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This is to certify that the
dissertation entitled

ROW WIDTH AND PLANT POPULATION EFFECTS ON
GLYPHOSATE-RESISTANT SUGARBEET PRODUCTION IN
MICHIGAN

presented by

Jon-Joseph Quincy Armstrong

has been accepted towards fulﬁllment
of the requirements for the

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ROW WIDTH AND PLANT POPULATION EFFECTS ON GLYPHOSATE-
RESISTANT SUGARBEET PRODUCTION IN MICHIGAN

By

Jon-Joseph Quincy Armstrong

A DISSERTATION

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY
Crop and Soil Sciences

2009

ABSTRACT

ROW WIDTH AND PLANT POPULATION EFFECTS ON GLYPHOSATE-
RESISTANT SUGARBEET PRODUCTION IN MICHIGAN

By
Jon-Joseph Quincy Armstrong

The 2008 commercial release of glyphosate-resistant (GR) sugarbeet provided
growers with the opportunity to achieve excellent control of many weed species common
to sugarbeet production with fewer herbicide active ingredients and fewer applications,
while eliminating the potential for crop injury. GR sugarbeet may allow growers to
reduce or potentially eliminate between-row cultivation and adopt planting in narrow
rows. Field trials were conducted in 2006, 2007, and 2008 at multiple locations in
Michigan to compare canopy cover, yield and quality, and weed control in GR sugarbeet
planted in 38-, 51-, and 76-cm rows widths at plant populations of 54,000; 78,000;
101,000; and 124,000 plants/ha In general, canopy cover developed more rapidly and
was greater in 38- and 51-cm row widths and at higher plant populations. At the Saginaw
Valley locations, GR sugarbeet planted in 51-cm rows produced the highest root yields.
At the East Lansing location, root yields were highest in 38-cm rows compared with 76-
cm rows in 2008. Sugarbeet quality, expressed as recoverable white sucrose per Mg of
root (RWSMg), also increased as plant population increased.

Weed control in GR sugarbeet is affected by row width. Weed population
densities and biomass were lower in narrow rows compared with 76-cm rows following a
single glyphosate application when weeds were 10-cm tall. The greater canopy cover
provided by narrow rows may reduce the number of glyphosate applications necessary

for season-long weed control. When averaged over row width, GR sugarbeet root yield

was similar to yield of the weed-free treatment for all herbicide treatments where
glyphosate was applied when weeds were 10-cm in height or smaller. However, root
yields were reduced when glyphosate applications were delayed until weeds averaged 15-
cm in height. Regardless of row width, initial glyphosate applications should be made
before weeds reach 10-cm in height to maximize yield and minimize weed competition.

The increased cost of GR sugarbeet seed may inﬂuence adoption of narrow row
sugarbeet production. At the Saginaw Valley locations, GR sugarbeet planted in 51 -cm
rows had an increase in gross margin of at least $200/ha compared with 38— and 76-cm
rows, when payment price was adjusted for sugarbeet quality. At East Lansing, gross
margins did not differ among all row widths and plant populations in 2007. In 2008,
plant populations of 78,000; 101,000; and 124,000 plants/ha in 38-cm rows resulted in
the highest gross margins. Despite observed increases in RWSMg at higher plant
populations, results from this analysis suggest that row width has more of an impact on
economic returns for GR sugarbeet production. The highest economic returns were for
sugarbeet planted in narrow rows.

Additional herbicides may be necessary for satisfactory control of weeds that are
more tolerant to glyphosate. In greenhouse trials, triﬂusulfuron was not effective for
control of 5- or 10-cm tall velvetleaf, Powell amaranth, or common lambsquarters. Some
combinations of glyphosate plus triﬂusulfuron were synergistic for weed control. All
combinations of glyphosate and triﬂusulfuron were additive for control of common
lambsquarters. However, triﬂusulfuron plus glyphosate applied to 5- and 10-cm weeds

did not improve weed control beyond using glyphosate alone at 840 g/ha.

ACKNOWLEDGMENTS

I wish to thank Dr. Christy Sprague for serving as my major professor for my
doctoral studies at Michigan State University. Michigan’s agricultural industry is lucky
to have someone as professional and devoted as Dr. Sprague and I feel very privileged to
have studied and completed my research under her guidance. I also thank Dr. Don
Penner, Dr. Karen Renner, and Dr. Scott Swinton for serving on my guidance committee
and sharing their research, teaching, and extension expertise and experiences with me.

I would also like to extend a special thank you to Gary Powell and Erin Taylor for
their assistance in the ﬁeld, lab, greenhouse, and ofﬁce. Their dedication, attention to
detail, and wonderful personalities are key reasons for the success of our research team.
As well, Paul Horny and Dennis Fleischman at the Saginaw Valley Bean and Beet
Research Farm were also very helpful and have been vital contributors to the MSU weed
science program. I am also very appreciative of Jim Stewart, Lee Hubbell, Corey Guza,
and the Michigan Sugar Company for coordinating the on-farm trials and providing the
necessary labor and funding to complete this research.

Many graduate and undergraduate students have also been great help with my
research. Scott Bolhnan, Kelly Barnett, Molly Buckham, Anthony Satkowiak, Alyn Kiel,
Megan Ross, Anna Timmerman, Michelle Cole, Kent Kim, Marc Hasenick, and Dave
Reif have all been excellent labmates and ﬁ'iends and made the work easy and enjoyable.

Finally, I wish to thank my wife, Eleri, for being a constant source of
encouragement during my studies. I am eternally grateful for her love, support, and
positive attitude that she shared with me during our time at MSU and I look forward to

our future adventures together.

iv

TABLE OF CONTENTS

LIST OF TABLES .................................................................................................... vii
LIST OF FIGURES ..................................................................................................... x
CHAPTER 1
LITERATURE REVIEW
INTRODUCTION ............................................................................................. 1
WEED CONTROL IN SUGARBEET ............................................................... 1
GLYPHOSATE-RESISTANT CROPS .............................................................. 3
GLYPHOSATE-RESISTANT SUGARBEET ................................................... 3
Row width and plant population effects .................................................. 4
Glyphosate application timing ................................................................ 7
Economic considerations ........................................................................ 8
Potential tank-mix partner with glyphosate ............................................. 9
LITERATURE CITED .................................................................................... 11
CHAPTER 2

INFLUENCE OF ROW WIDTH AND PLANT POPULATION ON WEED
GROWTH AND YIELD IN GLYPHOSATE-RESISTANT SUGARBEET

ABSTRACT .................................................................................................... 15
INTRODUCTION ........................................................................................... 16
MATERIALS AND METHODS ..................................................................... 19
RESULTS AND DISCUSSION ....................................................................... 22
Crop canopy development .................................................................... 22
Weed density and biomass ................................................................... 24
Sugarbeet root yield and quality ........................................................... 25
SOURCES OF MATERIALS .......................................................................... 28
LITERATURE CITED .................................................................................... 42
CHAPTER 3
WEED MANAGEMENT IN WIDE- AND NARROW-ROW GLYPHOSTATE
RESISTANT SUGARBEET
ABSTRACT .................................................................................................... 44
INTRODUCTION ........................................................................................... 45
MATERIALS AND METHODS ..................................................................... 47
RESULTS AND DISCUSSION ....................................................................... 50
Weed density and biomass ................................................................... 50
Sugarbeet root yield and quality ........................................................... 52
SOURCES OF MATERIALS .......................................................................... 53
LITERATURE CITED .................................................................................... 59

CHAPTER 4
ADJUSTMENTS IN PLANTING PRACTICES TO MAXIMIZE ECONOMIC
RETURN IN GLYPHOSATE-RESISTANT SUGARBEET

ABSTRACT .................................................................................................... 61

INTRODUCTION ........................................................................................... 62

MATERIALS AND METHODS ..................................................................... 65

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

SOURCES OF MATERIALS .......................................................................... 71

LITERATURE CITED .................................................................................... 78
CHAPTER 5

GLYPHOSATE AND TRIFLUSULFURON COMBINATIONS FOR CONTROL
OF VELVETLEAF, POWELL AMARANTH, AND COMMON

LAMBSQUARTERS

ABSTRACT .................................................................................................... 79
INTRODUCTION ........................................................................................... 80
MATERIALS AND METHODS ..................................................................... 81
RESULTS AND DISCUSSION ....................................................................... 83

Velvetleaf ............................................................................................. 83

Powell amaranth ................................................................................... 84

Common lambsquarters ........................................................................ 85
SOURCES OF MATERIALS .......................................................................... 86
LITERATURE CITED .................................................................................... 91

vi

LIST OF TABLES

CHAPTER 2
INFLUENCE OF ROW WIDTH AND PLANT POPULATION ON WEED
GROWTH AND YIELD IN GLYPHOSATE-RESISTANT SUGARBEET

Table 1. Within-row plant spacing and the number of plants/30-m of row for
glyphosate-resistant sugarbeet planted in three row widths and at four plant
populations. ..................................................................................................... 29

Table 2. Monthly and 30-yr average precipitation at the Saginaw Valley Bean
and Beet Research Farm near St. Charles in 2006, 2007, and 2008 and at East
Lansing in 2007 and 2008. ............................................................................... 30

Table 3. Weed population density and biomass in untreated plots in 2007 at the
Saginaw Valley locations and East Lansing location. Data are presented as main
effects since row width by plant population interaction was not signiﬁcant. ..... 31

Table 4. Weed population density and biomass in plots which received a single
glyphosate application when weeds were lO-cm in height in 2008 at the Saginaw
Valley locations and East Lansing location. Data are presented separately for
main effects since the interaction between row width and plant population was not
signiﬁcant. ....................................................................................................... 32

Table 5. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet
planted in two row widths at three populations at the Saginaw Valley Bean and
Beet Research Farm in 2006. Data are presented separately for main effects since
the interaction between row width and plant population was not signiﬁcant. 33

Table 6. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in
three row widths at four populations at the Saginaw Valley locations in 2007 and
2008. Data were combined across years and are presented separately for main
effects since the interaction between row width and plant population was not
signiﬁcant. ....................................................................................................... 34

Table 7. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in
two row widths at the East Lansing location. Data were combined across plant
populations. ..................................................................................................... 35

vii

Table 8. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in
four plant populations at the East Lansing location. Data were combined across
row widths. ...................................................................................................... 36

CHAPTER 3
WEED MANAGEMENT IN WIDE- AND NARROW-ROW GLYPHOSTATE
RESISTANT SUGARBEET

Table 9. Herbicide treatments, rates, and application timings in glyphosate-
resistant sugarbeet. ........................................................................................... 54

Table 10. Weed populations and biomass for herbicide treatments when averaged
over row width at the Saginaw Valley locations where 38-, 51- and 76-cm row
widths were compared and at the East Lansing location where 38- and 76-cm row
widths were compared. Data were pooled over 2007 and 2008 for the respective
locations. ......................................................................................................... 55

Table 11. Weed populations and biomass following a single glyphosate
application when weeds were 10-cm tall at the Saginaw Valley locations where
38-, 51- and 76-cm row widths were compared and at the East Lansing location
where 38- and 76-cm row widths were compared. Data were pooled over 2007
and 2008 for the respective locations. .............................................................. 56

Table 12. Sugarbeet root yield, recoverable white sucrose per Mg of root
(RWSMg), and recoverable white sucrose per hectare (RWSH) for herbicide
treatment when averaged over row width at the Saginaw Valley locations where
38-, 51— and 76-cm row widths were compared and at the East Lansing location
where 38- and 76-cm row widths were compared. Data were pooled over 2007
and 2008 for the respective locations. .............................................................. 57

Table 13. Sugarbeet root yield, recoverable white sucrose per Mg of root
(RWSMg), and recoverable white sucrose per hectare (RWSH) for row width
when averaged over herbicide treatment at the Saginaw Valley locations where
38-, 51- and 76-cm row widths were compared and at the East Lansing location
where 38- and 76-cm row widths were compared. Data were pooled over 2007
and 2008 for the respective locations. .............................................................. 58

CHAPTER 4
ADJUSTMENTS IN PLANTING PRACTICES TO MAXIMIZE ECONOMIC
RETURN IN GLYPHOSATE-RESISTANT SUGARBEET

Table I4. Within-row plant spacing and number of plants per 30-m of row for
glyphosate-resistant sugarbeet in three row widths and four plant populations. . 72

viii

Table 15. Summary of expenses used in the partial budget analysis comparing
glyphosate-resistant sugarbeet planted in three row widths and four plant
populations. A base price of $44/Mg of sugarbeet root was assumed. .............. 73

Table I 6. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
gross margins for glyphosate-resistant sugarbeet in three row widths and four
plant populations at the Saginaw Valley locations in 2007 and 2008. ............... 74

Table I 7. Root yield and recoverable white sucrose per Mg of root (RWSMg) for
glyphosate-resistant sugarbeet in two row widths at East Lansing in 2007 and
2008. ............................................................................................................... 75

Table 18. Root yield and recoverable white sucrose per Mg of root (RWSMg) for
glyphosate-resistant sugarbeet in four plant populations at East Lansing in 2007

and 2008. ......................................................................................................... 76

Table 19. Gross margins for glyphosate-resistant sugarbeet in two row widths

and four plant populations at East Lansing in 2007 and 2008. .......................... 77
CHAPTER 5

GLYPHOSATE AND TRIFLUSULFURON COMBINATIONS FOR CONTROL
OF VELVETLEAF, POWELL AMARANTH, AND COMMON
LAMBSQUARTERS

Table 20. Visual estimates of weed control compared to the untreated control 14
days after treatment for combinations of triﬂusulfuron and glyphosate for
velvetleaf, Powell amaranth, and common lambsquarters 5-cm tall at time of
application. ...................................................................................................... 87

Table 21. Dry weight reduction compared to the untreated control 14 days after
treatment for combinations of triﬂusulfuron and glyphosate for velvetleaf, Powell
amaranth, and common lambsquarters 5-cm tall at time of application. ............ 88

Table 22. Visual estimates of weed control compared to the untreated control 14
days after treatment for combinations of triﬂusulfuron and glyphosate for
velvetleaf, Powell amaranth, and common lambsquarters 10—cm tall at time of
application. ...................................................................................................... 89

Table 23. Dry weight reduction compared to the untreated control 14 days after

treatment for combinations of triﬂusulfuron and glyphosate for velvetleaf, Powell
amaranth, and common lambsquarters 10-cm tall at time of application. ...... 90

ix

LIST OF FIGURES

CHAPTER 2
INFLUENCE OF ROW WIDTH AND PLANT POPULATION ON WEED
GROWTH AND YIELD IN GLYPHOSATE-RESISTANT SUGARBEET

Figure I. Canopy cover development for glyphosate-resistant sugarbeet planted
in (a) 38-(0) and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I),
and 101 ,000 p1ants/ha(<>) at the Saginaw Valley Bean and Beet Research Farm in
2006. Vertical bars represent Fisher’s protected LSD at the p = 0.05 signiﬁcance
level. NS = not signiﬁcant. .............................................................................. 37

Figure 2. Canopy cover development for glyphosate-resistant sugarbeet planted
in (a) 38- (o), 51- (I), and 76-cm rows (0) and (b) populations of 54,000 (0),
78,000 (I), 101,000 (0), and 124,000 plants/ha (A) at the Saginaw Valley
locations in 2007. Vertical bars represent Fisher’s protected LSD at the p = 0.05
signiﬁcance level. NS = not signiﬁcant. ........................................................... 38

Figure 3. Canopy cover development for glyphosate-resistant sugarbeet planted
in (a) 38- (O), 51- (I), and 76-cm rows (0) and (b) populations of 54,000 (D),
78,000 (I), 101,000 (0), and 124,000 plants/ha (A) at the Saginaw Valley
locations in 2008. Vertical bars represent Fisher’s protected LSD at the p = 0.05
signiﬁcance level. NS = not signiﬁcant. .......................................................... 39

Figure 4. Canopy cover development for glyphosate-resistant sugarbeet planted
in (a) 38-(0) and 76—cm rows (0) and (b) populations of 54,00- (0), 78,000 (I),
101,000 (0), and 124,000 plants/ha (A) at East Lansing in 2007. NS = not
signiﬁcant. ....................................................................................................... 40

Figure 5. Canopy cover development for glyphosate-resistant sugarbeet planted
in (a) 38-(0) and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I),
101,000 (0), and 124,000 plants/ha (A) at East Lansing in 2008. NS = not
signiﬁcant. ....................................................................................................... 41

CHAPTER 1

LITERATURE REVIEW

INTRODUCTION

Sugarbeet (Beta vulgaris L.), a member of the Chenopodiaceae family, is a
biennial crop that is planted in early spring in most production regions. In the fall, before
reproductive growth occurs, aboveground leaf grth is removed. Sugarbeet roots are
then harvested and processed for sucrose production. In addition to sugar cane
(Saccharum spp.), sugarbeet is one of the primary sources of sucrose in the United States.
Sugarbeet was planted on an average of 544,000 hectares per year in the United States
from 2000 to 2008 and total crop production was valued at over one billion dollars per
year. Michigan is the fourth largest producer of sugarbeet in the United States and
sugarbeet was grown on approximately 55,000 hectares in Michigan in 2008 (USDA-

NASS 2009).

WEED CONTROL IN SUGARBEET
Weed control is often listed by sugarbeet producers as the most serious production
problem they face (Carlson et a1. 2008). Historically, growers have had few options for
efﬁcient and efﬁcacious weed control in sugarbeet. Until the early 19705, chemical weed
control options were limited mostly to herbicides applied and incorporated prior to
planting. These herbicides included cycloate, EPTC, and pyrazon (Schweizer and Dexter
1987). Growers also relied heavily on mechanical cultivation and hand labor to control

weeds, because few chemical weed control programs provided sufﬁcient control

(Grifﬁths 1994). In the mid-19603, the herbicides phenmedipham and desmedipham
were introduced (and later sold together as a premix). These herbicides provided growers
with additional options for postemergence weed control. Though these products were
used extensively, crop injury was a major concern when applied at labeled rates of 1.1 to
1.7 kg ai/ha. In the late 19708, research was conducted investigating applications of the
combination of phenmedipham + desmedipham split into two lower-rate applications
(“standard split”) of 0.56 or 0.84 kg ai/ha applied ﬁve to seven days apart. Split
applications reduced crop injury, especially when beets were at the cotyledon to 2-leaf
growth stage, and improved weed control (Dexter 1994). In 1998, reduced rate, or
“micro-rate,” herbicide programs were introduced (Dale et aI 2006). Micro-rate
programs included phenmedipham + desmedipham (0.045 + 0.045 kg ai/ha) plus
triﬂusulﬁlron (0.004 kg tha) plus clopyralid (0.023 kg ai/ha) plus methylated seed oil
(MSO) (1.5% v/v). Micro-rate applications provide good to excellent weed control while
minimizing crop injury. However, applications had to be made in a timely manner to
ensure satisfactory control. The ﬁrst micro-rate application needed to be made when
weeds are in the cotyledon growth stage, or less than 0.3-cm in height, with two to four
subsequent micro-rate applications generally made every ﬁve to seven days (Dale and
Renner 2005). Another beneﬁt of the micro-rate herbicide program is that growers can
make applications any time during the day, as opposed to standard-split herbicide
program applications which must be made in the late afternoon or evening to avoid
causing signiﬁcant crop injury (Dale and Renner 2006). Additionally, because micro-rate

applications are often broadcast applied, between-row cultivations were reduced. In fact,

in eastern North Dakota and Minnesota between—row cultivations decreased from an

average of 2.4 cultivations per ﬁeld per year in 1998 to 1.7 in 2006 (Carlson et a1. 2008).

GLYPHOSATE-RESIST ANT CROPS

Corn (Zea mays L.), soybean (Glycine max [L.] Merr.), cotton (Gossypium
hirsutum L.), canola (Brassica rapa L.), and alfalfa (Medicago sativa L.) are all
commonly grown agronomic crops that have been engineered to be resistant to
glyphosate. Many of these crops were rapidly adopted after their respective commercial
releases and are now used extensively in the United States. Glyphosate-resistant soybean
was commercially released in the United States in 1996. Adoption of glyphosate-
resistant soybean increased from 54% of the total soybean hectares in the US in 2000 to
92% in 2008 (U SDA-NASS 2008). Adoption of herbicide-resistant corn has progressed
in a similar manner, increasing from 7% of total corn acreage in 2000 to 63% in 2008
(U SDA-NASS 2008). Similarly, adoption of glyphosate-resistant sugarbeet varieties is
expected to be very rapid. In Michigan, approximately half of the sugarbeet area in 2008
was planted to glyphosate-resistant varieties. This adoption was limited primarily by the
availability of glyphosate-resistant seed. It is expected that over 90% of the sugarbeet
hectares in Michigan will be planted with glyphosate-resistant sugarbeet varieties in 2009

(C. Guza, personal communication).

GLYPHOSATE-RESISTANT SUGARBEET
Glyphosate-resistant sugarbeet will provide growers the opportunity to achieve

excellent control of many weed species common to sugarbeet production with fewer

herbicide active ingredients and applications, while eliminating the potential for crop
injury (Wilson et a1. 2002). In previous studies, glyphosate has provided excellent
control of many weed species with two or three glyphosate applications (Guza et a1.
2002; Kniss et a1. 2004; Wilson et a]. 2002). Additionally, the time between herbicide
applications may be longer with glyphosate-resistant sugarbeet compared with
conventional sugarbeet herbicide programs, as weed height at time of application is
generally not as limiting with glyphosate. Growers will also have a herbicide option for
weeds that have developed resistance to one or more of the conventional sugarbeet
herbicides.

Similar to trends of improved weed control following the adoption of micro-rate
applications, growers may be able to reduce or potentially eliminate between-row
cultivation with the use of glyphosate-resistant sugarbeet. Previous research has shown
that between-row cultivation, in the absence of weeds, does not improve sugarbeet yield
or quality (Dexter et a1. 1999). As a result, growers may be able to adopt narrow-row

planting practices.

Row width and plant population eﬂects. Numerous studies on the effect of row width and
plant population on crop yield have been conducted with many agronomic crops. Results
of these studies have been somewhat inconsistent and vary among crops; however, the
general outcome trends towards increased yields in narrower rows due to increased light
radiation interception (Andrade et al. 2002). Widdicombe and T helen (2002) reported
corn grain yields were highest in 38-cm rows compared with 56— and 76-cm rows. They

also reported grain yields were highest at the highest plant population. However, there

was no interaction between row width and plant population, indicating that yield
increases in narrow rows occurred across all plant populations. Johnson and Hoverstad
(2002) also reported higher corn yields when com was planted in 51-cm rows compared
with 76-cm rows in two of three years. Higher yields have also been reported in soybean
planted in narrow rows. Harder et al. (2007) observed higher grain yields in 19- and 38-
cm rows compared with 76-cm rows at each of four populations. However, not all
studies have shown increased yields in narrow rows. Pedersen and Lauer (2003)
compared yields in corn and soybean that were planted in 19-, 38-, and 76-cm rows and
found that the highest yield in corn was in 38- and 76-cm rows for corn and there were no
differences in yield among the three soybean row widths.

Faster and more complete canopy cover can occur for crops planted in narrow
rows. The greater canopy cover can also provide more shade of bare soil between rows,
thereby reducing late-season weed emergence and growth (Johnson and Haverstad 2002).
Yelverton and Coble (1991) observed a signiﬁcant decrease in weed density and biomass
in soybean planted in narrows rows compared with wide rows. Dalley et al. (2004b) also
observed similar results of reduced weed biomass in narrow-row soybean. In three of
four years, soybean planted in 19- and 38-cm rows had signiﬁcantly less weed growth
after an initial glyphosate application at 10-cm weeds compared with 76-cm rows. In
both studies, the reduction in weed grth was attributed to the greater canopy cover
provided by the narrow rows.

Sugarbeet is typically grown in row widths that range from 56- to 76-cm. In the
Red River Valley production area of northwestern Minnesota and eastern North Dakota,

97% of the sugarbeet hectares are planted in 56-cm rows (Grove et al. 2007). In

Michigan, a majority of the sugarbeet hectares are planted using 71- or 76-cm rows.
Similar to results from corn and soybean, previous research has shown a trend toward
increased sugarbeet yield when planted in narrow rows. Yonts and Smith (1997) found
that the highest sugar yield was obtained with 56-cm rows, when compared with 35- and
76-cm rows. Stebbing et al. (2000) showed an increase in root and sugar yield
(recoverable white sugar per hectare) with 46-cm rows compared with 56- and 76-cm
rows in one of two years. The authors attributed yield increases in 46-cm rows to
reduced intra-plant competition due to more spacing between plants within the row. In
addition to increased yield, sugarbeet planted in narrow rows can provide greater canopy
cover to suppress weed growth Alford et al. (2004) reported that weed biomass averaged
over multiple herbicide treatments was reduced signiﬁcantly when sugarbeet was planted
in 38- and 56-cm rows compared with 76-cm rows, due to earlier and greater canopy
cover in the narrow row widths.

Planting sugarbeet in narrow row widths also allows for higher plant populations
per area. These differences in within- and across-row plant spacing can have an effect on
both sugarbeet yield and quality. Due to the reduced space between plants within the row
and resulting smaller growth of each individual beet, a trend toward higher sucrose
concentrations can be observed at higher plant populations (Yonts and Smith 1997).
However, sucrose concentrations can also plateau at sugarbeet populations of more than
65,000 plants/ha, as observed by Yonts and Smith (1997). Winter (1989) also observed
higher sucrose concentrations in sugarbeet planted at higher populations.

Multiple applications of glyphosate will be necessary to ensure satisfactory,

season-long weed control in glyphosate-resistant sugarbeet. However, growers may be

able to incorporate cultural weed control methods to reduce weed growth during the
growing season. Dawson (1977) reported that annual weeds that emerge after July 1 can
be suppressed by shade provided from sugarbeet stands that form complete canopies, i.e.
sugarbeet planted in narrow rows. Planting glyphosate-resistant sugarbeet in narrow
rows may provide to growers the opportunity to have adequate weed control with fewer
herbicide applications and cultivations, while possibly improving yield and quality.
Little research has been conducted to evaluate the effects of plant population and row
spacing on weed growth, and sugarbeet yield and quality in glyphosate-resistant

sugarbeet.

Glyphosate application timing. Glyphosate provides excellent control of many broadleaf
and grass weeds over a wide range of grth stages. As a result of this ﬂexibility in
application timing, growers often delay glyphosate applications to maximize the number
of weeds controlled and minimize the number of applications necessary for season-long
controL However, delayed glyphosate applications can lead to yield losses due to the
lengthened duration of competition between crop and weed. For example, in glyphosate-
resistant com, glyphosate applications should be made when weeds are 10-cm or less in
height to prevent yield loss (Gower et aL 2003; Dalley et al. 2004a). Glyphosate-resistant
soybean has generally been shown to tolerate weed competition for longer periods of
time (Young et al. 2001; Coulter and Nafziger 2007). However, row width can also
effect the time at which glyphosate must be applied to prevent yield loss due to weed
competition. Dalley et al. (2004a) concluded that glyphosate applications should be

made when weeds were 5-cm or less in corn planted in 38—cm rows and lS-cm or less in

soybean planted in 19- and 38-cm rows to prevent yield loss. In corn and soybean
planted in 76-cm rows, weeds needed to be controlled by 10-cm and 30-cm, respectively,
to prevent yield loss. Despite this tolerance to relatively longer periods of weed
competition in wider row widths, glyphosate must be applied before weeds reach a
growth stage at which they will be difﬁcult to control with standard use rates of
glyphosate.

Previous research on application timing in glyphosate-resistant sugarbeet to
prevent yield loss has shown varying results. Kemp and Renner (unpublished data) found
that sugarbeet yields were similar for glyphosate application timings at weed heights up
to 30-cm. Wilson et al. (2002) concluded that the optimum glyphosate application timing
was when weeds were 10-cm in height. Again, despite tolerance to weed competition,

applications should be made at a time when glyphosate will provide sufﬁcient eﬂicacy.

Economic considerations. The availability of glyphosate-resistant sugarbeet varieties
provides growers a valuable tool for weed management. However, production costs for
sugarbeet are considerable and can reach as high as $1500/ha (Burgener 2001 ). In
addition to production expenses associated with planting, fertilization, fungicide and
herbicide applications, and harvesting, growers will pay a technology fee of $ 1 06 per unit
of 100,000 seeds when purchasing glyphosate-resistant sugarbeet seed, or approximately
$129/ha at a seeding rate of 124,000 seeds/ha. To recover this added expense, growers
must increase their economic returns by increasing yield and quality, reducing weed

control expenses, or reducing seeding rates to minimize cost. Growers must balance the

added expense of planting at higher seeding rates with the increases in sugarbeet quality
often observed ﬁom planting at higher plant populations.

To account for the increases in costs of inputs when adopting glyphosate-resistant
varieties, growers may adjust planting practices to maximize yield and economic return.
Two ways growers can adjust planting practices are to plant at lower populations or to
plant in narrow rows. As noted earlier, row width and plant population can effect root
and sugar yield. All sugarbeet production in Michigan is contracted through the
Michigan Sugar Company, a grower-owned cooperative. Grower payments through the
Michigan Sugar Company are structured as tournament contracts (Knoeber 1989), where
growers “compete” against one another, based on sugarbeet quality, to determine their
payment per Mg of sugarbeet root. The Michigan Sugar Company uses a quality
payment system price per ton of sugarbeet root paid to growers. In their formula, the
price per Mg of sugarbeet that a grower delivers is calculated by multiplying ratio of the
grower’s recoverable white sucrose per Mg of sugarbeet root (RWSMg) to the overall
company average RWSMg and multiplying it by the base price, adjusting the grower’s
per Mg price above or below the base price. As is the structure of tournament contracts,
growers are incentivized to produce high quality sugarbeet (i.e. high RWSMg), rather
than simply maximize root yield. Therefore, it will be even more important for growers
to balance the added expense of planting at higher seeding rates with the increases in

sugarbeet quality often observed from planting at higher plant populations.

Potential tank-mix partner with glyphosate. Glyphosate provides excellent control of

many weed species over many growth stages. However, several common weeds in

sugarbeet producing regions of the United States, including common waterhemp
(Amaranthus rudis L.), common ragweed (Ambrosia artemisiifolia L.), and giant ragweed
(Ambrosia trzﬁda L.), have been conﬁrmed to be resistant to glyphosate (Heap 2009).
Velvetleaf (Abutilon theophrasti Medik.) and common lambsquarters (Chenopodium
album L.), two common weeds in sugarbeet production, have also exhibited some
tolerance to glyphosate (Krausz et al. 1996; Young et al. 2001). To control glyphosate-
resistant and/or —tolerant weeds, it may become necessary to tank-mix additional
herbicides with glyphosate to achieve satisfactory weed control and prevent the future
spread of difﬁcult-to-control weeds (Hatzios and Penner 1985).

Triﬂusulfuron, an acetolactate synthase (ALS) inhibiting herbicide for
postemergence broadleaf and grass control in sugarbeet, has been shown to provide good
to excellent control of velvetleaf, depending on size (Starke et al. 1996), and some
suppression of common lambsquarters and redroot pigweed (Amaranthus retroﬂexus L.)
(Morishita and Downard 1995). Previous research has shown additive and antagonistic
effects for mixtures of glyphosate and other ALS-inhibiting herbicides for control of
common lambsquarters (glyphosate + thifensulfuron) and velvetleaf (glyphosate +
irnazethapyr and thifensulfuron), respectively (Lich et al. 1997). Combining an
additional herbicide mode of action with glyphosate may improve control of problematic

weeds and will give growers more options for controlling difﬁcult-to-control weeds.

10

LITERATURE CITED

Alford, C. M., S. D. Miller, and J. T. Cecil. 2004. Using row spacing to increase crop
competition with weeds. Proceedings of the 4th International Crop Science
Congress. Website: http:// www.cropscience.org.au/icsc2004/poster/
2/4/1/412_alfordcrnhtm Accessed: April 18, 2007.

Andrade, F. H., P. Calvino, A. Cirilo, and P. Barbieri. 2002. Yield responses to narrow
rows depends on increased radiation interception. Agron. J. 94:975-980.

National Agricultural Statistics Service. 2009. Crop production 2008 summary.
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01-12-2009.pd£ Accessed: March 27, 2009.

Ateh, C. M. and R. G. Harvey. 1999. Annual weed control by glyphosate in glyphosate-
resistant soybean (Glycine max). Weed Technol. 13:394-398.

Burgener, P. A. 2001. Economics of sugarbeet production. Pages 189-196 in R. G.
Wilson, ed. Sugarbeet Production Guide. University of Nebraska Cooperative
Extension. Lincoln, NE: University of Nebraska.

Carlson, A. L., J. L. Luecke, M. F. R. Khan, and A. G. Dexter. 2008. Survey of weed
control and production practices on sugarbeet in eastern North Dakota and
Minnesota in 2007. Sugarbeet Res. Ext. Rep. 38:64-68.

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

Coulter, J. A. and E. D. Nafziger. 2007. Planting date and glyphosate timing on
soybean. Weed Technol. 21:359-366.

Culpepper, A. S., A. C. York, R. B. Batts, and K M. Jennings. 2000. Weed
management in glufosinate- and glyphosate-resistant soybean (Glycine max).
Weed Technol. 14:77—88.

Dale, T. M. and K A. Renner. 2005. Timing of postemergence micro-rate applications
based on growing degree days in sugarbeet. J. Sugar Beet Res. 42:87-101.

Dale, T. M., K. A. Renner, A. N. Kravchenko. 2006. Effect of herbicides on weed
control and sugarbeet (Beta vulgaris) yield and quality. Weed Technol. 20:150-
156.

Dalley, C. D., J. J. Kells, and K A. Renner. 2004a. Effect of glyphosate application

timing and row spacing on corn (Zea mays) and soybean (Glycine max) yields.
Weed Technol. 18:165-176.

11

Dalley, C. D., J. J. Kells, and K A. Renner. 2004b. Effect of glyphosate application
timing and row spacing on weed growth in corn (Zea mays) and soybean (Glycine
max). Weed Technol. 18:177-182.

Dawson, J.H. 1977. Competition of late-emerging weeds with sugarbeets. Weed Sci.
25:168-170.

Dexter, A. G., J. L. Luecke, and L. J. Smith. 1999. Inﬂuence of cultivation on yield of
Roundup Ready and Liberty Link sugarbeet. Sugarbeet Res. Ext. Rep. 30:100-
101.

Dexter, A. G. 1994. History of Sugarbeet (Beta vulgaris) herbicide rate reduction in
North Dakota and Minnesota. Weed Technol. 8:334—337.

Gower, S. A, M. M. Loux, J. Cardina, S. K Harrison, P. L. Sprankle, N. J. Probst, T. T.
Bauman, W. Bugg, W. S. Curran, R. S. Currie, R. G. Harvey, W. G. Johnson, J.
J. Kells, M.D.K Owen, D. L. Regehr, C. H. Slack, M. Spaur, C. L. Sprague, M.
VanGessel, and B. G. Young. 2003. Effect of postemergence glyphosate
application timing on weed control and grain yield in glyphosate-resistant corn:
Results of a 2-yr multistate study. Weed Technol. 17:821-828.

Grifﬁths, W. 1994. Evolution of herbicide programs in sugarbeet. Weed Technol.
8:338-343.

Grove, T., M. Holy, A. Cattanach, and J. Christenson. 2007. Narrow row sugarbeet
production. Sugarbeet Res. Ext. Rep. 38:152-174.

Guza, C. J., C. V. Ransom, C. Mallory-Smith. 2002. Weed control in glyphosate-
resistant sugarbeet (Beta vulgaris L.). J. Sugar Beet Res. 39:109-123.

Harder, D. B., C. L. Sprague, and K A. Renner. 2007. Effect of soybean row width and
population on weeds, crop yield, and economic return. Weed Technol. 21 :744-
752.

Hatzios, K K and D. Penner. 1985. Interaction of herbicides with other agrochemicals
in higher plants. Rev. Weed Sci. 1:1-63.

Heap, I. 2009. International survey of herbicide resistant weeds. Website:
http://www.weedscience.com. Accessed March 22, 2009.

Johnson, G. A. and T. R. Hoverstad. 2002. Effect of row spacing and herbicide

application timing on weed control and grain yield in corn (Zea mays). Weed
Technol. 16:548-533.

12

Kniss, A. R., R. G. Wilson, A. R. Martin, P. A. Burgener, and D. M. Feuz. 2004.
Economic evaluation of glyphosate-resistant and conventional sugar beet. Weed
Technol. 18:388-396.

Knoeber, C. R. 1989. A real game of chicken: contracts, tournaments, and the
production of broilers. Journal of Law, Economics, and Organization 52271-292.

Krausz, R. F., G. Kapusta, and J. L. Matthews. 1996. Control of annual weeds with
glyphosate. Weed Technol. 10:957-962. '

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

Morishita, D. W. and R. W. Downard. 1995. Weed control in sugar beets with
triﬂusulfuron as inﬂuenced by herbicide combination, timing, and rate. J. Sugar
Beet Res. 32:23-35.

[USDA-NASS] US. Department of Agriculture-National Agricultural Statistics Service.
2008. Acreage. Website: http://usda.mannlib.comell.edu/usda/nass/Acre/
20005/2008/Acre-06-30-2008.pdf. Accessed: March 27, 2009.

[USDA-NASS] US Department of Agriculture-National Agricultural Statistics Service.
2009. Crop production 2008 summary. Website: http://usda.mannlib.comell.edu/
usda/current/CropProdSu/CropProdSu-O1-12-2009.pdf. Accessed: March 27,
2009.

Pedersen, P. and J. G. Lauer. 2003. Corn and soybean response to rotation sequence,
row spacing, and tillage system. Agron. J. 95:965-971.

Schweizer, EB. and A. G. Dexter. 1987. Weed control in sugarbeets (Beta vulgaris) in
North America. Rev. Weed Sci. 32113-133.

Starke, R. J., K A. Renner, D. Penner, and F. C. Roggenbuck. 1996. Inﬂuence of
adjuvants and desmedipham plus phenmedipham on velvetleaf (A butilon
theophrasti) and sugarbeet response to triﬂusulfuron. Weed Sci. 44:489-495.

Stebbing, J. A., R. G. Wilson, A. R. Martin, and J. A. Smith 2000. Row spacing,
redroot pigweed (Amaranthus retroﬂexus) density, and sugarbeet (Beta vulgaris)
cultivar effects on sugarbeet development. J. of Sugar Beet Res. 37:11-31.

Widdicombe, W. D. and K D. Thelen. 2002. Row width and plant density effects on
corn grain production in the northern corn belt. Agron. J. 94: 1 020-1023.

Wilson, R. G., C. D. Yonts, and J. A. Smith. 2002. Inﬂuence of glyphosate and

glufosinate on weed control and sugarbeet (Beta vulgaris) yield in herbicide-
tolerant sugarbeet. Weed Technol. 16:66-73.

13

Winter, S. R. Sugarbeet yield and quality response to irrigation, row width, and stand
density. J. Sugar Beet Res. 26:26-33.

Yelverton, F. H. and H. D. Coble. 1991. Narrow row spacing and canopy formation
reduces weed resurgence in soybeans (Glycine max). Weed Technol. 5:169-174.

Yonts, D. C. and J. A. Smith. 1997. Effects of plant population and row width on yield
of sugarbeet. J. of Sugar Beet Res. 34:21-30.

Young, B. G., J. M. Young, L. C. Gonzini, S. E. Hart, L. M. Wax, and G. Kapusta. 2001.

Weed management in narrow- and wide-row glyphosate-resistant soybean
(Glycine max). Weed Technol. 15:112-121.

14

CHAPTER 2
INFLUENCE OF ROW WIDTH AND PLANT POPULATION ON WEED

GROWTH AND YIELD IN GLYPHOSATE-RESISTANT SUGARBEET

Abstract: Studies were conducted in 2006, 2007, and 2008 at multiple locations in
Michigan to determine the effect of planting glyphosate-resistant sugarbeet in row widths
of 38-, 51-, and 76-cm and at populations of 54,000; 78,000; 101,000; and 124,000
plants/ha on canopy development, weed growth and sugarbeet yield and quality. In
general, sugarbeet canopy cover was greater and developed more rapidly in 38- and 51-
cm row widths and at higher plant populations. For nontreated plots, weed density was
similar for all row widths and plant populations. Following a single glyphosate
application when weeds were 10-cm in height, weed biomass was reduced by 88% and
77% in 38- and 51-cm rows, respectively, compared to 76-cm rows at the Saginaw Valley
locations. At East Lansing, a trend toward reduced density and biomass in narrow rows
following a glyphosate application occurred. Differences in weed density and biomass
following a glyphosate application among row widths and plant populations are likely
due to the differences in crop canopy development. At the Saginaw Valley locations,
glyphosate-resistant sugarbeet planted in 51 -cm rows produced the highest root yields.
At East Lansing where only 38— and 76-cm rows were investigated, root yields were
similar for both row widths in 2007. However, in 2008 when moisture was not limiting,
root yields were highest in 38-cm rows. Sugarbeet quality was similar among all row
widths; however sugarbeet quality increased as population increased. Total sucrose

yield, or recoverable white sucrose per hectare, followed the same pattern as root yield

15

and was generally highest in narrow rows. In addition to increased light interception
leading to increased yields in narrow rows, planting sugarbeet in narrow rows is a useful
form of cultural weed control, helping to shade out late-season weed growth.
Nomenclature: Glyphosate; sugarbeet, Beta vulgaris L.

Key words: Herbicide-resistant crops, plant population; row width; weed biomass.

INTRODUCTION

Glyphosate-resistant sugarbeet varieties were commercialized in 2008. In the ﬁrst
commercial year, approximately half of Michigan’s sugarbeet area (32,000 of 61 ,000
hectares) was planted to glyphosate-resistant varieties. Adoption was limited primarily
due to the availability of seed. It is expected that glyphosate-resistant sugarbeet varieties
will be planted on more than 90% of the sugarbeet hectares Michigan in 2009 (C. Guza,
personal communication). There are many positive attributes associated with the use of
glyphosate for weed control in glyphosate-resistant sugarbeet. Glyphosate provides
excellent weed control of many weed species common to sugarbeet production with
fewer herbicide active ingredients and possibly fewer herbicide applications (Guza et al.
2002; Kniss et al. 2004). Unlike current herbicides used for weed control in sugarbeet,
the potential for crop injury with glyphosate in glyphosate-resistant sugarbeet is
nonexistent (Wilson et al. 2002). Additionally, weed height at the time of glyphosate
application is generally not as limiting as herbicides currently used in sugarbeet.

Sugarbeet growers may be able to reduce or potentially eliminate between-row
cultivation with the use of glyphosate in glyphosate-resistant sugarbeet due to improved

weed control. As a result, growers may be able to adopt planting sugarbeet in narrow

l6

rows. Numerous studies on the effect of row width and plant population on crop yield
have been conducted in many agronomic crops. Results of these studies have been
inconsistent and vary among crops; however, the general outcome trends toward
increased yields in narrower rows due to increased light radiation interception (Andrade
et al. 2002). In addition to potential yield increases from faster and more complete
canopy cover with narrow rows, greater canopy cover can also provide more shade of
bare soil between rows, thereby reducing late-season weed emergence and growth
(Johnson and Haverstad 2002). Yelverton and Coble (1991) observed a signiﬁcant
decrease in weed density and biomass in soybean planted in narrows rows compared with
wide rows. Dalley et al. (2004) also observed a similar trend of reduced weed biomass in
narrow-row soybean. In three of four years, soybean planted in 19- and 38-cm rows had
signiﬁcantly less weed growth after an initial glyphosate application compared with 76-
cm rows. In both studies, the reduction in weed growth was attributed to the greater
canopy cover provided by the narrow rows.

Sugarbeet is typically grown in row widths ranging from 56- to 76-cm. Similar to
results from corn and soybean, previous research has shown a trend toward increased
sugarbeet yields when planted in narrow rows. Yonts and Smith (1997) found that the
highest sugar yield was obtained with 56-cm rows, when compared with 35- and 76-cm
rows. Stebbing et al. (2000) showed an increase in root and sucrose yield in 46-cm rows
compared with 56- and 76-cm rows in one of two years. The authors attributed the yield
increases in 46-cm rows to the reduced intra-plant competition due to more spacing
between plants within the row. In addition to increased yield, sugarbeet planted in

narrow rows can provide greater canopy cover to suppress weed growth. Alford et al.

17

(2004) observed signiﬁcantly reduced weed biomass production in 38- and 56-cm rows
compared with 76-cm rows, due to earlier and greater canopy cover in the narrow row
widths.

Planting sugarbeet in narrow row widths also allows for higher plant populations
per area. These differences in within- and across-row plant spacing can have an effect on
both sugarbeet yield and quality. Due to the reduced space between plants within the row
and resulting smaller growth of each individual beet, a trend toward higher sucrose
concentrations can be observed at higher plant populations (Yonts and Smith 1997).
However, sucrose concentrations can also plateau at sugarbeet populations of more than
65,000 plants/ha, as observed by Yonts and Smith (1997). Winter (1989) also observed
higher sucrose concentrations in sugarbeet planted at higher populations. These studies
were conducted under irrigated conditions where water was not limiting.

Multiple applications of glyphosate will be necessary to ensure satisfactory,
season-long weed control in glyphosate-resistant sugarbeet. However, growers may be
able to incorporate cultural weed control methods to reduce weed growth during the
growing season. Dawson (1977) reported that annual weeds that emerge after July 1 can
be suppressed by shade provided from sugarbeet stands that form complete canopies, i.e.
sugarbeet planted in narrow rows. Planting glyphosate-resistant sugarbeet in narrow
rows may provide growers the opportunity to have adequate weed control with fewer
herbicide applications and cultivations, while possibly improving yield and quality.

Little research has been conducted to evaluate the effects of plant population and
row spacing on weed growth, and sugarbeet yield and quality in glyphosate-resistant

sugarbeet on non-irrigated soils. Therefore, the objectives of this research were to: l)

18

determine the effect of planting glyphosate-resistant sugarbeet in three different row
widths on weed grth and yield, and 2) evaluate the effect of multiple plant populations

within each row width on sugarbeet yield and quality.

MATERIALS AND METHODS

Field trials were established in 2006, 2007, and 2008 at the Michigan State
University Saginaw Valley Bean and Beet Research Farm near St. Charles, Michigan,
and in 2007 and 2008 on commercial production ﬁelds near St. Charles and at the
Michigan State University Agronomy Research Farm in East Lansing, Michigan. The
soil at the Bean and Beet Research Farm was a Zilwaukee silty clay (ﬁne, mixed, mesic
Fluvaquentic Endoaquolls) with soil pH of 7.4 and 3.9% organic matter. The soil type at
the commercial production ﬁelds was a Sloan silty clay loam (ﬁne-loamy, mixed, mesic
Fluvaquentic Endoaquolls) with soil pH of 7.5 and 10.5% organic matter in 2007 and soil
pH of 7.2 and 3.3% organic matter in 2008. At East Lansing, the soil type was a Capac
ﬁne sandy loam (ﬁne-loamy, mixed, mesic Aquic Glossudalfs) with soil pH of 6.9 and
2.5% organic matter. Experiments followed soybean (Glycine max [L.] Merr.), wheat
(T riticum aestivum L.), and dry bean (Phaseolus vulgaris L.) in 2006, 2007, and 2008,
respectively, at the Bean and Beet Research Farm. At the commercial production ﬁelds
and East Lansing location, experiments followed corn (Zea mays L.) in 2007 and soybean
in 2008. Fields were fall-plowed followed by ﬁeld cultivation prior to planting in the

spring. Fertilizer applications were standard for sugarbeet production in Michigan. The

glyphosate-resistant sugarbeet variety, ‘Beta 3H021A RRI,’ was planted in 38- and 76-

cm rows at the Saginaw Valley Bean and Beet Research Farm in 2006. At all other sites,

19

the glyphosate-resistant sugarbeet variety, ‘Hilleshbg 90282,’ was planted. In 2007 and

2008, sugarbeet was planted in 38-, 51-, and 76-cm row widths at the two Saginaw
Valley locations and 38- and 76-cm row widths at East Lansing. Sugarbeet was planted
at a depth of 2.5-cm. Plot sizes were 3- or 4.57-m wide depending on location and 9.1 m
long. At the four-leaf growth stage, sugarbeet stands were thinned to populations of
54,000; 78,000; 101,000; or 124,000 plants/ha in 2007 and 2008. In 2006, populations of
54,000; 78,000; and 101,000 plants/ha were investigated. Populations were held constant
across row widths, leading to differences in within-row plant spacing for each population
(Table 1). Precipitation data was collected at the Saginaw Valley Bean and Beet
Research Farm and the East Lansing location during the growing season and is
summarized by month in Table 2.

The experimental design was a split-split-plot with row width as the main plot
factor, plant population as the sub-plot factor, and weed control treatment as the sub-sub-

plot factor. All treatments were replicated four times. Weed-free plots were established

each year and maintained with applications of glyphosate3 at 840 g ae/ha plus ammonium

sulfate (AMS) at 2% v/v starting at the cotyledon sugarbeet growth stage and repeated as
needed. In 2007, nontreated plots were also used to determine the effect of row width
and plant population on season-long weed growth. Due to excessive weed growth and
the lack of sugarbeet growth in the nontreated plots, it was decided to replace the
nontreated treatment with a single application of glyphosate at 840 g ae/ha plus AMS at
2% v/v when weeds averaged 10-cm in height in 2008. This treatment was used to
determine the effect of row width and plant population on new weed emergence and

growth after an initial glyphosate application.

20

Crop canopy measurements were taken in all weed-ﬂee plots at one to two week

intervals beginning in early-June. Measurements were collected using the Sunscan

Canopy Analysis System4, consisting of a 1 m by 13 mm wand used to measure light

beneath the crop canopy, a tripod-mounted sensor that measured both incident and

diffuse light above the crop canopy, and a handheld computer5 that recorded

simultaneous measurements of light above and beneath the crop canopy. Measurements
were taken at or near solar-noon by placing the wand on the soil perpendicular to the
center rows of each plot and were converted to percent canopy cover using the formula:
(1 — (below canopy measurement/above canopy measurement)) * 100.

Weed population density and aboveground biomass were collected ﬁom two 0.25

m2 quadrats placed in the center of the plots for the nontreated and 10-cm weed height

glyphosate application treatments in mid-August. Weed biomass was dried for 72 h in a
forced air oven at 60 C and weighed. Common lambsquarters (Chenopodium album L.)
and a combination ofredroot pigweed (Amaranthus retroflexus L.) and Powell amaranth
(A maranthus powellii S. Watson) were the predominant weed species at the Bean and
Beet Research Farm and the commercial production ﬁelds in 2007 and 2008. These
weed species, plus a mixture of annual grass weed species, were present at the East
Lansing locations in 2007 and 2008. In 2008, common purslane (Portulaca oleracea L.)
was also present at East Lansing.

Two rows of sugarbeet were mechanically harvested and weighed from each plot

in mid-September and a sub-sample of roots was analyzed for quality and purity by the

Michigan Sugar Company6. Sugarbeet quality is expressed as kg of recoverable white

21

sucrose per Mg of root (RWSMg). Total sucrose production is expressed as kg of

recoverable white sucrose per hectare (RWSH).

Data were subjected to ANOVA using PROC MIXED in SAS7 and treatment

means for canopy cover, weed density and biomass, root yield, RWSMg, and RWSH
were compared using Fisher’s Protected LSD at the p = 0.05 signiﬁcance level. Weed
density and biomass data were log (x + 1) transformed for analysis. Back-transformed
data are presented. Data were combined over environment, row width, or population and

presented for main effects when signiﬁcant interactions were not present.

RESULTS AND DISCUSSION
Crop canopy development. Despite similar rainfall totals for the 2006, 2007, and 2008
growing seasons (Table 2), canopy development was slower in 2007 than 2006 and 2008
due to dry conditions experienced during May, June, and July at the different locations.
Canopy cover measurements varied by year, therefore data are presented separately for
each year. Row width greatly inﬂuenced sugarbeet canopy cover in ﬁve out of the seven
environments, and there was not a signiﬁcant interaction between row width and plant
population for sugarbeet canopy development at the Saginaw Valley locations or East
Lansing location, so main effects of row width and plant population can be presented. In
2006 at the Saginaw Valley location, all measurements for canopy cover were greater in
38-cm rows compared with 76-cm rows beginning with the ﬁrst measurement 6 weeks
after planting (WAP) (Figure 1a). Differences in canopy between the two row widths
ranged from 4.6 to 13.5%. At 10 WAP canopy cover was 90% and 82% for sugarbeet

planted in 38- and 76-cm rows, respectively. The sugarbeet canopy developed at a much

22

slower rate in 2007 and canopy cover was similar among all row widths at the Saginaw
Valley locations until 9 WAP (Figure 2a). Lower precipitation in May and June at the
two Saginaw Valley locations as compared with the 30-year average most likely explains
the slower canopy development in 2007 (Table 2). At 9 and 10 WAP, both 38- and 51-
cm rows exhibited greater canopy cover than 76-cm rows. By 10 WAP, canopy cover
was only 74% with narrow rows (38- and 51-cm) and 70% with 76-cm rows.

Canopy development was more rapid in 2008 than 2007. In 2008 at the Saginaw
Valley locations, canopy cover was greater in 38-cm rows compared with 51- and 76-cm
rows starting 8 WAP (Figure 3a). By 9 WAP and continuing through the ﬁnal
measurement timing, canopy cover was greatest in both 38- and 51-cm rows. At the ﬁnal
measurement ll WAP, canopy cover was 91% in narrow rows (38- and 51-cm) and only
84% in 76-cm rows. At East Lansing in 2007 and 2008, canopy cover was similar
between the 38- and 76-cm row widths (Figures 4a and 5a). In 2007 sugarbeet canopy
only reached 72% cover by 14 WAP and in 2008 canopy cover was only 74% by 11
WAP.

Sugarbeet plant populations did not have as great of an effect on canopy cover as
row width Averaged across all row widths, canopy cover was similar among the three
populations investigated at the Saginaw Valley location in 2006 (Figure lb). This trend
was similar for the two Saginaw Valley locations in 2007, except at the initial
measurement timing at 7 WAP, where sugarbeet planted at the highest population of
124,000 plants/ha had signiﬁcantly greater canopy closure than the lower plant
populations (Figure 2b). In 2008, canopy cover was also greatest in the two highest plant

populations at the ﬁrst measurement timing at 7 WAP (Figure 3b). At 8 WAP, sugarbeet

23

planted at the highest population of 124,000 plants/ha provided the greatest canopy cover.
However, by 13 WAP, canopy cover was similar among all plant populations.

Similar to the effect of row width on canopy cover, canopy cover was similar
among all plant populations in 2007 and 2008 at the East Lansing location (Figures 4b
and 5b). Particularly in 2007, increased water use at higher plant populations and
reduced soil moisture conditions may have limited canopy development (Moraghan

1972)

Weed density and biomass. Among the nontreated plots in 2007, weed density was
similar for all row widths and plant populations at the Saginaw Valley locations (Table
3). This was likely due to the slow grth habit of sugarbeet, preventing it from
competing with faster growing weeds early in the season. At East Lansing, weed density
was also similar among row width and plant population. Weed biomass was similar for
38- and 76-cm row widths, but was signiﬁcantly reduced at populations of 101,000 and
124,000 plants/ha compared with 54,000 and 78,000 plants/ha.

For plots that received a single glyphosate application when weeds were lO-cm in
height, very few weeds emerged after the glyphosate application (Table 4). Weed
population density and biomass was inﬂuenced by row width and plant density at the
Saginaw Valley locations. Compared with 76-cm rows, subsequent weed growth was
reduced by 88% and 77% in 38- and 51-cm rows, respectively. Following a single
glyphosate application, weed densities were also lower in 38- and 51-cm rows compared
with 76-cm rows. Weed densities were similar among all plant populations following a

glyphosate application to lO-cm weeds. However, weed biomass decreased from 10.8

24

tol.0 g/m2 as plant population increased from 54,000 to 124,000 plants/ha. These results

are similar to those of Dalley et a1. (2004) and Harder et al. (2007), who observed
reduced weed growth following a glyphosate application in soybean planted in narrow
rows. At East Lansing, though weed densities and biomass were similar among row
widths, a trend toward reduced density and biomass in narrow rows following a
glyphosate application was present. Row width and plant population did not affect weed
density or biomass. Differences in weed density and biomass following a glyphosate
application among row width and plant population are likely due to the differences in
crop canopy development. Though it is unlikely a single application of glyphosate will
provide satisfactory season-long weed control, glyphosate-resistant sugarbeet planted in
narrow rows may suppress late-season weed grth and require fewer herbicide

applications than sugarbeet planted in wide rows.

Sugarbeet root yield and quality. In 2006, glyphosate-resistant sugarbeet root yields
increased from 59.1 Mg/ha in 76-cm rows to 76.4 Mg/ha in 38-cm rows in 2006 (Table
5). RWSMg was similar among row widths; however RWSH was greater in 38-cm rows
due to the increase in root yield. When averaged over row width, root yield, RWSMg,
and RWSH were similar for the three plant populations that were investigated (Table 5).
Data from the Saginaw Valley locations in 2007 and 2008 were combined across
year and location because no signiﬁcant interaction was observed for any of the response
variables. In 2007 and 2008 at the Saginaw Valley locations, root yield for glyphosate-
resistant sugarbeet planted in 51-cm rows was 79.1 Mg/ha, an increase of 4.9 and 5.2

Mg/ha compared with 38- and 76-cm rows, respectively (Table 6). Though RWSMg was

25

similar among all row widths, RWSH was also greatest in 51-cm rows due to increases in
root yield. When data were combined across row width, root yields were similar for all
plant populations (Table 6). RWSMg increased ﬁ'om 115.4 kg/Mg at 54,000 plants/ha to
120.1 kg/Mg at 124,000 plants/ha These results are similar to those reported by Ransom
et al. (1998), who also observed increases in RWSMg at higher plant populations of
glyphosate-resistant sugarbeet.

Data from the East Lansing location was combined across year where signiﬁcant
year by row width or plant population interactions were not present. In 2007 when
moisture limiting during April, May, and August, root yields and RWSH were similar for
both 38- and 76-cm rows (Table 7). In 2008, growing conditions were more favorable
and root yields in 38-cm rows were 10.2 Mg/ha higher than in 76-cm rows. In addition to
root yield, RWSH was also signiﬁcantly greater in the narrow row width. For data
combined over row width, root yield and RWSMg were not inﬂuenced by plant
population. In 2007, glyphosate-resistant sugarbeet in populations of 101,000 and
124,000 plants/ha resulted in the highest total sucrose yields, providing increases of at
least 400 kg/ha over populations of 54,000 and 78,000 plants/ha (Table 8). In 2008,
RWSH increased by at least 800 kg/ha for all populations greater than 54,000 plants/ha.

At most environments in this study, glyphosate-resistant sugarbeet root and sugar
yields were greater in narrow rows compared with 76-cm rows. In trials at the Saginaw
Valley locations where 38-, 51-, and 76-cm row widths were compared, the highest root
and sugar yields were observed in 51-cm rows. Root yield was similar among 38— and
76-rows at the East Lansing location in 2007; however, 38-cm rows provided greater root

yields than 76-cm rows in 2008. In addition to increased light interception leading to

26

increased yields in narrow rows, planting sugarbeet in narrow rows is also a useful form
of cultural weed control, helping to shade out late-season weed growth Narrow row
suppress late-season weed growth, which may reduce the number of glyphosate
applications necessary for satisfactory weed control.

The differences in root yield between the Saginaw Valley locations and the East
Lansing location may be explained by the differences in soil texture and water holding
capacity between locations. The sandy loam soil texture at the East Lansing location
would not have the same water holding capacity as the silty clay soil at the Bean and Beet
Research Farm or the silty clay loam soil at the commercial production ﬁelds. As a
result, under the dry conditions experienced in 2007, yield losses due to insufﬁcient soil
moisture were more evident at the East Lansing site (Morillo-Velarde and Ober 2006).
Likewise, differences in root yield between years at the East Lansing location may best
be explained by differences in precipitation during the growing season. Though root
yields were similar among all plant populations in these studies, growers should choose
planting densities that are appropriate for the soil moisture conditions to achieve
maximum yield and sugarbeet quality. From these studies, soils with greater water
holding capacities produced higher yields than soils with a coarser texture and less water
holding capacity. Because sugarbeet planted at higher populations will use more water
than low populations (Moraghan 1972), growers should consider the ﬁeld’s soil texture
when determining seeding density. However, based on the yield results from these
studies, plant populations do not need to be increased when switching to narrow row

widths.

27

SOURCES OF MATERIALS

1 Betaseed, Inc., 1788 Marschall Rd., PO. Box 195, Shakopee, MN 55379.
2 Syngenta Seeds Inc., 1020 Sugarrnill Rd., Longmont, CO 80501.

3 Roundup WeatherMAX, Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167.
4 Delta-T Device LTC, 128 Low Rd., Burwell, Cambridge CBS OEJ, England.
5 Psion Digital, 1810 Airport Exchange Blvd., Suite 500, Erlanger KY 41018.
6 Michigan Sugar Company, 2600 S. Euclid Ave., Bay City, MI 48706

7 The SAS System for Windows, Version 9.1, SAS Institute Inc., 100 SAS Campus Dr.,

Cary, NC 27513.

28

 

 

 

 

mm 2 mi 2 m3 S 0862
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E : 2: mm mm 2 83K
me em 2: cm 3 , we 25%
a 80 a Go a :5 Egan—m
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mac.“ Enron mac." :8. ﬂ m v.38 Eo-wm

 

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BB 8:: E 8:83 33ng ugﬁmonbﬁmoﬁgw no.“ 30.50 Edmuﬁda mo 598:: 2: can wﬁoam 28E 38-35:? .~ Saga

29

Table 2. Monthly and 30-yr average precipitation at the Saginaw Valley Bean and Beet
Research Farm near St. Charles in 2006, 2007, and 2008 and at East Lansing in 2007 and

2008.8

 

St. Charles East Lansing
Month 2006 2007 2008 30-yr ave. 2007 2008 30-yr ave.

 

 

 

 

 

mm
April 47 76 52 72 66 49 83
May 105 39 28 71 97 30 68
June 68 27 99 83 89 l 10 78
July 60 66 100 70 l 3 95 76
August 59 122 53 96 140 12 87
Total 339 330 332 392 405 296 392

 

a Precipitation data were collected from the Michigan Automated Weather Network
(http://www.agweather.geo.msu.edu/mawn/).

30

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31

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NEE «8%?» «SE NEEeeeB £33 20%
3.385 wee? 565w week, 3283 Be}, base—e 3e? mueebe £32
weaned “mum e>e=e> Begum

 

paaceemmqwﬁ 8: we? core—smog use—a use 523 38 5253 5385::

e5 eeﬁm mueete 55: How beﬁamem 3:585 e3 Sea 48:82 mamas “mam 28 80:82 >e=e> Begum e5 an moon 5 Ewe:
E 89.0— e53 383 8:3 553%? eﬁmonnbw e~w£m e 3382 £033 mac—q E wee—~85 use €me cotedaog wee? .V e3§

32

Table 5. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet planted in
two row widths at three populations at the Saginaw Valley Bean and Beet Research Farm
in 2006. Data are presented separately for main effects since the interaction between row

width and plant population was not significanta’b

 

 

Main effects Root yield RWSMg RWSH
Row width Mg/ha kg/Mg kg/ha
38-cm 76.4 a 122.8 a 9410 a
76-cm 59.1 b 122.3 a 7210 b
Population

(plants/ha)

54,000 66.2 a 122.6 a 8080 a
78,000 66.7 a 122.2 a 8170 a
101,000 70.3 a 122.9 a 8680 a

 

a Means within column followed by the same lowercase letter for each main effect are
not different according to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

33

Table 6. Root yield, recoverable white sucrose per Mg of root (RWSMg), and

recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in three row
widths at four p0pu1ations at the Saginaw Valley locations in 2007 and 2008. Data were
combined across years and are presented separately for main effects since the interaction

 

 

between row width and plant population was not signiﬁcanta’b’c

Main effects Root yield RWSMg RWSH
Row width Mg/ha kg/Mg kg/ha
38 cm 81.8b 119.1 a 9660b
51cm 87.2 a 118.4a 10240a
76 cm 81.5b 116.8 a 9460b
Population

(plants/ha)

54,000 83.5 a 115.4 b 9580 b
78,000 81.0 a 117.6 ab 9470 b
101,000 84.3 a 119.2 a 9940 ab
124,000 85.2 a 120.1 a 10160 a

 

a Means within column followed by the same lowercase letter are not different according
to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

6 Data were combined across the Saginaw Valley Bean and Beet Research Farm and
commercial production ﬁeld locations.

34

Table 7. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in two row

. . . . . ,b
Widths at the East Lansmg location. Data were comb1ned across plant populations.a

 

 

 

 

Root yield RWSMg RWSH
Row width 2007 2008 2007 & 2008 2007 2008
— Mg/ha — kg/Mg — kg/ha ——
38 cm 48.8 a 69.1 a 106.7 a 4800 a 7780 a
76 cm 51.2 a 58.9 b 105.1 a 5000 a 6650 b

 

a Means within column followed by the same lowercase letter are not different according
to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

35

Table 8. Root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per ha (RWSH) for glyphosate-resistant sugarbeet in four plant

populations at the East Lansing location. Data were combined across row widthsa’

 

 

 

 

Root yield RWSMg RWSH
Population 2007 & 2008 2007 & 2008 2007 2008
Plants/ha Mg/ha kg/Mg —— kg/ha —
54,000 52.2 a 105.1 a 4600 b 6760 b
78,000 56.9 a 102.6 a 4200 b 7710 a
101,000 60.2 a 107.5 a 5800 a 7190 ab
124,000 57.3 a 109.3 a 5000 ab _ 7580 a

 

a Means within column followed by the same lowercase letter are not different according
to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

36

 

100
(a)
90 —l
80 4
70 a
60 -

50..

Canopy cover (%)

30..

20*

104

 

 

 

01
CD
V
G)
(O
_s
O

11

 

(b)

80‘
70a

60‘

 

Canopy cover (%)
8

 

 

 

O I l r I l
5 6 7 8 9 10 11

Weeks after planting

Figure I. Canopy cover development for glyphosate-resistant sugarbeet planted in (a)
38-(0) and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I), and 101,000
(0) at the Saginaw Valley Bean and Beet Research Farm in 2006. Vertical bars represent
Fisher’s protected LSD at the p = 0.05 signiﬁcance level. NS = not signiﬁcant.

37

Canopy cover (%)

Canopy cover (%)

100

 

90‘

70‘

60‘

20-

10-

 

(3)

NS
NS

 

 

100

11

 

90~
80-
704
60-
50-
4o~
30-
20-

10']

 

0

0))

NS
NS

NS

 

 

6

I I I I

7 8 9 10

Weeks after planting

11

Figure 2. Canopy cover development for glyphosate-resistant sugarbeet planted in (a)

38- (c), 51— (I), and 76-cm rows (0) and (b) populations of 54,000 (O), 78,000 (I),
101,000 (0), and 124,000 plants/ha (A) at the Saginaw Valley locations in 2007.

Vertical bars represent Fisher’s protected LSD at the p = 0.05 signiﬁcance level. NS =
not signiﬁcant.

38

100

 

(a)
90 q

80*
70a

60-i

40..

Canopy cover (%)
8

301

20‘

10-

 

 

 

100

 

(b)
90 4

80‘
70‘
60a
50-

4o:

 

Canopy cover (%)

30-

20-

10a

 

 

 

0 T I I I

6 7 8 9 10 11 12

Weeks after planting

Figure 3. Canopy cover development for glyphosate-resistant sugarbeet planted in (a)
38- (o), 51- (I), and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I),
101,000 (0), and 124,000 plants/ha (A) at the Saginaw Valley locations in 2008.
Vertical bars represent Fisher’s protected LSD at the p = 0.05 signiﬁcance level. NS =
not signiﬁcant.

39

 

(3)

NS NS
NS

NS
NS

404

Canopy cover (%)
8

30J
20-1

10a

 

 

 

100

 

(b)

90 .
80‘-

70 ~

 

60 -

50.4

40 a

 

Canopy cover (%)

304

20 a

10 *

 

 

 

0 I I I I I I I I

6 7 8 9 10 11 12 13 14 15
Weeks after planting
Figure 4. Canopy cover development for glyphosate-resistant sugarbeet planted in (a)

38-(0) and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I), 101,000 (0),
and 124,000 plants/ha (A) at East Lansing in 2007. NS = not signiﬁcant.

40

100

 

(a)
90 -

8O ‘ NS

70 - RES

60 4 IVE;

50 -
NS

Canopy cover (%)

30 1
20 -

10 a

 

 

 

 

100
(b)
90 -
80 «
7o 4
60 -

50..

 

40d

Canopy cover (%)

30-

20 -

10 ~

 

 

 

0 T T T I I

6 7 8 9 10 11 12
Weeks after planting

Figure 5. Canopy cover development for glyphosate-resistant sugarbeet planted in (a)
38-(0) and 76-cm rows (0) and (b) populations of 54,000 (0), 78,000 (I), 101,000 (0),
and 124,000 plants/ha (A) at East Lansing in 2008. NS = not signiﬁcant.

41

LITERATURE CITED

Alford, C. M., S. D. Miller, and J. T. Cecil. 2004. Using row spacing to increase crop
competition with weeds. Proceedings of the 4th International Crop Science
Congress. Website: http://www.cropscienceorg.au/icsc2004/poster/
2/4/1/412_a1fordcm.htm. Accessed: March 31, 2009.

Andrade, F. H., P. Calvino, A. Cirilo, and P. Barbieri. 2002. Yield responses to narrow
rows depends on increased radiation interception. Agron. J. 94:975-980.

Ateh, C. M. and R. G. Harvey. 1999. Annual weed control by glyphosate in glyphosate-
resistant soybean (Glycine max). Weed Technol. 13:394-398.

Culpepper, A. S., A. C. York, R. B. Batts, and K M. Jennings. 2000. Weed
management in glufosinate- and glyphosate-resistant soybean (Glycine max).
Weed TechnoL 14:77-88.

Dalley, C. D., J. J. Kells, and K. A. Renner. 2004. Effect of glyphosate application
timing and row spacing on weed growth in corn (Zea mays) and soybean (Glycine
max). Weed Technol. 18:177-182.

Dawson, J.H. 1977. Competition of late-emerging weeds with sugarbeets. Weed Sci.
25:168-170.

Dexter, A. G., J. L. Luecke, and L. J. Smith. 1999. Inﬂuence of cultivation on yield of
Roundup Ready and Liberty Link sugarbeet. Sugarbeet Res. Ext. Rep. 30:100-
101.

Johnson, G. A. and T. R. Hoverstad. 2002. Effect of row spacing and herbicide
application timing on weed control and grain yield in corn (Zea mays). Weed
Technol. 16:548-533.

Moraghan, J. T. 1972. Water use by sugar beets in a semiarid environment as inﬂuenced
by population and nitrogen fertilizer. Agron. J. 64:759-762.

Morillo-Velarde, R. and E. S. Ober. 2006. Water use and irrigation. Pages 221-255 in
A. P. Draycott, ed. Sugar Beet. Ames, IA: Blackwell Publishing.

National Agricultural Statistics Service (NASS). 2008. Adoption of genetically
engineered cr0ps in the US. Website:http://www.ers.usda.gov/Data/
BiotechCrops/. Accessed: February 14, 2008.

Pedersen, P. and J. G. Lauer. 2003. Corn and soybean response to rotation sequence,
row spacing, and tillage system. Agron. J. 95:965-971.

42

Ransom, C. V., C. J. Guza, and J. Ishida. 1998. Row spacing and plant populations in
Roundup-resistant sugar beets. Oregon State University Malheur Experiment
Station Annual Report. Website: http://www.cropinfo.net/Annual '
Reports/1998/density.beet.htm Accessed: April 3, 2007.

Stebbing, J. A., R. G. Wilson, A. R. Martin, and J. A. Smith. 2000. Row spacing,
redroot pigweed (A maranthus retroﬂexus) density, and sugarbeet (Beta vulgaris)
cultivar effects on sugarbeet development. J. Sugar Beet Res. 37:11-31.

Widdicombe, W. D. and K D. Thelen. 2002. Row width and plant density effects on
corn grain production in the northern corn belt. Agron. J. 94:1020-1023.

Wilson, R. G., C. D. Yonts, and J. A. Smith. 2002. Inﬂuence of glyphosate and
glufosinate on weed control and sugarbeet (Beta vulgaris) yield in herbicide-
tolerant sugarbeet. Weed Technol. 16:66-73.

Winter, S. R. Sugarbeet yield and quality response to irrigation, row width, and stand
density. J. Sugar Beet Res. 26:26-33.

Yelverton, F. H. and H. D. Coble. 1991. Narrow row spacing and canopy formation
reduces weed resurgence in soybeans (Glycine max). Weed Technol. 52169-174.

Yonts, D. C. and J. A. Smith. 1997. Effects of plant population and row width on yield
of sugarbeet. J. Sugar Beet Res. 34:21-30.

Young, B. G., J. M. Young, L. C. Gonzini, s. E. Hart, L. M. wax, and G. Kapusta. 2001.

Weed management in narrow- and wide-row glyphosate-resistant soybean
(Glycine max). Weed Technol. 15:112-121

43

CHAPTER 3
WEED MANAGEMENT IN WIDE— AND NARROW-ROW GLYPHOSTATE-

RESISTANT SUGARBEET

Abstract: Planting glyphosate-resistant sugarbeet in narrow rows may provide growers
the opportunity to improve weed control with fewer herbicide applications and
cultivations. Field studies were conducted in 2007 and 2008 at multiple locations in
Michigan to compare weed management, sugarbeet yield and quality in glyphosate-
resistant sugarbeet planted in 38-, 51-, and 76-cm rows. At all locations, weed population
densities and biomass were less aﬁer glyphosate treatments than conventional herbicide
treatments. Weed population densities and biomass were lower in narrow rows compared
with 76-cm rows following a single glyphosate application when weeds were lO-cm tall.
This suggests that the greater canopy cover provided by narrow rows may potentially
reduce the number of glyphosate applications necessary for season-long weed control.
When averaged over row width, glyphosate-resistant sugarbeet root yield was similar to
the weed ﬁ'ee treatment for all herbicide treatments where glyphosate was applied when
weeds were lO-cm in height or smaller. However, root yields were reduced when
glyphosate applications were delayed until weeds averaged 15-cm in height. When
averaged over all herbicide treatments, sugarbeet root and sugar yields were highest in
the narrow row widths. Regardless of row width, initial glyphosate applications should
be made before weeds reach lO-cm in height to maximize yield and minimize crop
competition with weeds.

Nomenclature: Glyphosate; sugarbeet, Beta vulgaris L.

44

Key words: Herbicide-resistant crops, row width, weed biomass.

INTRODUCTION

Weed control is often listed by sugarbeet producers as their most serious
production issue (Carlson et al. 2008). Glyphosate-resistant sugarbeet was fully
commercialized in 2008. The use of glyphosate in glyphosate-resistant sugarbeet may
provide growers the opportunity for excellent control of many weed species common to
sugarbeet production with fewer herbicide active ingredients and applications (Guza et al.
2002; Kniss et a1. 2004), while eliminating the potential for crop injury (Wilson et al.
2002). Growers may also be able to reduce or potentially eliminate between-row
cultivation with the use of glyphosate-resistant sugarbeet. Additionally, the time between
herbicide applications may be longer with glyphosate-resistant sugarbeet compared with
conventional sugarbeet herbicide programs, because weed height at the time of
application is generally not as limiting with glyphosate. As a result of this ﬂexibility in
application timing, growers may delay glyphosate applications to maximize the number
of weeds controlled and minimize the number of applications necessary for season-long
control. However, delayed glyphosate applications have led to yield losses due to the
lengthened duration of competition between crop and weed in corn (Zea mays L.) and
soybean (Glycine max [L.] Merr.) (Gower et al. 2003; Dalley et al. 2004a). Previous
research on application timing in glyphosate-resistant sugarbeet has shown that sugarbeet
is generally tolerant of early-season weed competition. Kemp and Renner (unpublished
data) found that sugarbeet yields were similar for glyphosate application timings at weed

heights up to 30—cm. Wilson et al. (2002) concluded that the optimum glyphosate

45

application timing was when weeds were lO-cm in height. Despite some tolerance to
early-season weed competition, applications should be made at a time when glyphosate
will provide sufficient control.

Numerous studies on the effect of row width on crop yield have been conducted
with many agronomic crops. Results of these studies have been somewhat inconsistent
and vary among crop; however, the general outcome trends towards increased yields in
narrower rows due to increased light radiation interception (Andrade et al. 2002).
Narrow rows also provide more complete canopy cover that shades bare soil between
rows, thereby reducing late-season weed emergence and growth (Johnson and Haverstad
2002). Yelverton and Coble (1991) observed a signiﬁcant reduction in weed density and
biomass in soybean planted in narrows rows compared with wide rows. Dalley et al.
(2004b) also observed a similar trend of reduced weed biomass in narrow-row soybean.
In three of four years, soybean planted in 19- and 38-cm rows had signiﬁcantly less weed
growth after an initial glyphosate application compared with 76-cm rows. In both
studies, the reduction in weed growth was attributed to the greater canopy cover provided
by narrow rows.

Sugarbeet is typically grown in row widths ranging from 56- to 76-cm, depending
on growing region. In Michigan, a majority of sugarbeet production occurs in 71- or 76-
cm row widths (C. Guza, personal communication). Similar to results from corn and
soybean, previous research has shown an inverse relationship between sugarbeet row
width and yield. Cattanach and Schroeder (1979) summarized 31 prior research trials
comparing wide and narrow row sugarbeet production and concluded that narrow rows

produce higher sugar yields than wide rows. In their own trials, Cattanach and Schroeder

46

(1979) observed higher root and sugar yields in 51 -cm rows when compared with 76-cm
rows. Yonts and Smith (1997) found that the highest sugar yield was obtained with 56-
cm rows, when compared with 35- and 76-cm rows. Stebbing et al. (2000) showed an
increase in root and sugar yield with 46-cm rows compared with 56- and 76-cm rows in
one of two years. The authors attributed yield increases in 46-cm rows to the reduced
intra-plant competition due to greater within-row distance between plants. In a
comparison of glyphosate-resistant sugarbeet planted in 28- and 56-cm, Giles et al.
(2001) found the highest sugar yields in the narrower row width.

Planting glyphosate-resistant sugarbeet in narrow rows may provide growers the
opportunity to improve weed control with fewer herbicide applications and cultivations,
while potentially improving yield and quality. Though previous research has been
conducted examining the effects of row width on sugarbeet yield and weed growth in
conventional sugarbeet varieties, no research has been published comparing different
weed management strategies in wide and narrow row glyphosate-resistant sugarbeet.
Therefore, the objective of this research was to evaluate weed management and sugarbeet
yield and quality in glyphosate-resistant sugarbeet planted in wide and narrow row

widths.

MATERIALS AND METHODS
Field studies were conducted in 2007 and 2008 at three locations, two in the
Saginaw Valley region at the Michigan State University Saginaw Valley Bean and Beet
Research Farm and on commercial production ﬁelds near St. Charles, Michigan, and a

third location at the Michigan State University Crop and Soil Sciences Research Farm in

47

East Lansing, Michigan. The soil at the Saginaw Valley Bean and Beet Research Farm
was a Zilwaukee silty clay (ﬁne, mixed, mesic Fluvaquentic Endoaquolls) with soil pH of
7.4 and 3.9% organic matter. The soil type at the commercial production ﬁelds was a
Sloan silty clay loam (ﬁne-loamy, mixed, mesic F luvaquentic Endoaquolls) with soil pH
of 7.5 and 10.5% organic matter in 2007 and soil pH of 7.2 and 3.3% organic matter in
2008. At the East Lansing site, the soil type was a Capac ﬁne sandy loam (ﬁne-loamy,
mixed, mesic Aquic Glossudalfs) with soil pH of 6.9 and 2.5% organic matter.
Experiments followed soybean, wheat (T riticum aestivum L.), and dry bean (Phaseolus
vulgaris L.) in 2006, 2007, and 2008, respectively, at the Bean and Beet Research F arm.
At the commercial production ﬁelds and East Lansing location, experiments followed
corn in 2007and $0be in 2008. Fields were fall-plowed followed by ﬁeld cultivation

prior to planting in the spring. Fertilizer applications were standard for sugarbeet

production in Michigan. A glyphosate-resistant sugarbeet variety, ‘Hilleshog 90281,’

was planted at a depth of 2.5-cm in mid- to late-April. Sugarbeet was planted in 38-, 51-,
and 76-cm row widths at the Saginaw Valley locations. At the East Lansing location,
only 38- and 76-cm row widths were investigated. Plots were 11 rows (3 8-cm row
width), eight rows (SI-cm row width), and six rows wide (76-cm row width) by 9.1 m
long at the Bean and Beet Research Farm and commercial production ﬁelds. At the East
Lansing location, plots were seven and eight rows wide (38-cm row width) in 2007 and
2008, respectively, and four rows wide (76-cm rows) by 9.1 m long. Sugarbeet
populations were thinned to a uniform density of 77,000 plants/ha in all row widths when

sugarbeet were at the four-leaf growth stage.

48

The experiment was set-up as a split-plot design, with row width as the main plot

factor and weed control treatment as the sub-plot factor. All treatments were replicated

four times. Treatments were glyphosate2 at 840 g ae/ha plus ammonium sulfate (AMS)

at 2% v/v applied at various weed heights and conventional herbicide programs applied
as micro-rate or standard-split treatments. Weed control treatments, application timings,
and sugarbeet grth stage at application are summarized in Table 9. Micro-rate
herbicide treatments consisted of desmedipham + phenmedipham at 45 + 45 g/ha plus
triﬂusulﬁrron at 4.4 g/ha plus clopyralid at 26 g/ha plus methylated seed oil (MSO) at
1.5% v/v applied four times on 125 GDD (base 1.] C) intervals starting after planting.
Standard-split herbicide treatments consisted of desmedipham + phenmedipham at 180 +
180 g/ha plus triﬂusulfuron at 35 g/ha plus clopyralid at 104 g/ha applied twice, starting
222 GDD after planting with the second application made 236 GDD following the ﬁrst
application. A non-ionic surfactant at 0.25% v/v was included with the second standard-
split application. Weed free and nontreated wntrol plots were also established. Weed
free plots were maintained with applications of 840 g ae/ha plus AMS at 2% v/v as
needed, starting at 2-cm weeds. Herbicide applications were made using a tractor-

mounted compressed-air sprayer calibrated to deliver 178 L/ha at 207 kPa through
AirMix 110033 nozzles.

Common lambsquarters (Chenopodium album L.) and a combination of redroot
pigweed (Amaranthus retroﬂexus L.) and Powell amaranth (Amaranthus powellii S.

Watson) were the predominant weed species at the Saginaw Valley Bean and Beet

Research Farm and commercial production ﬁelds in 2007 and 2008. These weed species

49

plus a mixture of annual grass weed species was present at the East Lansing location in
2007 and 2008. In 2008, common purslane (Portulaca oleracea L.) was also present.

Weed population counts and aboveground weed biomass was harvested from two

0.25 m2 quadrats placed in the center of each plot in mid-August. Weed biomass was

dried for 72 h in a forced air oven at 60 C and weighed. Two rows of sugarbeet were

mechanically harvested from each plot and weighed in mid-September and a sub-sample

of roots was analyzed for quality and purity by the Michigan Sugar Company4.

Sugarbeet quality is expressed as kg of recoverable white sucrose per Mg of root
(RWSMg). Total sucrose production is expressed as kg of recoverable white sucrose per

hectare (RWSH).

Data were subjected to ANOVA using PROC MIXED in SAS5 and treatment

means for weed counts and biomass and sugarbeet root yield, RWSMg, and RWSH were
compared using Fisher’s Protected LSD at the p = 0.05 signiﬁcance level. Weed count
and biomass data were log (x + l) transformed for analysis and the back-transformed data
are presented. Interactions between main effects were also analyzed using the SLICE
option in the LSMEANS statement (Littell et al. 1996). Data were combined over

environment, row width, or treatment when interactions were not signiﬁcant.

RESULTS AND DISCUSSION
Weed population density and biomass. There was not an interaction between herbicide
treatment and row width; therefore weed population counts and biomass data were

combined over row width. This indicates that weeds responded similarly to the weed

50

control treatments, regardless of sugarbeet row width. Data are presented separately for
studies that had all three row widths (Saginaw Valley Bean and Beet Research Farm and
commercial production ﬁelds) and those that only compared 38- and 76-cm row widths
(East Lansing). Overall weed populations were lower at the Saginaw Valley locations
compared with the East Lansing location (Table 10); however, weed biomass in the
nontreated plots was greater at the Saginaw Valley locations.

At the Saginaw Valley locations, weed densities were similar among all
glyphosate treatments (Table 10), and weed densities and biomass were lower than in the
conventional herbicide treatments. Weed biomass was lowest in treatments that had two
glyphosate applications. Overall, the lowest weed density and biomass was in the
treatment where the initial glyphosate was applied when weeds were 5-cm in height with
a second application when weeds were lO-cm in height.

At the East Lansing location, data were also combined over row width because
there was not a herbicide treatment by row width interaction. Weed density and biomass
was lowest in the treatment where the initial glyphosate application was made when
weeds were 5-cm in height (Table 10). Among all glyphosate treatments, treatments that
consisted of two applications resulted in the lowest weed density and biomass at the end
of the growing season. All treatments that contained glyphosate resulted in lower weed
densities and less weed biomass compared with the conventional herbicide treatments.

Though the interaction of row width and herbicide treatment was not signiﬁcant,
signiﬁcant differences among row widths were observed for weed population density and
biomass following a single glyphosate application when weeds were 10-cm tall. At the

Saginaw Valley locations, weed population counts and biomass were reduced in the 38-

51

and Sl-cm rows compared with the 76-cm rows (Table 11). Likewise, weed biomass was
reduced in the 38-cm rows compared with the 76-cm rows at the East Lansing location.
Alford et al. (2004) observed signiﬁcant reductions in weed biomass in sugarbeet planted
38- and 56-cm rows compared with 76-cm rows, due to earlier and greater canopy cover
in the narrow row widths. These results indicate that sugarbeet planted in narrow rows
can suppress late-season weed growth, particularly following an initial glyphosate
application to control early-season weeds. Greater canopy cover in narrow rows may
potentially reduce the number of glyphosate applications necessary for season-long weed

control compared with wide rows.

Sugarbeet root yield and quality. Interactions between herbicide treatment and row
width were not signiﬁcant. When averaged over row width, glyphosate-resistant
sugarbeet root yield was similar to the weed free treatment for all herbicide treatments
where glyphosate was applied when weeds were lO-cm or less in height (Table 12).
However, due to increased length of competition with weeds, root yields were reduced
when glyphosate applications were delayed until weeds averaged 15-cm in height.
Additionally at the East Lansing location, yields were reduced in the conventional
herbicide treatment. Despite differences in root yield, RWSMg and RWSH were similar
among all herbicide treatments.

When averaged over all herbicide treatments, sugarbeet root yields were highest
in the 38- and 51-cm rows compared with 76-cm rows at the Saginaw Valley locations
(Table 13). RWSMg was also greatest in 38- and 51-cm rows. Likewise, at the East

Lansing location, root yield and RWSMg were greatest in 38-cm rows. As a result of

52

higher root yield and RWSMg, RWSH was also highest in narrow rows. Because plant
populations were kept constant across row width, it is likely that narrower rows produced
higher yields due to increased light interception, reduced within-row competition among
sugarbeet plants, and reduced competition with weeds.

Glyphosate-resistant sugarbeet varieties will offer producers the opportunity to
reduce or potentially eliminate between-row cultivation and potentially take advantage of
planting in narrow rows. Regardless of row width, multiple applications of glyphosate
will be necessary to ensure season-long weed control and initial glyphosate applications
should be made when weeds are lO-cm or less in height to prevent yield loss ﬁom
competition with weeds. In addition to increased yield, sugarbeet planted in narrow rows
can provide greater canopy cover to suppress weed growth later in the growing season.
Results from this research will provide sugarbeet growers information for maximizing
sugarbeet yield and quality, while reducing the effects of weed competition, when

adopting glyphosate-resistant sugarbeet varieties and planting in narrow rows.

SOURCES OF MATERIALS

1 Syngenta Seeds Inc., 1020 Sugarmill Rd., Longmont, co 80501.

2 Roundup WeatherMAX, Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167.
3 AirMix 11003, GreenleafTechnologies, PO. Box 1767, Covington, LA 70434.

4 Michigan Sugar Company, 2600 S. Euclid Ave, Bay City, MI 48706

5 The SAS System for Windows, Version 9.1, SAS Institute Inc., 100 SAS Campus Dr.,

Cary, NC 27513.

53

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55

Table 11. Weed populations and biomass following a single glyphosate application when
weeds were lO-cm tall at the Saginaw Valley locations where 38-, 51- and 76-cm row
widths were compared and at the East Lansing location where 38- and 76-cm row widths

were compared. Data were combined across 2007 and 2008 for the respective locations.a

 

 

 

Saginaw Valleyb East Lansing
Row width Weed density Weed biomass Weed density Weed biomass
weeds/m2 kg/ha weeds/m2 kg/ha
38—cm 0.6 a 0.4 a 11.8 a 4.6 a
51-cm 0.9 a 0.7 a J —
76-cm 2.7 b 3.9 b 23.3 a 12.2 b

 

a Means within column followed by the same lowercase letter are not different according
to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

Data were combined across the Saginaw Valley Bean and Beet Research Farm and
commercial production ﬁeld locations.

0 51-cm rows were not investigated at the East Lansing location.

56

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57

Table 13. Sugarbeet root yield, recoverable white sucrose per Mg of root (RWSMg), and
recoverable white sucrose per hectare (RWSH) for row width when averaged over
herbicide treatment at the Saginaw Valley locations where 38-, 51- and 76-cm row widths
were compared and at the East Lansing location where 38- and 76-cm row widths were

compared. Data were combined across 2007 and 2008 for the respective locations.a

 

Saginaw Valleyb East Lansing

 

 

Row widthc Root yield RWSMg RWSH Root yield RWSMg RWSH

Mg/ha kg/Mg kg/ha Mg/ha kg/Mg kg/ha

 

38-cm 82.8 a 116.6 a 9590 a 56.8 a 107.5 a 6400 a
51-cm 82-5 a 117.2 a 9660 a —d — —
76-cm 78.6 b 114.1 b 8920 b 48.1 b 103.7 b 4940 b

 

a Means within column followed by the same lowercase letter are not different according
to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b Data were combined across the Saginaw Valley Bean and Beet Research Farm and
commercial production ﬁeld locations.

c Herbicide treatments were combined over all row widths investigated at each location.

(1 . . . .
51-cm rows were not investigated at the East Lansmg location.

58

LITERATURE CITED

Alford, C. M., S. D. Miller, and J. T. Cecil. 2004. Using row spacing to increase crop
competition with weeds. Proceedings of the 4th International Crop Science
Congress. Website: http://www.cropscienceorg.au/icsc2004/poster/
2/4/1/412_alfordcm.htm. Accessed: April 18, 2007.

Andrade, F. H., P. Calvino, A. Cirilo, and P. Barbieri. 2002. Yield responses to narrow
rows depends on increased radiation interception. Agron. J. 94:975-980.

Carlson, A. L., J. L. Luecke, M. F. R. Khan, and A. G. Dexter. 2008. Survey of weed
control and production practices on sugarbeet in eastern North Dakota and
Minnesota in 2007. Sugarbeet Res. Ext. Rep. 38264-68.

Cattanach, A. and G. Schroeder. 1979. A comparison of 22 versus 30 inch row spacings
at equal plant populations in 1976-1977. Sugarbeet Res. Ext. Rep. 10:198-203.

Dalley, C. D., J. J. Kells, and K A. Renner. 2004a. Effect of glyphosate application
timing and row spacing on corn (Zea mays) and soybean (Glycine max) yields.

Weed Technol. 18:165-176.

Dalley, C. D., J. J. Kells, and K. A. Renner. 2004b. Effect of glyphosate application
timing and row spacing on weed growth in corn (Zea mays) and soybean (Glycine
max). Weed Technol. 18:177-182.

Giles, J. F., C. S. Von Holstein, R. Wilson, C. Ransom, C. Guza, J. Ishida, and A.
Cattanach. 2001. Effect of within-row spacing and row width on sugarbeet
production using glyphosate resistant sugarbeet. Proceedings of 3 1 st Biennial
Meeting of American Society of Sugar Beet Technologists pp. 68.

Gower, S. A, M. M. Loux, J. Cardina, S. K. Harrison, P. L. Sprankle, N. J. Probst, T. T.
Bauman, W. Bugg, W. S. Curran, R. S. Currie, R. G. Harvey, W. G. Johnson, J.
J. Kells, M.D.K. Owen, D. L. Regehr, C. H. Slack, M. Spaur, C. L. Sprague, M.
VanGessel, and B. G. Young. 2003. Effect of postemergence glyphosate
application timing on weed control and grain yield in glyphosate-resistant corn:
Results of a 2-yr multistate study. Weed Technol. 17:821-828.

Guza, C. J., C. V. Ransom, C. Mallory-Smith 2002. Weed control in glyphosate-
resistant sugarbeet (Beta vulgaris L.). J. Sugarbeet Res. 39:109-123.

JOhnson, G. A. and T. R. Hoverstad. 2002. Effect of row spacing and herbicide

application timing on weed control and grain yield in corn (Zea mays). Weed
Technol. 16:548-533.

59

Kniss, A. R., R. G. Wilson, A. R. Martin, P. A. Burgener, and D. M. Feuz. 2004.
Economic evaluation of glyphosate-resistant and conventional sugar beet. Weed
Technol. 18:388-396.

Littell, R. C., G. A. Milliken, W. W. Stroup, and R. D. Wolfinger. 1996. SAS® system
for mixed models. Cary, NC: SAS Institute, Inc. Pp. 52.

Wilson, R. G., C. D. Yonts, and J. A. Smith 2002. Inﬂuence of glyphosate and
glufosinate on weed control and sugarbeet (Beta vulgaris) yield in herbicide-
tolerant sugarbeet. Weed Technol. 16266-73.

Yelverton, F. H. and H. D. Coble. 199]. Narrow row spacing and canopy formation
reduces weed resurgence in soybeans (Glycine max). Weed Technol. 52169-174.

Yonts, D. C. and J. A. Smith. 1997. Effects of plant population and row width on yield
of sugarbeet. J. Sugar Beet Res. 34:21-30.

60

CHAPTER 4
ADJUSTMENTS IN PLANTING PRACTICES TO MAXIMIZE ECONOMIC

RETURN IN GLYPHOSATE-RESISTANT SUGARBEET

Abstract: In Michigan, sugarbeet production is contracted using a quality payment
system that adjusts the price paid per Mg of root weight according to the quality of the
sugarbeet root. Sugarbeet quality, or kg of recoverable white sucrose per Mg of root
(RWSMg), can be inﬂuenced by many factors including row width and plant population.
With the introduction of glyphosate-resistant sugarbeet, growers may consider adjusting
production practices, such as planting in narrow rows, to maximize sugarbeet production.
However, the higher cost of glyphosate-resistant sugarbeet seed may persuade growers to
reduce seeding rates to reduce production costs. The objective of this research was to
determine how row width and plant population can inﬂuence root yield, sugarbeet
quality, and economic return in glyphosate-resistant sugarbeet. Studies were conducted
in 2007 and 2008 at multiple locations in Michigan to determine the effect of planting
glyphosate-resistant sugarbeet in row widths of 38-, 51-, and 76-cm and populations of
54,000; 78,000; 101,000; and 124,000 plants/ha. Gross margins were calculated using a
base price weighted according to RWSMg and a constant base price. At the Saginaw
Valley locations, Sl-cm rows had the highest root yields and an increase in gross margin
of at least $200/ha compared with 38- and 76-cm rows, when the base price was adjusted
for quality. Using a constant base price, 38- and 76-cm had similar gross margins, but
were still signiﬁcantly lower than 51-cm rows. At the East Lansing location, root yields

and gross margins were similar for 38- and 76-cm rows in 2007. In 2008, 38-cm rows

61

provided a 10.2 Mg/ha root yield advantage over 76-cm rows. In 2008, plant populations
of 78,000; 101,000; and 124,000 plants/ha in 38-cm rows resulted in the highest gross
margins. Despite observed increases in RWSMg at higher plant populations, results from
this analysis suggest that economic returns for sugarbeet production are inﬂuenced
primarily by root yields and are highest for sugarbeet planted in narrow rows.
Nomenclature: Glyphosate; sugarbeet, Beta vulgaris L.

Key words: Economic analysis, herbicide-resistant crops, plant population; proﬁtability;

row width.

INTRODUCTION

Sugarbeet root quality is the most important factor affecting processing efficiency
(Dutton and Huijbregts 2006). Sugarbeet quality can be expressed by many different
factors, including sucrose and non-sucrose concentration in the root and clear juice
purity. From a practical standpoint, many sugarbeet processors deﬁne sugarbeet quality
as the kg of recoverable white sucrose per Mg of sugarbeet root weight (RWSMg).
RWSMg factors in the sucrose concentration of the root and the extractable clear juice
purity. Sugarbeet root quality is inﬂuenced by environmental and production factors
including: variety selection, planting and harvest date, nitrogen fertility, row width, plant
population, and storage (Dutton and Huijbregts 2006; Asadi 2007). Previous research has
shown that sucrose concentration in the sugarbeet root is generally higher in narrow rows
and at high plant populations (Y onts and Smith 1997). Under these conditions there is
less space between plants within and between rows. Yonts and Smith (1997) observed a

trend of higher sucrose concentrations, due to the smaller growth of each individual beet

62

at higher populations. However, sucrose concentration did not increase at plant
populations more than 65,000 plants/ha. Winter (1989) also observed higher sucrose
concentrations in sugarbeet planted at higher populations.

All sugarbeet production in Michigan is contracted through the Michigan Sugar
Company, a grower-owned cooperative. Sugarbeet contracts through the Michigan Sugar
Company are structured as tournament contracts to motivate growers to produce
sugarbeet with high RWSMg levels (Knoeber 1989). Under the terms of this contract
structure, growers “compete” against one another to determine their payment per Mg of
sugarbeet root. The Michigan Sugar Company uses a quality payment system based on

the formula:

Pgmwer = Pbase X (Grower RWSMg/Company average RWSMg)

where Pgmwer is the ﬁnal price per ton of sugarbeet root paid to the grower and Phase is

the base price per ton of sugarbeet root paid by Michigan Sugar Company. In this

formula, Pgmwer is calculated by multiplying Pbase by the ratio of the grower’s RWSMg

to the overall company average RWSMg. Pgrowe, can be adjusted above or below Pbasea

depending on the ratio of the RWSMg values. As is the structure of tournament
contracts, growers are incentivized to produce high quality sugarbeet (i.e. sugarbeet with
high RWSMg), rather than simply maximize root yield.

Weed control is often listed by sugarbeet growers as the most difﬁcult task they

face in production (Carlson et al. 2008). Similar to other glyphosate-resistant crops, the

63

commercial release of glyphosate-resistant sugarbeet in 2008 may provide growers the
opportunity to improve weed control with fewer herbicides, applications, and cultivations
and improve control of weed that are resistant to other herbicide modes of action.
Production costs for sugarbeet are considerable and can reach as high as $1 SOO/ha
(Burgener 2001). In addition to production expenses associated with planting,
fertilization, fungicide and herbicide applications, and harvesting, growers will pay a
technology fee of $ 1 06 per unit of 100,000 seeds when purchasing glyphosate-resistant
sugarbeet seed, or approximately $130/ha at a seeding rate of 124,000 seeds/ha To
recover this added expense, growers must increase their economic returns by increasing
yield and quality, reducing weed control expenses, or reducing seeding rates to minimize
cost. Growers must also balance the added expense of planting at higher seeding rates
with the increases in sugarbeet quality often observed from planting at higher plant
populations.

In Michigan, a majority of sugarbeet production occurs in 71- or 76-cm row
widths, with a target ﬁnal plant population of approximately 78,000 plants/ha (C. Guza,
personal communication). With the beneﬁts of glyphosate-resistant sugarbeet for
improved weed control and reduced need for between-row cultivation, growers may be
able to adopt narrow rows for planting. Previous research has compared yields and
economic returns ﬁom conventional and glyphosate-resistant sugarbeet (Kniss et al.
2004), however, no research has been published comparing glyphosate-resistant
sugarbeet production in multiple row widths and populations and the impact of these

production practices on economic return. Therefore, the objective of this research was to

64

determine how adjustments in row width and plant population inﬂuence economic return

for glyphosate-resistant sugarbeet production in Michigan.

MATERIALS AND METHODS

Field trials were conducted in 2007 and 2008 at the Michigan State University
Agronomy Research Farm in East Lansing, the Michigan State University Saginaw
Valley Bean and Beet Research Farm, and on commercial production ﬁelds near St.
Charles, Michigan. At the East Lansing location, the soil type was a Capac ﬁne sandy
loam (ﬁne—loamy, mixed, mesic Aquic Glossudalfs) with soil pH of 6.9 and 2.5% organic
matter. The soil at the Bean and Beet Research Farm was a Zilwaukee silty clay (ﬁne,
mixed, mesic Fluvaquentic Endoaquolls) with soil pH of 7.4 and 3.9% organic matter.
The soil type at the commercial production ﬁelds was a Sloan silty clay loam (ﬁne-
loamy, mixed, mesic Fluvaquentic Endoaquolls) with soil pH of 7.5 and 10.5% organic
matter in 2007 and soil pH of 7.2 and 3.3% organic matter in 2008. Fields were fall-
plowed followed by ﬁeld cultivation prior to planting in the spring. Fertilizer

applications were standard for sugarbeet production in Michigan. The glyphosate-

resistant sugarbeet variety, ‘Hilleshog 90282,’ was planted in 38-, 51-, and 76-cm row

widths to a depth of 2.5—cm. At East Lansing, only 38- and 76-cm row widths were
investigated. At the 4-leaf grth stage, stands were thinned to densities of 54,000;
78,000; 101,000; or 124,000 plants/ha. Populations were held constant across row
widths, leading to differences in within-row plant spacing for each population (Table 14).

Weed-free plots were established for all years of the study and maintained with

applications of glyphosate3 at 840 g ae/ha + ammonium sulfate (AMS) at 2% v/v as

65

needed. Two rows of sugarbeet were mechanically harvested and weighed from each

plot in mid-September and a sub-sample of roots was analyzed for quality and purity by

the Michigan Sugar Company4. Sugarbeet quality is expressed as kg of recoverable

white sucrose per Mg of root (RWSMg).

A split-plot experimental design was used for these studies, with row width as the
main plot factor and plant population as the sub plot factor. A partial budget analysis was
conducted to compare economic returns for sugarbeet root yield and quality as inﬂuenced

by row width and plant population. Gross margins were calculated using the formula:

Gross margin = (Y X (R WSMgplot / RWSMgm-al) X Phase) -
(W + (Srate X (Scost + D / 100.000»

where Y is root yield/ha, RWSMgplot and RWSMgm-a] represent the RWSMg values for

individual plots and the overall average for each trial, respectively, Pbase is base price

paid per ton of sugarbeet root, W is weed control expense per ha including herbicide and

application expenses, Smte is seeding rate per ha, T is the cost of the technology fee per

unit of 100,000 seeds, and Sam is the cost of seed per unit of 100,000 seeds minus the

technology fee. In this analysis, root yields and RWSMg values for each individual plot
were used and RWSMg values were compared to the trial average for each year and
location. A base price of $44/Mg of sugarbeet root was assumed. Base prices of $37 and
$51/Mg were also used to determine sensitivity of gross margin to changes in price. In

addition to calculating gross margins using a weighted base price, gross margins were

66

also calculated using a constant base price regardless of sugarbeet quality to compare two
methods for determining economic return. Because sugarbeet stands were thinned to
stand, a seeding rate of 167% of the desired population was used to calculate the total
cost of seed, assuming 60% germination and establishment. Herbicide expenses for
applications of glyphosate at 840 g ae/ha + AMS at 2% v/v were estimated using price
sheets from two agrichemical distributors in mid-Michigan. Herbicide application
expenses were derived from custom work estimates compiled by Stein (2008). Based on
weed control data from prior studies (Chapter 3), two applications were assumed for
glyphosate-resistant sugarbeet planted in 38- and Sl-cm row widths and three
applications were assumed for 76-cm row widths. All variable costs used in the partial

budget analysis are summarized in Table 15.

All data were subjected to ANOVA using PROC MIXED in SAS5 and treatment

means for gross margin were compared using Fisher’s Protected LSD at the p = 0.05
signiﬁcance level. Multiple signiﬁcance levels up to p = 0.20 were also used to compare
treatment means, however statistical signiﬁcance among treatments remained similar to
the p = 0.05 level. Data were combined over environment, row width, or population and

presented for main effects when signiﬁcant interactions were not present.

RESULTS AND DISCUSSION
Data are presented separately for studies that had all three row widths (Saginaw
Valley Bean and Beet Research Farm and commercial production ﬁelds) and those that
only compared 38- and 76-cm row widths (East Lansing). Data were combined across

year where signiﬁcant interactions involving these effects were not present. A signiﬁcant

67

interaction between row width and plant population was not observed for gross margins
at the Saginaw Valley locations and data are presented separately for row width and plant
population. The lack of signiﬁcant interaction between row width and plant population
indicates that economic returns for a certain row width would be similar for all plant
populations within that row width.

When averaged over all plant populations, glyphosate-resistant sugarbeet planted
in 51-cm rows had the highest root yield (Table 16). Similar to root yield, the highest
gross margins were observed in Sl-cm rows when calculated using a weighted base price
based on the RWSMg value for each plot compared to the overall average RWSMg for
each environment. Compared with 38- and 76-cm rows, gross margins in Sl-cm rows
were at least $200/ha greater. When a constant base price of $44 per Mg of sugarbeet
root was used to calculate gross margins, 5 1 -cm row widths also resulted in the highest
returns at $3290/ha. Gross margins for 38- and 76-cm rows were signiﬁcantly lower at
$3050 and $3000/ha, respectively. Based on the experimental data in this analysis, gross
margins were similar for both the weighted and constant base price payment calculation
methods. When comparing among plant populations, RWSMg increased at higher plant
populations at the Saginaw Valley locations and root yields were statistically similar
among all plant populations (Table 16). Despite the increase in RWSMg at higher
populations, the increase was not great enough to inﬂuence gross margin, as gross
margins were statistically similar among all plant populations (Table 16). Separation of
treatment means of gross margins were similar among all prices used in this analysis

(data not presented). Similar results were also observed at the East Lansing location in

68

2007 and 2008, where root yields, RWSMg, and gross margins were similar among all
plant populations (Table 18).

At the East Lansing location, root yields and RWSMg were similar among 38-
and 76-cm rows in both 2007 and 2008 (Table 17). Due to dry conditions during June
and July of 2007 when precipitation totals were 60 and 52 mm below the 30 year average
at St. Charles and East Lansing, respectively, root yields were comparably lower than in
2008 (Chapter 2). Sugarbeet root yields and RWSMg were similar for all plant
populations (Table 18). As a result, regardless of the method used to calculate gross
margin, gross margins were similar for all row width and plant population combinations
in 2007 (Table 19). When growing conditions were more favorable in 2008, root yields
were 10.2 Mg/ha higher in 38-cm rows than 76—cm rows. For gross margins, an
interaction between row width and plant population was observed at East Lansing in
2008. Comparing across all row width and plant populations, gross margins were highest
in populations of 78,000; 101,000; and 124,000 plants/ha in 38-cm rows when either a
weighted base price or constant base price was used to calculate gross margin.
Separation of treatment means of gross margins were similar among base prices of
$37/Mg to $51/Mg (data not presented).

Results from this analysis indicate that economic returns for glyphosate-resistant
sugarbeet production can be inﬂuenced by row width At locations where 38-, 51-, and
76-cm row widths were compared, root yields and economic returns were highest in 51-
cm rows. At locations where 38- and 76-cm row widths were compared, root yields and
economic returns were highest in 38-cm rows when moisture was not limiting. Gross

margins were similar whether or not sugarbeet quality was used to adjust the base price

69

for grower payments. Planting in narrow rows may also potentially ﬁirther reduce weed
control costs because of increased canopy cover and suppressed weed growth, requiring
fewer herbicide applications for season-long weed control.

Though planting at higher populations did increase sugarbeet quality, root yields
were similar among all plant populations at all locations. Overall, RWSMg values for
individual plots ranged from 20% below to 16% above the respective trial average, but
nearly 75% of all data points fell within 5% of the trial average. The purpose a
tournament contract, in the case of sugarbeet production contracted with the Michigan
Sugar Company, is to provide an incentive for growers to produce sugarbeet with high
RWSMg levels for the sugarbeet processor. Under the quality payment system, growers
receive a proportionally higher price per Mg of sugarbeet root for higher quality
sugarbeet. However, based on sugarbeet root yield and quality data ﬁom this analysis,
RWSMg values deviated very little from the overall average and thus, sugarbeet quality
had a relatively small effect on the price per Mg of sugarbeet root and overall
proﬁtability. Therefore, despite increases in RWSMg in higher plant p0pu1ations, results
from this analysis suggest that economic returns for sugarbeet production are inﬂuenced
primarily by higher root yields achieved by planting in narrow rows.

The higher cost of glyphosate-resistant sugarbeet seed may persuade growers to
reduce planting densities. Sugarbeet growers will also be reluctant to adjust production
practices due to expenses associated with purchasing or modifying equipment for
planting and harvesting in narrow rows. Other factors, including the age of their current
equipment (Krause and Black 1995) and crops in their rotation that could also be

switched to narrow-row production, can also inﬂuence the decision to adopt or the rate at

70

which adoption of narrow row production will occur. Additionally, costs associated with
potential increases in disease pressure in sugarbeet planted in narrow rows and increased
soil fertility requirements with higher yields should also be considered. Results of this

analysis suggest that economic returns are similar regardless of plant population, and that

proﬁtability is highest for glyphosate-resistant sugarbeet production in narrow rows

SOURCES OF MATERIALS

1 Betaseed, Inc., 1788 Marschall Rd., PO. Box 195, Shakopee, MN 55379.

2 Syngenta Seeds Inc., 1020 Sugarmill Rd., Longmont, co 80501.

3 Roundup WeatherMAX, Monsanto Co., 800 N. Lindbergh Blvd., St. Louis, MO 63167.
4 Michigan Sugar Company, 2600 S. Euclid Ave., Bay City, MI 48706.

5 The SAS System for Windows, Version 9.1, SAS Institute Inc., 100 SAS Campus Dr.,

Cary, NC 27513.

71

 

 

 

 

 

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72

Table 15. Summary of variable costs used in the partial budget analysis comparing
glyphosate-resistant sugarbeet planted in three row widths and four plant populations. A
base price of $44/Mg of sugarbeet root was assumed.

 

Seed cost $100/unita
Technology fee $106/unit

Total seed cost by plant populationb:

54,000 plants/ha $11 “ha

78,000 plants/ha $16l/ha

101,000 plants/ha 5208/1“

124,000 plants/ha 5255/1121
Herbicide application $15/applicationc
Glyphosate + ammonium sulfate (840 g ae/ha +2% v/v) $35/l‘1ad

Total herbicide cost by row width:

38-cm, 2 applications6 SIOO/ha
51-cm, 2 applications $100/ha
76-cm, 3 applications $150/ha

 

a 1 unit = 100,000 seeds

b A seeding rate of 167% of the desired population was used to calculate the total seed
cost, assuming 60% germination and establishment.

c Herbicide application costs were derived from custom work estimates compiled by
Stein (2008).

Herbicide prices were estimated using price sheets from two agrichemical distributors
in mid-Michigan.
e Based on prior studies (Chapter 3), two applications of glyphosate + ammonium sulfate

were assumed for glyphosate-resistant sugarbeet planted in 38- and 51-cm row widths
and three applications were assumed for 76-cm row widths.

73

Table 16. Root yield, recoverable white sucrose per Mg of root (RWSMg), and gross
margins for glyphosate-resistant sugarbeet in three row widths and four plant populations

at the Saginaw Valley locations in 2007 and 2008.a’b’c

 

Gross margin

 

 

Main effects Root yield RWSMg Adjusted for qualityd Constant pricee
Row width Mg/ha kg/Mg S/ha

38-cm 81.8 b 119.1 a 3090 b 3050 b
Sl-cm 87.2 a 118.4 a 3290 a 3290 a
76-cm 81.5 b 116.8 a 2960 b 3000 b
Population

(plants/ha)

54,000 83.5 a 115.4b 3110a 3210a
78,000 81.0 a 117.6 ab 3040 a 3030 a
101,000 84.3a 119.2a 3130a 3120a
124,000 85.2 a 120.1 a 3150 a 3100 a

 

 

 

a Means within column for each main effect followed by the same lowercase letter are
not different according to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

c Data were combined across the Saginaw Valley Bean and Beet Research Farm and
commercial production ﬁeld locations.

d Gross margins were calculated using a base price ($44/Mg) adjusted for quality
(RWSMg of each plot compared with the overall average RWSMg).

8 Gross margins were calculated using a constant base price of $44/Mg.

74

Table I 7. Root yield and recoverable white sucrose per Mg of root (RWSMg) for
glyphosate-resistant sugarbeet in two row widths at East Lansing in 2007 and 2008.a’

 

 

 

 

Root yield RWSMg
Row width 2007 2008 2007 & 2008
—— Mg/ha _ kg/Mg
38-cm 48.8 a 69.1 a 106.7 a
76-cm 51.2 a 58.9 b 105.1 a

 

a Means within column for each main effect followed by the same lowercase letter are
not different according to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

75

Table 18. Root yield and recoverable white sucrose per Mg of root (RWSMg) for
glyphosate-resistant sugarbeet in four plant populations at East Lansing in 2007 and

2008.8’b

 

 

Population Root yield RWSMg
Plants/ha Mg/ha kg/Mg
54,000 52.2 a 105.1 a
78,000 56.9 a 102.6 a
101,000 60.2 a 107.5 a
124,000 57.3 a 109.3 a

 

a Means within column for each main effect followed by the same lowercase letter are
not different according to Fisher’s Protected LSD at the p = 0.05 signiﬁcance level.

b All plots were kept weed free with applications of glyphosate at 840 g ae/ha +
ammonium sulfate at 2% v/v as needed.

76

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77

LITERATURE CITED

Asadi, M. 2007. Sugarbeet farming. Beet-sugar handbook. Hoboken, NJ: John Wiley
& Sons, Inc. Pp. 69.

Burgener, P. A. 2001. Economics of sugarbeet production. Pages 189-196 in R. G.
Wilson, ed. Sugarbeet Production Guide. University of Nebraska Cooperative
Extension. Lincoln, NE: University of Nebraska.

Carlson, A. L., J. L. Luecke, M. F. R. Khan, and A. G. Dexter. 2008. Survey of weed
control and production practices on sugarbeet in eastern North Dakota and
Minnesota in 2007. Sugarbeet Res. Ext. Rep. 38:64-68.

Dutton, J. and T. Hujibregts. 2006. Root quality and processing. Pages 409-442 in A. P.
Draycott, ed. Sugar Beet. Ames, IA: Blackwell Publishing.

Kniss, A. R., R. G. Wilson, A. R. Martin, P. A. Burgener, and D. M. Feuz. 2004.
Economic evaluation of glyphosate-resistant and conventional sugar beet. Weed
Technol. 18:388-396.

Knoeber, C. R. 1989. A real game of chicken: contracts, tournaments, and the
production of broilers. Journal of Law, Economics, and Organization 5:271-292.

Krause, M. A. and R. J. Black. 1995. Optimal adoption strategies for no-till technology
in Michigan. Rev. Ag. Econ. 17:299—310.

Stein, D. 2008. 2008-09 Machine custom and work rate estimates. Michigan State
University Extension. Website: http://www.msu.edu/user/steind. Accessed:
March 5, 2009.

Winter, S. R. Sugarbeet yield and quality response to irrigation, row width, and stand
density. J. Sugar Beet Res. 26:26-33.

Yonts, D. C. and J. A. Smith. 1997. Effects of plant population and row width on yield
of sugarbeet. J. Sugar Beet Res. 34:21-30.

78

CHAPTER 5
GLYPHOSATE AND TRIFLUSULFURON COMBINATION S FOR CONTROL
OF VELVETLEAF, POWELL AMARANTH, AND COMMON

LAMBSQUARTERS

Abstract: Combinations of other herbicides with glyphosate may be necessary for
satisfactory weed control in glyphosate-resistant sugarbeet. Greenhouse experiments
were conducted to characterize the response of 5- and lO-cm tall velvetleaf, Powell
amaranth, and common lambsquarters to triﬂusulfuron and combinations of glyphosate
and triﬂusulfuron. Combinations were labeled as synergistic, antagonistic, or additive for
weed control and dry weight reduction. Triﬂusulfuron alone did not successfully control
any of the weed species at either application timing. Combinations of glyphosate at 210
g ae/ha with triﬂusulfuron at 17.6 and 35.0 g ai/ha were synergistic for control and
biomass reduction of lO-cm tall velvetleaf; however, none of these synergistic
interactions provided greater control than glyphosate alone at the label recommended rate
of 840 g/ha. Tank-mixtures of glyphosate at 105 g/ha with triﬂusulfuron at 4.4 g/ha and
glyphosate at 210 g/ha with triﬂusulfuron at 17.6 g/ha were synergistic for Powell
amaranth control. All combinations of glyphosate and triﬂusulﬁiron were additive for
control of common lambsquarters. Tank-mixtures were predominantly additive for dry
weight reduction of velvetleaf, Powell amaranth, and common lambsquarters.
Combinations of triﬂusulfuron with glyphosate applied to 5- and lO-cm weeds does not

improve weed control beyond using glyphosate alone at 840 g/ha.

79

Nomenclature: Glyphosate; triﬂusulfuron; common lambsquarters, Chenopodium album
L. CHEAL; Powell amaranth, Amaranthus powellii S. Watson AMAPO; velvetleaf,
Abutilon theophrasti Medik. ABUTH; sugarbeet, Beta vulgaris L.

Key words: Glyphosate-resistant, herbicide interaction.

INTRODUCTION

The commercial release of glyphosate-resistant sugarbeet in 2008 has given
growers the opportunity to achieve excellent weed control of many weed species
common to sugarbeet production with fewer herbicides and applications (Guza et al.
2002; Kniss et al. 2004), while eliminating the potential for crop injury (Wilson et al.
2002). In previous studies, glyphosate has provided excellent control of many weed
species with two or three glyphosate applications (Guza et aL 2002; Wilson et al. 2002).
Additionally, time between herbicide applications may be longer with glyphosate-
resistant sugarbeet compared with conventional sugarbeet herbicide programs, as weed
height at the time of application is generally not as limiting with glyphosate.

Glyphosate provides excellent control of many weed species over many growth
stages. However, velvetleaf (A butilon theophrasti Medik.) and common lambsquarters
(Chenopodium album L.) have exhibited some tolerance to glyphosate (Krausz et a1.
1996; Young et al. 2001). Furthermore, several weeds common in sugarbeet producing
regions of the United States, including common waterhemp (Amaranthus rudis L.),
common ragweed (Ambrosia artemisiifolia L.), and giant ragweed (Ambrosia trzﬁda L.),
have been conﬁrmed to be resistant to glyphosate (Heap 2009). Triﬂusulfuron, an

acetolactate synthase (ALS) inhibiting herbicide for postemergence broadleaf and grass

80

control in sugarbeet, has been shown to provide good to excellent control of velvetleaf,
depending on size (Starke et al. 1996), and some suppression of common lambsquarters
and redroot pigweed (Amaranthus retroﬂexus L.), with minimal crop injury (Morishita
and Downard 1995). Previous research has shown additive and antagonistic effects for
mixtures of glyphosate and other ALS-inhibiting herbicides for control of 6-1eaf common
lambsquarters (glyphosate + thifensulfuron) and 4-leaf velvetleaf (glyphosate +
irnazethapyr and glyphosate + thifensulfuron), respectively (Lich et al. 1997). Starke and
Oliver (1998) also observed antagonistic interactions for combinations of glyphosate with
chlorimuron for control of l 8-cm tall velvetleaf. Combining an additional herbicide
mode of action with glyphosate will give sugarbeet growers more options for controlling
weeds that may be more tolerant to glyphosate. Reports from the Red River Valley
region have suggested that tank-mixes of glyphosate and triﬂusulfuron may improve
control of common lambsquarters in glyphosate-resistant sugarbeet. However, these
reports have not been veriﬁed. The objectives of this study were to l) evaluate
triﬂusulﬁrron for control of three broadleaf weed species if it is applied at weed heights
optimal for glyphosate application and 2) determine if combinations of triﬂusulfuron with

glyphosate would improve weed control beyond using glyphosate alone.

MATERIALS AND METHODS
Velvetleaf, Powell amaranth (Amaranthus powellii S. Watson), and common
lambsquarters, three weeds ﬁ'equently found in Michigan sugarbeet production ﬁelds,

were grown in 10 cm by 10 cm plastic pots ﬁlled with a commercial greenhouse potting

mix]. Velvetleaf; Powell amaranth, and common lambsquarters were planted one plant

81

per pot Greenhouse temperature was maintained at 25 i 5 C with a 16-h photoperiod of
natural sunlight supplemented with lighting to provide 1,000 umo l/mZ/s photosynthetic
photon ﬂux. Pots were watered daily to maintain adequate soil conditions for plant
growth. Plants were fertilized with 50 ml of fertilizer solution containing 7 mg/L of 20%

nitrogen, 20% P205, and 20% K20 as needed.

Trials were set up as a two-factor randomized complete block design with four

replications. Each trial was repeated twice. Factors were glyphosate2 rate (0, 105, 210,

420, and 840 g ae/ha) and triﬂusulfuron3 rate (0, 4.4, 8.8, 17.6, and 35.0 g ai/ha),

representing 0x, 0.125x, 0.25x, 0.5x, and IX of the label-recommended rate (Anonymous

2001; Anonymous 2007). A nonionic surfactant (N IS)5 was included at 0.25% v/v in

treatments containing only triflusulfuron. Ammonium sulfate was included at 2% v/v in
all treatments containing glyphosate. Herbicide applications were made when weeds
were 5 or 10 cm in height to determine the effect of weed size on control with the

herbicide combinations. Applications were made using a single-nozzle track sprayer with

an 8001 even ﬂat fan nozzle4 calibrated to deliver 187 um at a pressure of 234 kPa and

a speed of 1.6 km/hr. Visual estimates of weed control were taken 14 days after
treatment (DAT) on a scale of 0% (no control) to 100% (complete control) based on
injury. Plant height data were collected and above ground biomass was harvested 14
DAT. Plant samples were oven-dried at 60 C for 3 d and weights were recorded.
Herbicide combinations were determined to be synergistic, antagonistic, or

additive by comparing the observed plant response with the expected plant response. The

82

expected plant response was calculated using the equation E = X + Y —XY/1 00, developed
by Colby (1967). In this equation, X and Y is the percent growth inhibition by herbicides
A and B, respectively, and E is the expected percent growth inhibition by herbicides A

and B. All treated plants were compared to a nontreated control. Data were subjected to

ANOVA and analyzed using PROC MIXED in SAS 9.16. Expected and observed plant

response values were compared using the least signiﬁcant difference (LSD) at p = 0.05
signiﬁcance level. Herbicide combinations were labeled as synergistic, antagonistic, or
additive if the observed response was greater than, less than, or similar to the expected

response, respectively.

RESULTS AND DISCUSSION
Velvetleaf. Triﬂusulfuron alone provided a maximum of 28% control and 42% dry
weight reduction of 5-cm tall velvetleaf (Table 20). Synergistic interactions were
observed for velvetleaf control with several combinations with glyphosate at 210 and 420
g/ha (Table 21). However, the 840 g/ha rate of glyphosate provided 89% control and
none of the combinations with triﬂusulfuron provided greater control than glyphosate
alone. All herbicide combinations at the 5-cm weed height application timing were
additive for biomass reduction. Triﬂusulfuron alone was also not effective at controlling
10 cm tall velvetleaf (Table 22). Most combinations oftriﬂusulfuron and glyphosate
were additive (Table 23). Synergistic activity was observed for control of velvetleaf for
combinations of triﬂusulfuron at 17.6 and 35 g/ha with glyphosate at 105 and 210 g/ha.
The only herbicide combination that resulted in a synergistic response for biomass

reduction in 10 cm tall velvetleaf was triﬂusulfuron at 35 g/ha and glyphosate at 105

83

g/ha. At lO-cm weed height application timing, none of the herbicide combinations
provided greater control than glyphosate alone.

Previous research has investigated velvetleaf control with triﬂusulfuron at the
cotyledon, ﬁrst-leaf, and second-leafgrowth stage, with the greatest control observed
when triﬂusulfuron was applied to velvetleaf at the cotyledon growth stage (Starke et al.
1996). In this study, triﬂusulfuron did not provide satisfactory control of 5- or lO-cm tall
velvetleaf. However, synergistic interactions with glyphosate at sub-lethal rates indicate
that it may be a useful tank-mix partner if applied to weeds less than 5-cm in height,

should velvetleaf develop increased tolerance to glyphosate.

Powell amaranth. At the 5-cm application timing, Powell amaranth was the most
susceptible weed species to glyphosate and glyphosate alone at 210 g/ha provided 82%
control (Table 20). Triﬂusulﬁiron alone provided a maximum of 14% control and 30%
dry weight reduction of S-cm Powell amaranth. All herbicide combinations were
additive for control of Powell amaranth at the 5-cm weed height application timing.
Combinations of glyphosate at 105 g/ha and triﬂusulfuron at 4.4 and 8.8 g/ha were
antagonistic for dry weight reduction (Table 21 ). All other combinations were additive
for dry weight reduction. Powell amaranth the most susceptible weed species to
glyphosate at the lO-cm weed height application timing, with 93% control at the 840 g/ha
rate (Table 22). At the lO-cm application timing, triﬂusulfuron provided a maximum of
15% control and 16% dry weight reduction. Synergistic interactions for control were
observed with combinations of glyphosate at 105 g/ha with triflusulfuron at 4.4 g/ha and

glyphosate at 210 g/ha with triﬂusulfuron at 17.6 g/ha. For dry weight reduction, an

84

antagonistic interaction was observed with the combination of glyphosate at 105 g/ha
with triﬂusulfuron at 35.0 g/ha; however, a synergistic interaction was observed with

glyphosate at 210 gm with triﬂusulfuron at 17.6 g/ha (Table 23).

Common lambsquarters. Triﬂusulfuron alone did not control 5-cm tall common
lambsquarters (Table 20). All herbicide combinations were additive for common
lambsquarters control at the 5-cm application timing. The combination of glyphosate at
210 g/ha and triﬂusulfuron at 17.6 g/ha was antagonistic for dry weight reduction,
however all other combinations were additive (Table 21). Triﬂusulfuron alone provided
6% or less control of 10 cm tall common lambsquarters (Table 22). Glyphosate alone at
840 g/ha provided 68% control (Table 22) and 77% reduction in dry weight (Table 23),
and all combinations with triﬂusulfuron were additive for control and dry weight
reduction. Similar to velvetleaf and Powell amaranth, none of the herbicide combinations
provided better common lambsquarters control than glyphosate alone.

Results from this study show that triﬂusulﬁlron was not effective at control 5- or
10-cm tall velvetleaﬁ Powell amaranth, or common lambsquarters. Some combinations
of triﬂusulfuron and glyphosate at various rates were synergistic for control of velvetleaf
and Powell amaranth. However, none of these synergistic interactions provided greater
control of 5- and lO-cm tall weeds than glyphosate alone at 840 g/ha. Based on current
university and industry recommendations to apply glyphosate for weed control in
glyphosate-resistant sugarbeet at minimum rate of 840 g/ha, these results conﬁrm that
tank-mixing triﬂusulfuron with glyphosate does not improve weed control beyond using

glyphosate alone. Should any of the broadleaf weed species evaluated in this study

85

develop glyphosate-resistance, triﬂusulﬁiron would need to be applied when weeds are
less than 5-cm tall, as it will not provide adequate weed control of 5- or lO-cm tall weeds.
Furthermore, because several weed species have exh1bited multiple resistance to both
ALS-inhibiting herbicides and glyphosate (Heap 2009), combinations of glyphosate with
herbicides of other modds of action should also be evaluated for improved control of

glyphosate- resistant weeds.

SOURCES OF MATERIALS

1 Baccto Professional Potting Mix, Michigan Peat Company, P.O. Box 980129, Houston,
TX 77098.

2 Roundup WeatherMAX, Monsanto Co., 800 N. Lindbergh Blvd, St. Louis, MO 63167.
3 UpBeet, E. I. du Pont de Nemours and Co., Crop Protection, Wilmington, DE 19898.

4 Spraying Systems Co., PO. Box 7900, Wheaton, IL 60187.

5 Activator 9o, Loveland Products, PO. Box 1286, Greely, co, 80632.

6 The SAS System for Windows, Version 9.1, SAS Institute Inc., 100 SAS Campus Dr.,

Cary, NC 27513.

86

Table 20. Visual estimates of weed control compared to the untreated control 14 days
after treatment for combinations of triﬂusulﬁiron and glyphosate for velvetleaf, Powell

amaranth, and common lambsquarters 5-cm tall at time of application.a

 

 

 

 

 

 

 

 

Control
Herbicide rate 33me AMAPO CHEAL
Glyphosatcc Triﬂusulfurond Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ai/ha %

0 0 — 0 —— 0 —— 0

0 4.4 — 3 — 3 — 10

0 8.8 — 6 —— 1 1 — 21

0 17.6 — 13 — 14 — 13

0 35.0 — 28 — 13 — 1 1
105 0 — 45 —— 59 — 9
105 4.4 46 50 64 53 11 29
105 8.8 47 55 68 54 18 23
105 17.6 52 66 (+) 65 56 22 21
105 35.0 59 65 63 68 21 22
210 0 — 43 — 82 —- 46
210 4.4 44 ' 62 (+) 84 72 47 50
210 8.8 46 57 (+) 87 69 51 54
210 17.6 50 70 (+) 85 80 54 40
210 35.0 58 74 (+) 84 67 52 44
420 0 — 64 —— 86 —— 85
420 4.4 66 82 (+) 88 92 85 75
420 8.8 66 85 (+) 89 89 86 77
420 17.6 69 82 (+) 88 95 87 79
420 35.0 74 80 87 92 87 81
840 0 — 89 —— 99 — 96
840 4.4 90 91 99 99 96 94
840 8.8 90 89 99 98 97 95
840 17.6 91 94 99 98 97 91
840 35.0 92 97 99 97 97 96
LSD (0.05)c — 9 — 18 —- 14

 

+ and - denote a synerg18tic and antagonistic interactions for a given combmatlon of triﬂusulfuron and

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

Abbreviations: ABUTH, velvetleaf; AMAPO, Powell amaranth; CHEAL, common lambsquarters; Exp.,
expected; Obs., observed.

c
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
Treatments containing only triﬂusulfuron also included nonionic surfactant at 0.25% v/v.
C
LSD values may be used to compare observed values.

87

Table 21 . Dry weight reduction compared to the untreated control 14 days after
treatment for combinations of triﬂusulfuron and glyphosate for velvetleaf, Powell

amaranth, and common lambsquarters 5-cm tall at time of application.a

 

 

 

 

 

 

 

 

Dry weight
Herbicide rate ABU—mb AMAPO CHEAL
Glyphosatec Triﬂusulfurond Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ai/ha % reduction
0 0 — 0 — O — O
0 4.4 — 12 —— 18 — 26
0 8.8 —— 18 — 18 — l7
0 17.6 — 25 — 30 — 22
O 35.0 — 42 — 22 — 24
105 0 — 49 — 69 — 18
105 4.4 54 58 80 63 H 31 37
105 8.8 57 56 75 60 (—) 31 24
105 17.6 61 70 77 66 40 35
105 35.0 70 7O 77 79 34 36
210 0 — 47 — 77 — 65
210 4.4 54 66 84 80 71 72
210 8.8 57 65 82 74 72 72
210 17.6 60 72 84 86 78 57 (—)
210 35.0 70 76 82 78 73 61
420 0 — 68 — 92 — 89
420 4.4 73 81 95 93 91 85
420 8.8 75 82 94 90 91 86
420 17.6 76 81 94 92 93 86
420 35.0 82 82 94 92 92 86
840 O — 83 — 96 — 95
840 4.4 85 87 97 95 96 82
840 8.8 86 84 97 96 96 94
840 17.6 87 87 97 94 96 82
840 35.0 90 9O 97 95 96 93
LSD (0.05)° — 10 — 14 — l6

 

3 . . . . . . . . . .
+ and — denote a synergistic and antagonistic interactions for a given combination of triﬂusulfuron and

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

Abbreviations: ABUTH, velvetleaf; AMAPO, Powell amaranth; CHEAL, common lambsquarters; Exp.,
expected; Obs., observed.

c
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
Treatments containing only triﬂusulfuron also included nonionic surfactant at 0.25% v/v.

e
LSD values may be used to compare observed values.

88

Table 22. Visual estimates of weed control compared to the untreated control 14 days
after treatment for combinations of triﬂusulfuron and glyphosate for velvetleaf, Powell

amaranth, and common lambsquarters 10-cm tall at time of application.8

 

 

 

 

 

 

Control
Herbicide rate ABu—mb AMAPO CHEAL
Glyphosate“ Triﬂusulfm-ond Exp. Obs. Exp. Obs. Exp. Obs.
g ae/ha g ai/ha %

0 0 — 0 — 0 — 0

0 4.4 — 1 — 6 — 3

0 8.8 — 1 — 9 — 1

0 17.6 — 4 — 12 — 5

0 35.0 — 9 — 15 — 6
105 0 — 31 — 3o — 3
105 4.4 31 28 33 53 (+) 6 7
105 8.8 32 28 36 50 4 11
105 17.6 34 47 (+) 38 45 8 12
105 35.0 37 50 (+) 40 46 9 9
210 0 — 25 —— 59 — 6
210 4.4 26 33 61 68 9 13
210 8.8 26 27 61 69 8 8
210 17.6 29 43 (+) 64 85 (+) 11 7
210 35.0 32 53 (+) 64 72 12 8
420 0 — 51 —— 70 —— 53
420 4.4 52 53 72 72 55 52
420 8.8 52 45 71 71 54 61
420 17.6 54 50 73 87 55 61
420 35.0 56 58 73 77 56 56
840 0 —— 69 — 93 —— 68
840 4.4 70 65 94 99 68 72
840 8.8 70 66 93 99 69 79
840 17.6 71 74 94 99 69 77
840 35.0 73 80 93 97 69 76
LSD (0.05)° — 12 — 16 — 13

 

a . . . . . . . . .
+ and — denote a synergistic and antagonistic interactions for a given combination of triﬂusulfuron and

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

Abbreviations: ABUTH, velvetleaf; AMAPO, Powell amaranth; CHEAL, common lambsquarters; Exp.,
expected; Obs., observed.

c
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
d
Treatments containing only triﬂusulfuron also included nonionic surfactant at 0.25% v/v.

e
LSD values may be used to compare observed values.

89

Table 23. Dry weight reduction compared to the untreated control 14 days after
treatment for combinations of triﬂusulfuron and glyphosate for velvetleaf, Powell

amaranth, and common lambsquarters lO-cm tall at time of application.a

 

 

 

 

 

 

 

 

Dry weight
Herbicide rate ABUTH" AMAPO CHEAL
Glyphosatec Triﬂusulfurond Exp. Obs. Exp. Obs. Exp. Obs.
g 39,113 g ai/ha % reduction

0 0 — 0 — 0 — 0

0 4.4 — 1 — 13 — l6

0 8.8 — O —— 9 — 12

0 17.6 ——- 3 —— 8 ~-—— 10

0 35.0 —— 0 — 16 — 15
105 0 — 13 — 45 — 12
105 4.4 14 16 51 45 24 16
105 8.8 13 5 49 43 22 21
105 17.6 l6 18 49 39 20 20
105 35.0 13 33 (+) 51 39 (—) 23 17
210 0 — 13 —— 53 — 15
210 4.4 15 15 57 62 26 26
210 8.8 14 11 55 69 25 15
210 17.6 17 19 55 78 (+) 23 9
210 35.0 14 21 56 70 26 16
420 0 — 30 — 64 — 59
420 4.4 31 22 67 77 62 66
420 8.8 30 17 66 ' 70 63 68
420 17.6 33 24 66 76 62 69
420 35.0 30 33 67 71 62 60
840 0 — 42 — 81 — 77
840 4.4 43 46 82 82 79 78
840 8.8 42 36 82 81 79 85
840 17.6 45 43 81 85 78 83
840 35.0 42 52 82 84 79 77

LSD (0.05)e — 15 — 12 — 14

 

a . . . . . . . . . .
+ and — denote a synergistic and antagonistic interactions for a given combination of triﬂusulfuron and

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

Abbreviations: ABUTH, velvetleaf, AMAPO, Powell amaranth; CHEAL, common lambsquarters; Exp.,
expected; Obs., observed.

0
Treatments containing glyphosate also included ammonium sulfate at 2% v/v.
Treatments containing only triﬂusulfuron also included nonionic surfactant at 0.25% v/v.

e
LSD values may be used to compare observed values.

90

LITERATURE CITED

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Nemours and Company, Crop Protection.

Anonymous. 2007. Roundup WeatherMAX® herbicide label. St. Louis, MO: Monsanto
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Colby, S. R. 1967. Calculating synergistic and antagonistic responses of herbicide
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Guza, C. J., C. V. Ransom, C. Mallory-Smith. 2002. Weed control in glyphosate-
resistant sugarbeet (Beta vulgaris L.). J. Sugar Beet Res. 39:109-123.

Heap, I. 2009. International survey of herbicide resistant weeds. Website:
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Kniss, A. R., R. G. Wilson, A. R. Martin, P. A. Burgener, and D. M. Feuz. 2004.
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Krausz, R. F., G. Kapusta, and J. L. Matthews. 1996. Control of annual weeds with
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Lich, J. M., K. A. Renner, and D. Penner. 1997. Interaction of glyphosate with
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Morishita, D. W. and R. W. Downard. 1995. Weed 00an in sugarbeets with
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Starke, R. J. and L. R. Oliver. 1998. Interaction of glyphosate with chlorimuron,
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Starke, R. J., K. A. Renner, D. Penner, and F. C. Roggenbuck. 1996. Inﬂuence of
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Wilson, R. G., C. D. Yonts, and J. A. Smith 2002. Inﬂuence of glyphosate and
glufosinate on weed control and sugarbeet (Beta vulgaris) yield in herbicide-
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Young, B. G., J. M. Young, L. C. Gonzini, S. E. Hart, L. M. Wax, and G. Kapusta. 2001.

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