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LIBRARY
Michigan State
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This is to certify that the
thesis entitled

EFFECT OF SOYBEAN [Glycine max (L.) Merr] ROW WIDTH
AND PLANT POPULATION ON WEED COMPETITION AND
SOYBEAN YIELD
AND
INFLUENCE OF STEM-BORING INSECTS ON COMMON
LAMBSQUARTERS [Chenopodium album (L.)] CONTROL
WITH GLYPHOSATE

presented by

DANA BRIAN HARDER

has been accepted towards fulfillment
of the requirements for the

MS. degree in Crop and Soil Sciences

 

 

Major Professor’s Signature

Max; 4 2006
Date

MSU is an Afﬁrmative Action/Equal Opportunity Institution

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2/05 p:/CIRC/DateDue.indd-p.1

 

 

EFFECT OF SOYBEAN [Glycine max (L.) Merr] ROW WIDTH
AND PLANT POPULATION ON WEED COMPETITION AND
SOYBEAN YIELD

AND

INFLUENCE OF STEM-BORING INSECTS ON COMMON
LAMBSQUARTERS [Chenopodium album (L.)] CONTROL
WITH GLYPHOSATE

By

Dana Brian Harder

A THESIS

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

MASTER OF SCIENCE

Department of Crop & Soil Sciences

2006

ABSTRACT
EFFECT OF SOYBEAN [Glycine max (L.) Merr] ROW WIDTH AND PLANT
POPULATION ON WEED COMPETITION AND SOYBEAN YIELD
AND

INFLUENCE OF STEM-BORING INSECTS ON COMMON LAMBSQUARTERS
[Chenopodium album (L.)] CONTROL WITH GLYPHOSATE

By
Dana B. Harder

Field studies were conducted to determine the effect of soybean row width and
population on canopy closure, yield, yield components, weed biomass, weed emergence,
and economic return. Weed biomass decreased as soybean population increased. Under
weedy conditions, yield was greater in 19-Cm rows compared with 76-cm rows, regardless
of population in three of six site years. In weed-free conditions, yield was greater in 19-Cm
rows compared with 76-cm rows, regardless of population in ﬁve of six site years. Branch
pod number increased as row width or population decreased; however, mainstem pod
number only increased as population decreased. Field and greenhouse studies were
conducted to evaluate the eﬁ'ect of glyphosate rate, application timing, and insect larval
tunneling on common lambsquarters control. Insect larval tunneling in common
lambsquarters was wide-spread throughout Michigan and northern Indiana. Two insect
species, an unidentiﬁed larva from the order Diptera, family Agromyzidae, and the beet
petiole borer (Cosmobarz’s americana) were found in common lambsquarters stems.
Diptera:Agromyzidae was present prior to late-June glyphosate applications; however, the
beet petiole borer was not found in common lambsquarters stems until mid-July. Common
lambsquarters control with glyphosate was not inﬂuenced by insect larval tunneling.

Increasing glyphosate rate or applying glyphosate to smaller plants improved control.

ACKNOWLEDGMENTS

I would like to thank Karen A. Renner and Christy L. Sprague for allowing me the
opportunity to come to Michigan State University and pursue a Master’s degree.
Additionally, I would to thank my graduate committee members Christina D. DiFonzo and
Kurt D. Thelen for both their technical advice and work in helping me complete my
masters program. I would like to also thank the Michigan Soybean Promotion Committee
and Monsanto for ﬁnancially supporting this research.

Thank you to Gary Powell for helping me establish and complete my ﬁeld
experiments. I would like to thank my fellow graduate students Scott Bollman, Brad
Fronning, Amy Guza, Ann McCordick, Kathi-in Schirmacher, and Terry Schulz for their
help in work, and most importantly, their friendship. I would especially like to thank the
undergraduate students Ted Costigan, Alyn Kiel, and TJ. Ross for their help in doing the
“grunt” work on my projects and their friendship.

This degree would not be possible without the support of my wife Candi, along
with my daughter Madison. I would like to thank them for their support and patience with
me while I complete my education. I would also like to thank my parents, Byron and Linda

Harder for their support and encouragement of me as I pursued my education.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................... vii
LIST OF FIGURES ........................................................................................... x
CHAPTER 1
REVIEW OF LITERATURE

INTRODUCTION ....................................................................................... l

SOYBEAN ROW WIDTH AND POPULATION
I Yield ....................................................................................... 2

II. Moisture .................................................................................. 4
III. Yield Components .................................................................. 5
IV. Weed Control ......................................................................... 7
V. Canopy Development ........................................................... 10
VI. Canopy Physiology .............................................................. 1 1
COMMON LAMBSQUARTERS
1. Biology and Growth ............................................................. 13
II. Seed Production and Germination ....................................... 14
III. Competition .......................................................................... 19
VI. Control with Glyphosate ...................................................... 21
INSECT-WEED INTERACTIONS
1. Biology of beet petiole borer ............................................... 23
11. Inﬂuence of insects on weed control ................................... 23
LITERATURE CITED ............................................................................ 25
CHAPTER 2

EFFECT OF SOYBEAN ROW WIDTH AND POPULATION ON CANOPY
DEVELOPMENT, WEED BIOMASS, WEED EMERGENCE, YIELD, AND
ECONOMIC RETURN.

ABSTRACT ............................................................................................. 32
INTRODUCTION .................................................................................... 33
MATERIAL AND METHODS ............................................................... 36
General Methods for Field Experiments ..................................... 36
Soybean canopy development ............................................. 36

Weed emergence .................................................................. 37

Weed biomass ....................................................................... 37

Economic analysis ................................................................ 38

Statistical analysis ................................................................ 38

RESULTS AND DISCUSSION .............................................................. 40
Growing conditions ...................................................................... 40

iv

Soybean canopy development ..................................................... 40

Weed emergence .......................................................................... 42

Weed biomass .............................................................................. 44

Soybean yield ............................................................................... 45

Economic return ........................................................................... 47

LITERATURE CITED ............................................................................ 50
CHAPTER-3 '

EFFECT OF ROW WIDTH AND POPULATION ON SOYBEAN YIELD
COMPONENTS.

ABSTRACT ............................................................................................. 73
INTRODUCTION .................................................................................... 74
MATERIAL AND METHODS ............................................................... 77
RESULTS ................................................................................................. 79
Growing conditions ...................................................................... 79
Soybean yield ............................................................................... 79
Plant seed yield ............................................................................. 80
Pod number .................................................................................. 81
Plant weight .................................................................................. 81
DISCUSSION ........................................................................................... 82
LITERATURE CITED ............................................................................ 86
CHAPTER-4
INFLUENCE OF STEM-BORIN G INSECTS ON COMMON
LAMBSQUARTERS CONTROL WITH GLYPHOSATE ....................... 99
ABSTRACT ............................................................................................. 99
INTRODUCTION .................................................................................. 100
MATERIAL AND METHODS ............................................................. 104
Presence of insect larval tunneling in common
lambsquarters ............................................................................. 104
Factors inﬂuencing common lambsquarters control ................. 104
Response of 7 common lambsquarters populations to
glyphosate ................................................................................... 107
Statistical analysis ...................................................................... 107
RESULTS AND DISCUSSION ............................................................ 108
Presence of insect larval tunneling in common
lambsquarters ............................................................................. 109
Factors inﬂuencing common lambsquarters control ................. 110
Response of 7 common lambsquarters populations to
glyphosate ................................................................................... 113
LITERATURE CITED .......................................................................... 115
CHAPTER-5
TEMPORAL AND SPATIAL DISTRIBUTION OF IN COMMON
LAMBSQUARTERS ..................................................................................... 126

V

ABSTRACT ........................................................................................... 126

INTRODUCTION .................................................................................. 127
MATERIAL AND METHODS ............................................................. 130
RESULTS AND DISCUSSION ............................................................ 131
LITERATURE CITED .......................................................................... 135

vi

LIST OF TABLES

CHAPTER 2

EFFECT OF SOYBEAN ROW WIDTH AND POPULATION ON CANOPY
DEVELOPMENT, WEED BIOMASS, WEED EMERGENCE, YIELD, AND
ECONOMIC RETURN.

Table 1. Field characteristics for the three Michigan locations in 2004 and 2005. ......... 53

Table 2. Monthly precipitation recorded at the Clarksville Horticulture Experiment
Station in Clarksville, M1, at the Michigan State University Department of Horticulture
and Research Center, East Lansing, MI, and at the Saginaw Valley Bean and Beet

Farm, St. Charles, MI ......................................................................................................... 54

Table 3. Weed densities at Clarksville, East Lansing, and St. Charles in 2004 and
2005. ................................................................................................................................... 55

Table 4. Soybean canopy development at Clarksville and East Lansing in 2004.

Leaf area index (LAI) was obtained by a non-destructive measurement using the
SunScan Canopy Analysis System. Different letters within each column represents
mean separation at LSDo.05_ ............................................................................................... 56

Table 5. Soybean canopy development at East Lansing in 2004 and St. Charles in

2004 and 2005. Leaf area index (LAI) was obtained by a non-destructive

measurement using the SunScan Canopy Analysis System. Different letters within

each column represents mean separation at LSDODS, ........................................................ 57

Table 6. Soybean canopy development at Clarksville in 2005. Leaf area index
(LAI) was obtained by a non-destructive measurement using the SunScan Canopy

Analysis System. Different letters within each column represents mean separation at
LSDoos. ............................................................................................................................... 58

Table 7. Effect of soybean row width, population, and herbicide treatment on soybean
yield at Clarksville and East Lansing in 2004. .................................................................. 59

Table 8. Effect of soybean row width, population, and herbicide treatment
on soybean yield at East Lansing in 2005 and St. Charles in 2004 and 2005 .................. 60

Table 9. Effect of soybean row width, population, and herbicide treatment on
soybean yield at Clarksville in 2005. ............................................................................... 61

' Table 10. Gross margins for lO—cm glyphosate application at Clarksville and
East Lansing in 2004. ......................................................................................................... 62

Table 11. Gross margins for lO-cm glyphosate application at East Lansing in 2005
and St.Charles in 2004 and 2005. ..................................................................................... 63

Table 12. Gross margins for lO-Cm glyphosate application at Clarksville in 2005. ...... 64

CHAPTER 3
EFFECT OF ROW WIDTH AND POPULATION ON SOYBEAN YIELD
COMPONENTS.

Table 1. Field characteristics for three Michigan locations in 2004 and 2005. ............. 89

Table 2. Monthly precipitation recorded at the Clarksville Horticulture Experiment
Station in Clarksville, M1, at the Michigan State University Department of Horticulture
and Research Center, East Lansing, MI, and at the Saginaw Valley Bean and

Beet Farm, St. Charles, MI. .............................................................................................. 90

Table 3. Effect of soybean row width and population on total, mainstem, and

branch plant yield and hundred seedweight at Clarksville and East Lansing in 2004.
Numbers in parentheses indicates percentage of yield contributed by the mainstem
fraction. Values at the bottom of each yield component section indicate LSDoos ......... 91

Table 4. Effect of soybean row width and population on total, mainstem, and

branch plant yield and hundred seed weight at East Lansing in 2005 and St. Charles

in 2004 and 2005. Numbers in parentheses indicates percentage of yield contributed

by the mainstem fraction. Values at the bottom of each yield component section
indicate LSDoos. ................................................................................................................. 92

Table 5. Effect of soybean row width and population on total, mainstem, and
branch pod production and number of seed per pod at Clarksville and East Lansing
in 2004. Values at the bottom of each yield component section indicate LSDQOS. ........ 93

Table 6. Effect of soybean row width and population on total, mainstem, and branch
pod production and number of seed per pod at East Lansing in 2005 and St. Charles

in 2004 and 2005. Values at the bottom of each yield component section indicate
LSDO_05. ............................................................................................................................... 94

CHAPTER 4 .
INFLUENCE OF STEM-BORIN G INSECTS ON COMMON
LAMBSQUARTERS CONTROL WITH GLYPHOSATE

Table 1. Weather conditions before, during, and after glyphosate application for
ﬁeld studies in 2004 and 2005 at East Lansing. ............................................................. 118

Table 2. Percent of common lambsquarters plants with insect larval tunneling
prior to glyphosate application and common lambsquarters control (28 DAT)
for soybean planted in May 2004 at East Lansing. ........................................................ 119

Table 3. Percent of common lambsquarters plants with insect larval tunneling
prior to glyphosate application and common lambsquarters control (28 DAT)
for soybean planted in June 2004 at East Lansing. ........................................................ 120

Table 4. Percent of common lambsquarters plants with insect larval tunneling
with and without insecticide treatments prior to glyphosate application and
common lambsquarters control (28 DAT) for soybean planted in May 2005 at East

Lansing. ........................................................................................................................... 121
Table 5. The effect of glyphosate on caged and non-caged common lambsquarters
control 28 DAT. .............................................................................................................. 122
Table 6. Common lambsquarters control in cage and cage-ﬂee treatments

(28 DAT) in the greenhouse. .......................................................................................... 123
Table 7. Glyphosate rates associated with each growth reduction value for six

Michigan common lambsquarters biotypes. .................................................................. 124
CHAPTER 5

TEMPORAL AND SPATIAL DISTRIBUTION OF STEM-BORING INSECTS IN
COMMON LAMBSQUARTERS IN MICHIGAN AND INDIANA

Table 1. Frequency of insect larval tunneling in common lambsquarters
infested in soybean ﬁelds in Indiana and Michigan in August 2004. ........................... 137

Table 2. Frequency of insect larval tunneling in common lambsquarters
infested in soybean ﬁelds in Indiana and Michigan in June 2005. ................................ 141

Table 3. Frequency of insect larval tunneling common lambsquarters in Indiana and
Michigan in 2005 and 2005. ........................................................................................... 142

Table 4. Frequency of insect larval tunneling in common lambsquarters
infested in soybean ﬁelds in Indiana and Michigan in August 2005. ........................... 143

Table 5. Frequency of insect larval tunneling in common lambsquarters
infested in soybean ﬁelds in Indiana and Michigan in September 2004. ...................... 144

LIST OF FIGURES

CHAPTER 2

EFFECT OF SOYBEAN ROW WIDTH AND POPULATION ON CANOPY
DEVELOPMENT, WEED BIOMASS, WEED EMERGENCE, YIELD, AND
ECONOMIC RETURN.

Figure 1. Weed emergence following glyphosate application at Clarksville and East
Lansing in 2004. Vertical bars at each measurement indicate LSD0_05. Dotted vertical
line indicates canopy closure. ........................................................................................... 65

Figure 2. Weed emergence following glyphosate application at East Lansing
and St. Charles in 2005. Vertical bars at each measurement indicate LSDQ05.
Dotted vertical line indicates canopy closure ................................................................... 66

Figure 3. Effect of soybean row width and population on weed biomass at Clarksville
and East Lansing in 2004. Different letters above each column indicates mean
separation LSDogs. ............................................................................................................ 67

Figure 4. Effect of soybean row width and population on weed biomass at East Lansing
in 2005 and St. Charles in 2004 and 2005. Different letters above each column indicates
mean separation LSDoos. .................................................................................................. 68

Figure 5. Effect of soybean row width and population on weed biomass at Clarksville
in 2005. Different letters above each column indicates mean separation LSDogs. ........ 69

Figure 6. Effect of soybean row width and population on weed biomass in
lO-cm glyphosate treatment at East Lansing and Clarksville in 2004. Different
letters above each column indicates mean separation LSDoos. ....................................... 70

Figure 7. Effect of soybean row width and population on weed biomass in
lO-cm glyphosate treatment at East Lansing and St. Charles in 2005. Different
letters above each column indicates mean separation LSqus. ....................................... 71

Figure 8. Effect of soybean row width and population on weed biomass in
10-cm glyphosate treatment at Clarksville in 2005. Different letters above each column
indicates mean separation LSDogs. ................................................................................... 72

CHAPTER 3
EFFECT OF ROW WIDTH AND POPULATION ON SOYBEAN YIELD
COMPONENTS.

Figure 1. Effect of row width and population on soybean yield at Clarksville and East
Lansing in 2004. Different letters above each column represents signiﬁcant

X

differences at LSD0_05. ....................................................................................................... 95

Figure 2. Effect of row width and population on soybean yield at East Iansing
in 2005 and St. Charles in 2004 and 2005. Different letters above each column
represents signiﬁcant differences at LSD0,05. ................................................................... 96

Figure 3. Effect of soybean row width and population on total, mainstem, and

branch weights at Clarksville and East Lansing in 2004. Different letters above,
between, and at the base of each column represent signiﬁcant differences in

total, mainstem, and branch weights, respectively, at LSDogs. ....................................... 97

Figure 4. Effect of soybean row width and population on total, mainstem, and

branch weights at East Lansing in 2005 and St. Charles in 2004 and 2005. Different
letters above, between, and at the base of each column represent signiﬁcant differences
in total, mainstem, and branch weights, respectively, LSD0_05. ....................................... 98

CHAPTER 4
INFLUENCE OF STEM-BORING INSECTS ON COMMON
LAMBSQUARTERS CONTROL WITH GLYPHOSATE

Figure 1. Percent of common lambsquarters plants with insect larval
tunneling over accumulated grong degree days. ........................................................ 125

CHAPTER 5
TEMPORAL AND SPATIAL DISTRIBUTION OF STEM-BORING INSECTS IN
COMMON LAMBSQUARTERS IN MICHIGAN AND INDIANA

Figure 1. Regions sampled in Michigan and Indiana in 2004 and 2005. ............................... 142

CHAPTER 1

REVIEW OF LITERATURE

INTRODUCTION

The effect of row width and population on soybean (Glycine max (L.) Merr)
growth, competitiveness with weeds, and yield has been researched extensively. Soybean
can adjust to varying plant populations and row widths and still maintain yield; however,
maximum seed yield is thought to be obtained when the arrangement of plants approach
uniform distribution within and between rows (Wiggans 1939). In most studies, soybean
yield increases as row width decreases when environmental conditions are favorable
(Devlin et a1. 1995; Taylor 1980; Yelverton and Coble 1991). Producers have utilized
narrow rows and higher plant populations as a cultural method of weed control. Earlier
canopy closure prevents weed development due to lower light quality (Burnside and
Colville 1964; Carey and DeFelice 1991; Nelson and Renner 1999; Yelverton and Coble
1991). Increased seeding rates are required to maximize grain yields with narrow-row
soybean (Devlin et a1 1995); however, the drawbacks to increased soybean seeding rates
include increased seed cost, increased plant mortality due to competition, and increased
lodging (Costa et a1. 1980). Increased yield has been attributed to improved distribution of
soybean over the soil surface for the efﬁcient use of available water, light, and nutrients
i (Bertram and Pedersen 2004).

The success of common lambsquarters (Chenopodium album L.) as a competitive
weed is attributed to seed germination in a wide range of environments (Henson 1970),

early emergence during the growing season (Ogg and Dawson 1984), plasticity of growth

(Ervio 1971), proliﬁc seed production (Harrison 1990), and seed longevity (Lewis 1973).
Common lambsquarters has been reported as an increasingly problematic weed in
glyphosate resistant soybean (Schuster et al. 2004; Kniss et al. 2004). There is little
research on the inﬂuence of larval tunneling on weed control with glyphosate.

SOYBEAN ROW WIDTH AND POPULATION

I. YIELD

Soybean has greater yield potential in narrow rows (< 25cm) than soybean planted
in wide rows. Many researchers reported higher yields in narrow-compared with wide-row
soybean (Bertram and Pedersen 2004; Costa et al. 1980; Kratochvil et al. 2004; Lehman
and Lambert 1960). In Wisconsin, Costa et al. (1980) reported that soybean yield increased
21% in 27-cm rows compared with 76—cm rows. Kratochvil et al. (2004) reported that
soybean drilled in 19-cm rows produced signiﬁcantly better yields compared with 38-cm
rows in 2 of 3 years in Maryland. Yields were greater in 20-cm rows compared with 76-cm
rows, regardless of tillage system in Wisconsin (Oplinger and Philbrook 1992), and yields
were 9 and 10% greater in 19- and 38-cm rows, respectively, compared with 76—cm rows
(Bertram and Pedersen 2004).

Optimum soybean populations vary from 30 000 plants/ha to 500 000 plants/ha
(Board 2000). Cooper (1977) reported that a seeding rate of 375 000 seeds/ha was the
optimum seeding rate for 17-, 50-, and 75-cm row widths. There was a yield advantage of
10 and 20% from planting soybean in 17-cm rows compared with 50-cm and 75-cm rows,
respectively. Norsworthy and Frederick (2002) reported that a seeding rate 40% below the
current recommended standard of 620 OOO/ha for drilled soybean produced yields similar to

the recommended standard in South Carolina. However, yield was signiﬁcantly less when
2

the seeding rate was 40% lower than the recommended seeding rate of 432 250 seeds/ha in
Maryland, although seeding rates 20% less than the recommended seeding rate consistently
produced yields similar to the standard and produced an additional proﬁt of $14.30 to
$27.72/ha (Kratochvil et al. 2004). In Wisconsin, seeding recommendations for 19-, 38-,
and 76-cm rows are 556 000, 432 000, and 309 000 seeds/ha, respectively (Bertram and
Pedersen 2004). When these seeding rates were increased 20%, no differences in yield
were found between the recommended seeding rates and seeding rates 20% higher for each
respective row width. Oplinger and Philbrook (1992) reported that seeding rates for drilled
soybean need to be 32% greater in no—tillage and reduced-tillage systems than
conventional tillage. The determination of optimal plant population (the minimum
population for best yield) lowers seeding costs, reduces lodging, and prevents disease
problems (Boquet and Walker 1980).

Excessive intraspeciﬁc competition can occur when soybean is planted at high
populations. Increasing plant density decreases the number of branches per plant and
increases lodging (Costa et al. 1980). Peters et al. (1965) observed excessive intraspeciﬁc
competition when soybean was planted in 20- and 41-cm row widths; soybean had thin
stems, delayed maturity, small seed, and lodging. Harvested plant populations were
signiﬁcantly lower in no- and reduced-tillage compared with conventional tillage at seeding
rates greater than 247 000 seeds/ha (Oplinger and Philbrook 1992). Ethredge et al. (1989)
noticed that the number of plants producing seed in 76-cm rows was only 77% of the initial
population, whereas, the number of plants producing seed in 51- and 25- cm rows was 93

and 97%, respectively. Greater natural thinning occurred in wide rows compared with

narrow rows when plant population was constant (Ethredge et al. 1989). Board (2000) also
observed that soybean population declined 38% in 76-cm rows over the growing season.

Due to increased yields in narrow-row soybean, economic returns are generally
greater than wide-row soybean when similar weed management systems are implemented.
However, seeding rates and thus seeding costs are typically 20 to 45% greater in 19-cm
compared with 76-cm rows (Bertram and Pedersen 2004; Kratochvil 2004; Nelson and
Renner 1999; Norsworthy and Frederick 2002; Norsworthy and Oliver 2001). Nelson and
Renner (1999) reported $45 to $64/ha greater gross margins when soybean were grown in
19-cm rows at 494 000 plants/ha rather than 76-cm rows at 360 000 plants/ha; however,
seeding rates were higher for 19-cm rows. In other research, gross margins were $52/ha
greater in drilled soybean seeded at 185 000 seed/ha compared with the recommended
seeding rate of 432 000 seeds/ha in Arkansas (N orsworthy and Oliver 2001 ).
II. MOISTURE

In soybean, moisture is a critical factor for maximum yield. The amount and
duration of seasonal rainfall are the two most important factors in determining soybean
yield (Taylor 1980). Devlin et al. (1995) reported that under favorable environmental
conditions, yield was greater when soybean was planted in 20-cm rows compared with 76-
- cm rows at 378 000 plants/ha. Wide-row yields were greater than narrow-row soybean
when seeding rates were lower than 378 000 plants/ha. Devlin concluded that under
favorable environmental condition, the optimal seeding rate for soybean planted in 20— and
76-cm rows was 501 000 and 274 000 seeds/ha, respectively. In poor environmental
conditions, yields were greater in 76—cm rows than 20cm at all seeding rates. In contrast,
Taylor (1980) observed that in years when water was limiting, row width had no effect on

4

soybean yield. Greater water use early in the growing season resulted in less moisture
available during pod ﬁll for narrow-row soybean. Norris et al. (2002) also Observed that
soybean yields were similar between row widths when growing conditions mid- and late-
season were extremely dry.
III. YIELD COMPONENTS

Soybean can compensate for sparse plant populations resulting in similar yield per
area compared with higher plant populations (Wells 1991). Plant populations for
maximum yield depend on row width, cultivar, and planting date (Ethredge et al. 1989).
Increases in plant population results in lower branch yield (Carpenter and Board 1997),
yield per plant (Weber et al. 1966), fewer pods per plant (Ethredge et al. 1989), and in
some cases lower seed weight (Costa et al. 1980; Etheredge et a1. 1989). Moore (1991)
and Wright et al. (1984) reported that seed size was responsible for yield compensation at
lower populations; however, others have reported that yield compensation results from
increased pod production associated with greater branch development (Herbert and
Litchﬁeld 1982; Hicks et al. 1969; Lehman and Lambert 1960). Pod number per plant is
the most variable of seed yield components and the most likely to respond to changes in
row width or plant population (Lehman and Lambert 1960; Herbert and Litchﬁeld 1982;
Pedersen and Lauer 2004; Weber et al. 1966). Changes in seed weight and number of
seeds per pod due to changes in row width or soybean population has not been consistent
(Board et al. 2000; Carpenter and Board 1997; Herbert and Litchﬁeld 1982) Yield
component response to increasing soybean populations may differ based on soybean row
width. Ethredge et a1. (1989) observed that the pod number and yield per area were
similar across populations in 76-cm rows due to soybean at low populations producing

5

more pods on branches than soybean planted at higher populations. In the same study,
pod number and yield were greater at higher populations in 25- and 5 1 -Cm rows.

In general, row width inﬂuences soybean yield components; however, some report
little response in yield components to row width. Ethredge et al. (1989) observed that the
number of pods per plant was not affected by row width. Weber et al. (1966) observed that
seed size was independent of row width. In contrast, seed weight and the number of seeds
per pod were greater when soybean was planted in wide rows (Costa et al. 1980; Lehman
and Lambert 1960).

The partitioning of soybean yield to branch or mainstem ﬁactions is also inﬂuenced
by row width and population. Mainstem yield is greater in narrow-row soybean than wide-
row soybean and some soybean genotypes are capable of partitioning more resources to
increase branch seed yields in response to row width (N orsworthy and Shipe 2005).
Rigsby and Board (2003) also reported that there are genotypic differences in soybean
branching and branch yield at low populations. Branches produce a greater proportion of
seed yield at lower populations (Herbert and Litchﬁeld 1982).

Partitioning of yield components to branch or mainstem fraction is also inﬂuenced
by environmental conditions. The contribution of branch seed yield to total yield was
greater in years of higher rainfall (Norsworthy and Frederick 2002). In dry environments,
the mainstem portion of yield is greater and remains stable over environments (Board,
1987; Frederick et al. 2001). Yield was correlated to dry matter production, and total dry

matter per plant was greater in narrow rows with a greater fraction being produced on

branches (Board et al. 1990).

IV. WEED CONTROL

Soybean row width was traditionally limited to 76-cm rows to allow for late-season
row cultivation. Technological advancements in herbicide development and equipment
allow growers to plant narrow-row soybean and rely heavily on the use of herbicides as the
primary means of controlling weeds. Studies indicate that as soybean row width decreases,
weed control increases for a given herbicide treatment due to rapid canopy closure
(Burnside and Colville 1964; Legere and Schreiber 1989; Mickelson and Renner 1997;
Nelson and Renner 1999; Peters et al. 1965).

Narrow-row soybean is more competitive with weeds than wide-row soybean.
Young et al. (2001) reported that weed control with a single glyphosate application in 19-
and 38- cm rows was greater than 76-cm rows, and weed control in 38-cm rows was more
similar to 19cm rows than 76-cm rows. Common waterhemp (Amaranthus rudis) and
velvetleaf (Abutilon theophrasti) control was less in 76-cm rows and was more variable
compared with l9-cm rows. Chandler et al. (2001) reported that soybean planted at 400
000 seeds/ha in 19-cm rows reduced weed biomass by 56 and 47% compared with soybean
planted in 76-cm and twin-rows, respectively. Soybean planted in narrow- or twin-rows
reduced weed seed return compared with wide rows. In comparison to twin- and narrow-
row soybean, weeds in wide-row soybean contributed an additional 2651 and 2960 seeds
m'z, respectively. Weeds that emerged after the l- to 2- trifoliate stage did not increase the
total number of seeds in the seedbank or reduce soybean yield when compared with the
season-long weedy control.

Mickelson and Renner (1997) reported that soybean drilled in 19-cm rows at 469
300 seeds/ha reduced weed biomass by 30% compared with soybean planted at 358 150

7

seeds/ha in 76-cm rows. Soybean yield was 14% greater when soybean was drilled in
narrow rows compared with soybean planted in wide rows when averaged across herbicide
treatments. However, there was no difference in soybean yield in the weed-free control for
both years between narrow- and wide-row soybean. Common lambsquarters and velvetleaf
control in wide-row soybean was less than that in narrow rows.

Nice et al. (2001) conducted a study in Mississippi researching sicklepod (Senna
obtusifolia) development when soybean was planted in 19- and 38-cm rows at seeding rates
of 326 000, 652 000, and 976 000 seeds/ha, compared with a ‘standard’ soybean population
of 326 000 seeds/ha planted in 76-cm rows. They observed that soybean had little effect on
sicklepod density when planted in row widths less than 76-cm at 326 000 seeds/ha.
However, high soybean populations in either 38- or 19-cm row widths produced
signiﬁcantly fewer sicklepod plants than the standard 76-cm soybean population.
Furthermore, soybean planted in 19-Cm rows at the high seeding rate of 976 000 seeds/ha
reduced sicklepod populations up to 80%.

Patterson et a1. (1988) conducted a study in Alabama in which soybean was planted
in 15, 30, 45, and 90-cm rows at a single population of 430 000 plants/ha. Soybean
biomass and seed yield was affected more by sicklepod and common cocklebur
competition when soybean row width decreased. Soybean biomass and yield decreased 14
kg/ha and 12 kg/ha, respectively, for each centimeter increase in soybean row width in
season-long competition with sicklepod. Furthermore, sicklepod biomass increased 12
kg/ha for each centimeter increase in soybean row width. Soybean biomass and yield

decreased 10 kg/ha and 16 kg/ha, respectively, for each centimeter increase in row width in

season-long competition with common cocklebur. Furthermore, common cocklebur
biomass increased 10 kg/ha for each centimeter increase in soybean row width.

The time of weed removal in soybean is important in preventing unacceptable yield
loss. This term is often referred to as the critical time of weed removal (CTWR). In
Nebraska, the critical time of weed removal (CTWR) was delayed in narrow row widths at
all locations (Knezevic et al. 2003). The CTWR for soybean planted in 19-, 38-, and 76-
cm rows was V3-V4, V2, and V1 soybean growth stages, respectively. Furthermore, the
CTWR was 9 to 30 days longer when soybean was planted in 18-cm rows compared with
76-Cm rows (Mulugeta and Boerboom 2000). Glyphosate applied at the V2, V4, or R1
soybean growth stages provided season-long control of weeds in 18-Cm rows (Mulugeta
and Boerboom 2000). In wide-row soybean, broadleaves emerged when glyphosate was
applied at the V2 soybean growth stage due to lack of complete canopy closure. Mulugeta
and Boerboom (2000) reported that 85-90% of weeds emerged at the V4 soybean growth
stage, and that only 55 to 65% of total weed emergence occurred prior to the V2 soybean
growth stage. In contrast, Dalley et al. (2004a) concluded that narrow-row soybean was
more susceptible to early-season weed interference than wide-row soybean. Weed
interference reduced soybean yield when glyphosate application was delayed until weeds
were 15-cm or more in 19- and 38-cm rows. Dalley et al. (2004b) found that weed biomass
production decreased in 76-cm rows when glyphosate applications were delayed; however,
there was no beneﬁt of delaying glyphosate application in row widths less than 38-cm.

Weed biomass production was similar across all application timings for 19- and 38-cm

TOWS.

V. CANOPY DEVELOPMENT

Canopy development, which is a function of row width, seeding rate, and
environmental conditions, is an effective weed control tool (Duncan 1986; Peters et al.
1965). Increased soybean densities promote a quicker canopy closure by increasing the
leaf area index and light interception (Bertram and Pederson 2004). Beneﬁts of drilled
soybean include quicker canopy development and greater weed control (Mickelson and
Renner 1997). As row width decreased, the number of weeds that emerged after herbicide
application decreased linearly as a result of more light being intercepted by the canopy
(Y elverton and Coble 1991). Weed resurgence following herbicide applications was less
under irrigated conditions because of rapid soybean canopy formation; however, yield was
not signiﬁcantly affected. Yelverton and Coble (1991) stated that late emerging weeds
could contribute to the soil weed seedbank.

Planting soybean in 19- or 38-cm rows resulted in higher levels of light interception
compared with 76-cm rows (Dalley et al. 2004a). Maximum light interception occurred 64
d after soybean emergence and was greater than 98% when 30be was planted in row
widths less than 38 em, but when soybean was planted in 76-cm rows light interception
never exceeded 84%. Norsworthy and Oliver (2001) observed that the time to reach 90%
canopy closure decreased as soybean density increased; however, all densities intercepted
88-99% of available light 70 d after soybean emergence. Researchers in Nebraska and
Illinois reported canopy closure of soybean in 25-cm rows at 35 to 36 d after planting and
58 to 65 d after planting in 76-cm rows (Burnside and Colville 1964; Wax and Pendleton
1968). Carey and Defelice (1991) reported that soybean planted in 19-cm rows formed a
canopy on average of 20 days earlier than soybean grown in 76-cm rows. Nelson and

10

Renner (1999) reported soybean canopy closure occurred 45 and 80 days after planting for
19- and 76-Cm rows, respectively. Burnside and Colville (1964) observed that soybean
planted in 25-, 45-, 76-, and 90-cm rows completely shaded the ground in 36, 47, 68, and
67 days after emergence, respectively.
VI. CANOPY PHYSIOLOGY

Canopy physiology is dependent on plant density and row width. Decreased row
widths at equal plant densities produced more equidistant plant distribution (Shibles and
Weber, 1966). This equidistant plant distribution decreased plant-to-plant competition for
available water, nutrients, and light and increased radiation interception and biomass
production. Andrade et al. (2002) reported that as row width decreased, radiation
interception by the crop canopy increased. Therefore, yield response to reductions in
soybean row width can be partly attributed to an improvement in radiation interception at
the critical-pod setting period.

The leaf area index (LAI) that correlates to 95% solar radiation interception has
been adopted as the critical LAI (Gardner et al. 1985). Light interception approaches a
maximum asymptotically making it impossible to measure 100% light interception.

Furthermore, 95% light interception under maximum solar radiation of 2300 ,umol photons

2 l 2

m' sec' means that radiation level at the bottom of the canopy is 115 ,umol photons m'
sec'l which is the light compensation point for many species. Crop growth rate (CGR) did
not increase signiﬁcantly when light interception was above 95% (Shibles and Weber
1965). Norsworthy and Oliver (2001) found that yields over a range of seeding rates were

similar when 95% or greater of photosynthetically active radiation was intercepted, but

11

yields were reduced when soybean intercepted less than 95% photosynthetically active
radiation.

Soybean at low populations (80 000 plants/ha) can achieve the same yield as
medium (145 000 plants/ha) and high (390 000 plants/ha) populations when planted in 75-
cm rows (Board 2000). This was a result of greater net assimilation rate (NAR) during
vegetative growth and greater relative leaf area growth rate (RLAGR) during late
vegetative and early reproductive growth. Soybean planted at low populations had a
similar CGR compared with medium and high populations during the emergence to R5
growth period. CGR was similar between populations 14 to 21 days after emergence, but
after 21 days after emergence CGR was twice as great when soybean was planted at the
lower populations. CGR was consistently greater at low populations through the
reproductive growth stages of soybean. Light interception efﬁciency was also greater in
the low population compared with the high population and this explains the greater CGR at
the low population. At soybean growth stage of R1, LAl was greater at higher populations
compared with lower populations; however, LAI was similar between populations at R5.
Greater RLAGR in low populations was due to a greater number of leaves produced rather
than greater area on a per leaf basis.

Wells (1991) reported that canopy photosynthesis was linearly related to light
interception and LAI prior to canopy closure, but not afterwards. Soybean planted in 43-
cm rows had greater canopy apparent photosynthesis (CAP) than soybean planted in 96-cm
rows. CAP was not different for any treatment after R5; however, differences were present
prior to R5. The late season reduction in CAP was greater than indicated by light
interception alone. The loss of photosynthetically inactive leaves after canopy closure

12

explained the inability to relate LAI to light interception. Wells stated that when LAI was
above critical levels after canopy closure, factors other than photosynthesis were involved
in the response of yield to plant density. Weber et al. ( 1966) reported that leaf loss
increased with higher populations but was relatively constant across row widths. Higher
populations also increased the rate of LAI accumulation and resulted in greater rates of dry
3 weight accumulation. However, the greatest difference among the populations occurred in
narrow rows.
COMMON LAMBSQUARTERS
I. BIOLOGY AND GROWTH
Common lambsquarters is a successful colonizing species, and is one of the most
widely distributed weeds in the world (Holm et al. 1977). It is found in 47 different
countries in 40 different crops, and considered the principal weed pest in corn (Zea mays
L.), potato (Solanum tuberosum L.), soybean, and sugarbeet (Beta vulgaris L.) (Holm et a1.
1977; Mitich 1988). Common lambsquarters is native to Britain, but is found on all
continents ﬁ‘orn 70° N to 50° S except in areas of extreme desert (Holm 1977). Common
lambsquarters grow mainly in disturbed areas, particularly near concentrations of nitrogen
or organic matter (Mitich 1988). It is a common weed in plant communities and seedbanks
(Forcella et a1. 1997). The success of common lambsquarters as a competitive, wide-
spread weed is attributable to many factors including seed germination in a wide range of
environmental conditions (Henson 1970), early emergence during the crop growmg season
(Ogg and Dawson 1984), plasticity of growth (Ervio 1971), proliﬁc seed production

(Harrison 1990), and seed longevity (Lewis 1973).

13

Common lambsquarters is an annual plant with succulent stems and leaves, with
short alternate branches, that grows from 0.6 to 1.5 m tall (Mitich 1988). As plants mature,
stems may appear reddish from anthocyanin accumulation (Williams 1963). The leaves
and stems of common lambsquarters are powdered with a whitish-gray meal, and leaf
shape can vary from narrow to wide-pointed, toothed oval, or triangular with wavy teeth
(Mitich 1988).

II. SEED PRODUCTION AND GERMINATION

The seeds of common lambsquarters are polymorphic and although some are brown
(<3%) most are black and are either smooth or reticulate with raised lines (Williams and
Harper 1965). Brown seeds readily germinate while black seeds are more dormant. The
testae of black seeds are thicker and provide a physical barrier to prevent germination. All
of these seed types can be found on a single plant (Williams and Harper 1965). Progeny
grow in close association to the mother plant (Williams 1963) because a seed dispersal
mechanism is not present. Common lambsquarters is hexaploid (2n=6x=54), with 34
subspecies in North America that are minor variants of C. album (Bassett and Crompton
1978). Flowers are perfect and can be cross- or self-pollinated by wind.

Common lambsquarters is a proliﬁc seed producer, as seed production can range
from 30 000 to 176 000 seeds per plant (Harrison 1990); however, an average-sized plant
produces 72 450 seeds (Stevens 1932). Seed production generally varies according to plant
density and biomass, and is related to the distance between each plant and to the size of
neighboring plants (Harrison 1990). Seed yield per area remained constant regardless of
density since seed production per plant decreased as plant density increased (Ervio 1971).
In addition, total seed production increased as soil nitrate concentrations increased

14

(Williams and Harper 1965). Early sensitivity to photoperiod enables common
3 lambsquarters seedlings to adjust the duration of vegetative development according to the
length of the photoperiod (Huang et a1. 2001). Flowering is induced indeterrninately by a
14 h photoperiod allowing the plant to produce seed, regardless of plant developmental
stage (Huang et al. 2001).

Day length and fertility level have been shown to inﬂuence seed characteristics and
dormancy. Wuff et al. (1999) studied the progeny of ﬁve seed families of common
lambsquarters under different environmental conditions. Common lambsquarters grown
under low fertility produced seed that germinated at a higher frequency and more readily
than plants grown under high fertility. Seed polymorphism was not modiﬁed by nitrogen,
but there was evidence that early seed shed contained a higher than normal proportion of
brown seeds (Williams and Harper 1965). The amount of brown seed with a high seed
weight and a thin seed coat was promoted by short days during seed formation. A high
percentage of black dormant seed with thick testa were produced under long day lengths
(Bouwrneester and Karssen 1993; Cumming 1963; Henson 1970). These maternal effects
allow common lambsquarters to have a plastic response to environmental conditions and to
successfully colonize an area.

Common lambsquarters has two germination peaks, the ﬁrst in the autumn soon
after seed ripening, and the second in the spring in April-May (Williams and Harper 1965).
The ﬁrst coincides with the ability of brown seeds to germinate immediately upon release
and the latter follows a period of chilling. Harvey and Forcella (1993) observed that
common lambsquarters did not germinate at temperatures below 4 C, and that the optimum
temperature for germination was 24 C.

15

Common lambsquarters ﬂourishes in conventional tillage systems. Clements et al.
(1996) observed that the top 5 cm of soil contained the highest concentration of common
lambsquarters seeds, regardless of tillage type. Among tillage systems, moldboard plowing
allowed the greatest amount of common lambsquarters seed to remain in the seedbank;
however, in no-tillage systems there is a decrease in the total amount of seed. Tillage
allows exposes seed to light which promotes germination (Baskin and Baskin 1977). Seeds
that are buried remain viable and germinate in subsequent years when returned to a suitable
depth (Baskin and Baskin 1977). Seeds are small and have little endosperrn making it
difﬁcult for seedlings to emerge from soil depths greater than 2.5 cm (Weaver et al. 1988).
Two cultivations per year increased the rate of seed loss in the soil (Roberts and Dawkins
1967).

The number of viable seeds in the top 23 cm of soil follows a pattern of exponential
decay of 22% per year. Therefore, 1% of the initial population would remain after 18 years
(Roberts and Dawkins 1967). In one study, 6% of seed germinated after 39 years (T oole
and Brown 1946). Furthermore, seed germinated 89, 76, and 32% after 1, 2, and 20 years,
respectively, after being stored at a soil depth of 13 cm (Lewis 1973).

The conditions required to relieve seed dormancy in common lambsquarters are
complex and involve alternating temperature, nitrate, seed after-ripening, seed age, and
light. Seed germination is generally improved if a combination of these factors interact
together, but a single factor can replace another to initiate germination (Henson 1970).
Cumming (1963) demonstrated that common lambsquarters germinated over a wider range
of conditions than the less weedy species of the genus. In addition, Cumming stated that
dormancy factors contribute to the success of common lambsquarters as a weed. Nitrate

16

largely determines the germination response of young common lambsquarters seed. Light
will substitute for nitrate, but their dual effect is much more than additive at a constant
temperature of 23 C (Henson 1970). Younger seeds were more sensitive to nitrate and
light given together, but when applied separately germination was not initiated. Long
photoperiods inhibited germination compared with short photoperiods; however, seeds
became indifferent to light as they aged. Alternating temperatures of 10/30 C increased the
sensitivity to light and nitrates when given separately or together (Henson 1970).
Responsiveness to light exists or can be induced by nitrate, alternating temperatures, or
ageing of the seed. Increased nitrate fertilization during seed formation results in seeds that
are more likely to germinate due to increased endogenous nitrate levels (Bouwmeester and
Karssen 1993). Germination was highest at temperatures between 10 and 20 C; however,
when temperatures are above 30 C or below 10 C ﬂuctuation in germination was observed.
In addition, when common lambsquarters seeds were desiccated and then re-imbibed in
nitrate, 80-90% of the seeds germinated. Incomplete germination often occurred when
seeds were tested at 10 C. At alternating temperatures of 30/ 15 or 35/20 C, germination
occurred in darkness. Bouwmeester and Karssen (1993) stated that when indicators of a
position close to the surface such as desiccation or alternating temperatures were present
light is no longer required for germination.

The seed forms of common lambsquarters differ in dormancy and/or conditions to
relieve dormancy. Williams and Harper (1965) observed that brown seeds imbibed 76-
78% of their weight in water, while black reticulate and black smooth seeds imbibed 43%
and 6% of their weight in water in the ﬁrst 12 h, respectively. Brown seeds germinated
quickly when they were provided with water, even at temperatures of 0 C. Black-reticulate

17

seeds exhibited dormancy broken by nitrate, but not by chilling. Black-smooth seeds
exhibited dormancy that was broken by nitrate and partly replaceable by chilling.
Furthermore, the black seeds had chemical inhibitors present in the testa that prevented
germination. Mulugeta and Stoltenberg (1998) observed that germination was similar in
late-season cohort timings compared with early-season cohort timings after the testa was
removed.

Common lambsquarters seed germinate at a higher percentage in light with a high
red to far-red ratio (Cumming 1963). Established plants can alter the ratio of red to far-red
by ﬁltering it with their leaves which prevents seed from germinating in an unfavorable
~ environment. The germination of common lambsquarters can be reversibly controlled by
red and far-red light (Cumming 1959). Seeds did not gemrinate with water in the dark, but
when seeds were desiccated or placed in nitrate, 20% of the seeds germinated
(Bouwmeester and Karssen 1993).

Incomplete germination and the ability to continue germination when conditions are
favorable, allowed common lambsquarters the ability to adapt to a wide range of
environmental conditions (Cumming 1963). Seed exhibited incomplete germination in soil
with low moisture under a photoperiod of 16 h. In addition, incomplete germinated seed
remained viable for prolonged periods in moist or dry conditions, and rapidly continued
germination when transferred to optimum conditions. Low temperatures favored
' incomplete germination, but the alternating temperature of 10/30 C favored complete
germination despite photoperiod length (Bouwmeester and Karssen 1993). After the seeds
are imbibed, Pfr, gibberellins 4 and 7, and ethylene cause the splitting of the outer testa
layer. However, ABA inhibits the extension of the radicle from the seed coat, resulting in

18

incomplete germination. In addition, the seasonal changes in germination may be the result
of a combination of changes in the level or sensitivity to ABA and GA. Baskin and Baskin
(1987) observed that common lambsquarters required low temperatures to complete after-
ripening. Common lambsquarters must receive lto 3 months of low-temperature after-
ripening for 50% or more germination in March (15/6 C) and April (20/ 10 C). Common
lambsquarters is a C3 plant that gerrninates, has increased growth, and a higher
photosynthetic rate under temperatures that range from 20 to 25 C (Chu et al. 197 8). The
ability for optimum growth under cool conditions in combination with early germination
allows common lambsquarters to establish earlier and have a competitive advantage over a
C4 weed species like redroot pi gweed (Amaranthus retroﬂexus).

Huang et al. (2001) observed that the vegetative growth of common laranuarters
occurs over a wide temperature range. Shoot height increased as alternating temperatures
increased from 12/2 to 29/ 19 C, but declined when temperature increased to 45/35 C.
Common lambsquarters completes its reproductive development and produces mature
seeds at temperatures ranging ﬁ'om 23/13 to 35/25 C. The cardinal temperatures for shoot
elongation and radicle elongation are 25 and 26 C, respectively (Roman et al. 1999).
Juvenile plants were rapidly sensitive to photoperiod, allowing reproductive growth soon
after emergence under long-day lengths (Huang et al. 2001). This allowed plants to
produce seed at the end of the growing season, regardless of emergence date.

111. COMPETITION

Common lambsquarters is plastic in its response to intra- and interspeciﬁc
competition. Rohrig and Stutzel (2000) observed that with increasing competition in taller
crops, common lambsquarters allocated relatively more biomass to stems than to leaves to

19

outgrow competing plants. Under conditions of limited light, biomass was allocated to
increase leaf area and leaf biomass, and at low densities plants produced 20 to 30% less dry
matter than those planted at a 2.5-fold higher rate (Rohrig and Stutzel 2000). When grown
in monoculture, increased densities caused stem diameter and the number of branches to
decrease (Ervio 1971). However, plant height was greater when common lambsquarters
was grown at higher densities. Increased density had no effect on seed output per unit area
(Ervio 1971). When plants were subjected to competition there was a decrease in size
and/or number of plant parts, with a consequent decrease in weight per plant (Ervio 1971).

Colquhoun et al. (2001) observed that soybean was more competitive with common
lambsquarters than corn. Common lambsquarters grown in monoculture produced early-
season leaf area similar to that when grown in corn. Competition increased between
common lambsquarters and soybean due to below normal soil temperatures that favored the
continuous germination of common lambsquarters. Soybean height was not greatly
affected by common lambsquarters because soybean plant height increased at a rate greater
than soybean leaf area. This effect was due to soybean senescing lower leaves and new
. leaf tissue was produced near the apex of the plant. Plants increased in height after
maximum leaf area was attained and was attributed to inter- and intraspeciﬁc competition
for light due to a mediated red: far-red phytochrome response. Common lambsquarters
height and conical canopy shape allow for increased light capture.

Common lambsquarters at densities of 32 plants/10 m row reduced soybean yield
20% when common lambsquarters was present all season (Crook and Renner 1987). In
North Carolina, soybean yield was reduced 15% at weed densities of 16 plants/10 m row
(Shuttleff and Coble 1985). Harrison (1990) observed that for each kg/ha Of common

20

lambsquarters biomass there was a 0.25 kg/ha reduction in soybean yield. Soybean yield
was reduced 25% when common lambsquarters competed all season with soybean at 20
plants/ 10 m row. Corn yield was reduced 12% at weed densities Of 49 plants/ 10 m row
(Beckett et al. 1988). Sibuga and Bandeen (1980) observed that com yield was reduced 13
and 7% at common lambsquarters densities of 46 and 109 plants/m2, respectively. Sugar
beet yield was reduced 48% when 8 plants/10 m row were present all season (Schweizer
1983). Marketable tomato (Lycopersicon esculentum Mill.) yield was reduced 36% at
common lambsquarters densities of 640 plants/10 m row (Bhowmik and Reddy 1988).
Barley (Hordeum vulgare L.) yield was reduced 23 and 36% at common lambsquarters
densities of 150 and 300-400 plants/m2, respectively (Conn and Thomas 1987).

IV. CONTROL WITH GLYPHOSATE

Taylor et al. (1981) reported that it is difficult for postemergence herbicides to
control common lambsquarters due to limited absorption through the waxy surface of the
leaf. The wax forms a homogeneous covering over the entire leaf surface, though platelets
are less dense over the mid-ribs, large veins, and stomata vicinity. This wax contains a
substantial proportion of aldehydes which presents a barrier to penetration of polar
molecules through the cuticle. Furthermore, environmental factors inﬂuence herbicide
efficacy.

Ateh and Harvey (1999) reported that glyphosate at 310 g ae/ha controlled common
lambsquarters when weeds were small (>15 cm) and soybean was at the V2 growth stage.
When glyphosate was applied to larger weeds (>15 cm) at 840 g ae/ha, common
lambsquarters was also controlled. Weed control was also more consistent in narrow-row
soybean than in wide-row soybean.

21

Krausz et al. (1996) observed that common lambsquarters control was 100% when

glyphosate was applied to 10-cm tall plants, regardless of glyphosate rate or spray volume.
I When glyphosate was applied to 20-cm common lambsquarters, control increased as
glyphosate rate increased. Control was reduced 44% when glyphosate was applied at 560 g
ae/ha in 93 L/ha water compared with glyphosate at the same rate in 187 L/ha water;
however, there was no difference in control due to spray volumes when glyphosate rates
were greater than 560 g ae/ha.

Schuster et al. (2004) Observed that the glyphosate rate to reduce common
lambsquarters growth 40% (GR40) varied between populations. Common lambsquarters
collected from Ohio had the highest GR4o value when glyphosate was applied. The GR40
values were 0.27 and 3.97 times the suggested use rate for 2.5- and 15-cm tall plants,
respectively. In the same study, there were no differences in absorption or translocation of
glyphosate among growth stages in common lambsquarters collected from Nebraska.
Radioactivity trarrslocated equally to foliage above the treated leaf, foliage below the
treated leaf, and roots. Kniss et al. (2004) observed that as common lambsquarters growth
changed ﬁ'om 4-leaf to 10-leaf the GRso values doubled. The addition of ammonium
sulfate to glyphosate increased common lambsquarters control 73 to 91% and 80 to 89%

when applied to 10- and 25-cm plants, respectively.

22

INSECT-WEED INTERACTIONS

I. BIOLOGY OF BEET PETIOLE BORER

In the ﬁrst extensive study of the beet petiole borer (Cosmobaris americana),
Landis (197 0) observed that larvae overwintered, then pupated in May. The pupal stage
lasted 1-2 weeks. Some adult beetles cut holes in stems and emerged within 1-2 days while
others delayed emergence until July. Adults were found on May 17 at Grandview,
Washington, and May 19 at Stanﬁeld, Oregon. After emergence, the adults fed primarily at
nodes or stems of host plants. Once a female weevil was several weeks old, it laid a single
egg in one of the feeding pits it had made. On weed hosts, feeding and oviposition pits and
the shallow lesions were most abundant a short distance above the stem node. However,
lesions were not found on the small stems of weeds. Gall-like growths were reported to
develop on sugarbeet and common lambsquarters, but not on other weeds that serve as
hosts. Larvae were often found near the oviposition site and the stem was usually swollen.
Weed hosts did not appear stressed despite larval tunneling, with as many as 30 larvae
found within a single plant. Mature larvae entered diapause in the stems Of saltbrush
(Atriplex polycarpa) as early as August. The beet petiole borer is more commonly found in
weedy hosts than sugarbeet. In California, Gilbert (1964) reported that the most common
host for beet petiole borer was common lambsquarters.
II. INFLUENCE OF INSECTS ON WEED CONTROL

There are many reports of the use of insects for biological control of weeds;
however, there is little research on the effects of insect feeding on weeds and subsequent
control from herbicides. Westra et a1 (1981) observed that the weevil Notaris bimaculatus
reduced the effectiveness of glyphosate on quackgrass. N. bimaculatus adults fed on the

23

culms of quackgrass and deposited eggs later in old feeding galleries. When the soil-
insecticide chlordane was applied, the number of quackgrass shoots produced after
glyphosate application was reduced. Although 100% control of N. bimaculatus was not
observed, shoot counts were reduced 30% by using chlordane. In cage studies, there were
fewer shoots produced by insect-free quackgrass compared with insect-infested quackgrass
after glyphosate application.
From greenhouse studies, Ott et al. (2003) concluded that when giant ragweed was
sprayed at heights of 40-44 cm with glyphosate at rates of 0.76 and 1.52 kg ae/ha, control
was similar between plants infested with European corn borer and non-infested plants. In
contrast, giant ragweed control was lower in infested- compared with non-infested plants

when glyphosate was applied at the lowest rate of 0.63 kg ae/ha.

24

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

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

Baskin, J .M. and CC. Baskin. 1987. Temperature requirements for after-ripening in buried
seed of four summer annual weeds. Weed Res. 27:385-389.

Bassett, U. and CW. Crompton. 1978. The biology of Canadian weeds. 32 Chenopodium
album L. Can. J. Plant Sci. 58:1061-1072.

Beckett, T.H., E.W. Stoller, and L.M. Wax. 1988. Interference of four annual weeds in corn
(Zea mays). Weed Sci. 36:764-769.

Bertram, M.G., and P. Pedersen. 2004. Adjusting management practices using glyphosate-
resistant soybean cultivars. Agron. J. 96:462-468.

Bhomik, PC. and K.N. Reddy. 1988. Interference of common lambsquarters
(Chenopodium album) in transplanted tomato (Lycopersion esculentum). Weed Techno].
2:505-508

Board, J .E. 1987. Yield components related seed yield in determinate soybean. Crop Sci.
40:757-764.

Board, J .E. 2000. Light interception efﬁciency and light quality affect yield compensation
of soybean at low plant populations. Crop Sci. 40: 1285-1294.

Board, J .E., B.G. Harville, and A.M. Saxton. 1990. Branch dry weight in relation to seed
yield increases in narrow-row soybean. Agron. J. 82:540-544.

Boquet, DJ. and D.M. Walker. 1980. Seeding rates for soybeans in various planting
patterns. Lousiana Agric. 23:22-23.

Bouwmeester, H.J. and CM. Karssen. 1993. Season periodicity in germination seeds of
Chenopodium album L. Ann. Of Bot. 72:463-473.

‘ Burnside, CC. and W.L. Colville. 1964. Soybean and weed yields as affected by irrigation,
row spacing, tillage, and amiben. Weeds. 12:109-112.

Carey, J .B. and MS. DeFelice. 1991. Timing of chlorimuron and irnazaquin application for
weed control in nO-till soybeans (Glycine max). Weed Sci. 39:232-237.

25

Carpenter, AC. and J.E. Board. 1997. Branch yield components controlling soybean yield
stability across plant populations. Crop Sci. 37:885-991.

Chandler, K., A. Shrestha, and CJ. Swanton. 2001. Weed seed return as inﬂuenced by the
critical weed-free period and row spacing of no-till glyphosate-resistant soybean. Can. J.
Plant Sci. 81:877-880.

' Chu, C., P.M. Ludford, J.L. Ozbun, and RD. Sweet. 1978. Effects of temperature and
competition on the establishment and growth of redroot pigweed and common
lambsquarters. Crop Sci. 18:308-310.

Clements, D.R., D.L. Benoit, S.D. Murphy, and OJ. Swanton. 1996. Tillage effect on weed
seed return and seedbank composition. Weed Sci. 44:314-322.

Colquhoun, J ., D.E. Stoltenberg, L.K. Binning, and CM. Boerboom. 2001. Phenology of
common lambsquarters growth parameters. Weed Sci. 49:177-183.

Conn, J .S. and D.L. Thomas. 1987. Common lambsquarters (Chenopodium album)
interference in spring barley. Weed Techno]. 1:312-313.

Cooper, KL. 1977. Response of soybean cultivars to narrow rows and planting rates under
weed-ﬂee conditions. Agron. J. 69:89-92.

Costa, J .A., E.S. Oplinger, and J.W. Pendleton. 1980. Response of soybean cultivars to
planting patterns. Agron. J. 72:153-156.

. Crook, TM. and K.A. Renner. 1990. Common lambsquarters (Chenopodium album)
competition and time of removal in soybeans (Glycine max). Weed Sci. 38:358-364.

Cumming, B.G. 1963. The dependence of germination on photoperiod, light quality, and
temperature, in Chenopodium spp. Can. J. Bot. 41:1211-1233.

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 Techno].
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 com (Zea mays) and soybean (Glycine max). Weed
Techno]. 18:177-182.

Devlin, D.L., D.L. Fjell, J.P. Shroyer, W.B. Gordon, B.H. Marsh, L.D. Maddux, V.L.
Martin, and SR. Duncan. 1995. Row spacing and seeding rates for soybean in low and
high yielding environments. J. Prod. Agric. 82215-222.

Duncan, W.G. 1986 Planting patterns and soybean yields. CrOp Sci. 26:584-588.

26

Ervio, LR. 1971. The effect of intra-speciﬁc competition on the development of
Chenopodium album L. Weed Res. 11:124-134.

Ethredge, W.J., D.A. Asheley, and J.M. Woodruff. 1989. Row spacing and plant
population effects on yield components of soybean. Agron. J. 81:947-951.

Forcella, F., R.G. Wilson, J. Deckker, R.J. Kremer, J. Cardina, R.L., Anderson, D. Alm,
K.A. Renner, G. Harvey, S. Clay, and DD. Buhler. 1997. Weed seed bank emergence
across the Corn Belt. Weed Sci. 45:67-76.

Frederick, J .R., C.R. Camp, and P.J. Bauer. 2001. Drought-stress effect on branch and
mainstem seed yield and yield components of determinate soybean. Crop Sci. 41 :7 59-763.

Gardner, F .P., R.B. Pearce, and R.L. Mitchell. 1985. Physiology of Crop Plants. Iowa
State University Press, Ames Iowa. p. 31-56.

Gilbert, BE. 1964. The genus Barr's Germar in California. Univ. California Pub]. In
Entomol. 34:70-74.

Harrison, SK. 1990. Interference and seed production by common lambsquarters
(Chenopodium album) in soybeans (Glycine max). Weed Sci. 38:113-118.

Harvey, SJ. and F. Forcella. 1993. Vernal seedling emergence model for common
lambsquarters (Chenopodium album). Weed Sci. 41:309-316.

Henson, LE. 1970. The effects of light, potassium nitrate and temperature on the
germination of Chenopodium album L. Weed Res. 10:27-39

Herbert, SJ, and G.V. Litchﬁeld. 1982. Partitioning soybean seed yield components. Crop
Sci. 22:1074-1079.

. Hicks, D.R., J.W. Pendleton, R.L. Bernard, and T.J. Jonston. 1969. Response of soybean
plant type to planting patterns. Agron. J. 86:59-62.

Holm, L.G., D.L. Plucknett, J .V. Pancho, and J .P. Herberger. 1977. Chenopodium album L.
Chenopodiaceae, goosefoot family. Pages 84-91 in The World’s Worst Weeds:
Distribution and Ecology. Honolulu, HI: University Press of Hawaii.

Huang, J .Z., A. Shrestha, M. Tollenaar, W. Deen, H. Rahimian, and OJ. Swanton. 2001.

Effect of temperature and photoperiod on the phonological development of common
lambsquarters. Weed Sci. 49:500-508.

27

Kratochvil, R.J., J.T. Pearce, and MR. Harrison. 2004. Row-spacing and seeding rate
effects on glyphosate-resistant soybean for mid-atlantic production systems. Agron. J.
96:1029-1038.

Krausz, R.F., G. Kapusta, and J.L. Matthews. 1996. Control of annual weed with
glyphosate. Weed Techno]. 10:957-962.

Knezevic, S.Z., S.P. Evans, and M. Mainze. 2003. Row spacing inﬂuences the critical time
for weed removal in soybean (Glycine max). Weed Techno]. 17:666-673.

Kniss, A.D., SD. Miller, and RC. Wilson. 2004. Factors inﬂuencing common
lambsquarters control with glyphosate. Proc. N. Cent. Weed Sci. 59:85.

Landis, B.J., W.E. Peay, and L. Fox. 1970. Biology of Cosmobaris americana Casey, a
weevil attacking sugarbeets. J. Econ. Entomol.63:38-41.

Legere A. and M.M. Schreiber. 1989. Competition and canopy architecture as affected by
soybean (Glycine max) row width and density of redroot pigweed (Amaranthus
retroﬂexus). Weed Sci. 37:84-92.

Lehman, W.F. and J .W. Lambert. 1960. Effects of row spacing of soybean plants within
rows on yield and its components. Agron. J. 52:84-86.

Lewis, J. 1973. Longevity of crop and weed seeds. Weed Res. 13:179-191.

Mickelson, J .A. and K.A. Renner. 1997. Weed control using reduced rates of
postemergence herbicides in narrow and wide row soybean. J. Prod. Agric. 10:431-437.

Mitich, L.W. 1988. Intriguing world of weeds-common lambsquarters. Weed Techno].
2:550-552.

Moore, SH. 1991. Uniformity of plant spacing effect of soybean population parameters.
Crop Sci. 31:1049-1051.

Mulugeta, D. and CM. Boerboom. 2000. Critical time of weed removal in glyphosate-
resistant Glycine max. Weed Sci. 48:35-42.

Mulugeta, D. and DE. Stoltenberg. 1998. Inﬂuence of cohorts on Chenopodium album
demography. Weed Sci. 46:65-70.

Nelson, K.A. and K.A. Renner. 1998. Weed control in wide- and narrow-row soybean
(Glycine max) with irnazarnaox, irnazethapyr, and CGA-277476 plus quizalofop. Weed
Techno]. 12:137-144.

28

Nelson, K.A. and K.A. Renner. 1999. Weed management in wide- and narrow-row
glyphosate resistant soybean. J. Prod. Agric. 12:460-465.

Nice, G.R., N.W. Buehring, and DR. Shaw. 2001. Sicklepod (Senna obtusifolia) response
to shading, soybean (Glycine max) row spacing, and population in three management
systems. Weed Technol. 15: 155-162.

Norris, J.L., D.R. Shaw, and CE. Snipes. 2002. Inﬂuence of row spacing and residual
herbicides on weed control in glufosinate-resistant soybean (Glycine max). Weed Techno].
16:319-325.

Norsworthy, J .K. and LR. Oliver. 2001. Effect of seeding rate of drilled glyphosate-
resistant soybean (Glycine max) on seed yield and gross proﬁt margin. Weed Techno].
15:284-292.

Norsworthy, J .K. and J .R. Frederick. 2002. Reduced seeding rate for glyphosate-resistant,
drilled soybean on the southeastern coastal plan. Agron. J. 94:1282-1288.

Norsworthy, J .K. and ER. Shipe. 2005. Effect of row spacing and soybean genotype on
mainstem and branch yield. Agron. J. 97:919-923.

Ogg, A.G., Jr., and J .A. Dawson. 1984. Time of emergence eight weed species. Weed Sci.
32:327-335.

Oplinger ES. and 8D. Philbrook. 1992. Soybean planting date, row width, and seeding
rate response in three tillage systems. J. Prod. Agric. 5:94-99.

Ott, E.J., W.G. Johnson, J .L. Oberrneyer, and DJ. Childs. 2003. Glyphosate efﬁcacy on
giant ragweed infested with European corn borer. Proc. N. Cent. Weed Sci. 58:137.

Patterson, M.G., R.H. Walker, D.L. Colvin, G. Wehtje, and J.A. McGuire. 1988.
Comparison of soybean (Glycine max) — weed interference from large and small plots.
Weed Sci. 36:836-839.

Pedersen, P. and J .G. Lauer. 2004. Response of soybean yield components to management
systems and planting date. Agron. J. 96:1372-1381.

Peters, E.J., M.R. Gebhardt, and J .F. Stritzke. 1965. Interrelations of row spacing,
cultivations and herbicides for weed control in soybeans. Weeds 13:285-289.

Rigsby, B., and J .E. Board. 2003. Identiﬁcation of soybean cultivars that yield well at low
plant populations. Crop Sci. 43:234-239.

Roberts, HA. and PA. Dawkins. 1967. Effect of cultivation on the numbers of viable weed
' seed in soil. Weed Res. 7:290-301.

29

Rohrig, M. and H. Stutzel. 2001. Dry matter production and partitioning of Chenopodium
album in contrasting competitive environments. Weed Res. 41 :129-142.

Roman, E.S., A.G. Thomas, S.D. Murphy, and OJ. Swanton. 1999. Modeling germination
and seedling elongation of common lambsquarters (Chenopodium album). Weed Sci.
47:149-155.

Schuster, C.L., D.E. Shoup, and K. Al-Khatib. 2004. Common lambsquarters response to
glyphosate applied at three different growth stages. Proc. N. Cent. Weed Sci. 59:80.

Schweizer, BE. 1983. Common lambsquarters (Chenopodium album) interference in
sugarbeets (Beta vulgaris). Weed Sci. 31:5-8.

Shibles, R.M., and CR. Weber. 1965. Leaf area, solar radiation interception and dry
matter production by soybeans. Crop Sci. 5:575-578.

Shibles, RM. and CR. Weber. 1966. Interception of solar radiation and dry matter
production by various soybean planting patterns. Crop Sci. 6:55-59.

Shurtleff, J .L. and H.D. Coble. 1985. Intereference of certain broadleaf weed species in
soybeans (Glycine max). Weed Sci. 33:654-657.

Sibuga, K.P. and JD. Bandeen. 1980. Effects of green foxtail and lamb’s-quarters
interference in ﬁeld corn. Can. J. Plant Sci. 60: 1419-1425.

Stevens, GA. 1932. The number and weight of seeds produced by weeds. Am. J. Bot.
19:784-794.

Taylor, HM. 1980. Soybean growth as affected by row spacing and by seasonal water
supply. Agron. J. 72:543-546.

Taylor, F.E., L.E. Davies, and AH. Cobb. 1981. An analysis of the epicuticular was of
Chenopodium album leaves in relation to environmental change, leaf wettablility, and the
penetration of the herbicide bentazone. Ann. App]. Biol. 98:471-478.

Toole, B.H. and E. Brown. 1946. Finals results of the Durvel buried seed experiment. J.
Agric. Res. 72:210-210.

Wax, L.M. and J.W. Pendleton. 1968. Effects of row spacing on weed control in soybeans.
Weed Sci. 16:462-465.

Weaver, SB, CS. Tan, and P. Brain. 1988. Effect of temperature and soil moisture on time
of emergence of tomatoes and four weed species. Can. J. Plant Sci. 68:877-886.

30

Weber, C.R., R.M. Shibles, and DE. Byth. 1966. Effect of plant population and row
spacing on soybean development and production. Agron. J. 58:99-102.

Wells, R. 1991. Soybean growth response to plant density: relationships among canopy
photosynthesis, leaf area, and light interception. Crop Sci. 31:755-761.

Westra, P.H., D.L. Wyse, and BF. Cook. 1981. Weevil (Notaris bimaculatus) feeding
reduces effectiveness of glyphosate on quackgrass (Agropyron repens). Weed Sci. 29:540-
547.

Wiggans, J .R. 1939. Inﬂuence of space and arrangement on the production of soybean
plants. Agron. J. 31:314-321.

Williams, J .T. 1963. Biological ﬂora of the British Isles: Chenopodium album L. J. Ecol.
51 :71 1-725.

William, J .T. and J .L. Harper. 1965. Seed polymorphism and gerrnination-the inﬂuence of
nitrates and low temperatures on the germination of Chenopodium album. Weed Res.
5:141-150.

Wright, C.L., F.M. Shokes, and RR Sprenkel. 1984. Planting method and plant
population inﬂuence on soybean. Agron. J. 76:921-924.

Wuff, R.D., H.F. Causin, O. Berritez, and RA. Bacalini. 1999. Intraspeciﬁc variability and
maternal effects in the response to nutrient addition in Chenopodium album. Can. J. Bot.
77:1150-1158.

Yelverton, RH. and H.D. Coble. 1991. Narrow row spacing and canopy formation reduces
weed resurgence in soybean (Glycine max). Weed Techno]. 5:169-174.

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 Techn01.152112-121.

31

CHAPTER 2
EFFECT OF SOYBEAN ROW WIDTH AND POPULATION ON CANOPY
DEVELOPMENT, WEED BIOMASS, WEED EMERGENCE, YIELD, AND
ECONOMIC RETURN.
ABSTRACT
Field studies were conducted to determine the effect of soybean row width and population
on soybean canopy Closure and yield, as well as the effect of soybean population and row
width on weed biomass and economic return. Canopy closure occurred earlier in 19- and
38-cm rows compared with 76-cm rows. Soybean LAI was greater in 19- and 38-cm rows
compared with 76-cm rows, 43 to 58 days after planting. Increasing the soybean
population in 19- or 38-cm rows from 123 500 to 308 750 plants/ha increased soybean LAI
_ 71 to 74 DAP at Clarksville and East Lansing in 2004. Increasing the soybean population
in 19-cm rows ﬁ'om 197 600 to 444 600 plants/ha increased soybean LA] 56 to 64 DAP at
East Lansing in 2004 and St. Charles in 2004 and 2005. Canopy development was similar
in 76-cm rows at peak canopy, regardless of the soybean population. Fewer weeds
emerged in the 35 days following a single application of glyphosate in 19- and 38-cm rows
compared with 76-cm rows. Higher soybean populations reduced weed biomass; however,
there was a trend for reduced biomass in 19-cm row soybeans. Under weedy conditions,
soybean yield was greater in 19- and 38-cm rows at populations of 296 400 to 444 600
plants/ha, and in 76-cm rows at populations of 185 250 to 308 750 plants/ha. In weed-free
conditions, yield was greatest when soybean was planted at 308 750 to 444 600 in 19-cm
rows and 296 400 to 308 750 in 38-and 76-cm rows. The greatest economic return was in
19-cm rows at 308 750 plants/ha at Clarksville and East Lansing in 2004. The greatest

32

economic return was in 19-cm rows at 444 600 plants/ha at East Lansing in 2005 and St.
Charles in 2004 and 2005. Therefore, increased seeding rates in 19-cm rows resulted in
greater yield,while relatively lower seeding rates are appropriate for 76-cm rows.
Nomenclature: Glyphosate, N-(phosphonomethyl) glycine, soybean ‘AG 2701’, Glycine
max (L.) Merr.

4 Keywords: soybean populations, row spacing, weed emergence, canopy development,
weed competition.

Abbreviations: CGR, crop growth rate; DAP, days after planting; DAT, days after

treatment; POST, postemergence; LAI, leaf area index.

INTRODUCTION

Soybean row width has traditionally been limited to 76-cm rows to allow for late-
season row cultivation (Wax et al. 1977). However, advances in herbicide development
and equipment have allowed growers to plant soybean in narrow rows and rely heavily on
the use of herbicides to control weeds. Weed control is generally better in narrow rows
compared with wide rows (Chandler et al. 2001; Mickelson and Renner 1997, Mulugeta
and Boerboom 2000; Nelson and Renner 1999; Peter et a. 1965), due to more rapid canopy
closure (Burnside and Colville 1964; Burnside and Moomaw 1977; Legere and Schreiber
1989; Mickelson and Renner 1997; Peters et al. 1965, Yelverton and Coble 1991).

Canopy development, which is a function of row width, seeding rate, and
environmental conditions, is an effective weed control tool (Duncan 1986; Peters et al.
1965). Increasing soybean density promotes quicker canopy closure by increasing leaf area

index (LAI) and resulting light interception (Bertram and Pederson 2004). As row width

33

decreases, the number of weeds that emerge after herbicide application decreases linearly
because sunlight is intercepted by the crop canopy (Y elverton and Coble 1991).
Researchers in Nebraska and Illinois reported soybean canopy closure in 25-and 76-cm
rows 35 to 36 and 58 to 65 days after planting, respectively (Burnside and Colville, 1964;
Wax and Pendleton, 1968). Similarly, Carey and Defelice (1991) reported that soybean
planted in l9-cm rows formed a canopy an average of 20 days earlier than soybean grown
in 76-cm rows, while Nelson and Renner (1999) reported soybean canopy closure 45 and
80 days after planting for 19- and 76-cm rows, respectively.

When row width is narrowed, there is more equidistant plant distribution in the
ﬁeld (Shibles and Weber, 1966). Equisdistant plant distribution decreases intraspeciﬁc
competition for water, nutrients, and light, and increases radiation interception and biomass
production (Shibles and Weber, 1966). The LAI that correlates to 95% solar radiation
interception has been adopted as the critical LAI (Gardner et al. 1985). Soybean crop
grth rate (CGR) does not increase signiﬁcantly when light interception is greater than
95% (Shibles and Weber 1965). Furthermore, soybean yield over a range of seeding rates
was similar when 95% or more of photosynthetically active radiation was intercepted
(Norsworthy and Oliver 2001).

Soybean yield is usually greater in narrow-row compared with wide-row soybean
when water is not limited. This is partly due to better distribution of soybean plants over
the soil surface for more efﬁcient use available water, light, and mineral nutrients
(Bumside and Colville 1964). Soybean seeding rate can also inﬂuence soybean yield.
Bertram and Pedersen (2004) reported that there was no difference between the
recommended seeding rates and seeding rates 20% higher for 19-, 38-, and 76-cm row

34

widths. However, soybean yield decreased 6% when soybean populations were lowered
20% from the recommended seeding rates of 556 000, 432 000, and 309 000 for soybean
planted in 19-, 38-, and 76-cm rows, respectively. In contrast, Kratochvil et al. (2004)
observed that soybean seeding rates 20% less than the recommended seeding rate
consistently produced yields similar to the standard soybean seeding rate of 432 250
seeds/ha in 19- and 38-cm rows. An additional proﬁt of $14 to $28/ha was realized when
soybean was planted at 20% less than the standard seeding rate. Soybean yield and
economic returns were $45 to $65/ha greater in narrow-row compared with wide-row
soybean when similar management systems were implemented (Nelson and Renner 1999).
The cost of seeding glyphosate resistant soybean is $20-25/ha more than non-
glyphosate-resistant seed (Kratochvil et al. 2004). Seeding rates for narrow-row soybean
are 20 to 45% greater than wide-row soybean (Bertram and Pedersen 2004; Kratochvil et
al. 2004; Norsworthy and Frederick 2002). Lowering seeding rates is a strategy producers
can utilize to lower production costs. However, the inﬂuence of lower than Optimal
seeding rates on soybean competitiveness with weeds has not been researched extensively.
Therefore, the objectives of this study were to determine the effect of soybean row spacing
and population on 1) soybean canopy closure and soybean yield, 2) weed biomass, and 3)

the economic returns when seeding soybean at higher population and in narrow rows.

35

MATERIALS AND METHODS

Field experiments were conducted at three locations in Michigan in 2004 and 2005
(Table 1). An indeterminate group II soybean glyphosate-resistant cultivar, ‘AG 21071’ was
A planted in plots measuring 3 m wide by 10.7 m long in 2004, and 3 m wide by 9.1 m long
in 2005. Soybean was planted in three row widths (19-, 38-, and 76-cm) using a
customized toolbar with John Deere planter units. Soybean populations were thinned to
target populations of 197 600, 296 400, and 444 600 plants/ha prior to the V1 growth stage
Due to heavy rains following planting that lowered initial populations soybeans were
thinned to target population of 123 500, 185 250, and 308 750 plants/ha at East Lansing in
2004 and at Clarksville in 2004 and 2005.

Herbicide treatments at all locations included a POST application of glyphosate2 at
0.84 kg ae/ha + ammonium sulfate at 2% w/w to 10-cm weeds, a weed-free control, and a
weedy control. Weed-free plots were maintained with two POST glyphosate applications
at V2 and V5. All herbicides were applied using a tractor-mounted compressed-air sprayer
calibrated to deliver 178 L/ha at 207 kPa using Airmix 110033 nozzles. Soybean yield was
determined by harvesting the center 1.52 m of each plot for seed yield and adjusting seed
yield to 13% moisture.
Soybean Canopy Development

The amount of light transmitted through the soybean canopy was measured every 1
to 2 weeks at or near solar noon at each site beginning ﬁve weeks after soybean planting

until the canopy began to senesce. Measurements were taken in weed-free plots using the

 

‘ Asgrow Seed Co., Monsanto Co., 800 North Lindbergh Boulevard, St. Louis, MO 63167.
2 Roundup WeatherMAX, Monsanto., 800 North Lindbergh Boulevard, St. Louis, MO 63167.
3 Teejet Airmix 11003, Spraying Systems Co., North Avenue, Wheaton, IL 60188.

36

Sunscan Canopy Analysis System4. The SunScan system consisted of three components:
1) a wand that was 1 m long and 13 rmn wide with sensors placed every 15.6 mm along the
length of the wand with a spectral response of 400 to 700 nm to measure light beneath the
crop canopy; 2) a tripod-mounted sensor that measured both incident and diffuse light
above the crop canopy; and 3) a handheld Psion Workabout datalogger5 that recorded
' simultaneous measurements of light above and beneath the crop canopy. Light
transmission, as a percent of incident, was automatically calculated as each measurement
was taken perpendicular to the soybean row from the weed-free plots.
Weed Emergence

Weed emergence was recorded at Clarksville and East Lansing in 2004 and at East
Lansing and St. Charles in 2005. Weed emergence was not recorded at St. Charles in 2004
due to little or no weeds present following the glyphosate application. The number of
weeds that emerged after the 10-cm POST glyphosate application was recorded ﬁ'om 15-
by 150-cm quadrats (0.225 m2) that were established at the time of application. Two
quadrats were placed in the center of each plot, perpendicular to the crop row. Density of
' each weed species was recorded weekly beginning 14 DAT, and ending 42 DAT.
Weed Biomass

Weed biomass and density were measured in the weedy-control in mid-August.
Aboveground weed biomass was also measured in two quadrats placed in the 10-cm
glyphosate treatments at all locations except at St. Charles in 2004 where there was little or

no weed biomass. Quadrats were randomly placed in the center of each plot, with length

 

4 Delta-T Device LTC, 128 Low Road, Burwell, Cambridge CBS 0E], England.
5 Psion Digital, 1810 Airport Exchange Boulevard, Suite 500, Erlanger KY 41018.

37

perpendicular to the crop row. Weeds were separated by species, dried in a forced-air oven
at 60 C, and dry weights calculated (kg/ha).
Economic Analysis

An economic analysis determined the gross margin for the 10-cm glyphosate
treatment, since this is a common weed management system. Seed and herbicide prices
were obtained ﬁom local seed and agrichemical dealers. Weed management costs were the
sum of seed and herbicide costs. Seed cost was $0.81/kg of seed with a $0.62/kg seed
technology fee assessed for the glyphosate trait. Seed cost was based on a weight of 6600
seed/kg. Herbicide cost for glyphosate plus AMS was $25/ha, and application cost was
$15/ha. Weed management input costs for herbicide treatments included herbicide,
adjuvant, application, and seed costs. Gross receipts were the product of crop yield and the
assumed market price. Market prices of $0.18, 0.22, and 0.26/kg of seed yield were used to
determine gross receipts. Gross margin was the difference between the gross receipt and
weed management costs.
Statistical Analysis

The experiment design was a split-split plot with four replications. The main plot
was row width, the sub-plot was soybean population, and the sub-sub-plot was herbicide
treatment. Data were subjected to ANOVA using the PROC MIXED procedure in SAS
8.026 software. Main effects and all possible interactions were tested using the appropriate
expected mean square values as recommended by McIntosh (1983). Each location
combination was considered an environment sample at random from a population as

suggested by Carmer et al. (1989). Environments, replications (nested within

 

" SAS Institute Inc., 100 SAS Campus Drive, Cary, NC 27513,
38

environments), and all interactions containing these effects were declared random effects in
A the model; row width, population, and herbicide were designated as ﬁxed effects. Data
from locations with similar populations were combined and mean separation performed

using Fisher’s Protected LSD at a=0.05.

39

RESULTS AND DISCUSSION

Growing Conditions

Rainfall in 2004 was greater than the 30 year average at all locations (Table 2).
Soybean had difficulty emerging at Clarksville and East Lansing due to excessive May
rains and soil crusting after planting. In 2005, total rainfall was slightly lower than the 30
year average at East Lansing and St. Charles, and rainfall was below normal in the month
of August during the time Of soybean pod ﬁll in Michigan. At Clarksville in 2005, total
rainfall was about half the 30 yr average; however, soil crusting occurred again at this
location after planting and reduced soybean populations. Weed densities were slightly
lower in 2004 (36 weeds/m2) at Clarksville compared with 2005 (52 weeds/m2) (Table 3).
At East Lansing weed densities were similar both years. The biggest change in weed
density between years occurred at St. Charles. In 2004, weed density at St. Charles was 13
weeds/m2 compared to 71 weeds/m2 in 2005.
Soybean Canopy Development

At Clarksville and East Lansing in 2004, LA] did not differ due to soybean row
width or soybean population ﬁom 35-39 to 55-64 days after planting (DAP) (Table 4). At
55-64 DAP, LAI was greater in 19- and 38- cm rows compared with 76-cm rows at
soybean populations of 185 250 and 308 750 plants/ha. Soybean LA] in 19- and 38-cm
rows at the lowest population of 123 500 plants/ha was similar to soybean planted in 76-cm
rows at the highest population of 308 750 plants/ha at 71-82 DAP. This indicates that a
soybean populations of 123 500 plants/ha in 19- or 38-cm rows had greater LAI than
soybean planted at 308 750 plants/ha in 76-cm rows. Canopy development was greatest at
88-90 DAP for soybeans planted at all populations in each row width and the canopy began

40

to senesce shortly after. At 88-90 DAP, LAI was similar between 19- and 38-Cm rows at
308 750 plants/ha. Soybean population had little inﬂuence on soybean canopy
development in 76-cm rows despite a 2.5 fold difference between the low and high
populations.

At East Lansing in 2005 and St. Charles in 2004 and 2005, soybean canopy
development was similar between row widths at populations of 197 600 and 444 600
. plants/ha at 39-48 DAP (Table 5). By 76-83 DAP, soybean in 19- and 38-cm rows had
greater LAIs than soybean planted in 76-cm rows, regardless of soybean population.
Furthermore, LAI was greater in 19-cm rows at 444 600 plants/ha compared with 197 600
plants/ha. By 85-93 DAP, soybean planted in 38-cm rows had greater LAIs a than 76-cm
row soybean, regardless of population. Canopy senescence began at 98-103 DAP; leaf area
at this time was similar among all row spacings and populations. From 70-103 DAP,
canopy development was similar in 38- and 76-cm rows. These results indicate that row
width inﬂuenced canopy development more than soybean population at East Lansing and
St. Charles.

At Clarksville in 2005, LAI was greater in 19- and 38-cm rows compared with 76-
cm rows at 185 250 plants/ha at 58 DAP; however, canopy development was similar
between treatments 64 DAP (Table 6). At 76 and 90 DAP, LAI was greater in 19- and 38-
cm rows compared with 76-cm rows, regardless of population. Canopy development was
greatest at 96 DAP; LAI was similar among 19- and 38-cm rows, regardless of population.

These results show that at peak canopy development, LAI was greater in 19- and
38-cm rows compared with 76-cm rows in 5 of 6 site years. At Clarksville in 2005, LAI
was similar at between row widths at 185 250 plants/ha, probably due to very low rainfall.

41

Furthermore, the high population of 185 250 at Clarksville is sub-optimal for 19-, 38, and
76-cm rows (Bertram and Pedersen 2004). At peak canopy development, LAI was greater
in 19- and 38-cm rows at 308 750 plants/ha compared with 123 500 plants/ha at Clarksville
and East Lansing in 2004. Soybean planted at 444 600 plants/ha had greater LAI compared
with 197 600 plants/ha in 19-cm rows at East Lansing in 2005 and St. Charles in 2004 and
2005. Soybean population in 76-cm rows had no effect on soybean LAI in 5 of 6 site
years.

The LAI that correlates to 95% solar radiation interception has been adopted as
critical LAI (Gardner et al. 1985). When there is 95% light interception under maximum
solar radiation of 2300 ,umol photons m’2 sec’l radiation at the bottom of the canopy is 115
' umol photons m'2 sec'l which is the light compensation point for many species. For these
studies, 95% light interception occurred when LAI was around 5.5 (data not shown).
Canopy closure occurred approximately 16 d earlier in 19- and 38-cm rows at Clarksville
and East Lansing and 6-12 (1 earlier at East Lansing and St. Charles compare with 76-cm
rows. Other researchers have also shown earlier canopy closure in narrow rows (Burnside
and Colville 1964; Carey and Defelice 1991; Nelson and Renner 1999; Wax and Pendleton
1968)

Weed Emergence

Weed emergence following the 10-cm glyphosate application was lower in narrow
row soybeans; soybean population had no effect on weed emergence. Data are therefore
combined across soybean populations. At Clarksville and East Lansing in 2004, weed
emergence in 19- and 38-cm rows was reduced compared to emergence in 76-cm rows 21
DAT (Figure l). Soybean canopy measured 55-64 DAP corresponds to weed emergence

42

14 DAT. Canopy closure occurred when LAI reached a value of 5.5 which ﬁrst occurred
in 19- and 38-cm rows at 308 750 plants/ha when weed emergence was recorded 21 DAT.
Since the soybean canopy developed more slowly in 76-cm rows, weed emergence was
‘ greater 35 DAT.

At East Lansing in 2005 and St. Charles in 2004 and 2005, weed emergence in 38-
cm rows was similar to emergence in 76-cm rows 14 and 21 DAT (Figure 2). By 35 DAT,
weed emergence was greater in 76-cm rows compared with emergence in 19- and 38-cm
rows. Soybean LAI was greater in 19- and 38-cm rows compared with 76-cm rows from
49-58 DAP until 76-83 DAP. Canopy closure occurred around 70-71 DAP which
corresponds to weed emergence 28 DAT, thus explaining higher weed emergence early on
at East Lansing in 2005 and St. Charles in 2004 and 2005 compared with Clarksville and
East Lansing in 2004. At Clarksville and East Lansing in 2004, canopy closure occurred at
weed emergence 21 DAT. The number of weeds continued to decline over time in 19- and
38-cm compared with 76-cm rows, because the light available was less than the light
compensation point.

Soybean planted in 19- or 38-cm rows reduced weed emergence following
herbicide application in 5 of 5 site years, resulting in better weed control in comparison to
76-cm rows. Other researchers have also reported better weed control in narrow-row
soybean due to earlier canopy closure (Burnside and Collville 1964; Chandler et al. 2001;
Mickelson and Renner 1997; Nelson and Renner 1999). Our results support those of
Yelverton and Coble (1991) who observed low weed emergence after herbicide application
in narrow-row soybean. Weeds that emerge later in season may not reduce yield, but
contribute to the seed bank (Y elverton and Coble 1991 ).

43

Weed Biomass

Weed biomass in the weedy-control treatment was similar among row widths at
each population at Clarksville and East Lansing in 2004 (Figure 3); however, weed
biomass was reduced in soybean planted at higher populations in l9-cm rows. There was a
trend for reduced weed biomass in 19- and 38-cm rows compared with 76-cm rows. A
similar trend in regards to row width was observed at East Lansing in 2004 and St. Charles
in 2004 and 2005 at 197 600 and 444 600 plants/ha (Figure 4). However, weed biomass
was lower in 19-cm rows compared with 38- and 76-cm rows at 296 400 plants/ha. At
Clarksville in 2005, weed biomass was similar among treatments (Figure 5).

There were few weeds following glyphosate application, and many of the harvested
weeds were small in size. Weed biomass after the glyphosate application was similar
among soybean row widths and populations at Clarksville and East Lansing in 2004
(Figure 6). Weed biomass was greatest in soybean planted at 197 600 plants/ha in 76-cm
rows; however, weed biomass was similar between 19- and 38-cm rows, regardless of
population in 76-cm rows at 296 400 and 444 600 plants/ha (Figure 7). At Clarksville in
2005, weed biomass was similar across treatments, but the only measurable biomass was
produced in 76-cm rows (Figure 8).

Weed biomass in weedy control plots was reduced by increasing soybean
population; however, there was a trend for greater weed biomass in 76-cm rows. Previous
research has shown that narrow-row soybean reduces weed biomass when no herbicide is
used (Burnside and Collville 1964; Dalley et al. 2004b; Nice et al. 2001; Patterson et al.
1988). Our research supports those results. At the lowest soybean population, biomass in
the weedy-control was similar regardless of row width; however, increasing the soybean

44

population in narrow rows provided a greater reduction of weed biomass. Nice et al.
(2001) reported similar results with sicklepod (Senna obtusifolia) in soybean. Weed
biomass after glyphosate application was variable but there was a trend for less biomass in
narrow-row soybean at higher plant populations in 4 of 6 site years, supporting research in
Wisconsin (Ateh and Harvey 1999), Illinois (Young et al. 2001), and Michigan research
(Dalley et al. 2004b; Nelson and Renner 1999).
Soybean Yield

At Clarksville and East Lansing in 2004, soybean yield was greater in 19- and 38-
cm rows compared with 76-cm rows at each population (Table 7); however, yields were
' similar between 19- and 38-cm rows. Yield was greater at the high population of 308 750
plants/ha compared with the low population of 123 500 plants/ha in each row width. The
intermediate population of 185 250 plants/ha yielded similar to the high population in 38-
and 76-cm rows. Yields were similar between weed-free and 10-cm glyphosate treatments,
despite weed emergence following glyphosate application. Soybean yields in 10-cm
glyphosate treatments were similar between 19- and 38-cm rows and were greater than 76-
cm rows at 123 500 and 185 250 plants/ha. Yield of soybean planted at 308 750 plants/ha
was similar for 38- and 76-cm rows. Soybean yield in the weedy-controls was much lower
than yield in the lO-cm glyphosate and weed-ﬂee treatments. At 123 500 and 185 250
plants/Ira, yields of soybean in the weedy-control treatment were similar across row width.
At 308 750 plants/ha, yield was greater in 19- and 38-cm rows compared with 76-cm rows.

At St. Charles in 2004 and 2005 and East Lansing in 2005, which had higher
populations, weed-free soybean yield was greater in 19- and 38-cm rows compared with
76-cm rows, regardless of population (Table 8). Increasing the soybean population did not

45

increase soybean yield in 76-cm rows; however, yields were greater when soybean was
planted at 444 600 plants/ha compared with 197 600 plants/ha in 19- and 38-cm rows.
Yields were similar between 19- and 38-Cm rows for each respective population. Yields
were similar between weed-free and 10-cm glyphosate treatments. Yield of soybean
treated with glyphosate was similar in the 19- and 38-cm rows and yield was greater than
yield in 76-cm rows at each population. Soybean yields were greater at 444 600 plants/ha
compared with 197 600 plants/ha in 19- and 38-cm rows, but were similar in 76-cm rows.
Weedy-control yields were greater in l9-Cm rows compared with 76-cm rows at each
population. Yields were similar between populations in both 19- and 76-cm rows, but in
38-cm rows soybean at 444 600 plants/ha had greater yields than 197 600 plants/ha.

At Clarksville in 2005, soybean yield in the weed-free plots was greater in 19-cm
rows compared with 76-cm rows at 185 250 plants/ha; however, yields were similar at 123
500 plants/ha (Table 7). Yields were similar in the 10-cm glyphosate and weed-free
control treatments. Similar to weed-free yields, yield of soybean treated with glyphosate
was greater at 185 250 plants/ha in 19-cm row compared with 76-cm rows.

Planting soybean in narrow rows increases soybean yield (Wiggans 1939;
Etheredge et al. 1989; Ikeda 1992; Board and Harville 1993; Egli 1994). Our research
supports those ﬁndings. Average weed-ﬂee soybean yield was 4139 kg/ha at Clarksville
and East Lansing in 2004 and 3913 kg/ha at St. Charles and East Lansing in 2004 and
2005. Despite having lower soybean populations at Clarksville and East Lansing, weed-
free yield was higher compared with St. Charles and East Lansing and was probably due to
greater rainfall in 2004. Despite having studies with two different ranges of populations,
yield was greater in 19-and 38-cm rows compared with 76-cm rows for each population.

46

Trends were similar between studies in regard to 19- and 38-Cm rows, but differed in
response to population in 76-cm rows. Yields were geater at higher populations in 76-cm
rows at Clarksville and East Lansing, possibly due to both greater rainfall and lower
populations. Seeding recommendations for 76-cm rows is 309 000 seeds/ha which
. corresponds to the high populations at Clarksville and East Lansing, Recommended
seeding rates for 19- and 38-cm row are 556 000 and 432 000 seeds/ha (Bertram and
Pedersen 2004), higher populations than the populations in our research.

Weed biomass after glyphosate application did not affect yield in comparison to
weed-free plots. Similar results have also been reported (Dalley et al. 2004a; Yelverton
and Coble 1991). Similar to weed-free yields, planting soybean at higher populations
increased yield in each row width at Clarksville and East Lansing in 2004; however, this
trend was also observed in l9- and 38-cm rows at East Lansing in 2004 and St. Charles in
2004 and 2005. Soybean yield in the weedy-control was greater at higher populations in
19-crn rows at Clarksville and East Lansing in 2004 and in 38-cm rows at East Lansing in
2005 and St. Charles in 2004 and 2005. Planting soybean in 19-cm compared with 76-cm
rows increased soybean yield at East Lansing in 2004 and St. Charles and 2005 for each
population; however, this was true at 308 750 plants/ha at Clarksville and East Lansing in
2004.

Economic Return

At Clarksville and East Lansing, soybean planted in 19-cm rows at 308 750
plants/ha had the geatest goss margin, regardless of gain price (Table 10). In 38-Cm
rows, goss margins were similar regardless of population; however, goss margins tended
to be higher as soybean population increased. Gross margins were geater in 19-cm rows

47

compared with 76-cm rows for each respective population. In 76-cm rows, goss margins
were similar between 185 250 and 308 750 plants/ha, but were geater than 123 500
plants/ha. Furthermore, there was a trend for geater goss margins as population increased
in 38- and 76-cm rows. At East Lansing and St. Charles, the goss margins were similar
among populations in 19- and 38-cm rows(Table 11); however, goss margins increased as
population increased in 19-cm rows. Gross margins were geater in 19- and 38-cm rows
compared with 76-cm rows at 444 600 plants/ha. In 76-cm rows the highest return
. occurred at 296 400 plants/ha. At Clarksville in 2005, goss margins were similar among
populations in 19- and 76-cm rows, but goss margins were geater at 185 250 compared
with 123 500 plants/ha in 38-cm rows (Table 12). There was no difference in goss
margins among row widths at 185 250 plants/ha.

In conclusion, soybean LAI was higher in 19- and 38-Cm rows compared with 76-
cm rows. Increasing population in 19- or 38-cm rows resulted in geater LAI; however,
LAI was similar regardless of population in 76-cm rows at peak canopy development.
Canopy closure occurred 15-22 days earlier in 19- and 38-cm rows compared with 76-cm
rows. Weed emergence after a single application of glyphosate was lower in 19- and 38-
cm rows than 76-cm rows 35 DAT; weed biomass was variable. Weed biomass was
. reduced in the weedy control treatment by planting higher soybean populations within a
row width. There was a trend for a reduction in weed biomass as row width narrowed.
Under weedy conditions, yields were geatest when soybean was planted at 296 400 to 444
600 plants/ha in 19- and 38-cm rows, and 185 250 to 308 750 plants/ha in 76-cm rows. In
weed-free conditions, yield was geatest when soybean was planted at 308 750 to 444 600
in 19-cm rows and 296 400 to 308 750 in 38-and 76-cm rows. The geatest economic

48

return was in 19-cm rows at 308 750 plants/ha at Clarksville and East Lansing in 2004.
The geatest economic return was in 19-cm rows at 444 600 plants/ha at East Lansing in

2005 and St. Charles in 2004 and 2005.

49

LITERATURE CITED

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

Bertram, M.G., and P. Pedersen. 2004. Adjusting management practices using glyphosate-
. resistant soybean cultivars. Agon. J. 96:462-468.

Burnside, 0C. and W.L. Colville. 1964. Soybean and weed yields as affected by irrigation,
row spacing, tillage, and arrriben. Weeds. 12:109-112.

Burnside, DC. and RS. Moomaw. 1977. Control of weeds in narrow-row soybeans.
Agon. J. 69:793-796.

Carey, J .B. and MS. DeFelice. 1991. Timing of chlorimuron and imazaquin application for
weed control in no-till soybeans (Glycine max). Weed Sci. 39:232-237.

Carmer, S.G., W.E. Nygquist, and W.N. Walker. 1989. Least signiﬁcant differences for
combined analysis of experiments with two or three-factor treatment designs. Agon. J.
81:665-672.

Chandler, K., A. Shrestha, and C.J. Swanton. 2001. Weed seed return as inﬂuenced by the
critical weed-ﬂee period and row spacing of nO-till glyphosate-resistant soybean. Can. J.
Plant Sci. 81:877-880.

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

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

Dalley, C.D., J .J . Kells, and K.A. Renner. 2004. Effect of glyphosate application timing
and row spacing on weed gowth in corn (Zea mays) and soybean (Glycine max). Weed
Techno]. 183177-182.

Devlin, D.L., D.L. Fjell, J.P. Shroyer, W.B. Gordon, B.H. Marsh, L.D. Maddux, V.L.
Martin, and SR. Duncan. 1995. Row spacing and seeding rates for soybean in low and
high yielding environments. J. Prod. Agic. 8:215-222.

Egli, DB. 1994. Mechanisms responsible for soybean yield response to equidistant
patterns. Agon J. 86:1046-1049.

Gardner, F.P., R.B. Pearce, and R.L. Mitchell. 1985. Physiology of Crop Plants. Iowa
State University Press, Ames Iowa. p. 31-56.

Ikeda, T. 1992. Soybean planting patterns in relation to yield and yield components.
Agon. J. 84:923-926.

50

Kratochvil, R.J., J.T. Pearce, and MR. Harrison. 2004. Row-spacing and seeding rate
effects on glyphosate-resistant soybean for mid-atlantic production systems. Agon. J.
96:1029-1038.

Légére A. and M.M. Schreiber. 1989. Competition and canopy architecture as affected by
soybean (Glycine max) row width and density Of redroot pigweed (Amaranthus
retroﬂexus). Weed Sci. 37:84-92.

McIntosh, MS. 1983. Analysis of combined experiments. Agon. J. 75:153-155.

Mickelson, J .A. and K.A. Renner. 1997. Weed control using reduced rates of
postemergence herbicides in narrow and wide row soybean. J. Prod. Agic. 10:431-437.

Mulugeta, D. and CM. Boerboom. 2000. Critical time of weed removal in glyphosate-
resistant Glycine max. Weed Sci. 48:35-42.

Nelson, K.A. and K.A. Renner. 1999. Weed management in wide- and narrow-row
glyphosate resistant soybean. J. Prod. Agric. 12:460-465.

Nice, G.R., N.W. Buehring, and DR. Shaw. 2001. Sicklepod (Senna obtusifolia) respnse
to shading, soybean (Glycine max) row spacing, and population in three management
systems. Weed Techno]. 15:155-162.

Norris, J.L., D.R. Shaw, and CE. Snipes. 2002. Inﬂuence of row spacing and residual
herbicides on weed control in glufosinate-resistant soybean (Glycine max). Weed Techno].
16:319-325.

Norsworthy, J .K. and J .R. Frederick. 2002. Reduced seeding rate for glyphosate-resistant,
drilled soybean on the southeastern coastal plan. Agon. J. 94: 1282-1288.

Norsworthy, J .K. and LR. Oliver. 2001. Effect of seeding rate of drilled glyphosate-
resistant soybean (Glycine max) on seed yield and goss proﬁt margin. Weed Techno].
' 15:284-292.

Peters, E.J., M.R. Gebhardt, and J.F. Stritzke. 1965. Interrelations of row spacing,
cultivations and herbicides for weed control in soybeans. Weeds 13:285-289.

Shibles, R.M., and CR. Weber. 1965. Leaf area, solar radiation interception and dry
matter production by soybeans. Crop Sci. 5:575-578.

Shibles, RM. and CR. Weber. 1966. Interception of solar radiation and dry matter
production by various soybean planting patterns. Crop Sci. 6:55-59.

51

Taylor, HM. 1980. Soybean gowth as affected by row spacing and by seasonal water
supply. Agon. J. 72:543-546.

Wax, L.M. and J .W. Pendleton. 1968. Effects of row spacing on weed control in soybeans.
Weed Sci. 16:462-465.

Wax, L.M, W.R. Nave, and R.L. Cooper. 1977. Weed control in narrow and wide-row
soybeans. Weed Sci. 25:73-78.

Yelverton, PH. and H.D. Coble. 1991. Narrow row spacing and canopy formation reduces
weed resurgence in soybean (Glycine max). Weed Techno]. 5:169-174.

52

 

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Table 2. Monthly precipitation recorded at the Clarksville Horticulture Experiment Station
in Clarksville, M1, at the Michigan State University Department of Horticulture and

Research Center, East Lansing, MI, and at the Saginaw Valley Bean and Beet Farm, St.
Charles, M].

 

 

 

 

 

Precipitation (cm)
Clarksville East Lansing St. Charles
2004 2005 30 yr. 2004 2005 30 yr. 2004 2005 30 yr.
May 21.8 4.5 7.4 20.5 3.3 6.9 16.5 4.4 6.3
June 7.6 4.1 9.7 8.9 10.9 9.0 6.9 12.6 7.8
July 12.2 5.2 6.0 10.2 11.6 7.7 5.1 8.1 7.2
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Total 48.2 16.2 32.3 48.3 27.4 31.5 34.4 27.2 29.7

 

54

Table 3. Weed densities at Clarksville, East Lansing, and St. Charles in 2004 and 2005.“

 

Year ABUTHb AMARE AMBEL ANGR BARVU BRAKA CHEAL Total

 

 

 

 

 

 

 

weeds/{at Clarksville
2004 o 2 3 7 21 o 3 36
2005 1 1 2 l8 8 o 22 52
weeds/m2 at East Lansing
2004 3 4 8 80 o 6 1 102
2005 2 2 13 72 o 6 11 106
weeds/m2 at St. Charles
2004 o 1 2 1 o 0 9 13
2005 o 16 o 12 o o 43 71

 

3 Reported weed densities were measured at time of weed harvest.

bABUTH-=velvetleaf, AMARE=redroot pi gweed, AMBEL=common ragweed,
ANGR=annual gass (including giant foxtail, geen foxtail, yellow foxtail, and
bamyardgass), BARVU=yellow rocket, BRAKA=wild mustard, and CHEAL=common
lambsquarters.

55

Table 4. Soybean canopy development at Clarksville and East Lansing in 2004. Leaf area
’ index (LAI) was obtained by a non-destructive measurement using the SunScan Canopy
Analysis System. Different letters within each column represent mean separation at

LSDocs.

 

 

 

 

 

 

 

Days after planting
Population 35-39 43-48 55-64 71-74 81-82 88-90 96-98
19-cm LAI
123 500 0.53 cde 0.83 e 1.72 c 4.23 c 5.13 Cd 5.99 d 4.89 c
185 250 0.53 b-e 1.17 be 2.14 be 4.83 c 5.74 b 6.68 Cd 5.01 c
308 750 0.60 abc 1.39 a 2.94 a 6.77 b 6.21 ab 7.26 abc 6.32 ab
38-cm
123 500 0.51 de 0.94 de 2.02 be 4.86 c 5.49 be 6.71 bcd 5.39 be
185 250 0.52 de 1.05 cd 2.69 ab 5.90 b 6.70 a 7.46 ab 5.52 bc
308 750 0.65 a 1.30 ab 3.35 a 7.94 a 7.05 a 8.00 a 6.80 a
76-cm
123 500 0.49 e 0.98 de 1.60 c 2.90 d 3.67 e 5.62 d 4.76 c
185 250 0.57 bcd 1.00 d 1.90 c 3.00 d 4.37 de 6.10 d 4.99 c
308 750 0.63 ab 1.21 abc 2.05 be 3.90 Cd 4.60 Cd 6.42 cd 5.30 bc

 

56

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57

Table 6. Soybean canopy development at Clarksville in 2005. Leaf area index (LAI) was
obtained by a non—destructive measurement using the SunScan Canopy Analysis System.
Different letters within each column represent mean separation at LSDo,05_

 

 

 

 

 

 

 

Days after planting

Population 58 64 76 90 96 106
l9-cm LAI

123 500 1.7 ab 3.1 a 5.0 ab 5.8 a 6.5 a 5.0 a

185 250 2.0 a 3.3 a 4.8 b 6.3 a 5.9 a 3.9 b
38-em

123 500 1.6 be 3.1 a 4.8 b 5.8 a 6.3 a 4.5 a

185 250 1.8 a 3.1 a 5.3 a 6.3 a 6.5 a 4.7 a
76-cm

123 500 1.3 c 2.5 a 4.0 d 4.9 b 4.8 b 3.7 b

185 250 1.3 c 2.7 a 4.5 c 4.6 b 5.8 a 3.9 b

 

58

Table 7. Effect of soybean row width, population, and herbicide treatment on soybean
1 yield at Clarksville and East Lansing in 2004.“

 

Soybean Yield (kg/ha)

Population Weed-free Woody-control Glyphosate

 

l9-cm

 

123 500 3966 D(cde) 1250 D (jk) 3832 D(def)

185 250 4262 BC(a-d) 1660 BCD(hij) 4147 BC(b-e)

308 750 4598 A(ab) 2642 A(g) 4638 A(a)

38-cm

 

123 500 3959 D(cde) 1479 BCD(ijk) 3939 CD(de)

185 250 4289 BC(a-d) 1909 BC(hi) 4060 BC(cde)

308 750 4423 AB(abc) 2077 AB(gh) 4215 B(a-d)

76-cm

 

123 500 3677 E(et) 1049 D04) 3381 E(e)

185 250 3959 D(c-e) 1318 CD(jk) 3778 D(def)

308 750 4114 CD(b-e) 1398 CD(ijk) 4040 BC(cde)

 

aMean separation (LSDogs) within herbicide treatment are denoted by capital letters.
l’Mean separation (LSDQ05) between herbicide treatments are denoted by lower case letters
in parenthwes.

S9

Table 8. Effect of soybean row width, population, and herbicide treatment on soybean
yield at East Lansing in 2005 and St. Charles in 2004 and 2005.ab

 

Soybean Yield (kg/ha)

Population Weed-free Weedy-control Glyphosate

 

1 9-cm

 

197 600 3986 AB(a-d) 2084 ABC(ef) 4087 BC(a-d)

296 400 4141 A(a-d) 2393 AB(e) 4255 AB(ab)

444 600 4255 A(ab) 2406 A(e) 4423 A(a)

38-cm

 

197 600 3805 BC(bcd) 1721 CD(fg) 3959 CD(a-d)

296 400 4020 AB(a-d) 2057 ABC(et) 4215 AB(abc)

444 600 4053 AB(a-d) 2285 AB(e) 4322 AB(ab)

 

76-cm
197 600 3643 C(d) 1499 D(g) 3630 E(d)
296 400 3711 C(c) 1707 CD(fg) 3953 CD(a-d)
444 600 3610 C(d) 1882 BCD(efg) 3711 DE(cd)

 

alMean separation (LSD0_05) within herbicide treatment are denoted by capital letters.

bMean separation (LSDogs) between herbicide treatments are denoted by lower case letters
in parentheses.

6O

Table 9. Effect of soybean row width, population, and herbicide treatment on soybean
yield at Clarksville in 2005.ab

 

 

 

 

Soybean Yield (kg/ha)
Population Weed-free Weedy-control Glyphosate
19-cm
123 500 3756 AB(ab) 759 AB(fg) 3566 ABC(bcd)
185 250 3838 A(a) 502 C(h) 3742 A(ab)
38-cm
123 500 3371 C(de) 613 BC(gh) 3281 D(e)

185 250 3613 ABC(a-d) 617 BC(gh) 3653 AB(abc)

76-cm

 

123 500 3481 BC(cde) 952 A(f) 3396 CD(de)

185 250 3404 C(cde) 537 BC(gh) 3525 BC(b-e)

 

aMean separation (LSDon) within herbicide treatment are denoted by capital letters.
bMean separation (LSD0_05) between herbicide treatments are denoted by lower case letters
in parentheses.

61 .-

Table 10. Gross margins for 10-cm glyphosate application at Clarksville and East Lansing

 

 

 

 

 

 

 

in 2004.
Gross Margin
Population $0.18/kg 0.22/kg 0.26/kg
19-cm (S/ha)
123 500 637 778 919
185 250 682 834 987
308 750 746 916 1087
38-cm
123 500 657 802 947
185 250 666 815 964
308 750 668 823 978
76-cm
123 500 555 679 803
185 250 614 753 892
308 750 636 784 933
LSDmos) 42 52 59

 

62

Table 11. Gross margins for lO-cm glyphosate application at East Lansing in 2005 and
St.Charles in 2004 and 2005.

 

 

 

 

 

 

 

Gross Margin
Population $0.18/kg 0.22/kg 0.26/kg
l9-cm ($/ha)
197 600 661 810 958
296 400 675 831 987
444 600 685 849 1014
38-cm
197 600 64-4 790 936
296 400 670 825 980
444 600 657 816 976
76-cm
197 600 583 716 849
296 400 627 773 920
444 600 548 685 822
LSDwos) 45 54 62

 

63

Table 12. Gross margins for 10-cm glyphosate application at Clarksville in 2005.

 

 

 

 

 

 

 

Gross margins

Population $0.1 8/kg 0.22/kg 0.26/kg
19-cm ($/ha)

123 500 589 720 851

185 250 607 745 882
38-cm

123 500 536 657 777

185 250 591 725 860
76-cm

123 500 557 682 807

185 250 568 697 827

LSD(0,05) 52 57 67

 

64

Figure l. Weed emergence following glyphosate application at Clarksville and East
Lansing in 2004. Vertical bars at each measurement indicate LSDoos. Dotted vertical line
indicates canopy closure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

16 5
”a 14 .—7-.
€12-----7‘=.- 3:
g 10 NS I r
“5 8 > a ?“ I ’ I \ \ .L
g 6 §+¢ \‘7\
8 4 \
Z 2

O T l l l l

10 15 20 25 30 35 40
Daysaﬂertreatment

19-cm — — 38-cm - - - - 76-cm

 

65

Figure 2. Weed emergence following glyphosate application at East Lansing and St.

Charles in 2005. Vertical bars at each measurement indicate LSD0_05. .

line indicates canopy closure.

-2

Number of weeds m

14
12
10

ON-bQOO

Dotted vertical

 

 

 

 

 

 

 

 

 

 

 

10

15 20 25 30 35
Days alter treatment

19-cm — — 38-cm - - - - 76-cm

 

66

4O

Figure 3. Effect of soybean row width and population on weed biomass at Clarksville and
East Lansing in 2004. Different letters above each column indicate mean separation
LSDoos.

 

 

 

 

 

 

 

7%:—
%o
g;

/._ 2

19-cm row width 38-cm row width 76-cm row width

I 123 500 plants/ha 185 250 plants/ha a 308 750 plants/ha

67

weed biomass at East Lansing in
005. Different letters above each column indicate mean

. Effect of soybean row width and population on
harles ' 004 and

n
4d0
.h

 

 

19-cmro

 

 

 

lants/ha

I 197 600 plants/ha 296 400 plants/ha E 444 600 p

5. Effect of soybean row width and population on
2005. Different letters above each column indicate

m
W
F

 

////////////

///// /mu

   

 

 

 

 

mmmmmm

ELEV 8885 e83

Figure 6. Effect of soybean row width and population on weed biomass in lO-cm
glyphosate treatment at East Lansing and Clarksville in 2004. Different letters above each
column indicate mean separation LSD0_05.

 

&
U!
C

 

 

 

 

"’8
U]
C

 

Weed biomass (kg/ha)
'— N N w
8 8 8 8

§

 

 

 

%_

19—cm row width 38-cm row width 76-cm row width

I 123 500 plants/113 185 250 plants/ha E 308 750 plants/ha

70

Figure 7. Effect of soybean row width and population on weed biomass in 10-cm
glyphosate treatment at East Lansing and St. Charles in 2005. Different letters above each

column indicate mean separation LSD0_05.

250

§

150

Weed biomass (kg/ha)
8

M
O

bb bbb

 

l9-cm row width 38-cm row width 76—cm row width
I 197 600 plants/ha 296 400 plants/ha E 444 600 plants/ha

71

. Figure 8. Effect of soybean row width and population on weed biomass in lO-cm
glyphosate treatment at Clarksville in 2005. Different letters above each column indicate

mean separation LSDogs.

 

25

 

 

N
O

 

p—t
M

 

 

Weed biomass (kg/ha)
2'5

 

 

{II

 

a a a a

 

 

19—cm row width 38—cm row width 76-cm row width
I 123 500 plants/ha 185 250 plants/ha

72

CHAPTER 3
EFFECT OF ROW WIDTH AND POPULATION ON SOYBEAN YIELD
COMPONENTS.
ABSTRACT

Understanding how soybean can compensate for changes in population and row width will
help identify the optimal population for a particular row width. The objective of this study
was to determine soybean yield and yield components of the mainstem and branch fraction
of soybean grown in three different row widths at three different seeding rates. Soybean
was planted in 19-, 38- and 76-cm rows at 123 500, 185 250, and 308 750 plants/ha at
Clarksville and East Lansing in 2004, and 197 600, 296 400, 444 600 plants/ha at East
Lansing in 2005 and St. Charles in 2004 and 2005. Optimal plant populations were 308
750 to 444 600 plants/ha for soybean planted in 19- or 38-cm rows, and 185 250 to 308 750

for soybean planted in 76-cm rows. Pod number per plant was the most responsive yield
I component to changes in population and row width. A greater proportion of yield was
composed from branch yield components in narrow rows and at lower populations.
Mainstem plant weight was responsive to changes in population but was similar across row
widths at each population. Branch plant weight was responsive to changes in populations,
but also responded to changes in row width at lower populations. In conclusion, branch
pod number was responsive to changes in row width and population, while mainstem pod
number was responsive to changes in population only.
Nomenclature: Glyphosate, N-(phosphonomethyl) glycine; soybean ‘AG 2701’, Glycine

max (L.) Merr.

73

 

 

Keywords: soybean populations, row spacing, yield components, mainstem seed yield,
branch seed yield.

Abbreviations: CGR, crop growth rate; LAI, leaf area index.

INTRODUCTION

Soybean yield is dependent on row width, cultivar, population, and planting date
' (Ethredge et a1. 1989). The effect of row width on soybean growth and yield has been
researched extensively. Generally, yield is greater in narrow-row soybean compared with
wide-row soybean when environmental factors are favorable (Devlin et al. 1995; Taylor
1980; Yelverton and Coble 1991). Increased yield in narrow-row soybean is partly due to
more efficient use of available water, light, and mineral nutrients by soybean plants spaced
at a more equidistant spacing (Burnside and Colville 1964).

Yield response to reductions in row width can be partly attributed to an
improvement in radiation interception during pod set (Andrade et al. 2002). However,
canopy photosynthesis is linearly related to light interception and LAI prior to canopy
closure, but not afterwards (Wells 1991). The leaf area index (LAI) that correlates to 95%
solar radiation interception has been adopted as the critical LAI (Weber et al. 1966).
Soybean crop growth rate (CGR) does not increase signiﬁcantly when light interception is
above 95% (Shibles and Weber 1965). Furthermore, yields over a range of seeding rates
are similar when 95% of photosynthetically active radiation is intercepted (Norsworthy and
Oliver 2001). Board (2000) observed that soybean at low populations (80 000 plants/ha)

can yield the same as medium (145 000 plants/ha) and high (390 000 plants/ha) populations

74

when planted in 75-cm rows due to greater CGR and light interception efficiency by
soybean at lower populations.

The impact of row width on soybean yield components varies by study. Ethredge
et a1. (1989) observed that the number of pods per plant was not affected by row width.
Weber et al. (1966) observed that seed size was independent of row width. In contrast,
seed weight and the number of seeds per pod were greater when soybean was planted in
wide rows (Costa et al. 1980; Lehman and Lambert 1960).

Soybean can compensate for sparse plant populations (Wells 1991). Increased pod
production associated with greater branch development occurs at low soybean populations
(Carpenter and Board 1997; Herbert and Litchﬁeld 1982; Hicks et al. 1969; Lehman and
Lambert 1960). Seed size has also been implicated as one factor in yield compensation due
to larger seeds at lower populations (Moore 1991; Wright et al. 1984). However, the
changes in seed weight and number of seeds per pod due to soybean population are
inconsistent (Board 2000; Carpenter and Board 1997; Costa et a1. 1980; Etheredge et al.
1989; Herbert and Litchﬁeld 1982). Of the seed yield components, pod number per plant is
the most responsive to changes in row width or plant population (Lehman and Lambert
1960; Herbert and Litchﬁeld 1982; Pedersen and Lauer 2004; Weber et al. 1966). At
higher soybean populations there are fewer pods per plant (Ethredge et al. 1989).

The partitioning of soybean yield to branch or mainstem fractions is inﬂuenced by
. both row width and population. Mainstem yield is greater in narrow-row soybean than
wide-row soybean, and some soybean genotypes are capable of partitioning more resources
to increased branch seed yields in response to row width (Norsworthy and Shipe 2005).
Rigsby and Board (2003) reported genotypic differences in soybean branching and branch

75

yield at low populations. Branches produce a greater proportion of seed yield at lower
populations (Herbert and Litchﬁeld 1982).

The partitioning of yield components to branch or mainstem fraction is also
inﬂuenced by environmental conditions. When moisture is limiting there is often no yield
beneﬁt in planting narrow-row soybean (Devlin et al. 1995; Norris et al. 2002; Taylor
1980). One explanation for this is that the contribution of branch seed yield to total yield is
greater in years of higher rainfall (Norsworthy and Frederick 2002). In dry conditions, the
mainstem portion of yield is greater, indicating that mainstem yield is stable over
environments (Board, 1987; Frederick et al. 2001). Furthermore, yield has been correlated
to dry matter production, and total dry matter per plant is greater in narrow rows, with a
greater fraction being produced on branches (Board et al. 1990).

The optimal seeding rate for soybean varies from 30 000 plants/ha to 500 000
' plants/ha (Board 2000). Understanding how soybean compensated for changes in
population and row width will help identify the optimal population for a particular row
width. There are few studies comparing soybean yield and yield components across
various row widths. Etheredge et al. (1989) studied yield component response to 25-, 51-,
and 76-cm rows with seeding rates remaining constant across row widths. However, there
are no studies comparing constant seeding rates across 19-, 38-, and 76-cm rows.
Therefore, the objective of this study was to determine soybean yield and yield components
of the mainstem and branch fraction of soybean grown in three different row widths at

three different seeding rates.

76

MATERIALS AND METHODS

Field experiments were conducted in Michigan at three locations in 2004 and two
locations in 2005 (Table 1). An indeterminate group II glyphosate-resistant soybean
cultivar ‘AG 21071 ’was planted in plots measuring 3 m wide by 10.7 m long in 2004, and 3
m wide by 9.1 m long in 2005. Soybean was planted in three row widths (19-, 38-, and 76-
cm) using a customized toolbar with John Deere planter units. Target populations were
197 600, 296 400, and 444 600 plants/ha at all locations; however, heavy rains following
planting lowered populations at Clarksville and East Lansing in 2004. Populations were
thinned prior to the V1 growth stage. Weed-control was accomplished by two
postemergence glyphosate2 applications at 0.84 kg ae/ha at the V2 and V5 growth stage of
soybean using a tractor-mounted compressed-air sprayer calibrated to deliver 178 L/ha at
207 kPa with Airrnix 110033 nozzles.

At physiological maturity, all soybean plants in 15- by ISO-cm quadrats (0.225 m2)
were harvested at the soil surface ﬁom weed-free plots. Branches were separated from the
mainstem fraction of the soybean plant and weighed and divided by the number of plants in
, each quadrat to report data on a per plant basis. From three randomly selected plants in
each sampled quadrat, pod number and seed number per plant were counted. The number
of seeds per pod was determined by dividing the number of seeds per plant by the number
of pods per plant. Weight of 100 seed was recorded. Soybean yield was determined by
harvesting the center rows of each plot. Seed yield was adjusted to 13% moisture and for

soybean removal from quadrats in weed-free plots.

 

1 Asgrow Seed Co., Monsanto Co., 800 North Lindbergh Boulevard, St. Louis, MO 63167.
2 Roundup WeatherMAX, Monsanto Co. 800 North Lindbergh Boulevard, St. Louis, MO 63167.
3 Teejet Airmix 11003, Spraying Systems Co., North Avenue, Wheaton, IL 60188.

77

The experiment design was a split plot with four replications. The main plot was
row width and the sub-plot was soybean population. Data were subjected to AN OVA
using the PROC MIXED procedure in SAS 8.024 software. Main effects and all possible
interactions were tested using the appropriate expected mean square values as
recommended by McIntosh (1983). Each location combination was considered an
environment sampled at random from a population as suggested by Canner et al. (1989).
Environments, replications (nested within environments), and all interactions containing
these effects were declared random effects in the model. Data from locations with similar
populations were combined and mean separation performed using Fisher’s Protected LSD

' at a=0.05.

 

4 SAS Institute Inc., 100 SAS Campus Drive, Cary, NC 27513,
78

RESULTS

Growing conditions
. Rainfall in 2004 was greater than the 30 year average at all locations (Table 2).
May rainfall was approximately three times greater than the 30 year average at Clarksville
and East Lansing where soil crusting inhibited soybean emergence. Rainfall at St. Charles
during May 2004 was approximately two times greater than the 30 year average as well. In
2005, total rainfall was slightly lower than the 30 year average at East Lansing and St.
Charles. Rainfall was low in the month of August in 2005, which corresponds to the time
of soybean pod ﬁll in Michigan.
Soybean Yield

At Clarksville and East Lansing in 2004, soybean yield was greater in 19- and 38-
cm rows compared with 76-cm rows at each population (Figure 1); yields were similar
between 19- and 38-cm rows. Yield was greater at the high population of 308 750
plants/ha compared with the low population of 123 500 plants/ha in each row width. The
medium population of 185 250 plants/ha yielded similar to the high population in 38- and
76-cm rows.

At St. Charles in 2004 and 2005 and East Lansing in 2005, soybean yield was
greater in 19- and 38-cm rows compared with 76-cm rows, regardless of population (Figure
2). There was no difference in yield between populations in 76-cm rows; however, yields
were greater when soybean was planted at 444 600 plants/ha compared with 197 600
plants/ha in 19- and 38-cm rows. Yields were similar between 19- and 38-cm rows at each

population.

79

Plant Seed Yield

Total, mainstem, and branch seed yields were greater at the low population
compared with the high population in each row width at Clarksville and East Lansing in
2004 (Table 3). At 185 250 and 308 750 plants/ha, total, mainstem, and branch seed yields
were similar across row widths. At the low population, mainstem seed yield was similar
across row widths; however, total and branch seed yields were greater in 19-cm rows
compared with 38- and 76-cm rows. Mainstem seed yield was statistically similar across
row width at each population, but a greater proportion of yield was produced on the
mainstem in 76-cm rows compared with 19-cm rows. For example, soybean in 19-cm
rows at 123 500 plants/ha produced 43% of seed yield on the mainstem fraction compared
with 53% in 76-cm rows. As population increased, the mainstem pr0portion of seed yield
also increased. Soybean planted in 38-cm rows at 123 500 plants/ha produced 48% of seed
yield on the mainstem ﬁaction compared with 67% at 308 750 plants/ha

Total, mainstem, and branch seed yields per plant were greater at the low
. population compared with the high population in each row width at St. Charles in 2004 and
2005 and East Lansing in 2004 (Table 4). Total and mainstem seed yields were similar
across row widths at each population. Branch seed yield was greater in l9-cm rows
compared with 38- and 76-cm rows at 296 400 plants/ha and 76-cm rows at 197 600
plants/ha. A trend similar to Clarksville and East Lansing was observed in regards to the
proportion of seed yield produced on the mainstem fraction; however, there was little

change in the percentage of seed yield produced at 444 600 plants/ha across row width.

80

Pod Number

Total, mainstem, and branch pod production were greater at the low population
compared with the high population in each row width at Clarksville and East Lansing in
2004 (Table 3). Total and mainstem pod number was similar across row widths at each
population. Branch pod number was similar across row widths at 308 750 plants/ha;
however, pod number was greater in 19-cm rows compared with 76-cm rows at 123 500
. and 185 250 plants/ha.

Total, mainstem, and branch pod production were greater at the low population
compared with the high population in each row width at St. Charles in 2004 and 2005 and
East Lansing in 2005 (Table 4). Total and mainstem pod number were similar across row
width at 296 400 and 444 600 plants/ha Total pod number was greater in 19-cm compared
with 76-cm rows at 197 600 plants/ha, but mainstem pod number was similar. Branch pod
number was greater in 19-cm rows compared with 76-rows at 197 600 plants/ha.
Furthermore, branch pod number in 19-cm rows was greater than 38- and 76-cm rows at
296 400 plants/ha, respectively.

Plant weight

Total plant weight was greater at the low population of 123 500 plants/ha compared
with the high population of 308 750 plants/ha across row widths at Clarksville and East
Lansing in 2004 (Figure 3). At the high and medium populations, plant weights were
similar across row widths; however, at the low population plant weight was greater in 19-
cm rows compared with 38- and 76-cm rows. Mainstem weight was greater in 19-cm rows
compared with 76-cm rows at all populations. Branch weight was greater at the low
populations compared with high population at all row widths. Branch weight was similar

81

at the high and medium populations across row width. At the low population, branch
weight was greater in 19- and 38-cm rows compared with 76-cm rows.

Total plant weight was greater at the low population of 197 600 plants/ha compared
with the high population of 444 600 plants/ha across row widths at St. Charles in 2004 and
2005 and East Lansing in 2004 (Figure 4). Total plant weight was similar between row
widths at the low and high population; however, plant weight was greater in 19-cm rows
compared with 38- and 76-cm rows at the medium population. Mainstem plant weight was
greater at the low population compared with the high population in each row width.
Weights were similar across row width at each population. Branch weight was greater at
the low population compared with the high population in each row width. At the high
population, branch weight was similar across row widths; however, branch weight was
greater in 19-cm rows compared with 38- and 76-cm rows at 197 600 and 296 400
plants/ha.

DISCUSSION

Planting soybean in narrow row widths increased soybean yield in agreement with
previous research (Wiggans 1939; Etheredge et al. 1989; Ikeda 1992; Board and Harville
1993; Egli 1994). None of these studies compared the three row widths that were used in
this study; however, Etheredge et al. (1989) used 25-, 51, and 76-cm row widths and
concluded yield was greater and more consistent in 25-cm rows. Despite having lower
~ populations at Clarksville and East Lansing in 2004, yield was greater compared with St.
Charles in 2004 and 2005 and East Lansing in 2004, probably due to greater rainfall in
2004. Soybean yield was greater in 19—and 38-cm rows compared with 76-cm rows for
each population, regardless of soybean population range. Trends were similar between

82

studies in regard to population in 19- and 38-cm rows, but differed in response to
population in 76-cm rows. Soybean yields were greater at higher populations in 76-cm
rows at Clarksville and East Lansing, possibly due to both greater rainfall and lower overall

soybean populations. The seeding recommendation for 76-cm rows is 309 000 seeds/ha
- (Bertram and Pedersen 2004) which corresponds to the high population at Clarksville and
East Lansing in 2004. The optimal plant populations ﬁom our results were 308 750 to 444
600 plants/ha for soybean planted in 19- or 38-cm rows, and 185 250 to 308 750 for
soybean planted in 76-cm rows.

Total seed yield per plant was inﬂuenced more by changes in plant population than
changes in row width. Soybean compensated for lower populations by increasing branch
seed yield. Total seed yield per plant was greater at lower populations and in narrow rows.
The branch seed number comprised a larger proportion of total seed yield in narrow rows
and at lower populations, while the mainstem seed yield comprised a higher percentage of
' total seed yield at higher populations and at wide row widths.

The number of seeds per pod did not change as row width or population changed at
any location in either year, supporting previous research (Carpenter and Board 1997;
Herbert and Litchﬁeld 1982). Furthermore, seed weight did not change as row width or
population changed at any location in either year, supporting previous research (Carpenter
and Board 1997; Herbert and Litchﬁeld 1982; Lehman and Lambert 1960; Moore 1991;
Wright et a1 1984). Seed weights were greater at Clarksville and East Lansing compared
with St. Charles and East Lansing. This was probably due to differences in rainfall during

August, the time of seed ﬁll.

83

Pod number per plant was ﬂie most responsive yield component to changes in
population and row width. Other researchers have reported pod production as the most
responsive yield component to changes in row width or population (Board 1987; Carpenter
and Board 1997; Etheredge et al. 1989; Herbert and Litchﬁeld 1982). Our data supports
results that pod production varies in response to changes in population. Previous research
reported that adjustments in yield per plant to changing plant population were accounted
for by changes in branch pod per plant (Carpenter and Board 1997; Board et al. 1990;
Herbert and Litchﬁeld 1982). While total pod production in 19-cm rows compared with
76-cm rows was not always statistically signiﬁcant, trends showed that pod production was
greater in 19-cm rows. Mainstem pod production was statistically similar across row
width; however, branch pod number differed across row widths at lower populations. This
suggests that branch pod production is more dynamic, while mainstem pod production is
more stable in response to changes in row width.

Mainstem plant weight was responsive to changes in population but was similar
across row widths at each population. Branch plant weight was also responsive to changes
in population, but also responded to changes in row width at lower populations. Previous
research reported that increased branch dry weight correlated to yield as row width and
A population changed (Board et al. 1980; Carpenter and Board 1997).

In conclusion, optimal plant populations were 308 750 to 444 600 plants/ha for
soybean planted in 19- or 38-cm rows, and 185 250 to 308 750 for soybean planted in 76-
cm rows. Pod number per plant was the most responsive yield component to changes in
population and row width. The number of seeds per pod and seed weight was not
inﬂuenced by changes in row width and population. A greater proportion of yield was

84

composed from branch yield components in narrow rows and at lower populations.
Mainstem plant weight was responsive to changes in population but was similar across row
widths at each population. Branch plant weight was also responsive to changes in

populations, but also responded to changes in row width at lower populations.

85

LITERATURE CITED

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

Bertram, M.G., and P. Pedersen. 2004. Adjusting management practices using glyphosate-
resistant soybean cultivars. Agron. J. 96:462-468.

Board, J .E. 1987. Yield components related to seed yield in determinate soybean. Crop
Sci. 40:757-764.

Board, J .E. 2000. Light interception efﬁciency and light quality affect yield compensation
of soybean at low plant populations. Crop Sci. 40: 1285-1294.

Board, J.E., and B.G. Harville. 1993. Soybean yield component responses to a light
interception gradient during the reproductive period. Agron. J. 88:567-572.

Board, J .E., B.G. Harville, and A.M. Saxton. 1990. Branch dry weight in relation to seed
yield increases in narrow-row soybean. Agron. J. 82:540-544.

Burnside, CC. and W.L. Colville. 1964. Soybean and weed yields as affected by irrigation,
row spacing, tillage, and arniben. Weeds. 12:109-112.

Canner, S.G., W.B. Nygquist, and W.N. Walker. 1989. Least signiﬁcant differences for
‘ combined analysis of experiments with two or three-factor treatment designs. Agron. J.
81:665-672.

Carpenter, AC. and J .E. Board. 1997. Branch yield components controlling soybean yield
stability across plant populations. Crop Sci. 37:885-991.

Costa, J.A., E.S. Oplinger, and J.W. Pendleton. 1980. Response of soybean cultivars to
planting pattems. Agron. J. 72:153-156.

Devlin, D.L., D.L. Fjell, J.P. Shroyer, W.B. Gordon, B.H. Marsh, L.D. Maddux, V.L.
Martin, and SR. Duncan. 1995. Row spacing and seeding rates for soybean in low and
high yielding environments. J. Prod. Agric. 8:215-222.

Egli, DB. 1994. Mechanisms responsible for soybean yield response to equidistant
patterns. Agron J. 86: 1046-1049.

Ethredge, W.J., D.A. Asheley, and J.M. Woodruff. 1989. Row spacing and plant
population effects on yield components of soybean. Agron. J. 81:947-951.

. Frederick, J.R., C.R. Camp, and P.J. Bauer. 2001. Drought-stress effect on branch and
mainstem seed yield and yield components of determinate soybean. Crop Sci. 41 :7 59-763.

86

Herbert, S.J., and G.V. Litchﬁeld. 1982. Partitioning soybean seed yield components. Crop
Sci. 22:1074—1079.

Hicks, D.R., J.W. Pendleton, R.L. Bernard, and T.J. Jonston. 1969. Response of soybean
plant type to planting patterns. Agron. J. 86259-62.

Ikeda, T. 1992. Soybean planting patterns in relation to yield and yield components.
Agron. J. 84:923-926.

Lehman, W.F. and J .W. Lambert. 1960. Effects of row spacing of soybean plants within
4 rows on yield and its components. Agron. J. 52:84-86.

McIntosh, MS. 1983. Analysis of combined experiments. Agron. J. 75:153-155.

Moore, SH. 1991. Uniformity of plant spacing effect of soybean population parameters.
Crop Sci. 31:1049-1051.

Norris, J.L., D.R. Shaw, and CE. Snipes. 2002. Inﬂuence of row spacing and residual
herbicides on weed control in glufosinate-resistant soybean (Glycine max). Weed Technol.
16:319-325.

Norsworthy, J .K. and J .R. Frederick. 2002. Reduced seeding rate for glyphosate-resistant,
drilled soybean on the southeastern coastal plan. Agron. J. 94:1282-1288.

Norsworthy, J .K. and LR. Oliver. 2001. Effect of seeding rate of drilled glyphosate-
resistant soybean (Glycine max) on seed yield and gross proﬁt margin. Weed Technol.
152284-292.

Norsworthy, J.K. and ER. Shipe. 2005. Effect of row spacing and soybean genotype on
mainstem and branch yield. Agron. J. 97:919-923.

Pedersen, P. and J .G. Lauer. 2004. Response of soybean yield components to management
systems and planting date. Agron. J. 96:1372-1381.

Rigsby, B., and J .E. Board. 2003. Identiﬁcation of soybean cultivars that yield well at low
plant populations. Crop Sci. 43:234-239.

Taylor, HM. 1980. Soybean growth as affected by row spacing and by seasonal water
supply. Agron. J. 72:543-546.

Shibles, R.M., and CR. Weber. 1965. Leaf area, solar radiation interception and dry
matter production by soybeans. Crop Sci. 5:575-578.

87

Weber, C.R., R.M. Shibles, and DE. Byth. 1966. Effect of plant population and row
spacing on soybean development and production. Agron. J. 58:99—102.

Wells, R. 1991. Soybean growth response to plant density: relationships among canopy
photosynthesis, leaf area, and light interception. Crop Sci. 31:755-761.

Wiggans, J .R. 1939. Inﬂuence of space and arrangement on the production of soybean
plants. Agron. J. 31:314-321.

Wright, C.L., F.M. Shokes, and R.K. Sprenkel. 1984. Planting method and plant
population inﬂuence on soybean. Agron. J. 76:921-924.

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

88

 

 

 

 

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89

Table 2. Monthly precipitation recorded at the Clarksville Horticulture Experiment Station,
Clarksville, M1, at the Michigan State University Department of Horticulture and Research
Center, East Lansing, MI, and at the Saginaw Valley Bean and Beet Farm, St. Charles, MI.

 

 

 

 

 

Precipitation (cm)
Clarksville East Lansing St. Charles

2004 30 yr. 2004 2005 30 yr. 2004 2005 30 yr.
May 21.8 7.4 3.3 6.9 16.5 4.4 6.3
June 7.6 9.7 10.9 9.0 6.9 12.6 7.8
July 12.2 6.0 11.6 7.7 5.1 8.1 7.2
Aug. 6.6 9.2 1.6 7.9 5.9 2.1 8.4
Total 48.2 32.3 27.4 31.5 34.4 27.2 29.7

 

90

Table 3. Effect of soybean row width and population on total, mainstem, and branch plant
yield and hundred seed weight at Clarksville and East Lansing in 2004. Numbers in
parentheses indicates percentage of yield contributed by the mainstem fraction. Values at
the bottom of each yield component section indicate LSDoos.

 

 

 

 

 

 

 

Row width
Population 1 9-cm 3 8-cm 76-cm
Total seed yield per plant
123 500 163.2 143.4 131.0
185250 111.4 117.9 103.8
308 750 81.1 74.1 76.0
LSD0_05 18.5
Mainstem seed yield per plant ----------
123 500 71.1 (43) 68.4 (48) 69.5 (53)
185 250 60.0 (52) 59.2 (50) 67.1 (65)
308 750 52.6 (64) 50.9 (67) 54.1 (72)
LSDogs 9.2
Branch seed yield per plant --------------
123 500 94.4 75.0 61.5
185 250 51.4 58.7 36.7
308 750 28.5 23.6 21.9
LSDogs 15.6
Seed weight g per 100 seed -------------
123 500 17.1 16.9 17.5
185 250 16.8 16.8 17.6
308 750 17.2 17.4 17.4
LSD0_05 NS

 

91

Table 4. Effect of soybean row width and population on total, mainstem, and branch plant
yield and hundred swd weight at East Lansing in 2005 and St. Charles in 2004 and 2005.
Numbers in parentheses indicates percentage of yield contributed by the mainstem fraction.
Values at the bottom of each yield component section indicate LSD0,05.

 

 

 

 

 

 

 

Row width
Population l9-cm 38-cm 76-cm
Total seed yield per plant
197600 118.8 117.9 111.5
296 400 90.8 85.2 90.2
444 600 68.9 66.4 68.5
LSDQ05 13.9
Mainstem seed yield per plant----------
197 600 60.6 (51) 62.5 (53) 63.4 (57)
296 400 54.3 (60) 56.5 (66) 60.7 (67)
444 600 51.7 (75) 52.2 (79) 49.3 (72)
LSD0_05 5.9
Branch seed yield per plant --------------
197 600 58.5 55.5 47.7
296 400 43.4 28.8 29.7
444 600 19.4 14.5 19.3
LSDogs 9.1
Seed weight g per 100 seed -------------
197 600 14.8 14.8 15.0
296 400 14.2 14.6 15.2
444 600 14.2 15.2 15.0
LSDoos NS

 

92

Table 5. Effect of soybean row width and population on total, mainstem, and branch pod
production and number of seed per pod at Clarksville and East Lansing in 2004. Values at
the bottom of each yield component section indicate LSDaos.

 

 

 

 

 

 

 

 

 

 

Row width
Population 19-cm 38-cm 76-cm
Total pods per plant
123 500 82.8 73.3 67.4
185 250 56.6 62.7 50.6
308 750 43.0 38.1 38.0
LSDODS 10.7
Mainstem pods per plant
123 500 35.8 34.6 35.5
185 250 30.0 31.0 32.3
308 750 27.9 25.8 26.9
LSDogs 3.9
Branch pods per plant
123 500 47.0 38.7 31.9
185 250 26.6 31.8 18.3
308 750 15.2 12.5 11.1
LSD0_05 8.1
Seed number per pod
123 500 2.0 2.0 2.0
185 250 2.0 1.9 2.1
308 750 1.9 2.0 2.0
LSDODS NS

 

93

Table 6. Effect of soybean row width and population on total, mainstem, and branch pod
production and number of seed per pod at East Lansing in 2005 and St. Charles in 2004 and
2005. Values at the bottom of each yield component section indicate LSDQOS.

 

 

 

 

 

 

 

 

 

 

Row width
Population 1 9-cm 3 8-cm 76-cm
Total pods per plant
197 600 62.3 59.8 55.3
296 400 50.5 44.0 45.0
444 600 34.8 32.8 34.6
LSDaos 5.9
Mainstem pods per plant
197600 31.7 31.6 31.5
296 400 31.0 29.3 30.2
444 600 26.8 25.4 24.9
LSD0_05 2.4
Branch pods per plant
197 600 30.8 28.5 23.8
296 400 23.0 15.0 15.0
444 600 10.0 7.6 9.8
LSD0,05 4.3
Seed number per pod
197 600 1.9 2.0 2.0
296 400 1.9 1.9 2.0
444 600 2.0 2.0 2.0
LSD0_05 NS

 

94

oybean yield at Clarksville and East

Lansing in 2004. Different letters above each column represent signiﬁcant differences at

Figure 1. Effect of row width and population on s

 

 

 

 

  

     

 

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oybean yield at East Lansing in 2005

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96

Figure 3. Effect of soybean row width and population on total, mainstem, and branch
weights at Clarksville and East Lansing in 2004. Different letters above, between, and at
the base of each column represent signiﬁcant differences in total, mainstem, and branch
weights, respectively, at LSDogs.

 

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97

Figure 4. Effect of soybean row width and population on total, mainstem, and branch
weights at East Lansing in 2005 and St. Charles in 2004 and 2005. Different letters above,
between, and at the base of each column represent signiﬁcant differences in total,
mainstem, and branch weights, respectively, LSDogs.

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98

CHAPTER 4

INFLUENCE OF STEM-BORING INSECTS ON COMMON
LAMBSQUARTERS CONTROL WITH GLYPHOSATE

ABSTRACT
Common lambsquarters is the most problematic weed for soybean producers in Michigan.
Recently, insect tunneling was found inside the stems of many plants that were not
controlled with glyphosate. Field and greenhouse studies were conducted to identify insect
larvae found tunneling in common lambsquarters; to determine if tunneling occurred prior
to or following postemergence glyphosate applications, and to evaluate the effect of
- glyphosate rate, application timing, and insect larval tunneling on the control of common
lambsquarters populations with glyphosate. Two insect species, the beet petiole borer
(Cosmobaris americana Casey) and a leaﬁniner ﬂy larvae (Diptera:Agromyzidae) were
found inside common lambsquarters stems. The leafminer ﬂy larvae were present in late-
June when most postemergence glyphosate applications are made in Michigan; however,
the beet petiole borer was not found in common lambsquarters stems until mid-July and
would only be present in common lambsquarters plants if glyphosate applications were
delayed. Common lambsquarters control with glyphosate was not affected by leaﬁniner ﬂy
larvae tunneling. Applying glyphosate to smaller plants or at rates greater than 0.84 kg
ae/ha improved common lambsquarters control. Control of common lambsquarters with
' glyphosate varied between common lambsquarters populations, suggesting there may be a

genetic basis for reduced control of some common lambsquarters populations.

99

Nomenclature: Soybean, ‘AG 2701’, Glycine max (L.) Merr.; common lambsquarters,
Chenopodium album( L.); Glyphosate, N-(phosphonomethyl)glycine; beet petiole borer,
Cosmobaris americana; ﬂy maggot, Diptera:Agromyzidae
Additional index words: Insect-weed interactions, common lambsquarters, glyphosate,
dose-response.
Abbreviations: AMS, ammonium sulfate; DAT, days after treatment; Gst, rate causing
25% growth reduction; GRso, rate causing 50% growth reduction; GR75, rate causing 75%
growth reduction
INTRODUCTION

Common lambsquarters is a successful colonizing species, and one of the most
widely distributed weeds in the world (Holm et al. 1977). It is found in 47 different
countries in 40 different crops, and considered the principal weed pest in corn (Zea mays
L.), potato (Solanum tuberosum L.), soybean (Glycine max (L.) Merr.), and sugarbeet (Beta
vulgaris L.) (Holm et al. 1977; Mitich 1988). Common lambsquarters is ranked as the
most problematic weed by soybean producers in Michigan (Sprague 2004). Soybean yield
was reduced 15 (Shurtleff and Coble 1985) to 28% (Harrison 1990) from season-long
competition at common lambsquarters densities of 16 and 10 plants/m row, respectively.
The success of common lambsquarters as a competitive, wide-spread weed is attributable to
many factors including seed germination in a wide range of environmental conditions
(Henson 1970), early emergence during the crop growing season (0g and Dawson 1984),
plasticity of growth (Ervio 1971), proliﬁc seed production (Harrison 1990), and seed

longevity (Lewis 1973).

100

Glyphosate-resistant soybean varieties are planted in 87% of the soybean ﬁelds in
the United States (NASS 2005). Growers have adopted this technology because glyphosate
offers greater ﬂexibility in application timing and weed control than conventional
herbicides and tillage have provided in the past (Culpepper and York 1998; McKinley et al.
1999; VanGessel et a1. 2000). Glyphosate has traditionally controlled common
lambsquarters. Ateh and Harvey (1999) reported that glyphosate at 0.31 kg ae/ha
controlled plants less than 15-cm in height, and the standard rate of 0.84 kg ae/ha
controlled plants greater than 15-cm in height. Krausz et al. (1996) observed that common
lambsquarters control was 100% when glyphosate was applied at 0.56 kg ae/ha to 10-cm
plants. Recently, there have been reports of poor common lambsquarters control with
glyphosate (Kniss et al. 2004; Schuster et a1. 2004). Common lambsquarters has been
difﬁcult to control with other postemergence herbicides due to reduced herbicide
absorption through epicuticular waxes on the leafs surface (Taylor et al. 1981). The waxes
form a homogeneous covering over the entire leaf surface and are a barrier to penetration of
polar molecules through the cuticle. Furthermore, environmental factors inﬂuence the
thickness of the epicuticular waxes leading to reduced herbicide efﬁcacy.

In some cases of poor weed control with glyphosate, insect larvae were found
tunneling or feeding in the vascular tissue (Maertens 2003, Ott et al. 2003; Westra et al.
1981). Since glyphosate is a systemic herbicide, it was hypothesized that weed control
with glyphosate may be reduced if insect larval tunneling or feeding is present in the plant
at the time of the herbicide application. There are many reports of the use of insects as

biological weed control agents (Bacher and Schwab 2000; Julien 1998; Sheldon and Creed

101

1995). However, there is limited research on the effect of insect feeding on weeds and the
subsequent control from herbicides. Westra et al. (1981) observed that the weevil (Notaris
bimaculatus) reduced the effectiveness of glyphosate on quackgrass (Agropyron repens).
In contrast, Ott et al. (2003) reported that giant ragweed (Ambrosia triﬁda) control was
similar in plants infested with European corn borer (Ostrinia nubilalis) and non-infested
plants. In contrast, Williams et a1. (2004) reported that Colorado potato beetle
(Leptinotarsa decemlineata) feeding in combination with reduced ﬂuroxypyr rates
enhanced volunteer potato (Solanum tuberosum L.) control compared with either strategy
alone.

In 2003, tunneling was found throughout the vascular system of common
lambsquarters that survived applications of glyphosate in Michigan. The larvae were later
identiﬁed as the beet petiole borer (Cosmobaris americana Casey). Landis et al. (1970)
published an extensive study on the lifecycle of the beet petiole borer after discovering it
on sugar beet in the western United States. Larvae of the beet petiole borer overwintered in
feeding galleries of dead host plants. Larvae pupated in May and adult weevils emerged
within 1-2 weeks. Soon after emergence, the weevils fed primarily at nodes or stems of
host plants. Female weevils mated after emergence and deposited a single egg in feeding
pits in the host plant. Larvae were often found near the oviposition site, and stems of host
plants were usually swollen. Weed hosts did not appear stressed despite having as many as
30 larvae tunneling per plant. Mature larvae entered diapause in the stems of saltbrush

(Atriplex polycarpa) as early as August in Washington. The beet petiole borer was more

102

commonly found in weedy hosts than sugarbeet. In California, Gilbert (1964) reported that
the most common host for beet petiole borer was common lambsquarters.

Many producers have readily adopted glyphosate-resistant crops, and with over
80% of soybean acres planted with glyphosate-resistant soybean incidents of reduced
common lambsquarters control are a major concern. Therefore, the objectives of this study
were to: 1) identify the insect larvae found tunneling common lambsquarters 2) determine
if the tunneling of these insects occurred prior to of following postemergence glyphosate
application timings in Michigan, 3) evaluate the effect of glyphosate rate, application
timing, and insect larval tunneling on common lambsquarters control, and 4) determine if

different Michigan common lambsquarters populations vary in control to glyphosate.

103

MATERIALS AND METHODS

Presence of Insect Larval Tunneling in Common Lambsquarters

A natural population of common lambsquarters was grown in monoculture in the
ﬁeld. Every two weeks, forty common lambsquarters plants were longitudinally dissected
beginning May 15 and ending July 29 and August 5 in 2004 and 2005, respectively, to
assess larval tunneling in common lambsquarters over the growing season. Weather data
from the Michigan Automated Weather Network1 was used to calculate growing degree
days (GDD) for each sampling date. Corresponding growing degree days (GDD) were
calculated using common lambsquarters base temperature of 4 C at each sampling date
(Harvey and Forcella 1993). GDD were calculated by averaging the maximum and
minimum daily temperatures and subtracting the base temperature of 4 C.

Factors Influencing Common Lambsquarters Control

Field Studies. Field studies were established at East Lansing on May 6 and June 4, 2004
and May 4, 2005 to evaluate the effect of glyphosate rate, application timing, and insect
larval tunneling on common lambsquarters control. Soybean ‘AG 21072’was planted in
76-cm rows at 395,000 seeds/ha. The experimental design was a randomized complete
block in a factorial arrangement with four replications. Plot size was 3.1 m by 9.1 m. In
2004, the experiment was a 3x4 factorial. The ﬁrst factor was glyphosate application
timing based on common lambsquarters heights of 10-, 25-, and 46-cm; the second factor

was glyphosate rates of 0, 0.63, 0.84, and 1.7 kg ae/ha. In 2005 the experiment was a 2 X 3

 

‘ Michigan Automated Weather Network, Michigan Climatological Resources Program 417 Natural Sciences
Building, East Lansing, MI 48824.

2 Asgrow Seed Co., Monsanto Co., 800 North Lindbergh Boulevard, St. Louis, MO 63167.

104

X 4 factorial. The additional factor of bi-weekly application of the insecticide lambda-
cyhalothrin3 at 21 g ai/ha were added to keep half of the study area insect-free.

Prior to each glyphosate application, 10 common lambsquarters plants per
treatment (2004) or per plot (2005) were dissected and examined for insect larval tunneling.
Glyphosate4 plus ammonium sulfate (AMS) at 2% w/w was applied using a tractor-
mounted compressed-air sprayer calibrated to deliver 17 8 L/ha at 207 kPa using Airmix
110035 nozzles at the appropriate common lambsquarters heights, with environmental
conditions documented (Table 1). Common lambsquarters control was visually evaluated
28 DAT on 0 to 100% scale with 0 indicating no control and 100% indicating complete
plant death.

In 2005, an additional ﬁeld study was established on May 15 to examine the effect
of insect larval tunneling on common lambsquarters control with glyphosate. Cages l-m3
in size were constructed of PVC pipe and no-see-um mesh6. Nine cages were randomly
placed in a conventionally-tilled ﬁeld with a known natural population of common
lambsquarters. Cages were used to keep common lambsquarters plants insect-free, while
nine areas were left cage-free to allow for insect-infestation. Glyphosate at 0.84 kg ae/ha
plus AMS at 2% w/w was applied to 25-cm plants with a C02 backpack sprayer calibrated
to deliver 187 L/ha at 207 kPa using 80037 ﬂat fan nozzles. Prior to glyphosate application,
three common lambsquarters plants in each caged and cage-free areas were dissected to

determine the presence and extent of insect larval tunneling. Common lambsquarters

 

3 Warrior, Syngenta Crop Protection, Inc. PO. Box 18300, Greensboro, North Carolina 27409
‘ Roundup WeatherMAX, Monsanto., 800 North Lindbergh Boulevard St. Louis, MO 63167.
5 Teejet Airmix 11003, Spraying Systems Co., North Avenue, Wheaten, IL 60188.

6 No-see-um mesh, Venture textiles, 115 Messina Dr. PO. Box 850289, Braintree, MA 02185.
7 Teejet ﬂat fan 8003, Spraying Systems Co., North Avenue, Wheaton, IL 60189

105

control was visually assessed 28 DAT. The experiment was a completely randomized
design with nine replications.

Greenhouse Studies. A greenhouse experiment was designed to evaluate the effect of beet
petiole borer feeding on common lambsquarters control with glyphosate. Common
lambsquarters stems collected from the ﬁeld in mid-October were sealed in nylon bags and
placed in the greenhouse. Based on preliminary growth chamber research, beet petiole
borer adults emerged around 470 growing degree days at a base temperature of 4 C.
Greenhouse temperature was maintained at 25 i 2 C. Once pupae of the beet petiole borer
developed into adult weevils, common lambsquarters stems were Split, and the adult
weevils were removed. Concurrently, common lambsquarters seeds were planted at a
depth of 1.5-cm into 1000 cm3 pots ﬁlled with BACCTO8 potting mix. Seedlings were
grown in the greenhouse and natural sunlight was supplemented with sodium vapor
lighting to provide a total midday intensity of 1000 u/m/s photosynthetic photon ﬂux at
plant height in a 16 h day. Plants were watered daily and fertilized weekly with a complete
fertilizer. Plants were thinned to one plant per pot 1 week after emergence. Plants were
then placed in 0.9 m x 0.9 m x 1.2 m wood-framed cages covered with no-see-um netting.
Half of the cages were infested when plants were lO-cm in height, with four beet petiole
borer adults per pot were allowed to feed and mate on common lambsquarters plants for 30
(1. Based on previous growth chamber research a minimum of 15 d provided enough GDD
to ensure adult weevils; however, it was unknown how long it would take weevils to mate

and lay eggs. New weevils were reared for each experimental run. When plants were 46-

 

" BACCTO, Michigan Peat Co., PO. Box 980129, Houston, TX 77098.

106

and 60-cm in height, herbicide treatments were applied with a single tip track-sprayer with
a Teejet9 8003B ﬂat-fan nozzle calibrated to deliver 187 L ha"l at 207 kPa. Glyphosate
rates of 0, 0.84, 1.7, and 3.4 kg ae/ha and AMS at 2% w/w was applied. At 28 DAT, all
aboveground plant tissue was then harvested, oven-dried at 60 C for two days, and weighed
to determine reduction of plant biomass. Data were then converted to percent of control for
data presentation. The experimental design was a split-plot with sub-factors arranged in a
completely randomized design with six replications and the experiment was repeated. The
whole-plot was insect presence; sub-factors were common lambsquarters heights of 46-

and 60-cm, and glyphosate rates of 0, 0.84, 1.7, and 3.4 kg ae/ha.

Response of Seven Common Lambsquarters Populations to Glyphosate

An experiment was designed to evaluate the response of six Michigan common
lambsquarters populations from Eaton, Gratiot, Ingham, Montcalm, Saginaw, and
Shiawassee Counties to glyphosate. These populations were compared with a control
population from F&J seeds"). In mid-October of 2004, seed was collected from soybean
ﬁelds in Eaton, Gratiot, Ingham, Montcalm, Saginaw, and Shiawassee Counties where
common lambsquarters was not controlled with glyphosate. Following the same general
experimental procedures as stated above, common lambsquarters plants were treated with
glyphosate at rates of 0, 0.21, 0.42, 0.84, 1.68, 3.4, and 6.7 kg ae/ha + AMS at 2% w/w
when plants were 8- to 10-cm tall. At 28 DAT, common lambsquarters were visually

evaluated for control, dry plant biomass was determined, and then converted to percent of

 

9 Teejet ﬂat fan 8003B, Spraying Systems Co., North Avenue, Wheaton, IL 60189
'0 F&J Seeds, P.O. Box 82, Woodstock, IL 60098.

107

control. The experiment was a two factor factorial in a completely randomized design with
four replications and was repeated.

Statistical Analysis. All data were subjected to ANOVA using the PROC MIXED
procedure in SAS 8.02ll software. Field experiments are presented separately due to
treatment by environment interactions. Greenhouse experiments were combined over runs
since no interaction between repeated experiments was observed. Means were separated
using Fisher’s Protected LSD at (1:005. In the common lambsquarters populations
response to glyphosate experiment, growth reduction (GR) values were calculated for plant
dry weights using the dose-response curve equation Y=A+B/[1+(X/C)D], where Y is the
herbicide activity as a percent control, X is the rate of application, A is the upper limit, B is
the lower limit, C is the dose that causes the desired growth reduction, and D is the slope of
the curve around the GRso. TableCurve 2D12 software was used to calculate regression
curves and equations for each replication. Corresponding GR values were calculated using

regression curves for each replication and subjected to ANOVA.

 

” SAS Institute Inc., 100 SAS Campus Drive, Cary, NC 27513
”TableCurve 21) v. 5.01. Jandel Stientiﬁc, 2591 Kemer Blvd, San Rafael, CA 94901.

108

RESULTS AND DISCUSSION
Presence of Insect Larval Tunneling in Common Lambsquarters

Beet petiole adults were found inside common lambsquarters stems from the
previous year on May 15 in 2004 and May 24 in 2005. Based on preliminary growth
chamber research, beet petiole borers emerge around 470 growing degree days at a base
temperature of 4 C (data not shown). The beet petiole borer and leafrniner ﬂy larvae
(Diptera:Agromyzidae) were the only insects found tunneling in common lambsquarters
both years. The leafrniner ﬂy larvae were found on June 13 in 2004 and 2005 at 790 and
616 GDD, respectively. Tunneling by the leafrniner ﬂy larvae was narrow and contained to
the center of stem, causing little damage to vascular tissue. Furthermore, plants with
leafrniner ﬂy larvae were not visually stressed.

The beet petiole borer (BPB) larvae were found in plants on July 13 and July 8 in
2004 and 2005, respectively, corresponding to 1245 and 1036 GDD. Tunneling by the
BPB was much greater than that of the leafminer ﬂy larvae and the pith tissue of plants was
destroyed. Plants that contained many beet petiole borer larvae had swollen stems and
were slightly stunted in height.

In 2004, the proportion of common lambsquarters plants infested with insect larvae
increased steadily from July 1 to August 5 where 90% of plants were infested (Figure 1).
In 2005, insect tunneling increased steadily until July 29 when 88% of plants were infested.
These observations on the life cycle of the beet petiole borer in Michigan agree with those

of Landis (1970) who reported BPB adult emergence in mid-May in Washington and

109

Oregon, and larvae were full grown by August, and overwintering of larvae in the stems of
weed hosts.

Based on Michigan State University research from the last 10 years, glyphosate
applications in Michigan are typically made from June 20 to July 3. The leafrniner ﬂy
larvae is present when glyphosate is applied for common lambsquarters control. However,
the BPB larvae are only present in common lambsquarters plants if glyphosate applications
are delayed past July 8 or 1053 GDD.

Factors inﬂuencing common lambsquarters control

Common lambsquarters control was similar across glyphosate rates at the lO-cm
application timing (Table 2). However, control of 25-cm common lambsquarters decreased
I when glyphosate was applied at 0.63 kg ae/ha compared to 1.7 kg ae/ha. Leafminer larval
tunneling was only present in the 46-cm application timing for the May planting, when
40% of plants were infested. Glyphosate applications were made on May 26, June 16, and
July 13 when 552, 841, and 1245 GDD had accumulated, respectively. Tunneling found in
plants prior to application corresponded to tunneling found in sampled plants grown in an
adjacent area Common lambsquarters control was lower at the 46-cm application timing
compared with earlier glyphosate applications. The higher glyphosate rate of 1.7 kg ae/ha
improved control of 46-cm tall common lambsquarters; however control was still less than
64%. Reduced control may have been due to poor coverage since common lambsquarters
density was high at 43 plants/m2.

There was insect larval tunneling the by the leafminer in common lambsquarters

prior to all glyphosate applications for the June planting (Table 3). Both the BPB and

110

leaﬁniner larvae were found in sampled plants. In the June 2004 planting, glyphosate
applications were made on July 13, July 23, and July 29 when 1245, 1411, and 1492 GDD
were accumulated, respectively. Unlike the May planting, common lambsquarters control
. was similar (>85%) when glyphosate was applied at 0.84 kg ae/ha and 1.7 kg ae/ha to 25-
and 46-crn lambsquarters. Common lambsquarters density was 5 plants/m2 and was 9.5
times greater in the May planting in comparison to the June planting (data not Shown).
Higher densities in the 2004 May planting may have reduced common lambsquarters
control. Furthermore, cooler conditions present during the 2004 May planting could
possibly explain lower common lambsquarters control compared with the 2004 June
planting and 2005 May planting (Table 1).

In 2005, insect larval tunneling was evident at the 25- and 46-cm application
timings (Table 4). The only insect present was the leaﬁniner. In 2005, glyphosate
applications were made on June 8, June 17, and June 21 when 516, 670, and 728 GDD
were accumulated. Bi-weekly applications of lambda-cyhalothrin Signiﬁcantly reduced the
number of plants infested prior to glyphosate application at the 25- and 46-cm applications.
Of the plants sampled, 65 and 66% of common lambsquarters contained tunneling at these
applications; however, insecticide treatment did not inﬂuence common lambsquarters
control with glyphosate. Common lambsquarters control was similar when glyphosate was
applied at 1.7 kg ae/ha, regardless of application timing; however, control was lower at the
46-cm timing at the low rate of 0.63 kg ae/ha. Common lambsquarters density was 9
plants/m2 and control with glyphosate was greater than 92% indicating coverage was not an

issue.

111

In the cage study, plants inside cages were completely insect-free and plants
outside cages were completely infested with leafrniner larvae at the time of glyphosate
applications. Common lambsquarters control with glyphosate was 96 and 97% for caged
and non-caged treatments indicating that insect tunneling did not inﬂuence control with

glyphosate (Table 5).

Greenhouse studies. Plants infested with the BPB were stunted by adult feeding, and
tended to produce branches after feeding. Due to differences in heights between infested
and non-infested plants, glyphosate applications were made when non-infested plants were
46- and 60 cm in height. Furthermore, applications were made at these heights to allow
time for larval development and tunneling inside of plants. Common lambsquarters control
was greater when glyphosate was applied at 0.84 and 1.68 kg ae/ha to 46-cm plants
compared to 0.63 kg ae/ha (Table 6). Control by 0.63 kg ae/ha glyphosate was less than
68%. Insect infestation did not affect control with glyphosate, regardless of application
timing. In infested plants, there were no differences in larvae number between treatments
indicating larval pressure was uniform, and plants averaged about 3 larvae per plant. There
was no difference in control between glyphosate rates when applied to 60-cm plants;

however, control was unusually low and ranged from 3 to 17%.

112

Response of 7 Common Lambsquarters Populations to Glyphosate

Common lambsquarters populations from Gratiot, Saginaw, and Shiawassee
Counties required lower glyphosate rates in comparison the F&J biotype to reduce growth
25% (Table 7). Eaton, Montcalm, and Ingham County populations required 0.36 kg ae/ha
to reduce growth by 25%, a rate comparable to that needed for the F&J biotype. Common
lambsquarters collected from Shiawassee County was the only population that required a
lower use rate than the F &J biotype to reduce growth 50%. The Eaton, Ingham, and
Montcalm County populations required 1.4,1.5, and 1.8 times the F&J biotype use rate of
0.49 kg ae/ha, respectively, to reduce common lambsquarters growth by 50%.

Other researchers have also noted variability in control with glyphosate to certain
weed biotypes. For example, Patzoldt et al. (2002) reported variability in the response of
common waterhemp (Amaranthus rudis) to glyphosate rate of 0.21 and 0.84 kg ae/ha.
Schuster et al. (2004) also found that common lambsquarters populations from different
states vary in their tolerance to glyphosate. Our results show that there is signiﬁcant
variation in common lambsquarters populations collected between adjacent counties in
Michigan.

The level of tolerance by common lambsquarters biotypes in our study was less
than that of identiﬁed biotypes in common waterhemp (Zelaya and Owen 2005),
horseweed (Conyza canadensis) (V anGessel 2001), goosegrass (Eleusine indica) (Lee and
Ngim 2000), and rigid ryegrass (Lolium rigidum) (Powles et al. 1998). However, the

continued use of glyphosate in glyphosate resistant crops increases the potential risk for the

113

development of common lambsquarters that will not be controlled with normal ﬁeld use
rates.

In conclusion, common lambsquarters control with glyphosate does not appear to
be inﬂuenced by leafminer tunneling. The leafminer was present when most glyphosate
applications are made in Michigan; however, if glyphosate applications are made later in
the season the BPB can be present in common lambsquarters plants at application. These
two insects were the only species found inside plants in 2004 and 2005. Leafminer
tunneling coincides with typical glyphosate applications made in late June or early July
making it possible to assume escapes are due to tunneling. In general, applying glyphosate
to smaller plants or at increased rates improved control. Tolerance to glyphosate appears to
vary somewhat between common lambsquarters populations suggesting there maybe a

genetic basis for plants escaping control with glyphosate.

114

LITERATURE CITED

Anonymous. 2005. Crop Production August 2005. USDA National Agricultural Statistics
Service Website. http://www.nass.suda.gov/QuickStats/.

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

Bacher, S. and Schwab. 2000. Effect of herbivore density, timing of attack, and plant

community on performance of creeping thistle (Cirsium arvense (L.) Scop.). Biocontrol
Sci. and Technol. 10:343-352.

Culpepper, A. S. and A. C. York. 1998. Weed management in glyphosate-tolerant cotton.
J. Cotton Sci. 4:174-185.

Ervio, L. R. 1971. The effect of intra-speciﬁc competition on the development of
Chenopodium album L. Weed Res. 11:124-134.

Gilbert, EB. 1964. The genus Barr's Germar in California. Univ. California Publ. In
Entomol. 34:70-74.

Harrison, S. K. 1990. Interference and seed production by common lambsquarters
(Chenopodium album) in soybeans (Glycine max). Weed Sci. 38:113-118.

Harvey, SJ. and F. Forcella. 1993. Vernal seedling emergence model for common
lambsquarters (Chenopodium album). Weed Sci. 41:309-316.

Henson, LE. 1970. The effects of light, potassium nitrate and temperature on the
germination of Chenopodium album L. Weed Res. 10:27-39

Holm, L.G., D.L. Plucknett, J .V. Pancho, and J .P. Herberger. 1977. Chenopodium album L.

Chenopodiaceae, goosefoot family. Pages 84-91 in The World’s Worst Weeds:
Distribution and Ecology. Honolulu, HI: University Press of Hawaii.

Julien, M.H. 1998. Biological Control of Weeds: A World Catalogue of Agents and Their
Target Weeds. Wallingford, Oxfor: CAB Int. 4th ed.

Kniss, A.D., SD. Miller, and R.G. Wilson. 2004. Factors inﬂuencing common
lambsquarters control with glyphosate. Proc. N. Cent. Weed Sci. 59:85.

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

115

Landis, B.J., W.B. Peay, and L. Fox. 1970. Biology of Cosmobaris americana Casey, a
weevil attacking sugarbeets. J. Econ. Entomol. 63:38-41.

Lee, LG, and J. Ngim. 2000 A ﬁrst report of glyphosate-resistant goosegrass (Eleusine
indica) in Malaysia. Pest Manag Sci. 56:336-339.

Lewis, J. 1973. Longevity of crop and weed seeds. Weed Res. 13:179-191.

Maertens, K.D. 2003. Giant ragweed emergence, growth, and interference in soybeans.
MS. Thesis. University of Illinois. Champaign, IL 65 p.

McKinley, T.L., R.K. Roberts, R.M. Hayes, and BC. English. 1999. Economic comparison
of herbicides for johsongrass (Sorghum helpense) control in glyposate-tolerant soybean
(Glycine max). Weed Technol. 13:30-36.

Mitich, L.W. 1988. Intriguing world of weeds-common lambsquarters. Weed Technol.
2:550-552.

Ogg, A.G., Jr., and J .A. Dawson. 1984. Time of emergence of eight weed species. Weed
Sci. 32:327-335.

Ott, E.J., W.G. Johnson, J .L. Obermeyer, and DJ. Childs. 2003. Glyphosate efﬁcacy on
giant ragweed infested with European corn borer. Proc. N. Cent. Weed Sci. 58:137.

Patzoldt, W.L., P.J. Tranel, and AG. Hager. 2002. Variable herbicide responses among
Illinois waterhemp (Amaranthus rudis and A. tuberculatus) populations. Crop Protect.
21:707-712.

Powles, S.B., D.F. Lorraine-Colwill, J.J. Dellow, and C. Preston. 1998. Evolved
resistance to glyphosate in rigid ryegrass (Lolium rigidum) in Australia. Weed Sci. 46:604-
607.

Schuster, C.L., D.E. Shoup, and K. Al-Khatib. 2004. Common lambsquarters response to
glyphosate applied at three different growth stages. Proc. N. Cent. Weed Sci. 59:80.

. Sheldon, SP. and RP. Creed. 1995. Use of native insects as biological control for an
introduced weed. Ecol. Appl. 5:1122-1132.

Shurtleff, J.L. and H.D. Coble. 1985. Interference of certain broadleaf weed species in
soybeans (Glycine max). Weed Sci. 33:654-657.

Sprague, CL. 2004. Five weeds to fear-top weed escapes in Michigan corn and soybean
ﬁelds. Michigan State University Fact Sheet.

116

Taylor, F.E., L.E. Davies, and AH. Cobb. 1981. An analysis of the epicuticular wax of
Chenopodium album leaves in relation to environmental change, leaf wettability, and the
penetration of the herbicide bentazon. Ann. Appl. Biol. 98:471-478.

VanGessel, M.J. 2001. Glyphosate-resistant horseweed from Delaware. Weed sci.
49:703-705.

VanGessel, M.J., A.O. Ayeni, and B.A. Majek. 2000. Optimum glyphosate timing with or
without residual herbicide in glyphosate-resistant soybean (Glycine max) under full-season
conventional tillage. Weed Technol. 14:140-149.

Westra, P.H., D.L. Wyse, and BF. Cook. 1981. Weevil (Notaris bimaculatus) feeding
reduces effectiveness of glyphosate on quackgrass (A gropyron repens). Weed Sci. 29:540-
547.

Williams, M.M., D.B. Walsh, and R.A. Boydston. 2004. Integrating arthropod herbivory
and reduced herbicide use for weed management. Weed Sci. 52:1018-1025.

Zelaya, LA. and MK. Owen. 2005. Differential response ofAmaranthus tuberculatus to
glyphosate. Pest Manag. Sci. 61:936-950.

117

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118

Table 2. Percent of common lambsquarters plants with insect larval tunneling prior to
glyphosate application and common lambsquarters control (28 DAT) for soybean planted
in May 2004 at East Lansing.

 

Common lambsquarters application heights

 

 

 

 

 

lO-cm 25-cm 46-cm
Plants with insect 0 0 40
larval tunnelinga (%)
Glyphosate rateb control (%)
0.63 kg ae/ha 75 abcc 72 be 42 d
0.84 kg ae/ha 79 ab 76 abc 49 d
' 1.70 kg ae/ha 81 ab 88 a 64 c

 

a Insect identiﬁed tunneling in common lambsquarters was a leaﬁniner ﬂy larvae.

b All glyphosate applications included 2% w/w ammonium sulfate.

° Means followed by the same letter are not statistically different according to Fisher’s
Protected LSD0,05

119

Table 3. Percent of common lambsquarters plants with insect larval tunneling prior to
glyphosate application and common lambsquarters control (28 DAT) for soybean planted

 

 

 

 

 

 

' in June 2004 at East Lansing.
Common lambsquarters application heights

10-cm 25-cm 46-cm
Plants with insect 40 60 70
larval tunneling“ (%)
Glyphosate rateb control (%)
0.63 kg ae/ha 88 bc° 92 ab 83 c
0.84 kg ae/ha 93 be 92 ab 88 be
1.70 kg ae/ha 98 a 97 ab 93 ab

 

a Insects identiﬁed tunneling in common lambsquarters were a leaﬁniner ﬂy larvae and the
beet petiole borer (Cosmobaris americana).

b All glyphosate applications included 2% w/w ammonium sulfate.

° Means followed by the same letter are not statistically different according to Fisher’s

Protected LSD0,05

120

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121

Table 5. The effect of glyphosate on caged and non-caged common lambsquarters control

 

 

 

28 DAT. a
No Cage Cage
Plants with 100 A” 0 B
insect larval
tunnelingb (%)
—— control (%)
97 ab 96 a

 

a Insects identiﬁed tunneling in common lambsquarters was Diptera larvae in the family
Agromyzidae.

b Means followed by the same letter are not statistically different according to Fisher’s
Protected LSDQOS. Capital letters represent differences between insecticide treatment and
lower case letters represent differences between herbicide treatments.

122

Table 6. Common lambsquarters control in cage and cage-ﬂee treatments (28 DAT) in the

 

 

 

 

 

 

greenhouse.

Common lambsquarters application heights

46-cm 60-cm
Infested“ Non-infested Infested Non-infested
b

Glyphosate rate control (%)
0.63 kg ae/ha 9 cdc 22 c 8 cd 3 d
0.84kgae/ha 51b 44b 9cd llcd
1.70kgae/ha 68a 40b 130d l7cd

 

3 Plants were infested with beet petiole borer (Cosmobaris americana).

b All glyphosate applications included 2% w/w ammonium sulfate.

° Means followed by the same letter are not statistically different according to Fisher’s
Protected LSDQOS

123

Table 7. Glyphosate rates associated with each growth reduction value for six Michigan
common lambsquarters biotypes. a

 

Biomass reduction

 

 

 

 

Biotypes GR25a GRso GR75
kg ae/ha
F&J 0.36 bb 0.49 c 0.74 a
Eaton Co. 0.57 b 0.67 ab 0.84 a
Gratiot Co. 0.28 c 0.52 c 1.13 a
Ingham Co. 0.46 b 0.74 a 1.39 a
Montcalm Co. 0.44 c 0.66 ab 1.23 a
Saginaw Co. 0.32 c 0.54 be 1.60 a
Shiawassee Co. 0.31 c 0.45 c 0.82 a

 

alBiotypes collected from a single ﬁeld from each county.

bMean separation (LSDoos) between populations are denoted by lower case letters within
columns.

124

Figure 1. Percent of common lambsquarters plants with insect larval tunneling over
accumulated growing degree days.

Plants Infested (%)

100

80

60

40

20

 

 

 

 

 

 

 

 

 

500 1000 1500 2000
Growing Degree Days (4 C)

125

__.2004
—o—2005

CHAPTER 5
TEMPORAL AND SPATIAL DISTRIBUTION OF STEM-BORING INSECTS IN
COMMON LAMBSQUARTERS IN MICHIGAN AND INDIANA
ABSTRACT
In 2004 and 2005, Michigan and northern Indiana soybean ﬁelds were surveyed for insect
larval tunneling in common lambsquarters. Insect larval tunneling of common
lambsquarters was found to be wide-spread throughout Michigan and northern Indiana.
In June of 2005, leaﬁniner larvae (Diptera:Agromyzidae) were found tunneling in
common lambsquarters stems. Leaﬁniner ﬂy larvae were also found during the August
sample time in Michigan, but not in Indiana. Beet petiole borer larvae were found in both
' states during the August sample timing. Most glyphosate is applied applications in late-
June in Indiana and Michigan, coinciding with leafminer tunneling. Since glyphosate is a
systemic herbicide, it was hypothesized that insect tunneling in common lambsquarters
could reduce efﬁcacy.
Nomenclature: Common lambsquarters, Chenopodium album L.; beet petiole borer,
Cosmobaris americana; leaﬁniner ﬂy, Diptera:Agromyzidae.

Additional index words: Survey, insect weed-interactions, common lambsquarters.

126

INTRODUCTION

Few plants are immune to attack by insects and interactions between weeds and
insects occur more often than what is recognized. Norris and Kogan (2000) reported that
three outcomes occur from insect and weed interactions; these consist of energy/resource
ﬂow, habitat modiﬁcation, and control tactics to mitigate pests. Therefore, Weber et al.
(1990) suggested that weed scientists and entomologists need to work together to
understand the effect of weed management on insect population dynamics; moreover we
should understand what effect insect populations have on weed management.

Common lambsquarters is a successful colonizing species, and one of the most
widely distributed weeds in the world (Holm et al. 1977). It is found in 47 different
countries in 40 different crops, and considered the principal weed pest in corn (Zea mays
L.), potato (Solanum tuberosum L.), soybean (Glycine max (L.) Merr.), and sugarbeet
(Beta vulgaris L.) (Holm et al. 1977; Mitich 1988). Common lambsquarters is ranked as
the most problematic weed for soybean producers in Michigan (Sprague 2004). The
success of common lambsquarters as a competitive, wide-spread weed is attributable to
many factors, including seed germination in a wide range of environmental conditions
(Henson 1970), early emergence during the crop growing season (Ogg and Dawson
1984), plasticity of growth (Ervio 1971), proliﬁc seed production (Harrison 1990), and
seed longevity (Lewis 1973).

In some cases where weed control was poor with glyphosate, insect larvae were
found tunneling or feeding in the vascular tissue (Maertens et al. 2003, Ott et a1 2003;
Westra et a1. 1981). Since glyphosate is a systemic herbicide, it is hypothesized that
weed control with glyphosate may be reduced if insect larval tunneling or feeding is

127

present in the plant at the time of the herbicide application. While there are many reports
of using of insects as biological control agents for weeds (Bacher and Schwab 2000;
Julien 1998; Sheldon and Creed 1995), there is limited research on the effects of insect
feeding on weed control from herbicides. Westra et al. (1981) observed that the weevil
(Notaris bimaculatus) reduced the effectiveness of glyphosate on quackgrass (Elytrigia
repens). In contrast, Ott et a1. (2003) reported that giant ragweed (Ambrosia triﬁda)
control was not affected by infestation with the European corn borer (Ostrinia nubilalis).
Furthermore, Williams et al. (2004) reported that Colorado potato beetle (Leptinotarsa
decemlineata) feeding in combination with reduced ﬂuroxypyr rates enhanced volunteer
potato (Solanum tuberosum L.) control compared with either strategy alone.

In 2003, insect larval tunneling was found throughout the vascular system of
common lambsquarters that survived applications of glyphosate in Michigan. The larvae
were later identiﬁed as the beet petiole borer (Cosmobaris americana Casey). Gilbert
(1964) reported that the most common host for this insect in California was common
lambsquarters and as many as 30 larvae were found within a single plant (Landis et al.
1970). However, there is limited information on the biology of this insect in the
Midwest.

Many producers readily adopted glyphosate-resistant crops, and with over 87% of
soybean acres planted with glyphosate-resistant soybean (NASS 2005) incidents of
reduced effectiveness are a major concern. Understanding the potential for interactions
between insect damage and glyphosate effectiveness is important. Prior to this work,
there was no information on the extent and distribution of insect larval tunneling in
common lambsquarters in Michigan or Indiana. Therefore the objective of this study was

128

to determine the temporal and spatial distribution of insect larval tunneling in common
lambsquarters in Michigan and northern Indiana, in relation to glyphosate application

timing.

129

MATERIALS AND METHODS

In 2004 and 2005, sampling was done in conjunction with Purdue University to
examine the extent and distribution of insect larval tunneling in common lambsquarters in
Michigan and northern Indiana. In 2004, random soybean ﬁelds in Michigan and Indiana
were sampled between July 28 and August 9. Ten common lambsquarters plants were
collected from 29 samples in 29 different counties in Michigan and 8 ﬁelds in 7 different
counties in Indiana. Locations were marked with GPS, and plant height, stem diameter,
insect tunnel-length, number of live larvae present, and insect specie were recorded.

In 2005, common lambsquarters plants were sampled at three different times
throughout the growing season. The ﬁrst sample period occurred June 23-24, when most
glyphosate applications are made. The second and third sample periods occurred August
8-12 and September 14-17, respectively Four regions in Michigan (northeast, northwest,
southeast, and southwest) and three regions in Indiana (northeast, northwest, and central)
were sampled. Five ﬁelds per region were sampled, except for the August sampling
period in Michigan were seven ﬁelds per region were sampled (Figure 1).

The survey data were treated as completely randomized, with each ﬁeld in each
region treated as a replication. Plant measurement data were subjected to correlation
using the PROC CORR procedure in SAS 8.02l software. Survey data were subjected to
ANOVA using the PROC MIXED procedure in SAS and since no interaction between
repeated data for the Michigan August sample period occurred, data were combined over
years. Indiana data from August 2005 was analyzed separately. Means were separated

with Fisher’s Protected LSD at (1:0. 1.

 

' SAS Institute Inc., 100 SAS Campus Drive, Cary, NC 27513,
130

RESULTS AND DISCUSSION

In 2004, insect tunneling of common lambsquarters stems was wide-spread
throughout Michigan and northern Indiana. In August, 55% of the total larvae found
tunneling in common lambsquarters were beet petiole borers (BPB) in Michigan (data not
shown). In the Michigan Counties of Huron, Ingham, Jackson, Ignawee, Montcalm,
‘ Saginaw, and Tuscola 100% of common lambsquarters plants contained tunneling (Table
1). In Indiana, 100% of the total larvae found tunneling in common lambsquarters were
BPB. In Caroll County, 100% of the common lambsquarters plants contained tunneling;
however, Jasper County had the greatest percentage of plants with live larvae in Indiana.
There were 2.9 and 1.3 larvae per plant that were BPB and leafrniner, respectively. There
were no strong correlations between stem diameter or plant height to tunnel length
P=0.76 and 0.66 respectively. This indicates that either insect have little preference in
regards to plant size or plant growth is unaffected by larval tunneling. Tunneling by the
leafrniner larvae was narrow and was contained to the center of stem causing little
damage to vascular tissue. Tunneling by the beet BPB larvae was much greater than that
by leafrniner larvae and the pith tissue of plants was damaged. Plants that contained
many BPB larvae appeared to have swollen stems and were slightly stunted in height.
The common lambsquarters plants sampled during this time frame were presumed to
have escaped control with glyphosate in glyphosate-resistant soybean. Since glyphosate
is a systemic herbicide it was hypothesized that insect tunneling in common
lambsquarters could reduce efﬁcacy.

Insect tunneling for the June 2005 sampling time was quite variable; the
percentage of plants with tunneling ranged from 10 to 100% in Michigan (Table 2).

131

Gratiot County had the most common lambsquarters plants with live leaﬁniner larvae,
and on average there were 1.4 larvae per plant for this sample period. In Indiana,
tunneling ranged from 10 to 60% in Jasper and Boone Counties, respectively, however,
there were no live larvae found in plants. There were no differences between regions in
Michigan and Indiana in regards to the percentage of plants with tunneling and plants
with live insects in June (Table 3). Of the plants sample, 47% contained tunneling, and
the leafrniner was the only insect found in 22% of dissected plants. At this sample
period, the only larvae found inside of plants was the leaﬁniner larvae indicating that this
species is the ﬁrst to tunnel in common lambsquarters plants. Most glyphosate
‘ applications in Michigan are made in late-June. This means that insect larval tunneling
by the leafrniner is most likely to be present in common lambsquarters during this
timefrarne.

In August 2005, Cass and St. Clair Counties had the highest percentage of plants
with insect tunneling at 100 and 90%, respectively, in Michigan (Table 4). In Indiana,
Noble, Pike, and White Counties had the greatest percentage of plants with tunneling.
Tunneling was similar between regions in Michigan (Table 3). Tunneling was less in
August 2005 compared with August 2004. Furthermore, tunneling in August was less
than the June sample period. This may be due to control of common lambsquarters with
glyphosate applied in June resulting in fewer plants with tunneling for the August sample
period. Of the plants sampled, 9 to 27% of contained live larvae (Table 3). In Michigan
and Indiana, 81 and 100% of total larvae found were BPB, respectively. There were 2.5
and 1.5 larvae per plant that were the BPB and leafrniner, respectively. The northeast and
southeast regions in Michigan contained plants with the most live larvae present. The

132

northwest region of Indiana contained the most BPB larvae inside plants. The number of
leafrniner ﬂy larvae was the greatest in northeast region of Michigan. In Indiana, the
only insect found in plants was the BPB and was in 14 to 28% of the plants sampled. In
studies conducted at a similar time, the ﬁrst larvae found within common lambsquarters
was the leaf-miner ﬂy larvae on June 13 in 2004 and 2005. Furthermore, the BPB larvae
were found within plants on July 13 and July 8 in 2004 and 2005. Our observations on
the life cycle of the beet petiole borer in Michigan agree with those of Landis (1970) who
reported that BPB adults emerged in May Washington and Oregon and larvae were full
grown by August and then overwinter in the stems of weed hosts.

In September 2005, tunneling was similar between regions in which 42% of the
plants contained tunneling (Table 5). The only live larvae found in plants at this time
were the BPB, averaging 2.3 larvae per plant. The northwest region of Michigan had the
' greatest percent of infested plants. There were no insects found in the southeast region.
Shiawassee and St. Joseph Counties had the greatest percentage of plants with tunneling.
However, the counties with the greatest percentage of plants with live larvae were
Gratiot, Ionia, and Jackson. Insect tunneling for this sample period was similar to August
timing, but less than the June timing. In Indiana, tunneling ranged from 20 to 80%, and
the BPB was the only insect larvae found. The central region was the only region which
live BPB larvae were found.

In conclusion, the insect tunneling of common lambsquarters was wide-spread
throughout Michigan and northern Indiana. The insects involved included the BPB as
well as a still to be identiﬁed leaﬁniner ﬂy larvae. In June, the leaﬁniner larvae were
common in plants during the timeframe when glyphosate is ﬁrst applied. In August, the

133

 

leafrniner ﬂy larvae were still present in Michigan, but not in Indiana. BPB larvae were
found in Indiana and Michigan in August indicating that BPB tunneling occurs later in
the season. The lifecycle of the BPB coincided with earlier published reports from beet
and weed host in the western US. Most glyphosate applications in Michigan and Indiana
are made in late-June and coincide with leafrniner tunneling. However, tunneling by
leafrniner ﬂy larvae did not produce any visual damage to plants. BPB damage was more
extensive, but occurred later in the season after most glyphosate applications are made.
However, if glyphosate applications were delayed, BPB tunneling could interfere with

translocation.

134

LITERATURE CITED

Bacher, S. and Schwab. 2000. Effect of herbivore density, timing of attack, and plant
community on performance of creeping thistle (Cirsium arvense (L.) Scop.). Biocontrol
Sci. and Technol. 10:343-352.

Ervio, LR. 1971. The effect of intra-speciﬁc competition on the development of
Chenopodium album L. Weed Res. 11:124-134.

Gilbert, BE. 1964. The genus Baris Germar in California. Univ. California Publ. In
Entomol., 34:70-74.

Harrison, SK. 1990. Interference and seed production by common lambsquarters
(Chenopodium album) in soybeans (Glycine max). Weed Sci. 38:113-118.

Henson, LE. 1970. The effects of light, potassium nitrate and temperature on the
germination of Chenopodium album L. Weed Res. 10:27-39.

Holm, L.G., D.L. Plucknett, J.V. Pancho, and J .P. Herberger. 1977. Chenopodium album
L. Chenopodiaceae, goosefoot family. Pages 84-91 in The World’s Worst Weeds:
Distribution and Ecology. Honolulu, HI: University Press of Hawaii.

Julien, M.H. 1998. Biological Control of Weeds: A World Catalogue of Agents and Their
Target Weeds. Wallingford, Oxford: CAB Int. 4“1 ed.

Landis, B.J., W.B. Peay, and L. Fox. 1970. Biology of Cosmobaris americana Casey, a
weevil attacking sugarbeets. J. Econ. Entomol. 63:38-41.

Lewis, J. 1973. Longevity of crop and weed seeds. Weed Res. 13:179-191.

Maertens, K.D. 2003. Giant ragweed emergence, growth, and interference in soybeans.
MS. Thesis. University of Illinois. Champaign, IL 65 p.

Mitich, L.W. 1988. Intriguing world of weeds-common lambsquarters. Weed Technol.
2:550-552.

‘ National Agricultural Statistics Service (NASS), USDA, 2005. Acreage.
http://usda.mannlib.comell.edu/reports/nassr/ﬁeld/pcp-bba/acrg0605.pdf. Accessed
October 6, 2005.

Norris RF. and M. Kogan. 2000. Interactions between weeds, arthropod pests, and their
natural enemies in managed ecosystems. Weed Sci. 48:94-158.

135

Ogg, A.G., Jr. and J.A. Dawson. 1984. Time of emergence for eight weed species. Weed
Sci. 32:327-335.

Ott, E.J., W.G. Johnson, J .L. Obermeyer, and DJ. Childs. 2003. Glyphosate efﬁcacy on
giant ragweed infested with European corn borer. Proc. N. Cent. Weed Sci. 58: 137.

Sheldon, SF. and RP. Creed. 1995. Use of native insects as biological control for an
introduced weed. Ecol. Appl. 5:1122-1132.

Sprague, CL. 2004. Five weeds to fear-top weed escapes in Michigan corn and soybean
ﬁelds. Michigan State University Fact Sheet.

Weber, D.C., F.X. Mangan, D.N. Ferro, and H.V. Marsh, Jr. 1990. Effect of weed
abundance on European corn borer (LepidopterazPyralidae) infestation of sweet corn.
Environ. Entomol. 19:1 858-1865.

Westra, P.H., D.L. Wyse, and BF. Cook. 1981. Weevil (Notaris bimaculatus) feeding
reduces effectiveness of glyphosate on quackgrass (Agropyron repens). Weed Sci.
29:540-547.

Williams, M.M., D.B. Walsh, and RA. Boydston. 2004. Integrating arthropod herbivory
and reduced herbicide use for weed management. Weed Sci. 52:1018-102

136

Table 1. Frequency of insect larval tunneling in common lambsquarters collected in
soybean ﬁelds in Indiana and Michigan, August 2004.

 

 

 

 

 

 

 

Plants with Plants with Plants with Plants with
Region County tunnelinga live larvae beet petiole Diptera larvaeb
borer larvae
(%)

MI-N E Huron 100 50 0 50
Lapeer 90 30 0 30
Saginaw 100 30 0 30

Shiawassee 20 20 20 0
Sanilac 90 20 0 20
St. Clair 90 20 10 10

MI-NW Allegan 60 20 20 0
Barry 90 20 20 0
Clinton 80 20 10 10
Gratiot 90 20 10 10
Ionia 90 30 20 10

Kent 30 0 O O
Montcalm 100 80 0 80

MI-SE Hillsdale 20 0 0 0
Ingham 100 50 30 20

Jackson 100 50 50 0

Lenawee 100 50 50 0

Livingston 80 0 0 0
Monroe 40 20 0 20

Washtenaw 0 0 0 0

MI-SW Berrien 40 0 O 0
Branch 60 20 20 O

Calhoun 6O 0 0 0
Cass 30 20 10 10

Eaton 40 0 0 0

Kalamazoo 40 0 0 0

St. Joseph 70 30 20 10

Van Burren 80 20 20 0

Indiana Blackford 80 60 60 0
Carroll 100 80 80 0

Grant 70 0 0 0

Jasper 90 9O 9O 0

Marshall-l 90 20 20 0

Marshall-2 40 0 0 O

Noble 60 20 20 O

Whitley 70 20 20 O

 

a10 total plants sampled per location.
I’Unidentiﬁed leaﬁniner ﬂy larvae (Diptera:Agromyzidae).

137

Table 2. Frequency of insect larval tunneling in common lambsquarters collected in
soybean ﬁelds in Indiana and Michigan in June 2005.

 

 

 

 

 

 

 

 

 

Plants with Plants with Plants with beet Plants with
Region County tunnelinga live larvae petiole borer Diptera larvae”
larvae
(%)

MI-NE Genesse 10 0 0 0
Lapeer 40 10 O 10
Saginaw 30 30 0 30
Shiawassee 70 30 0 3O
Tuscola 30 30 O 20
MI-N W Clinton 40 20 0 . 20
Gratiot 70 60 0 6O

Ionia 20 0 0 0

Montcalm-l 40 0 0 0
Montcalm-2 50 30 0 30
MI-SE Eaton 40 30 0 30
Hillsdale 60 40 0 40
Ingham 70 20 0 20
Jackson 50 40 0 40
Lenawee 90 40 0 40

MI-SW Branch-l 6O 20 0 20
Branch-2 100 20 O 20
Calhoun 30 10 0 IO

Kalamazoo-1 3O 0 0 O
Kalamazoo-2 10 0 0 0

IN-NE Elkhart 50 0 0 0
Marshall 40 O 0 0

St. Joseph 10 0 0 0

Whitley-l 30 0 0 O

Whitley-2 40 0 0 0

IN-NW Fountain 60 0 0 0
Jasper 10 0 0 0

Jasper 30 0 0 0

Pulaski 4O 0 0 0

White 20 O 0 0

IN -C Boone 60 0 0 0
Hamilton 20 0 O 0

Morgan 30 0 0 0

Putnam-l 40 0 0 0

Putnam-2 20 0 0 0

 

810 total plants sampled per location.
l’Unidentiﬁed leafrniner ﬂy larvae (Diptera:Agromyzidae).

138

Table 3. Frequency of insect larval tunneling in common lambsquarters in Indiana and
Michigan in 2004 and 2005.

 

 

 

 

Plants with Plants with Plants with Plants with
Region tunneling“ live larvae beet petiole borer Diptera larvae
larvae
(%)
June
MI-NE 36 20 0 20
MI-NW 44 22 0 22
MI-SE 62 34 0 34
MI-SW 46 10 0 10
LSD“), .) NS NS NS NS
IN-NE 32 0 O 0
IN-NW 34 0 0 O
IN-C 34 O 0 O
LSD(o.1) NS NS NS NS
August
MI-NE 64 27 8 19
Ml-NW 61 19 11 8
MI-SE 53 25 21 4
MI-SW 43 9 4 5
LSD(0,1) NS 11 9 10
IN-NE 44 24 24 0
IN-NW 48 28 28 0
IN-C 14 14 14 0
LSDw,” NS NS NS NS
September
MI-NE 38 14 14 O
MI-NW 52 26 26 O
MI-SE 30 0 0 0
MI-SW 48 18 18 0
LSD(0.|) NS 15 15 NS
IN-NE 44 0 0 0
IN-NW 34 O 0 0
lN-C 52 8 8 0
LSD(0.I) NS 6.3 6.3 NS

 

a Frequency was calculated form 50 plants per region for the June, August, and
September sampling time in Indiana and 70 plants per region for the Michigan August
sampling time.

139

Table 4. Frequency of insect larval tunneling in common lambsquarters collected in
soybean ﬁelds in Indiana and Michigan, August 2005.

 

 

 

 

 

 

 

 

 

Plants with Plants with Plants with Plants with
County tunneling“ live larvae beet petiole Diptera larvaeb
borer larvae
(%)

MI-N E Huron 60 20 0 20
Lapeer 10 0 0 0

Saginaw 60 30 0 30

Shiawassee 60 10 0 10

Sanilac 10 10 O 10

Tuscola 20 10 10 ' 0

MI-NW Allegan 40 10 10 0
Barry 20 10 10 0

Clinton 20 10 10 O

Gratiot 50 30 30 O

Ionia 60 10 10 0

Kent 60 0 O 0

Montcalm 70 0 0 0

MI-SE Hillsdale 10 10 10 O
Ingham 50 4O 40 0

Jackson 30 30 30 0
Lenawee 60 20 10 10

Livingston 10 10 10 0

Monroe 10 10 10 O

Washtenaw 10 0 0 0

MI-SW Berrien 10 O 0 0
Branch 30 O 0 0

Calhoun 20 0 O 0

Cass 100 40 0 40
Eaton 30 20 0 20

Kalamazoo 30 0 0 0

St. Joseph 60 30 30 0

Van Burren 30 0 0 0

IN-N E Dekalb 30 20 20 0
Miami-1 3O 10 10 0

Miami-2 30 10 10 0

Noble 80 40 4O 0

Wells 70 60 60 0

IN-N W Benton 0 0 0 0
Cass 50 O 0 0

Starke 60 10 10 0

White-l 20 0 0 0

White-2 80 60 60 0

IN-C Hendricks 40 10 10 0
Pike 80 80 80 O

Putnam-l 40 20 20 0

Putnam-2 30 10 10 O

Sullivan 30 0 0 O

 

‘ 810 total plants sampled per location.
bUnidentiﬁed leafrniner ﬂy larvae (Diptera:Agromyzidae).

140

Table 5. Frequency of insect larval tunneling in common lambsquarters collected in
soybean bean ﬁelds in Indiana and Michigan, September 2005

 

 

 

 

 

 

 

 

Plants with Plants with Plants with beet Plants with
Region County tunneling“ live larvae petiole borer Diptera larvaeb
larvae

MI-NE Bay 20 0 0 O
Lapeer 40 20 20 0
Saginaw-l 30 0 0 O
Saginaw-2 50 30 3O 0
Tuscola 50 20 20 0
MI-N W Clinton 50 20 20 0
Gratiot 50 40 40 0
Ionia 50 40 40 0
Ionia-2 40 10 10 0
Montcalm 70 20 20 0
MI-SE Ingham 30 0 0 0
Jackson 60 50 50 0
Lenawee lO 0 0 O
Lenawee-2 3O 0 0 0
Lenawee-3 10 0 O O
MI-SW Branch 40 0 0 0
Branch-2 40 20 20 O
Calhoun 40 10 10 0
Eaton 6O 10 10 0
St. Joseph 70 0 0 O
IN-N E Miami 20 O 0 O
Wabash-l 30 0 0 O
Wabash-2 40 0 0 0
Wells 50 0 0 0
DeKalb 30 0 0 0
IN-NW White 30 0 0 O
Jasper-l 50 0 O 0
Jasper-2 20 0 0 0
Cass 80 0 O 0
White-2 40 0 0 0
IN-C Boone-2 50 20 20 0
Hamilton 60 10 10 0
Hancock 60 10 10 0
Hendricks 70 0 0 0
Boone-2 20 0 0 0

 

2‘10 total plants sampled per location.
bUnidentiﬁed leaﬁniner ﬂy larvae (Diptera:Agromyzidae).

141

Figure 1. Regions sampled in Michigan and Indiana in 2004 and 2005.

 

 

142

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