxtail or velvetleaf the use rate
of ﬂumioxazin may need to be adjusted appropriately depending on the SOM content and
soil pH. Further testing is still necessary to evaluate how soil characteristics affect
ﬂumioxazin persistence, which determines residual weed control. Growers can achieve
adequate weed control in variable soils by adapting herbicide rates to manage different

weed species growing.

SOURCES OF MATERIALS

1 Plus White Clay, Charles B. Chrystal Co., Inc., 30 Vesey Street, New York, NY
1 0007.

2 Premimum play sand, The Quikrete Companies, 3490 Piedmont Road, Atlanta, GA
30329.

3 Redroot pigweed (Amaranthus retroﬂexus L.) seed, Azlin Seed Service, PO. Box 914,
Leland, MS 38756.

4 Flumioxazin, Valor SX 51WDG. Valent U.S.A. Corporation, PO. Box 8025, Walnut
Creek, CA 94596.

5 PROC MIXED, Statistical Analysis Systems (SAS) software, Version 9.1. Statistical
Analysis Systems Institute, Inc., PO. Box 8000, Cary, NC 25712

28

Table 1. Properties of soils used to evaluate efﬁcacy of ﬂumioxazin.a

 

 

 

Soil Sand Silt Clay SOM JH CEC
Sand 97.7 0.07 2.1 0.1 10 0.6
10% Clay 88.2 0.4 11.2 0.2 9.3 1.5
20% Clay 78.8 0.6 20.4 0.2 9 2.9
30% Clay 66.5 2.6 30.7 0.2 8.8 3.7
40% Clay 56.2 3.4 40.2 0.2 8.7 4.9
50% Clay 43.7 5.4 50.6 0.3 8.7 5.4
60% Clay 29.4 9.6 60.7 0.3 8.4 6.4
70% Clay 18.8 9.6 71.1 0.5 8.3 6.9
0.5% SOM 93.3 0.7 5.4 0.6 9.1 2.8
1% SOM 92.7 0.7 5.4 1.2 8.8 3
2% SOM 91.7 0.7 5.4 2.2 7.8 17.1
3% SOM 90.9 0.7 5.4 3 7.8 24.2
4% SOM 89.8 0.7 5.4 4.1 7.3 30
8% SOM 85 1.7 5.4 7.9 7.1 35
16% SOM 77.4 1.4 5.4 15.8 6.9 75.8
32% SOM 62 0.9 5.4 31.7 6.6 121.6
pH 4 68.4 10.8 16.8 4 4.07 6.6
pH 5 69.8 11 15.4 3.8 4.93 7.2
pH 6 68.2 12.6 14.3 4.9 6.07 5.5
pH 7 70.1 10.4 16.8 2.7 7.07 7.1

 

a abbreviations: SOM, soil organic matter; CEC, cation exchange capacity.

29

Table 2. Seedling count of weed species averaged by soil and regression equation used to
model weed control for clay, SOM and pH soils.a

 

 

 

 

 

Soil Species Emergence Modelb r2
# Plants

Clay
ABUTH 26 NS NS
AMARE 29 NS NS
ECHCG 88 NS NS
SETFA 18 NS NS

SOM
ABUTH 41 y = 94.64 - 0.69b 0.31
AMARE 70 NS NS
ECHCG 86 y = 95.69 — 1.06b 0.66
SETFA 28 y = 92.03 - 0.89b 0.48

pH
ABUTH 32 y = 139.24 — (256.33 / b) 0.78
AMARE 22 NS NS
ECHCG 65 NS NS
SETFA 20 y = 126.43 — (200.38 / b) 0.53

 

a abbreviations: SOM, organic matter; ABUTH, velvetleaf; AMARE, redroot pigweed;
ECHCG, barnyardgrass; SETFA, giant foxtail; NS, not signiﬁcant.

regression models ﬁt to data include linear (y = a + bx) and inverse ﬁrst-order
regression (y = b + a/x)

30

 

 

 

 

100 - i . . . g I 2 l
80 -
’3
g 60 -
'5
L-
‘E
O 40 "
U
20 ‘ Q velvetleaf
I redroot pigweed
O barnyardgrass
0 i A giant foxtail
0 10 20 30 40 50 60 70
Clay (%)

Figure 1. Efﬁcacy of ﬂumioxazin as affected by soil organic matter content. The vertical
bars represent the standard error of means.

31

 

100 ‘

Control (%)

Q velvetleaf

I redroot pigweed
O barnyardgrass
0 ‘ A giant foxtail

 

 

 

 

0 5 1O 15 20 25 30 35
Organic Matter (%)

Figure 2. Efﬁcacy of ﬂumioxazin as affected by soil organic matter content. Fitted lines
are calculated by linear regression equation for velvetleaf; barnyardgrass and giant
foxtail. The vertical bars represent the standard error of means.

32

 

 

 

 

 

100 -
80 a
g 60 -
ﬂ
C
8
4o -
e"
20 d O velvetleaf ——
I redroot pigweed
Q barnyardgrass
O ‘ A giant foxtail — — —
4 5 6 7
pH

Figure 3. Efficacy of ﬂumioxazin as affected by soil pH. Fitted lines are calculated by
the inverse ﬁrst-order regression equation for velvetleaf and giant foxtail. The vertical
bars represent the standard error of means.

33

LITERATURE CITED

Alister, C., S. Rojas, P. GOmez, and M. Kogan. 2008. Dissipation and movement of
ﬂumioxazin in soil at four ﬁeld sites in Chile. Pest Manag. Sci. 64:579-583.

Benoit, P., I. Madrigal, C. M. Preston, C. Chenu, and E. Barriuso. 2008. Sorption and
desorption of non-ionic herbicides onto particulate organic matter from the
surface soils under different land uses. European Journal of Soil Science. 59: 1 78-
189.

Calvet, R. 1980. Adsorption-desorption phenomena. pp 1-30 in R.J. Hance, ed.
Interactions between herbicides and the soil. New York: Academic Press.

Clewis, S. B., W. J. Everman, D. L. Jordan, and J. W. Wilcut. 2007. Weed management
in North Carolina peanuts (A rachis hyogaea) with S-metoalchlor, diclo sulam,
ﬂumioxazin, and sulfentrazone systems. Weed Technol. 21:629-635.

Everman, W. J., S. B. Clewis, A. C. York, and J. W. Wilcut. 2009. Weed Control and
Yield with Flumioxazin, Fomesafen, and S—Metolachlor Systems for Glufosinate-
Resistant Cotton Residual Weed Management. Weed Technol. 23: 391-397.

Ferrell, J. A., W. K Vencill, K Xia, and T. L. Grey. 2005. Sorption and desorption of
ﬂumioxazin to soil, clay minerals and ion-exchange resin. Pest Manag.
Sci.6l 240-46.

Ferreira, J. A., O. R. Nascimento, and L. Martin-Neto. 2001. Hydrophobic interactions
between spin-label 5-sasl and humic acid as revealed by ESR spectroscopy.
Environ. Sci. and Technol. 35:761-765.

Grey, T. L. and G. R. Wehtje. 2005. Residual herbicide weed control systems in peanut.
Weed Technol. 19:560-567.

Kah, M. and C. D. Brown. 2006. Absorption of ionisable pesticides in soils. Rev.
Environ. Contam. Toxicol. 188:149-217.

Koskinen, W. C. and T. B. Moorman. 1992. Effect of soil properties and processes on
herbicide performance. pp 365-402 in McWhorter, C. G. and J. R. Abernathy, eds.
Weeds of cotton: characterization and control. Tennessee: The Cotton
Foundation.

Monaco, T. J., S. C.hWeller, and F. M. Ashton, eds. 2002. Weed science principles and
practices, 4t ed. pp 127-145. New York: John Wiley & Sons, Inc.

Niekamp, J. W. and W. G. Johnson. 2001. Weed management with sulfentrazone and
ﬂumioxazin in no-tillage soyabean (Glycine max). Crop Prot. 20:215-220.

34

Norsworthy, J. K, M. McClelland, and G. M. Grifﬁth. 2009. Conyza canadensis (1.)
cronquist response to pro-plant application of residual herbicides in cotton
(Gossypium hirsutum 1.). Crop Prot. 28:62-67.

Peter, C. J. and J. B. Weber. 1985. Adsorption, mobility, and efficacy ofalachlor and
metolachlor as inﬂuenced by soil properties. Weed Sci. 33:874-881.

Price, A. J., C. H. Koger, J. W. Wilcut, D. Miller, and E. V. Santen. 2008. Efﬁcacy of
residual and non-residual herbicides used in cotton production systems when
applied with glyphosate, glufosinate, or MSMA. Weed Technol. 22:459-466.

Sposito, G., N. T. Skipper, R. Sutton, S. Park, A. K Soper, and J. A. Greathouse. 1999.
Surface geochemistry of clay minerals. Proc. Natl. Acad. Sci. 96:3358-3364.

Taylor-Lovell, S., L. M. Wax, and G. Bollero. 2002. Preemergence ﬂumioxazin and
pendimethalin and postemergence herbicide systems for soybean (Glycine max).
Weed Technol. 16:502-511.

Walker, A. 1980. Activity and Selectivity in the ﬁeld. pp 203-222 in R.J. Hance, ed.
Interactions between herbicides and the soil. New York: Academic Press.

Walker, A. and C. R. Austin. 2003. Effect of recent cropping history and herbicide use
on degradation rates of isoproturon in soils. Eur. Weed Res. 4415-11.

Wauchope, D. R., S. Yeh, J. B. Linders, R. Kloskowski, K Tanka, B. Rubin, A.
Katayama, W. KOrdel, Z. Gerstl, M. Lane, and J. B. UnswortlL 2002. Pesticide
soil sorption parameters: theory, measurement, uses, limitations and reliability.
Pest Manag. Sci. 58:419-445.

Weber, J. B., R. L. Warren, L. R. Swain, and F. H. Yelverton. 2007. Physicochemical
property effects of three herbicides and three soils on herbicide mobility in ﬁeld
lysimeters. Crop Prot. 26:299-311.

Westhoven, A. M., J. M. Stachler, M. M. Loux, and W. G. Johnson. 2008. Management
ofglyphosate-tolerant common lambsquarters (Chenopodium album) in
glyphosate-resistant soybean. Weed Technol. 22:628-634.

Whitney, D. A. 1998. Soil salinty. 59-61 in J. R. Brown, ed. Recommended chemical
soil test procedures for the North Central region, North Central Research
publication number 221 (revised). Missouri Agriculture Experiment Station,
University of Missouri, Columbia.

Wilson, D. E., S. J. Nissen, and A. Thompson. 2002. Potato (Solanum tuberosum)

variety and weed response to sulfentrazone and ﬂumioxazin. Weed Technol.
16:567-574.

35

CHAPTER 3

EFFECT SOIL ORGANIC MATTER CONTENT AND SOIL PH ON RESIDUAL
CONTROL WITH F LUMIOXAZIN

Abstract: Two greenhouse studies were conducted to evaluate the effect of soil organic
matter content and soil pH on ﬂumioxazin residual weed control, utilizing artiﬁcial and
ﬁeld soils. Eight wks after treatment ﬂumioxazin gave 0% control of giant foxtail
(Seteriafaberi Herrm.) and velvetleaf (Abutilon theophrasti L.) in all soils tested.
However, eight wks after treatment 0% control was only observed for common
lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroﬂexus L.)
when grown in the muck soil or when soil pH was above 7. Control of common
lambsquarters and redroot pigweed was 100% for the duration of the experiment, except
when soil organic matter content was greater than 3% or soil pH was 7. Control of giant
fo xtail and velvetleaf decreased as soil organic matter content and soil pH increased.
Similar results in control were observed when comparing artiﬁcial pH soils to ﬁeld pH
soils, however differences in control were Observed between artiﬁcial organic matter soils
and ﬁeld organic matter soils. Results indicate that herbicide use rate needs to be
adjusted to account for soil type and prevalent weed species.

Nomenclature: Common lambsquarters, Chenopodium album L.; ﬂumioxazin; giant
foxtail, Seteriafaberi Hemn.; redroot pigweed, Amaranthus retroﬂexus L.; velvetleaf,
Abutilon theophrasti L.

Key words: persistence, efficacy, herbicide bio-assay

36

INTRODUCTION

F lumioxazin, a non-ionic, N—phenyl phthalimide herbicide, inhibits chlorophyll
biosynthesis by preventing the formation of protoporphyrino gen precursors (Senseman
2007). Currently, ﬂumioxazin is labeled for use in many crops including alfalfa, cotton,
peanuts, potato, and soybeans. Flumioxazin is in the protoporphyrinogen oxidase
inhibiting family of herbicides used to manage glyphosate and acetolactate synthase
resistant weed species due to its unique mode of action (Taylor-Lovell et al. 2002; Clewis
et al. 2007; Everman et al. 2009). Weed control with ﬂumioxazin has been shown to
vary between locations, on the same species and at the same timing (Taylor-Lovell et a1.
2002; Grey and Wehtje 2005; Norsworthy et al. 2009). The differences observed in weed
control with ﬂumioxazin may be due in part to variations in the soils to which it is
applied.

Interactions between an herbicide, like ﬂumioxazin, and the soil medium are
complex. After an herbicide is applied to the soil, it rapidly interfaces with soil
components and reaches a relative equilibrium in the soil solution (Monaco et al. 2002).
Herbicides that are not sorbed to the soil and are in solution are generally accepted as
herbicides available for weed uptake and control (Peter and Weber 1985; Monaco et al.
2002). Therefore, as herbicide adsorption increases, subsequent weed control decreases;
however, the amount and types of particles in a soil and the soil pH can greatly affect
herbicide adsorption.

Non-ionic herbicides, such as ﬂumioxazin, have limited interactions with soil
particles (Calvet 1980; Kah and Brown 2006). Adsorption of non-ionizable herbicides in

soils is mainly attributed to one phenomenon, hydrophobic binding, which is the result of

37

decrease in entropy due to partitioning of the hydrophilic herbicide in the hydrophobic
regions of soil (Calvet 1980; Koskinen and Moorman 1992). Soil organic matter (SOM)
and the interlayer of clays provide conditions necessary to adsorb ﬂumioxazin due to the
hydrophobicity of the particles. F crreira et al. (2001) found SOM to increase in
hydrophobicity, when the soil pH was lower than 5, which could increase ﬂumioxazin
adsorption. SOM tends to solubilize at pH values greater than 7 and would decrease
available sites for adsorption. Therefore, interactions between SOM content and pH have
a large inﬂuence on ﬂumio xazin adsorption, subsequently affecting its persistence.
Soil-applied herbicides, including ﬂumioxazin, need to persist long enough to
provide adequate weed control, but not so long as to interfere with subsequent crops or
cause negative impacts on the environment. The persistence of an herbicide in a soil is a
function of its loss from the soil system and degradation (Hurle and Walker 1980; Peter
and Weber 1985; Monaco 2002). Herbicide can be lost ﬁom a system due to
volatilization, leaching, surface runoff, and loss of soil with sorbed herbicide (Hance
1980; Monaco et al. 2002; Kah and Brown 2006). Herbicide breakdown is due to the
combination of chemical decomposition, photodecomposition, and biological
decomposition (Torstensson 1980; Kwon et al. 2004). Soil microbes readily degrade
ﬂumioxazin and are the main pathway of degradation when soil solution pH is not greater
than 7 (Ferrell et al. 2005). When soil pH is greater than 7, hydrolysis increases and
becomes the major degredation pathway (Kwon et al. 2004). Soils high in organic matter
are reported as having greater microbial activity which would be expected to increase
degradation of ﬂumioxazin (Goyal et a1. 1999; Kah and Brown 2006). Conversely, an

increase in SOM would in turn increase herbicide adsorption, making the herbicide

38

unavailable for microbial degradation. For this reason, determining the persistence of
ﬂumioxazin is difﬁcult without experimentation.

Researchers have found the adsorption of ﬂumioxazin to be correlated with SOM
and certain types of clay particles using batch equilibrium and ﬁeld experiments (Ferrell
et al. 2005; Alister et a1. 2008). However, these experiments focused extensively on
herbicide adsorption. Although weed control with ﬂumioxazin is in part affected by
adsorption, it is also dependent on the interaction of the soil, soil microbes, and the weeds
themselves. To determine the effect of soil type on weed control, ﬁeld studies are often
conducted but these are complicated due to soil variations within a study, differences in
weather, spatial variation in weed population and density, and a lack in variation of soil
parameters tested such as SOM or soil pH (Walker 1980; Kah and Brown 2006). Two
greenhouse studies were conducted to evaluate the effect of SOM and soil pH on the

residual control of ﬂumioxazin.

MATERIALS AND METHODS
Two separate greenhouse studies were conducted in 2009 at Michigan State

University to investigate the effect of l) SOM and 2) soil pH on ﬂumioxazin residual
control. The studies were arranged in a randomized complete block with a factorial
arrangement of treatments and were repeated in time. Factors included: four weed
species, two herbicide treatments (treated with ﬂumioxazin or non-treated), and ﬁve
planting times (0, 2, 4, 6, and 8 wks after treatment (WAT)) with 3 replications. The
soils utilized for the study were either ﬁeld soils collected based on desired properties

with no prior history of ﬂumioxazin application or soils that were artiﬁcially adjusted to

39

provide a range of values for the characteristics investigated. Soils collected ﬁ'om the
ﬁeld were taken from uniform areas in respective locations from the top 13 cm of soil.
The adjusted soils will hereafter be referred to as ‘lab soils’. Soil particle size
distribution, pH, cation exchange capacity, and SOM content were determined for each
soil used (Table 3). Field soils were investigated to determine if results from the lab soils

were representative of expected ﬁeld results.

Organic Matter Soils. Organic soil was obtained from the Michigan State University
Muck Farm and is described as a Houghton muck soil derived ﬁ'om reed sedge plant
materials containing 82% organic matter by mass. The organic soil was passed through a
2-mm sieve to remove large debris prior to mixing and was added to sand on a dry weight
to weight basis to achieve 0, l, and 3% SOM. Field soils of 3% SOM (Capac loam, ﬁne-
loamy, mixed, mesic Aeric Ochraqualfs) and the unadjusted organic soil were also

included for comparison.

pH Soils. A base soil of pH 6 from a Capac loam (ﬁne-loamy, mixed, mesic Aeric

Ochraqualfs) in a com-soybean rotation was adjusted to desired pHs of 5 and 7 using

H3PO4 and Ca(OH)2, respectively. As with the organic soil, the base soil was passed

1 through a 2-mm sieve prior to acid or base treatment to remove debris and large particles.
To adjust the pH, calculated amounts of acid and base were dissolved in 3 L ofde-
ionized water and added to 8 kg of soil to create a soil solution. Once in a solution, soil
was mixed thoroughly and spread over a large surface area to allow for rapid drying to

prevent prolonged anaerobic conditions. Soil was mixed every 3 hours until gravimetric

40

water had evaporated. Field soils of pH 5 from a Capac loam (ﬁne-loamy, mixed, mesic
Aeric Ochraqualfs) and pH 7 from a Spinks loam (mixed, mesic Psammentic Hapludalfs)
both ﬁ'om com-wheat-soybean rotations currently planted to wheat underseeded with red
clover were also included for comparison.

Weed species consisted of velvetleaf (Abutilon theophrasti Medik.), common
lambsquarters (Chenopodium album L. ), and giant foxtail (Setariafaberi Herrm.)
collected from local populations in ﬁelds under corn and soybean rotations ﬁeld at the

Michigan State University Agronomy Farm Redroot pigweed seed (Amaranthus

. . l .
retroﬁexus L.) was obtained from a commercral source . Seeds of each specres were

planted at 150 seeds per pot except for velvetleaf which was planted at 65 seeds per pot
to Obtain a target population of 50 seedlings. Lab soil and ﬁeld soil were added to 7 by 7

by 6.4 cm pots brought to ﬁeld capacity, and were either left non-treated or were treated
with formulated ﬂumioxazin2 at 71 g ai ha'1 with a track sprayer delivering 187 L ha-l.
Once treated, pots were placed in a greenhouse maintained at 25 i 5 C° with a 16 hour
photoperiod of natural sunlight supplemented with high-pressure sodium lighting to

provide 1,000 umol m'2 photosynthetic photon ﬂux. Weed seeds were planted by

randomly scattering one of the four species onto the soil surface then incorporating them
with forceps to a depth of 0.5 to 1 cm at 0, 2, 4, 6, and 8 WAT. At each timing weeds

were planted into treated and non-treated soil to evaluate residual control of ﬂumioxazin
and to assure that emergence of weeds in treated soils was due solely to chemical control

and not changes in the soil. The day after application, 0.64 cm of water was added over

41

the top of all pots to simulate incorporation by rainfall with subsequent moisture provided

by sub-irrigation and weekly topical watering of 0.64 cm.

Data Collection and analysis. Emerged weeds were counted and removed from pots
weekly using forceps careﬁrlly removing the growing point to minimize soil mixing.
Seedling counts were taken for 3 wks after each respective planting with 94% of weed
emergence taking place between planting and the ﬁrst count at 1 wk after planting. Weed

control was calculated using the equation:

y = 100 - ((3100)

where y is percent control, t is number of weeds that emerged in treated soil and n is the

average emergence of weeds in the respective non-treated soil. Weed control was

analyzed with SAS4 using PROC MIXED to test for signiﬁcant interactions between

runs, weed species, time after application, and soil effect on weed control (P<0.05). No
signiﬁcant differences were found between experiments, therefore data were pooled.
Due to signiﬁcant species by soil by time interactions, and the large main effect of soil
characteristic, weed control was evaluated separately by soil characteristic with

comparisons among species. Weed control for species as affected by soil differences was

ﬁt with trend lines using Sigma Plot software3 and was modeled using either linear or

logistic regression. Logistic regression ﬁt to data is described as:

42

where y is weed control achieved at level x with an upper asymptote of a (with forced
upper limit of 100) and slope ofc with the point of inﬂection b (Ratkowsky 1990;

Seefeldt et al. 1995; Mueller-Warrant 1999). Time elapsed in wks until a 50% reduction

in weed control was observed (150) was calculated for each soil and weed species using

the respective regression equation to compare weed control between species and soils

(Seefeldt et al. 1995).

Results and Discussion
Weed control with ﬂumioxazin varied by soil type and generally decreased over
time. Residual weed control was best modeled as a logistic response (24 of 40 models)
with 4 models sufﬁciently explained by linear regression and 12 with no signiﬁcant
regression model (Table 4 and 5). Models that were signiﬁcant ranged in coefficient of

determination values ﬁom 0.72 to 0.98 but in most cases were 0.9 or higher.

Organic Soils. Organic matter content greatly inﬂuenced control Of weeds species by
ﬂumioxazin (Figure 4). Weed control at 0 WAT ranged ﬁ'om 77.4 to 100% with 150
values ranging from 1.7 to 13 (Table 4). Lab soil with 0% SOM (100% sand material)
had relatively no effect on weed control and not until 4 WAT was control reduced for

giant foxtail and velvetleaf (Figure 4). Lab soil with 1% SOM resulted in decreased

control ofvelvetleaf after application and by 2 WAT, control was reduced by 23.3%.

43

Control of giant foxtail was affected by SOM content, with reduced control at 2 WAT at
1% SOM compared to 4 WAT for 0% SOM. Control of common lambsquarters and
redroot pigweed was not reduced during the duration of the experiment at 1% SOM lab
soil, however control was reduced when SOM was 3% and seeds were planted 4 WAT.
Initial and residual control of giant foxtail and velvetleaf was greater at 1% SOM than at
3% SOM, and was also greater in the ﬁeld soil than the lab soil. Control of common
lambsquarters and redroot pigweed in ﬁeld soil showed no differences, however reduced
control was observed as SOM changed in lab soil (Figure 4).

Digression between results of lab and ﬁeld soil at 3% SOM could be due to the
type of organic matter in each soil. The SOM in the organic soil used to adjust the lab
soil could have a greater afﬁnity for ﬂumioxazin (more hydrophobic) than the SOM
found in the ﬁeld soil (Torrents and Jayasundera 1997; Walker and Austin 2003; Kah and
Brown 2006). Differences in weed control in the two soils also could be due to the
microbial populations associated with the soil with populations in the lab soils derived
from the organic soil more apt to metabolize ﬂumioxazin (Torstensson 1980) or cause a

synergistic control of weeds (André and Rahe 1992). Lastly, control was greatly affected

by the organic soil with I 50 values of 7.3, 1.7, 6.9, and 1.9 for common lambsquarters,

giant foxtail, redroot pigweed, and velvetleaf, respectively (Table 4). Weed control at 0
WAT for the organic soil was 80 and 77.4% for giant foxtail and velvetleaf respectively
which was the lowest initial control observed for either species (Figure 4, 5).

It was observed that weed control generally decreased as SOM content increased.
Control of weed species in response to SOM was similar for the larger seeded broadleaf

and grass weed species (giant foxtail and velvetleaf) and the smaller seeded broadleaves

44

(common lambsquarters and redroot pigweed). However, control of velvetleaf tended to

be slightly higher than giant foxtail control with the exception of at 1% SOM lab soil,

where the 150 value for giant foxtail was 0.58 greater than velvetleaf.

Soil pH. The residual control of ﬂumioxazin varied greatly by soil pH and species

(Figure 5). Initial weed control ranged from 90.6 to 100% and 150 values ranged from

2.37 to 5.93 (Table 5). For both lab and ﬁeld soil at pH 5, control ofcommon
lambsquarters and redroot pigweed remained at 100% for 8 wks while giant foxtail and

velvetleaf control decreased (Figure 5). Control of giant foxtail and velvetleaf at pH 5
lab and ﬁeld soil, began to decrease 2 WAT with 150 values Of 5.1 and 4.8, respectively.
Minimal differences were observed between the lab and ﬁeld soil at pH 5 for weed
control, with the greatest difference observed in 150 values for giant foxtail being 0.57

WAT. Control of common lambsquarters and redroot pigweed was 100% for the

duration of the study at a soil pH of 6, similar to results at a soil pH of 5. Control of giant

foxtail and velvetleaf at pH 6 decreased with a 47 and 37% reduction in I 50 values,

respectively. Loss in weed control ﬁom pH 5 to 6 could be due to an increase in the
ability of the microbial population to degrade the herbicide (Corbin and Upchurch 1967;

Leahy and Colwell 1990; Anderson and Domsch 1992). Control of weed species at pH 7

lab and ﬁeld soil were similar and only differed by 150 values being 0.18 to 0.48 lower

for all species except giant foxtail (1.46) in the ﬁeld soil. Control of common

lambsquarters and redroot pigweed did not decrease until 4 WAT at pH 7, regardless of

45

being lab or ﬁeld soil. However, at pH 7 lab and ﬁeld soil, control of giant foxtail and
velvetleaf were similar to control at pH 6. Reduction in control of common
lambsquarters and redroot pigweed but not giant foxtail and velvetleaf could be due to a
slight decrease in herbicide concentration caused by hydrolysis at the higher pH (Kwon et
al. 2004). This decrease in herbicide concentration however, was not enough to cause a
signiﬁcant reduction in control of the larger seeded weed species.

Control of all species decreased over time as sOil pH increased (Figure 5).
Reduction in control of common lambsquarters and redroot pigweed only occurred at the
highest soil pH tested; however, control of giant foxtail and velvetleaf decreased when
pH was raised from 5 to 6. Comparing species response to soil pH, it was observed that
similar to SOM soils, common lambsquarters and redroot pigweed had similar responses
while giant foxtail and velvetleaf responded similarly. The reason for differences
between the two pairs of weed species and similarities within the pairs could be attributed
to weed seed size which has been shown to inﬂuence herbicide uptake (Scott and Phillips
1971).

Initial weed control and weed control over time decreased as SOM content
increased. Reductions in weed control with increasing SOM content can be attributed to
several factors including an increase in available sites for hydrophobic bonding or greater
amounts of microbial activity. Increasing the soil pH tended to decrease the time needed
to reach a 50% reduction in control, but did not have an appreciable effect on initial
control. Previous research has shown little to no differences in adsorption of ﬂumioxazin
due to soil pH (Ferrell et al. 2005; Alister et a1. 2008). The authors attributed this to the

non-ionic nature of ﬂumioxazin. Our research shows that increasing solution pH

46

decreases ﬂumio xazin residual control, indicating that the reduction in residual control is
potentially due to an effect on the microbial degradation of the herbicide. When
comparing lab pH soils to ﬁeld pH soils, similar control was observed, while differences
in control were Observed when comparing lab SOM soils to ﬁeld SOM soils indicating
the origin of the SOM has a critical effect on ﬂumioxazin adsorption. By understanding
the effect of different soil characteristics on ﬂumioxazin residual control, researchers will
be able to make soil and weed species speciﬁc herbicide recommendations. Adjusting
herbicide recommendations due to soil type and prevalent weed species will potentially
reduce herbicide use or improve weed control by matching the necessary rate to the

situation.

SOURCES OF MATERIALS

1 Premimum play sand, The Quikrete Companies, 3490 Piedmont Road, Atlanta, GA
30329.

2 Redroot pigweed (Amaranthus retroﬂexus L.) seed. Azlin Seed Service, PO. Box 914,
Leland, MS 38756.

3 Flumioxazin, Valor SX 51WDG. Valent U.S.A. Corporation, PO. Box 8025, Walnut
Creek, CA 94596.

4 PROC MIXED, Statistical Analysis Systems (SAS) software, Version 9.1. Statistical
Analysis Systems Institute, Inc., PO. Box 8000, Cary, NC 25712.

47

Table 3. Properties of lab and ﬁeld soils to evaluate ﬂumioxazin’s persistencea

 

 

Soil Sand Silt Clay SOM pH CEC
Lab Soil pH 5 50.4 31 16.8 2.8 5.1 21
Field Soil pH 5 49.8 36.8 16.8 2.3 4.9 6.6
Field Soil pH 6 37.7 33.0 23.5 3.2 6 19.6
Lab Soil pH 7 48.2 29.4 20.8 3 7 19.7
Field Soil pH 7 40 29.6 27.8 2.6 7.1 12
Lab Soil 0% SOM 97.7 0.1 2.1 0.1 10 0.6
Lab Soil 1% SOM 92.7 0.7 5.4 1.2 8 3
Lab Soil 3% SOM 90.9 0.7 5.4 3 7.6 24.2
Field Soil 3% SOM 37.7 33 23.5 3.2 6 19.6
Muck 7.3 9.2 1.8 81.7 6.4 142.3

 

a abbreviations: SOM, soil organic matter; CEC, cation exchange capacity.

48

Table 4. Seedling emergence of various weed species averaged over time, 150, and

regression equation used to model weed control for organic matter soils.a

 

 

Soil Species Emer I 50 Modelb r2

Ls 0%

SOM
ABUTH 36.7 57 y = 100 / 1 + (x / 5,67)9°85 0.98
AMARE 39.7 NS NS NS
CHEAL 33.5 NS NS NS
SETFA 41.6 6.3 y = 96.48 / 1 +(x/6.29)10'36 098

LS 1%

SOM
ABUTH 37.5 5.4 y = 96.86 / 1 + (x/ 5.51)“‘29 0.95
AMARE 38.9 NS NS Ns
CHEAL 35.5 NS NS NS
SETFA 40.4 4.6 y = 97.13 — 10.22x 0.90

LS 3%

SOM
ABUTH 38.9 4.4 y = 93.63 — 10x 0.97
AMARE 38.3 11.6 y = 100 / 1 + (x/ 1157):"63 0.72
CHEAL 35.5 13 y = 100 / 1 + (x/ 13.04)2'88 0.92
SETFA 40.6 3.5 y = 90.7 — 11.65x

FS 3%

SOM

2 9 _ 1.82 0 81

ABUTH 34.5 - y — 97.76 / 1 + (x/ 2.92) .
AMARE 32.5 NS NS NS
CHEAL 32.6 NS NS NS
SETFA 38.5 2-8 y = 92.1 / 1 + (x / 3.03)2'4 0.94

Organic

Soil
ABUTH 35 1.9 y = 77.42 / 1 + (x/ 2.44)2'6 0.95
AMARE 38.9 6.9 y = 100 / 1 + (x / 6.92)9'28 0.97
CHEAL 34.8 7.3 y=100/1+(x/7.27)7°29 0.98
SETFA 37.5 1.7 y = 80.09/ 1 + (x/ 1.99)3'12 0.93

 

a abbreviations: Emer, emergence; SOM, soil organic matter; FS, ﬁeld soil; LS, lab soil;
ABUTH, velvetleaf; AMARE, redroot pigweed; CHEAL, common lambsquarters;

SETFA, giant foxtail; I50, wks until a 50% reduction in control; NS, not signiﬁcant.

 

models ﬁt to data include linear (y = a + bx) and logistic regression (y =

49

Table 5. Seedling emergence of various weed species averaged over time, I 50, and

regression equation used to model weed control for pH soils. a

 

 

 

 

Soil Species Emer 150 Modelb r2
Plants
LS pH5
ABUTH 349 y = 943714117: (x / 0.95
4.49 4.53) '
AMARE 33.1 NS NS NS
CHEAL 32.6 NS NS NS
SETFA 41-8 5.60 y = 93.55 / 1 + (x/ 5.74)5'58 09
F8 pH 5
ABUTH 34.1 y = 93'981/415 M 0.98
4.49 4.53) '
AMARE 34.2 Ns NS NS
CHEAL 32 NS NS NS
SETFA 39 5.03 y = 95.68 / 1 + (x/ 5.11)5°55 0.96
FS pH 6
ABUTH 34-5 2.85 y = 97.76 / 1 + (x/2.92)1'82 0.81
AMARE 32.5 NS NS NS
CHEAL 32.6 NS NS NS
SETFA 38.5 2.82 y = 92.1 / 1 + (x/ 3.03)2‘4 0.94
LS pH 7
ABUTH 35.8 3.25 y = 97.67 / 1 + (x/ 3.27)9‘26 0.97
AMARE 34 5.86 y = 100 / 1 + (x / 5.86)5'94 0.95
CHEAL 34-3 5.93 y = 100 / 1 + (x / 5.93)6'69 0.97
SETFA 42.9 3.83 y = 90.63 — 10.6lx 0.96
FS pH 7
ABUTH 35-2 2.78 y = 99.13 / 1 + (x/ 2.79)3'31 0.98
AMARE 32 5.64 y = 100 / 1 + (x / 5.64)5'71 0.88
CHEAL 31-8 5.75 y = 100 / 1 + (x / 5.75)5'24 087
SET FA 38 2.37 y = 92.98 / 1 + (x/2.62)1'53 0.91

 

a abbreviations: Emer, emergence; FS, ﬁeld soil; LS, lab soil; ABUTH, velvetleaf;

AMARE, redroot pigweed; CHEAL, common lambsquarters; SETFA, giant foxtail; I 50,
wks until a 50% reduction in control; NS, not signiﬁcant.

 

b models ﬁt to data include linear (y = a + bx) 311d 10813119 regression (y = “a

50

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52

LITERATURE CITED

Alister, C., S. Rojas, P. Gomez, and M. Kogan. 2008. Dissipation and movement of
flumioxazin in soil at four ﬁeld sites in Chile. Pest Manag. Sci. 642579-583.

Anderson, T. H. and K H. Domsch. 1992. The metabolic quotient for C02 (qCOz) as a
speciﬁc activity parameter to assess the effects of environmental conditions, such
as pH, on the microbial biomass of forest soils. Soil Biol. Biochem. 25:393-395.

Andre, C. L. and J. E. Rahe. 1992. Herbicide interactions with fungal root pathogens,
with special reference to glyphosate. Annu. Rev. Phytopathol. 30:579-602.

Benoit, P., I. Madrigal, C. M. Preston, C. Chenu, and E. Barriuso. 2008. Sorption and
desorption of non-ionic herbicides onto particulate organic matter from the
surface soils under different land uses. Eur. J. Soil Sci. 59:178-189.

Calvet, R. 1980. Adsorption-desorption phenomena. pp 1-30 in R.J. Hance, ed.
Interactions between herbicides and the soil. New York: Academic Press.

Clewis, S. B., W. J. Everman, D. L. Jordan, and J. W. Wilcut. 2007. Weed management
in North Carolina peanuts (A rachis hyogaea) with S-metoalchlor, diclosulam,
ﬂumioxazin, and sulfentrazone systems. Weed Technol. 21:629-635.

Corbin, F. T. and R. P. Upchurch. 1967. Inﬂuence of pH on detoxication of herbicides
in soil. Weeds. 15:370-377.

Everman, W. J., S. B. Clewis, A. C. York, and J. W. Wilcut. 2009. Weed control and
yield with ﬂumioxazin, fomesafen, and s-metolachlor systems for glufosinate-
resistant cotton residual weed management. Weed Technol. 23: 391-397.

Ferrell, J. A., W. K Vencill, K Xia, and T. L. Grey. 2005. Sorption and desorption of
ﬂumioxazin to soil, clay minerals and ion-exchange resin. Pest Manag. Sci.
61:40-46.

Ferreira, J. A., O. R. Nascimento, and L. Martin-Neto. 2001. Hydrophobic interactions
between spin-label 5-sasl and humic acid as revealed by esr spectroscopy.
Environ. Sci. and Technol. 352761-765.

Goyal, S., K Chander, M. C. Mundra, and K K Kapoor. 1999. Inﬂuence of inorganic
fertilizers and organic amendemtns on soil organic matter and soil microbial

properties under tropical conditions. Biol. Fert. Soils 29:196-200.

Grey, T. L. and G. R. Wehtje. 2005. Residual herbicide weed control systems in peanut.
Weed Technol. 19:560-567.

53

Hance, R. J. 1980. Transport in the vapor phase. pp 59-82 in R.J. Hance, ed. Interactions
between herbicides and the soil. New York: Academic Press.

Hurle, K and A. Walker. 1980. Persistence and its prediction. pp 83-122 in R.J. Hance,
ed. Interactions between herbicides and the soil. New York: Academic Press.

Kah, M. and C. D. Brown. 2006. Absorption of ionisable pesticides in soils. Rev.
Environ. Contam. Toxicol. 188:149-217.

Koskinen, W. C. and T. B. Moorman. 1992. Effect of soil properties and processes on
herbicide performance. pp 365-402 in McWhorter, C. G. and J. R. Abernathy, eds.
Weeds of cotton: characterization and control. Tennessee: The Cotton
Foundation.

Kwon, J ., K L. Armbrust, and T. L. Grey. 2004. Hydrolysis and photolysis of
ﬂumioxazin in aqueous buffer solutions. Pest Manag. Sci. 60:939-943.

Monaco, T. J., S. C.hWeller, and F. M. Ashton, eds. 2002. Weed science principles and
practices, 4t ed. pp 127-145. New York: John Wiley & Sons, Inc.

Mueller-Warrant, G. W. 1999. Duration of control from preemergence herbicides for
use in nonbumed grass seed crops. Weed Technol. 13: 439-449.

Norsworthy, J. K, M. McClelland, and G. M. Gn'fﬁth. 2009. Conyza canadensis (1.)
cronquist response to pre-plant application of residual herbicides in cotton

(Gossypium hirsutum L.). Crop Prot. 28:62-67.

Peter, C. J. and J. B. Weber. 1985. Adsorption, mobility, and efficacy of alachlor and
metolachlor as inﬂuenced by soil properties. Weed Sci. 33:874-881.

Ratkowsky, D. A. 1990. Handbook of nonlinear regression models. New York: Marcel
Dekker.

Scott, H. D. and R. E. Phillips. 1971. Diffusion of herbicides to seed. Weed Sci. 19:128-
132.

Seefeldt, S. S., J. E. Jensen, and E. P. Fuerst. 1995. Log-logistic analysis of herbicide
dose-response relationships. Weed Technol. 9:218-227.

Senseman, S. A, ed. 2007. Herbicide Handbook. 9th ed. Kansas: Weed Sci. Soc. of
America.

Taylor-Lovell, S., L. M. Wax, and G. Bollero. 2002. Preemergence ﬂumioxazin and

pendimethalin and postemergence herbicide systems for soybean (Glycine max).
Weed Technol. 16:502-511.

54

Torrents, A. and S. Jayasundera. 1997. The sorption of non-ionic pesticides onto clay
and the inﬂuence of natural organic carbon. Chemosphere 7:1549-1565.

Torstensson, L. 1980. Role of microorganisms in decomposition. pp 159-178 in R.J.

Hance, ed. Interactions between herbicides and the soil. New York: Academic
Press.

Walker, A. 1980. Activity and Selectivity in the ﬁeld. pp 203-222 in R.J. Hance, ed.
Interactions between herbicides and the soil. New York: Academic Press.

Walker, A. and C. R. Austin. 2003. Effect of recent cropping history and herbicide use
on degradation rates of isoproturon in soils. Eur. Weed Res. 44:5-11.

55

CHAPTER 4

TOLERANCE OF POTATO MINI-TUBERS TO PREEMERGENCE AND
POSTEMERGENCE HERBICIDES

Abstract: Current cultural practices for producing potatoes from mini-tubers are adopted
from potatoes grown from cut seed pieces, including weed management programs. Mini-
tubers are physiologically different from cut seed pieces and may differ intolerance to
herbicides labeled for potatoes. Field trials were conducted at the Montcalm Research
Farm near Entrican, MI in 2008 and 2009 to evaluate the effect of herbicides labeled for
potatoes on three cultivars of potato mini-tubers. Preemergence treatments of S-
metolachlor plus linuron caused chlorosis injury in both years whereas rimsulﬁJron and
dimethenamid-p only caused injury in 2009. Imazosulfuron applied preemergence and
treatments containing postemergence application ofrimsulfuron with or without
metribuzin following preemergence applications of S-metolachlor plus linuron reduced
yields in 2008 and 2009, while in 2009, treatments of dimethenamid-p, S—metolachlor,
pyrasulfatole and pendimethalin alone reduced yields. Results from this study indicate
greater yield losses when multiple stress factors are present. Several herbicides including
linuron, metribuzin, and rimsulﬁlron were observed to be safe for plants grown from
mini-tubers when applied preemergence.

Nomenclature: Dimethenamid-p; glyphosate; imazosulfuron; pyrasulfatole; linuron;
metribuzin; potato, Solanum tuberosum; rimsulﬁ1ron;S-metolachlor.

Key Words: sensitivty, plant stress, delayed preemergence treatment.

56

 

INTRODUCTION

Unique to potato production is the utilization of whole or cut potato tubers as the
seed source for commercial production. Potato plants grown from tuber pieces have
increased vigor as compared to plants grown from true seed and additional beneﬁts such
as production of “true-to-type” plants (Struik and Wiersema 1999). However, potato
tuber pieces may harbor harmﬁJl pathogens such as Phytophthora infestans (late blight)
and potato virus Y (PVY) (Allen et al. 1992; Bus and Wustman 2007; Whitworth and
Davidson 2008). Planting infected tuber pieces may result in the spread of disease.
Depending on the infection cycle of the pathogen, the spread of disease can be inﬂuenced
by cultural practices and the incidence of insect pests. PVY can rapidly spread via aphid
vectors (Basky and Almasi 2005; Valkonen 2007) increasing the importance of removing
contaminated seed. Potato seed certiﬁcation programs to regulate the sale and production
of seed potatoes.

Technological advancements and increased availability of tissue culture have
allowed for the production of in vitro plantlets to create pathogen free pre-nuclear (seed
planted to generate nuclear or ﬁrst generation seed) plant material (Struik and Wiersema
1999). Over time, production of early generation material has changed and potato
plantlets are now used to produce micro and mini-tubers as the preferred initial seed
source for commercial production. Production of potato mini-tubers has received much
attention and consideration, resulting in research with the intent to maximize production
and quality of mini-tubers (Ranalli et al. 1994; Struik and Lommen 1999). Although
mini-tubers are similar to cut seed pieces used in production, there are unique difﬁculties

in utilizing them. Researchers have observed agronomic differences when planting mini-

57

tubers as opposed to cut seed pieces, such as reduced stem number, delayed emergence,
and reduced canopy closure (Struik and Lommen 1999). Research done by Ranalli et al.
(1994) showed that 51 days aﬂer planting plants grown ﬁ‘om mini-tubers provided only
37.8% canopy closure, 34.6% less cover than plants grown from cut seed pieces reducing
the crops ability to compete with weeds (Monaco et al. 2002). The potato plants are less
able to compete with weeds due to the reduction in the crops growth. This makes
preemergence and postemergence applications of herbicides often a necessity.
Preemergence and postemergence herbicide applications are effective methods of
weed control. Researchers have noted injury and yield reductions caused by several
herbicides (Bailey et al. 2002; Richardson et al. 2004; Hutchinson et al. 2005; Hutchinson
et al. 2006) this indicates the importance of careﬁil herbicide selection to control weeds
and reduce crop injury to maximize yield. Potato cultivars have variable sensitivity to
herbicides attributed to differences in absorption, translocation, or metabolism of the
herbicide (Hinks 1977; Bailey et al. 2003). Herbicide sensitivity, speciﬁcally to
metribuzin, has been reported to be an inheritable trait with a relative high frequency in
selected progeny making it a prevalent recurring trait (De Jong 1983). Metribuzin was
reported by Friesen and Wall (1984) to cause injury and yield reductions of 22 different
potato cultivars including reduced yields of the cultivar ‘Alaska Red’ by 68% with
preemergence applications of metribuzin at 1 kg ai/ha. Cultivar sensitivity was reported
by Hutchinson et a1. (2005) of the cultivar ‘Ranger Russet’ to preemergence applications
of ﬂumioxazin ﬁ'om 53 to 140 g ai/ha, which caused total yield reductions of l 3 to 20%.
Cultivar sensitivity adds difﬁculty in managing weeds in potatoes due to potential yield

reductions which limit the already small number of herbicides available for them.

58

 

‘\7_1..-"—‘_‘n 4 - 5.4

The physiological differences of potato mini-tubers from cut seed pieces have
been recognized as a concern by researchers when utilizing cut seed piece management
practices (Lommen and Struik 1994; Ranalli et al. 1994; Struik and Lommen 1999).
Mini-tubers have a lower level of carbohydrate reserves and a greater surface area to
volume ratio when compared to cut seed pieces. These differences have been found to
cause plants grown from mini-tubers to emerge later (Ranalli et a1. 1994; Struik and
Lommen 1999), have generally only one stem (Ahloowalia 1994; Struik and Lommen
1999), and produce smaller sprouts (Lommen 1994). Mini-tubers producing smaller
sprouts and plants which are less vigorous could be more susceptible to herbicide injury
(Scott and Phillips 1971 ). A study was designed to evaluate the various effects
herbicides have on yield and quality of seed potatoes produced by mini-tubers and

whether potato mini-tubers exhibit cultivar sensitivity to herbicides.

MATERIALS AND METHODS

Field trials were conducted in 2008 and 2009 at the Montcalm Research Farm in
Entrican, MI. Soil type at the farm was a Montcalm and McBride loamy sand and sandy
loam (mesic Haplic Glossudalf) with a soil pH of 5.6 and organic matter content of 1.5%
with the previous crop in both years being ﬁeld corn. Spring tillage consisted of disking
three times and ﬁeld cultivating prior to planting. Cultivars planted were ‘Atlantic’, and
2 Frito-Lay (FL) cultivars ‘FLl ’ and ‘F L2’, which are chipping cultivars commercially
planted in Michigan. Mini-tubers planted each year were generated from the same
producer and averaged 1.5 to 2 cm in diameter. Mini-tubers were planted on May 12,

2008 and on May 11, 2009 with a one row plot planter into rows 86.4 cm apart, 6.4 cm

59

deep, at 20.3 cm spacing. Plots were 6.1 m by 2.6 m in dimension containing 3 rows per
plot. Plots were billed in both years before early bulking (9 wks after planting) and
maintained weed ﬁ'ee by hand weeding to ensure effects observed were due to treatments
and not weed competition. Supplemental irrigation was applied using a center pivot
system and fertilizer was applied according to Michigan State University
recommendations (Warncke et al. 2009). The experimental design was a randomized

complete split-strip block with 4 replications with whole plot factor as herbicide

treatment and sub plot factor as cultivar. Herbicide treatments were applied with a C02-

pressurized backpack sprayer delivering 187 L/ha at rates recommended for use in
Michigan (Table 6). Preemergence herbicides were applied as a delayed application on
May 28, 2008 and May 29, 2009. Postemergence treatments were applied on June 24,
2008 and July 8, 2009.

Injury ratings were visually assessed 1, 2, and 4 wks after preemergence
application and rated 1 and 2 wks after postemergence application on a 0—100% scale
with 0% corresponding to no injury and 100% being plant death (Frans et al. 1986).
Potatoes were harvested on September 18, 2008 and on September 10, 2009. Yield was
determined from 3 m of the 6.1 m row. Tubers were graded by yield and quantity of US
#l tubers (3.8cm —- 8.3cm in diameter and less than 340g), smaller than US #1, larger than
US #1 and tubers with defects. Data was analyzed using the MIXED procedure in SAS
at a 0.05 signiﬁcance level with treatment means separated by Fisher’s Protected LSD.
ANOVA assumptions of normality of data were met by arcsine square root transforming
injury ratings and log transforming non-normal yield data. Non-transformed means are

presented for clarity.

60

RESULTS AND DISCUSSION

Crop emergence and development varied in 2008 and 2009 due to mini-tuber
dormancy and below average temperatures in 2009. Crop emergence was variable by
cultivar in both 2008 and 2009. Emergence of the FL lines in 2008 was similar 1 wk
after preemergence herbicide applications, but differed in their emergence relative to each
other in 2009 (Table 7). The Atlantic cultivar in 2008 had yet to emerge 1 wk after
preemergence herbicide application, whereas in 2009 were almost fully emerged (Table
7). Early season grth was similar in 2008 and 2009. However, in 2009 Michigan
experienced its second coldest July and growing degree day accumulation after June until
crop senescence was on average 150 units less than in 2008. Overall, less than ideal
growing conditions in 2009 caused irregular crop growth and delayed postemergence

applications by 2 wks compared to 2008.

Crop Injury. Signiﬁcant year by treatment interactions were observed for all injury
ratings. Additionally a year by treatment by cultivar interaction was observed for injury
2 wks after emergence in 2008. Injury observed in both years for all treatments consisted
of leaf chlorosis and malformation of leaf tissue and was signiﬁcant by treatment for 1
and 2 wks aﬂer emergence in both years (Table 8). Injury reported 1 wk after
preemergence application in 2008 does not include the Atlantic cultivar because it had
not emerged.

Greater injury was observed in 2008 than 2009 for most treatments. In 2008, the

greatest injury 1 wk after preemergence application, 16%, was observed following S-

61

metolachlor applied alone whereas in 2009 injury was less than 1% for the same
treatment (Table 8). Injury observed in 2008, 1 wk after preemergence application was
generally higher than injury in 2009 (Table 8). Differences in injury in 2008 and 2009
could be due to delayed emergence of plants in 2009 because of a decrease in
interception of chemical by growing shoots (Bailey et al. 2002). Treatments of linuron,
metribuzin, pendimethalin, rimsulfuron, and imazosulfuron alone caused minimal injury
1 wk after application in both years (Table 8). There was a signiﬁcant interaction of
treatment and cultivar for injury 2 wks after preemergence application in 2008 but not in
2009. This is due to minimal observed injury on the Atlantic cultivar which had delayed
emergence (Table 8). Signiﬁcant amounts of injury were observed with treatments of S-
metolachlor plus linuron in both FL cultivars ranging from 5 to 13% in 2008 and 5 to 8%
in 2009 (Table 8). Similarly, in 2009, 5% injury was observed following application of
rimsulfuron or dimethenamid-p. Early season injury following dimethenamid-p on cut
seed pieces has been previously reported (Richardson et al. 2004). Treatments of linuron,
metribuzin, pendimethalin, and imazosulfuron alone caused no injury 2 wks after
application and through the remainder of the season. Injury in 2008 appeared to be the
greatest 1 wk after preemergence herbicide treatment and decreased slightly 2 wks after
treatment with injury becoming transient by 4 wks. However, injury in 2009 was less
extensive 1 wk after preemergence application and increased in severity at 2 wks.
Although weather differences in years caused variations in the effect of treatments on
potato mini-tubers, treatments of S-metolachlor plus linuron sometimes caused early
season injury while treatments of linuron, metribuzin, pendimethalin, and imazosulfuron

alone caused no signiﬁcant injury early in the season.

62

Crop Yield. Signiﬁcant year by treatment interactions were observed for all yield
parameters measured making analysis by year necessary. Treatment by cultivar
interactions were not signiﬁcant for yield parameters measured thus data were pooled
across cultivars. No signiﬁcant differences in yield or tuber quantity for larger and
smaller than US #1 sized tubers were observed (data not shown). Similarly, no
signiﬁcant differences were observed for tubers categorized as having abnormal growths
or that were odd in shape (data not shown). Herbicide treatment effects on yield of US
#1 tubers were signiﬁcant in both 2008 and 2009 (Table 9). Treatments of metribuzin,
linuron, and rimsulfuron did not reduce yields of US #1 tubers which is consistent with
previous research on cut seed piece potato production (Ackley et al.1996; Renner and
Powell 1998; Bailey et al. 2002). Imazosulfuron reduced yield of US #1 tubers ﬁ‘om the
highest yielding treatment by 41.2% and 20.3% in 2008 and 2009 respectively.
Reductions of US #1 tuber yield by imazosulfuron are most likely due to its effect on
tuber yield per plant since it reduced tuber count per plant by 30.4% compared to the
highest yielding treatment (Table 9). Although yields of US #1 tubers were reduced both
years by imazosulﬁiron, in neither year was visual injury greater than 2%. Early season
injury was observed in both years by treatments of S-metolachlor plus linuron applied
together. However, yield reductions were only observed when S-metolachlor plus
linuron was followed by 'a postemergence application of rimsulfuron alone or with
metribuzin in 2008, and only when followed by rimsulfuron plus metribuzin in 2009. US

#1 tuber yield per plant wuld account for yield reductions observed in 2008 due to S-

63

metolachlor plus linuron followed by rimsulfuron plus metribuzin which reduced tuber
count by 23.9% compared to the highest yielding treatment.

Compared to the highest yielding treatment in 2009, root or shoot inhibitors
including dimethenamid-p, pyrasulfatole, S-metolachlor, and pendimethalin applied alone
reduced yields of US #1 tubers from 14.7% to 22.5% and was not consistent with early
season injury. Root or shoot growth inhibitors when applied in combination with other
herbicides also reduced yields of US #1 tubers in 2009 with the exception of S-
metolachlor when applied with linuron plus metribuzin. S-metolachlor plus metribuzin
plus pendimethalin with or without glyphosate caused the greatest yield reductions of US
#1 tubers in 2009 at 24.2 and 25.5%, respectively, indicating that the combination of root
and shoot growth inhibitors had a negative effect. Although tuber yield per plant was not
signiﬁcant in 2009, all treatments that reduced yields of US #1 tubers compared to the
highest yielding treatment had 14.3 to 21.4% fewer tubers suggesting that yield
reductions could be due to plants yielding fewer tubers. Total tuber yield and total
number of tubers per plant were similar to treatment effects on yield and quantity of US
#1 tubers (Table 10). Similarities in treatment effects on tuber yield and quantity of all
tubers and US #1 tubers is important to note, due to implications on marketing the seed
produced. If treatments affect only total yields and not US #1 tuber yields, a grower
would still have the same amount of certiﬁed seed to sell. However, if treatments reduce
the total yield and yield of US #1 tubers similarly, the grower would overall have less
certiﬁed seed to market.

Despite large differences in years due to weather patterns, noticeable trends were

observed in both years. Treatments of linuron, metribuzin, and rimsulfuron when applied

64

alone were safe for weed management in potato mini-tubers, whereas imazosulfuron
caused yield reductions. The varieties tested did not show signiﬁcant differences in yield
response to herbicide treatments in either year. Similarly, varieties tested in our study
have not been reported to have differential sensitivity to herbicides when grown from cut
seed pieces and only represent round chipping varieties. Further research needs to be
conducted on additional varieties to determine if correlations are present for varietal
sensitivity of mini-tubers and cut seed pieces.

Yield reductions in 2008 were only observed where S-metolachlor plus linuron
were followed by a postemergence herbicide application of rimsulﬁiron alone or with
metribuzin. However, in 2009 preemergence treatments containing root or shoot grth
inhibitors reduced yields which could be due to herbicide phytotoxicity early in the
season that was exaggerated by a cool growing season. Although yields were reduced by
several treatments, herbicides alone and in combination are still warranted for use in
mini-tubers to control weeds due to limited options and the need for season long control.
Use of multiple modes of herbicide action for weed control in potatoes is becoming
increasingly important as frequency of weed resistance is increasing due to long term
dependency on photosystem inhibitors such as metribuzin. Knowing the impacts
herbicides have on crop development will allow growers to manage their potato crop to

maximize economic return.

65

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70

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