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EVALUATION OF TRANSGENIC CORN (Zea mays L.)
RESISTANT TO BOTH GLYPHOSATE AND WESTERN
CORN ROOTWORM (Diabrotica virgifera virgifera LeConte)
IN MICHIGAN

presented by

KATHRIN SCHIRMACHER

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Ph.D. degree in Crop and Soil Science

 

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6/07 p:lCIRC/DateDue.indd-p.1

EVALUATION OF TRANSGENIC CORN (Zea mays L.) RESISTANT TO
BOTH GLYPHOSATE AND WESTERN CORN ROOTWORM
(Diabrotica virgg'fera virgrfera LeConte) IN MICHIGAN
By

Kathrin Schirmacher

A DISSERTATION

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

DOCTOR OF PHILOSOPHY
Department of Crop and Soil Sciences

2007

ABSTRACT
EVALUATION OF TRAN SGENIC CORN (Zea mays L.) RESISTANT TO
BOTH GLYPHOSATE AND WESTERN CORN ROOTWORM
(Diabrotica virgrfera virgifera LeConte) IN MICHIGAN
By
Kathrin Schirmacher
Annual weeds and western corn rootworm (Diabrotica virgifera virgifera

LeConte) (WCR) can limit corn (Zea mays L.) grain yield. With the failure of a corn and
soybean [Glycine max (L.) Merr.] rotation as an effective control program for WCR,
growers are relying more heavily on conventional insecticides to control WCR.
Glyphosate has been used as a postemergence (POST) weed control program since the
introduction of glyphosate-resistant corn hybrids in 1998. The adoption of glyphosate-
resistant com has increased. The glyphosate-resistant trait is often stacked with other
resistance traits. The use of herbicide and insect resistance traits gives producers new
options in pest control program. Many studies have looked at the agronomic and
economic considerations of using either using insect or herbicide resistance traits in corn
hybrids. However, no study has been conducted on corn hybrids containing resistance
traits to both herbicides and insects. The objective of this study was to determine the
consistency of conventional programs and programs using transgenic corn for control of
WCR and annual weeds and to examine the profitability of these programs under a range
of Michigan conditions. Field studies were conducted in 2004, 2005, and 2006 at four
locations in Mid-Michigan. Sites were selected to reflect a range of annual weed and

WCR densities. Treatments consisted of conventional weed management and a

management program using glyphosate-resistant corn in combinations with WCR

management programs. Good weed control resulted in increased corn yields at all
locations all years. Good weed control was obtained with both glyphosate-based and
conventional herbicide programs. Under low WCR densities, the use of any of the WCR
control programs tested increased corn yields in one of six environments. Under high
WCR densities, the use of the transgenic Bt corn hybrid resulted in increased corn yields
in three of six environments compared to no WCR control. In those years where WCR
damage was high, all control programs resulted in corn yields greater than when left
untreated, with the transgenic Br corn hybrid consistently providing the greatest corn
yields. Weed control costs were economically justified under both low and high weed
densities, based on gross margins over weed control costs. Gains in gross margins
relative to no weed control were reported for all weed control strategies at all locations all
years. The presence and intensity of WCR larvae feeding on corn roots varied by year
and was less predictable than weed density. The overall gross margin of the no WCR
control program at the low WCR sites was often higher than the gross margins of the
WCR programs. This indicated that, unlike weed control, the costs associated with the
control of WCR in many instances was not justified. At the high WCR sites, the cost of
WCR control via either Bt-com or conventional seed or soil insecticide treatment was
justified in two of six environments. In those two environments, the Bt-hybrid
consistently had the highest gross margin gains relative to no WCR control. The adoption
of stacked transgenic corn hybrids will likely be related to economic return associated
with the control of weeds and WCR. Since gross margins were positively correlated with
com yield (1'2 = 0.98), growers should focus on yield potential by choosing high yielding

hybrids adapted to local growing conditions.

Fiir meine liebe Mutter

Marianne Schirmacher
Geb. Schneider

1952-2005

Wir wollen nicht trauem,

dass wir sie verloren haben,

sondem wir wollen uns freuen,

dass wir sie gehabt haben und noch haben,
denn wer im Herrn stirbt,

der bleibt in der Familie

iv

ACKNOWLEDGEMENTS

This dissertation would not have been possible without the financial support
provided by Project GREEEN and the Corn Marketing Program of Michigan. I am
extremely thankful for Dr. Jim Kells for taking me on as a student. Dr. Kells was
instrumental in guiding my graduate program and provided me with many professional
opportunities that most students are not able to experience. Dr. Chris DiFonzo has been a
key player in my graduate program from the very beginning and has become a personal
mentor along the way. I would also like to thank Dr. Penner and Dr. Swinton for serving

on my graduate committee and for assisting me with corrections.

Several technicians have assisted me in conducting field research: Andy Chomas,
Mike Jewett, Keith Dysinger, and Bill Widdicombe. Without their hard work, my
research plots would not have been planted or sprayed as quickly and efficiently as they

were .

I would also like to thank past and present graduate students and post-docs in the
weed science program. I especially wanted to acknowledge Dr. Aaron F ranssen, Ann

McCordick, Dr. David Hillger, and Dr. Christy Sprague for their friendship, words of

encouragement, and many laughs.

The biggest credit for finishing this degree goes to my family. My parents have
always told me to not forget where I came from — the farm. They have instilled in me a

love for the land as well as good values, for this I am thankful.

TABLE OF CONTENTS

List of Tables ....................................................................................
List of Figures ....................................................................................

List of Tables in Appendix ....................................................................

Chapter 1
Agronomic Evaluation of Transgenic Corn (Zea mays L.) Resistant to Both
Glyphosate and Western Corn Rootworm (Diabrotica virgifera virgifera LeConte)

in Michigan .......................................................................................

Abstract ...................................................................................
Introduction ..............................................................................
Materials and Methods ..................................................................
Results and Discussion ..................................................................
Literature Cited ..........................................................................

Chapter 2
F arm-Level Profitability of Transgenic Corn (Zea mays L.) Resistant to Both
Glyphosate and Western Corn Rootworm (Diabrotica virgifera virngera LeConte)

in Michigan .......................................................................................

Abstract ...................................................................................
Introduction ..............................................................................
Materials and Methods ..................................................................
Results and Discussion ..................................................................
Literature Cited ..........................................................................

Appendix ..........................................................................................

vi

vii

viii

X

1

2
4
7
ll
22

38

39
41
42
47
57

73

LIST OF TABLES
CHAPTER 1: Agronomic Evaluation of Transgenic Corn (Zea mays L.) Resistant to
Both Glyphosate and Western Corn Rootworm (Diabrotica virgifera
virgifera LeConte) in Michigan.

Table l. Anticipated weed and corn rootworm (WCR) density levels, soil

characteristics, and planting dates at each location in 2004, 2005, and 2006 ............ 26
Table 2. Treatments combining weed and corn rootworm management

programs, Michigan (2004-2006) .............................................................. 27
Table 3. Weed densities in a permanently established quadrat at high and low

weed density level sites level prior to postemergence herbicide application ............. 28
Table 4. Monthly precipitation recorded at East Lansing, M1 (2004-2006) ............. 29
Table 5. Corn yield at all locations as influenced by weed control program ............ 30
Table 6. Corn yield at all locations as influenced by WCR control program ............ 31
Table 7. Corn stand density by WCR control progam at all locations in 2005 ......... 32

Table 8. Combination of best and worst WCR and weed control programs
available to predict corn yield loss ............................................................ 33

CHAPTER 2: Farm-Level Profitability of Transgenic Corn (Zea mays L.) Resistant
to Both Glyphosate and Western Corn Rootworm (Diabrotica
virgrfera virgifera LeConte) in Michigan.

Table 1. Anticipated weed and corn rootworm (WCR) density levels, soil
characteristics, and planting dates at each location in 2004, 2005, and 2006 ............ 60

Table 2. Treatments combining weed and corn rootworm management
strategies, Michigan (2004-2006) .............................................................. 61

Table 3. Cost assumptions used in profitability analysis ................................... 62

vii

LIST OF FIGURES

CHAPTER 1: Agronomic Evaluation of Transgenic Corn (Zea mays L.) Resistant to
Both Glyphosate and Western Corn Rootworm (Diabrotica virgifera
virgifera LeConte) in Michigan.

Figure l. Boxplot figures representing total weed density (plants/m2) at the end

of the growing season at all four research sites. Data summarized from 2004,

2005, and 2006. Means of each treatment are indicated by the thicker black bar

inside of each boxplot. The thinner black bar inside of each boxplot denotes the

treatment median. The letter ‘T’ denotes a transgenic corn program for weed control that

is based on the herbicide glyphosate; C, denotes a conventional herbicide program. Each
herbicide treatment n=96 and no weed control n=72 ........................................ 34

Figure 2. Boxplot figures representing total weed biomass (g/mz) at the end

of the growing season at all four research sites. Data summarized from 2004,

2005, and 2006. Means of each treatment are indicated by the thicker black bar

inside of each boxplot. The thinner black bar inside of each boxplot denotes the

treatment median. The letter ‘T’ denotes a transgenic corn program for weed control that

is based on the herbicide glyphosate; C, denotes a conventional herbicide program. Each
herbicide treatment n=96 and no weed control n=72 ........................................ 35

Figure 3. Corn root damage rating by WCR control programs: in 2004 (El),
2005 (I), and 2006 (I) at all locations ........................................................ 36

CHAPTER 2: Farm-Level Profitability of Transgenic Corn (Zea mays L.) Resistant
to Both Glyphosate and Western Corn Rootworm (Diabrotica
virgifera virgrfera LeConte) in Michigan.

Figure 1. Gross margins gains of weed control programs relative to no weed control
(= 0) in 2004 (El), 2005 (I), and 2006 (I) at all locations. The letter ‘T’ denotes a
glyphosate-based herbicide program and ‘C’ denoted a conventional herbicide

program 63

Figure 2. Gross margins gains of WCR control programs: relative to no insect
control (= 0) in 2004 (El), 2005 (I), and 2006 (I) at all locations ........................ 65

Figure 3. Sensitivity analysis of gross margin gains from the sequential (PRE fb.

POST), glyphosate-based weed control program by weed density and corn price

($/Mg) in comparison to no weed control (S/ha means d: 1 standard deviation). The
horizontal line in the bars represents the mean ............................................... 67

Figure 4. Sensitivity analysis of gross margin gains from the glyphosate fb.

glyphosate weed control program by weed density and corn price ($/M g) in

comparison to no weed control ($/ha means i 1 standard deviation). The horizontal

line in the bars represents the mean ............................................................ 68

viii

Figure 5. Analysis of gross margin gains from glyphosate-based and conventional
weed control programs by weed density in comparison to no weed control ($/ha

means i 1 standard deviation). The horizontal line in the bars represents the mean. . ..

Figure 6. Sensitivity analysis of gross margin gains from Bt-corn (assuming 20%
refuge) by WCR density and corn price ($/Mg) in comparison to no WCR control
(($lha means i 1 standard deviation). The horizontal line in the bars represents the
mean ................................................................................................

Figure 7. Analysis of gross margin gains from Bt-corn by WCR density under
varying refuge requirements (no refuge, 10% refuge, 20% refuge) in comparison to
no WCR control (($lha means :I: 1 standard deviation). The horizontal line in the
bars represents the mean ........................................................................

Figure 8. Analysis of gross margin gains from Bt-corn (assumes 20% refuge) and
conventional WCR control programs (SAI, SAI + LST, HST) by WCR density in
comparison to no WCR control (($/ha means i 1 standard deviation). The horizontal
line in the bars represents the mean ............................................................

ix

69

7O

71

72

LIST OF TABLES IN APPENDIX

Table 1. Gross marginsf ($/ha) for no weed and no WCR control in 2004, 2005,
and 2006 at all locations ......................................................................... 74

Table 2. Cost? ($/unit) of additives, herbicides, and insecticides used in the weed
and insect control programs ..................................................................... 75

Table 3. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $1 .SO/bushel ......................................... 76

Table 4. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $2.50/bushel ......................................... 77

Table 5. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $3.50/bushel ......................................... 78

Table 6. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $4.50/bushel ......................................... 79

Table 7. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $1 .SO/bushel ......................................... 80

Table 8. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $2.50/bushel ......................................... 81

Table 9. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $3.50/bushel ......................................... 82

Table 10. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $4.50/bushel ......................................... 83

Table 11. Gross margins for insect control programs at Mason/Eaton Rapids for
varying refuge requirements at a corn selling price of $1.50/bushel ....................... 84

Table 12. Gross margins for insect control programs at Mason/Eaton Rapids for
varying refuge requirements at a corn selling price of $2.50/bushel ...................... 85

Table 13. Gross margins for insect control programs at Mason/Eaton Rapids for
varying refuge requirements at a corn selling price of $3.50/bushel ...................... 86

Table 14. Gross margins for insect control programs at Mason/Eaton Rapids for
varying refuge requirements at a corn selling price of $4.50/bushel ...................... 87

Table 15. Gross margins for insect control programs at Westphalia for varying
refuge requirements at a corn selling price of $1 .50/bushel ................................ 88

Table 16. Gross margins for insect control programs at Westphalia for varying
refiige requirements at a corn selling price of $2.50/bushel ................................ 89

Table 17. Gross margins for insect control programs at Westphalia for varying
refuge requirements at a corn selling price of $3.50/bushel ................................ 90

Table 18. Gross margins for insect control programs at Westphalia for varying
refuge requirements at a corn selling price of $4.50/bushel ................................ 91

xi

CHAPTER I
Agronomic Evaluation of Transgenic Corn (Zea mays L.) Resistant
to Both Glyphosate and Western Corn Rootworm

(Diabrotica virgtfera virgifera LeConte) in Michigan

ABSTRACT

Stacked insect resistant and herbicide resistant traits in field corn are becoming
more common in the marketplace. Major in-field stresses affecting Michigan corn
yields include competition from annual weeds and western corn rootworm feeding
damage. This three-year study examines the consistency of conventional herbicide and
insecticide programs and Bt-corn/glyphosate-based programs for control of insects and
weeds under a range of Michigan conditions. Good weed control increased corn yields
at all locations all years. Good weed control was obtained with both glyphosate-based
and traditional herbicide programs. Under low western corn rootworm (WCR) densities,
the use of control methods increased corn yields in one of six environments. Under high
WCR densities, the use of control programs increased corn yields in three of six
environments. In those years where WCR damage was high, all control programs
provided corn yields higher than when left untreated, with the Bt-hybrid consistently
providing the greatest yields. Under high WCR damage at Westphalia in 2005 and
2006, the WCR control programs in order of most to least consistent were: the Bt-
hybrid, soil-applied insecticide (SAI) + low seed treatment (LST), SAI, and high seed
treatment (HST). WCR density, rather than the weed density, is likely to be one of the

important factors in the adoption of these stacked trait corn hybrids.

Nomenclature: atrazine; glyphosate; mesotrione; s-metolachlor; clothianidin;
tefluthrin; European corn borer, Ostrinia nubilalis Htibner; western corn rootworm,
Diabrotica virgifera virgifera LeConte; corn, Zea mays L. ‘DKC46-24’, ‘DKC46-28’,

‘DKC46-22’, ‘DKC47-10’.

Key Words: insect resistance, herbicide resistance, multiple resistance traits, stacked

traits, transgenic, western corn rootworm, corn, yield.

Abbreviations: PRE, preemergence; POST, postemergence; ib., followed by; R,
glyphosate resistant; WCR, western corn rootworm; ECB, European corn borer; Bt,
Bacillus thuringiensis; HST, high seed treatment; LST, low seed treatment; SAI, soil-

applied insecticide.

INTRODUCTION

Inter-specific gene transfer technology has led to the development of traits that
provide crops with herbicide and insect resistance. The use of herbicide and insect
resistant traits gives producers new options in crop protection and broadens the options
in pest control programs. Seed companies are now stacking more than one trait into a
single corn hybrid, leading to corn hybrids that contain resistance for both herbicides
and insects. The trend of increased numbers of stacked transgenic traits marketed by
seed companies, and bundled with pesticides sales as a package, will likely continue in

the foreseeable future.

A pest that can limit corn grain yield is western corn rootworm (Diabrotica
virgifera virgifera LeConte) (WCR). With its widespread range and abundance in North
America (Krysan and Branson 1983), the WCR is one of the most economically
important pests of corn (Zea mays L.) (Levine and Oloumi-Sadeghi 1991). Both the
larval and adult stage of the WCR damages corn. The larvae injure corn plants by
feeding on root tissue, interfering with normal root fimctions such as nutrient and water
absorption, and plant anchorage (Levine and Oloumi-Sadeghi 1991). In the case of
strong winds and rainstorms, plant lodging may occur resulting in yield losses as well as
harvesting difficulties. The adults interfere with the reproductive success of the plants
by damaging silks and tassels, resulting in poor ear development. The estimated cost of
control and yield losses associated with corn rootworms in corn is roughly $1 billion
annually in the US (Gray 2000; Metcalf 1986). The insect can adapt to cultural
practices, increasing the risk of economic losses. In the Midwest, a com-soybean

[Glycine max (L.) Merr.)] crop rotation was for a long time the recommended program

to prevent root injury caused by the WCR. WCR oviposition occurs primarily in corn
fields and larvae must feed on corn roots the following spring to complete their life
cycle (Levine and Oloumi-Sadeghi 1991). Long-term use of this rotational system
selected for a variant strain of the WCR capable of laying eggs not only in corn but also
in soybean, oats (A vena sativa L.), and alfalfa (Medicago sativa L.) circumventing crop
rotation as a management tool (Levine et al. 2002; Rondon and Gray 2003, 2004). Since
the failure of a com-soybean rotation as an effective control program growers have had
to rely on soil-applied insecticides and corn kernels treated with insecticides to control
WCR (Levine and Oloumi-Sadeghi 1991). Corn producing insecticidal toxins from
Bacillus thuringiensis (Bt) has the potential of simplifying WCR management. The
genes allowing for the expression of Cry3Bbl (Monsanto), Cry34Ab1/Cry35Abl (Dow
AgroSciences), and Cry3A (Syngenta) proteins were inserted into corn thus conferring
host-plant resistance. This allows for the control of corn rootworm without the

application of broad-spectrum insecticides (Vaughn et al. 2005).

Weeds interfering with corn can affect the quality and quantity of marketable
product. Summer annual weed species are usually problematic in summer annual crops
such as corn and soybean (Davis et al. 2005). For example, common lambsquarters
(Chenopodium album L.) when left untreated caused corn yield loss as high as 58%
(Sibuga and Bandeen 1980). A maximum yield loss of 12% was recorded by Beckett et
al. (1988) at a density of 4.9 common lambsquarters plants per m of corn row. Another
troublesome weed in row crops in the Midwestern states is velvetleaf (A butilon
theophrasti Medic.) (Bello et al. 1995; Stubbendieck 1995). Lindquist et al. (1996)

reported corn yield losses of 15-20% in Michigan with velvetleaf at a density of 10

plants per m. Giant foxtail (Setariafaberi Hemn.) and other foxtail spp. were
considered by F ausey et al. (1997) to be some of the most problematic and widespread
annual grass weeds in Midwestern row crop production. In Michigan, 10 giant foxtail
plants per m of row reduced corn yields by 14% through season-long competition

(Fausey et al. 1997).

Glyphosate [N-(phosphonomethyl)glycine] is a non-selective herbicide that was
initially used to control vegetation in non-cropland areas (Carlson and Burnside 1984;
Wilson et al. 1985). Corn hybrids resistant to the herbicide glyphosate have been used
as an alternative option for post-emergence weed control programs since 1998 (Duke
2005). The adoption rate of glyphosate-resistant corn, although lower than that of
glyphosate-resistant soybean, has increased over the last several years (Dill 2005). In
the US, glyphosate was applied to 31 % of planted corn acres in 2005, a 12 % increase
in glyphosate usage from 2003 (USDA-NASS 2004, 2006). Furthermore, glyphosate-
resistance is often stacked with other resistance traits. Previous research on glyphosate-
resistant crops dealt with the effectiveness of weed control (Tharp and Kells 2002;
Zuver et al. 2006) and application timing (Dalley et al. 2004; Gower et al. 2003) as

opposed to the integration with other pest control programs.

Many studies have looked at either insect resistance or herbicide resistance
traits. To date, a single study conducted in cotton (Gossypium hirsutum L.) documented
the stability of cotton yield among conventional and Bt/glyphosate-resistant cultivars
(Blanche et al. 2006). No such study has been conducted on corn hybrids containing
multiple-resistance traits. As with any new insect or weed management technology,

management programs must be evaluated as part of an integrated system. Thus, the

objective of our study was to determine the consistency of conventional herbicide and
insecticide programs and programs using transgenic corn for control of WCR and

annual weeds under a range of Michigan conditions.

MATERIALS AND METHODS

Experimental Description. Field experiments were conducted in 2004, 2005 and 2006,
at four locations each year. These were two separate sites on the Crop and Soil Sciences
Research Farm at Michigan State University (MSU) in East Lansing and two off-
campus sites on commercial farms within 50 km of the MSU campus (Table 1). Sites
were selected to reflect a range of weed density and WCR densities experienced by M1
producers. Experimental sites were chosen based on past history of pest infestation.
High WCR density sites had a history of damage in corn planted after corn. Low WCR
density sites were planted to corn in fields annually rotated between corn and soybean.

Near-isogenic corn hybridsl were used throughout the experiment to minimize
agronomic differences. In 2004, two corn hybrids were used: 1) ‘DKC46-28’ with
glyphosate resistance (R) and 2) ‘DKC46-24’ with resistance to corn rootworm in
addition to RR (WCR/RR). In 2005, a three-way stacked hybrid with resistance to
European corn borer (Ostrinia nubilalis Hiibner) (ECB), WCR, R was approved for
commercial production in the US. Thus, in 2005 and 2006, we used isogenic hybrid
lines with RR/ECB (‘DKC47-10’) and WCR/RR/ECB (‘DKC46-24’) to minimize
experimental error attributable to ECB. Corn hybrids with the rootworm resistance traits
(‘DKC46-24’ and ‘DKC46-22’) were available commercially only with a seed

treatment of clothianidin2 at a low dose (0.25 mg a.i./kemel) (LST) to control soil

insects at planting. ‘DKC46-28’ and ‘DKC47-10’ were commercially available
untreated or with a low or high (1.25 mg a.i./kemel) (HST) dose of clothianidin.

All corn hybrids were planted in rows 0.76 m apart at a seeding rate of 74,000
seed/ha. Plots were four rows wide by 10.7 m long. The experimental design was a
randomized complete block with four replications and 22 treatments (Table 2).
Treatments consisted of combinations of conventional insecticide and herbicide
programs and Bt-corn/glyphosate-based weed and WCR management programs.
Appropriate controls were included in the design of the experiment and consisted of
combinations of weed (no weed control; weed free) and WCR (untreated; low dose of
clothianidin [0.25 mg a.i/kemel]; Bt-hybrid expressing Cry3Bb1) control programs. The
control program with the low dose of clothianidin seed treatment was included because
the Bt-hybrid was commercially only available with a low dose of the clothianidin seed

treatment.

Weed Control and Evaluations. A weed control program based on glyphosate
resistant corn using postemergence (POST) applications of glyphosate3 and a
conventional weed control program using selected herbicides to control weed species
present were used throughout the study. Glyphosate-based weed management programs
included (1) a preemergence (PRE) herbicide application of atrazine (0.91 kg ai/ha) plus
S-metolachlor4 (0.71 kg ai/ha) followed by a POST herbicide application of glyphosate
(0.87 kg/ha), and (2) two separate POST herbicide applications of glyphosate (0.87
kg/ha each). All glyphosate applications included 2% (w/w) ammonium sulfate.
Conventional weed management programs included (1) a PRE herbicide application of

mesotrione (0.19 kg ai/ha) plus S-metolachlor (1.88 kg ai/ha) plus atrazineS (0.70 kg

ai/ha), and (2) a PRE herbicide application of S-metolachlor6 (1.39 kg ai/ha) followed
by a POST herbicide application (determined by scouting for weed species and density).
Herbicide treatments were applied with a tractor mounted, compressed-air sprayer
calibrated to deliver 187 L/ha at 207 kPa through 8003 flat fan nozzles7. Predominant
annual broadleaf and grass weed species were counted by species prior to the first
POST herbicide application (except for plots treated with PRE herbicides). At
physiological maturity, all weed species in two permanent quadrats (0.76 x 1 m) placed
within the center two rows of each plot were counted. The above-ground parts of these

weeds were harvested, dried for 5 days at 60 C, and weighed.

Corn Rootworm Control and Evaluations. WCR control programs included (1) a
hybrid expressing Cry3Bb1 Br, (2) the conventional soil-applied granular insecticide
(SAI) tefluthrin8 applied in-furrow at a rate of 6.16 kg/ha, (3) a combination of the
conventional SAI tefluthrin applied in-furrow at a rate of 6.16 kg/ha + a commercially
applied seed treatment of clothianidin at a low rate (0.25 mg a.i./kemel) (LST), and (4)
a commercially applied seed treatment of clothianidin at a high rate (1.25 mg
a.i./kernel) (HST).

Larval injury was evaluated by digging three root masses from each treatment in
late-July/early-August of each year. All roots were taken from the outer two rows of
each plot (i.e. non-yield rows). Root masses were soaked then cleaned with a power
washer. Injury was visually assessed using the Iowa State University Node-Injury Scale
(Oleson et al. 2005; Nowatzki et al. 2002), described as 0.0 = no feeding damage; 1.0 =
one node or the equivalent of an entire node, eaten back to within approximately 5 cm

of the stalk; 2.0 = two nodes eaten; and 3.0 = three or more nodes eaten. Additionally, a

score of 0.01 stood for only light scarring/ or channeling (shallow grooves on the
outside of a root), score of 0.10 represented one pruned root, and two to three pruned

roots represented a node-injury score of 0.25.

Corn stand and yield. Stand counts were taken in the middle two rows of each plot
after crop emergence to ensure uniformity of corn density across a trial. The middle two
rows of each plot were harvested with a plot combine at maturity. Corn grain yields

were adjusted to 15.5% moisture.

Data Analysis

Weed Control. To illustrate the level and consistency of weed control, weed densities
and weed biomass data are presented using boxplot figures. Boxplots are an indicator
of consistency (Ott and Longnecker 2001). In each boxplot, the box represents 50 % of
the observations and the line outside the boxes represents 90 % of the observations.
Shorter boxes and lines indicate greater consistency among observations. The thicker-
horizontal black bar across each boxplot indicates the mean of the observations and the
thinner-horizontal back bar indicates the median of the observations.

Root damage. Levels of damage were different across years at all sites (p < 0.0001 for
all sites) and sites by years are described separately. Root data were log transformed for
statistical analysis and back-transformed for data presentation. Data were analyzed by
year using the PROC MIXED function in SAS (SAS Institute 2007) and the differences
in treatments were separated by comparing the differences of Least Square Means (a =

0.05).

10

Corn Yield. By eliminating the controls, the remaining treatments formed a factorial
design. Corn yield potential varied by site and was analyzed separately by location and
by year. There were no interactions among herbicide and insecticide treatments on corn
yield at any of the sites. However, both factors were themselves key in affecting corn
yields as they related to pest density levels. Corn yield data were subjected to analysis
of variance using PROC GLM function in SAS (SAS Institute 2007). Weed and WCR

treatments means were separated using Fisher’s Protected LSD test (d = 0.05).

RESULTS AND DISCUSSION
Weed Control. As expected, weed densities at the MSU2 and Mason/Eaton Rapids
sites were high, ranging from 138 to 819 weeds per m2 prior to POST herbicide
application (Table 3). The field locations at MSU] and Westphalia were selected prior
to planting to have low weed densites. As expected, weed density was low at these
locations, ranging from 4 to 24 weeds per m2 prior to POST herbicide application
(Table 3). The dominant weeds present at the high weed density sites were annual
grasses which consisted mostly of giant foxtail and common lambsquarters. Only at
MSU2 was common ragweed (Ambrosia artemisiifolia L.) present in high numbers. The
MSU2 trial was located in the same field site in 2004 and 2006 and in an adjacent field
in 2005. MSU 1, Westphalia, and Mason/Eaton Rapids trials were located in different
fields every year.
Low weed density locations. At MSUl, at the end of the growing season, plots receiving
conventional herbicides had lower weed densities than the plots receiving glyphosate

(Figure l). The higher weed densities in the plots receiving glyphosate did not result

11

into higher weed biomass (Figure 2), indicating that most weeds present were small. At
Westphalia, mean weed density values were similar for all plots with herbicide
applications (Figure 1). At Westphalia, the highest and most variable weed biomass
mean value was for weeds collected in the conventional PRE herbicide program plots
(Figure 2). At both sites, the use of herbicides decreased the total number of weeds and
weed biomass relative to no weed control (Figures 1 and 2).

High weed density locations. At MSU2, the conventional PRE fb. POST herbicide
application program resulted in the lowest weed density plots, while the remaining
programs resulted in higher, more variable densities (Figure 1). There were no distinct
trends in weed densities when comparing the glyphosate-based versus conventional
weed control programs plots and single-pass versus sequential herbicide programs plots
at MSU2. At Mason/Eaton Rapids, plots receiving either the PRE fb. POST herbicide
applications in the conventional and glyphosate-based weed control programs had the
least variable and lowest weed densities. The conventional PRE herbicide program
resulted in the highest and most variable weed density mean (Figure 1). At both sites,
all herbicide programs decreased the total number of weeds relative to no weed control
(Figure 1).

High weed densities did not translate into high weed biomass (Figure 2),
indicating that most weeds present were small. At both MSU2 and Mason/Eaton Rapids
sites, the conventional PRE herbicide application resulted in the greatest and most
variable weed biomass (Figure 2). PRE herbicide applications allow for critical early
season weed control. The residual activity of these products is highly dependent on

moisture afier application to activate the herbicide and to provide adequate, season-long

12

weed control (Rabaey and Harvey 1997; Spandl et al. 1997). Tharp and Kells (2002)
recommended the use of residual herbicide combinations with POST herbicide

applications to increase season-long weed control.

Corn Rootworm Control. The field locations at Westphalia and Mason/Eaton Rapids
were selected prior to planting for high WCR densities. Unlike weed density, WCR
density was more difficult to predict from year to year. Based on root damage and
number of WCR adults at the research sites, WCR density was high at Westphalia in
2005 and 2006 and at Mason/Eaton Rapids in 2006. However, the WCR density ranged
from low at Westphalia in 2004 and Mason/Eaton Rapids in 2005 to moderate at
Mason/Eaton Rapids in 2004. The field locations at MSUl and were selected prior to
planting to have low WCR density. WCR density was low in most years but increased
to moderate levels at MSU2 in 2006.

Low WCR density locations. At MSU], root damage was low in all three years of the
study (Figure 3). At MSU2, overall root damage was low (0.01) in 2004 and 2005
(Figure 3). A score of 0.01 indicates very light scarring and denotes that the root system
is not perfect (i.e. score = 0). Despite differences in treatment mean values at both sites,
the low amount of damage was expected in a com-soybean rotation. These differences
are not considered to be important due to the overall low amount of damage observed.
In 2006 at MSU2, injury level in the untreated control was slightly higher (0.3) than in
previous years (Figure 3). A score of 0.3 indicates three pruned roots on the root mass.
Oleson et al. (2005) noted that root damage above 0.1 constitutes major root damage.
This is an indication that the WCR variant, resistant to a com-soybean rotation, is

present on the MSU campus. In this trial, all corn rootworm control programs protected

13

corn roots with the Bt-hybrid, the SAI, and the SAI + LST providing the best protection
(Figure 3).

High WCR density locations. At Westphalia, in 2004, heavy rainfall flooded the plot
area and delayed planting until early June (Table l). The previous season, the producer
reported heavy WCR damage in the field. However, the plots in 2004 had low damage,
even in the untreated control (Figure 3). Hoffman et al. (2000) noted that delaying corn
planting was an effective cultural control method against WCR root feeding. The co-
occurrence of a very susceptible corn growth phase and a peak rootworm larval
population is prevented by delaying corn planting (Carlson and Gauge 1989). At the
same site in 2005 and 2006 there was considerable larval feeding (1.00 to 1.25) on corn
roots that had no protection. A score of 1.00 indicates that one entire root node has been
pruned off of the root mass. Under high WCR conditions, both the Bt-hybrid and the
conventional insecticide treatments protected corn roots fiom feeding, with the Bt-
hybrid having the least amount of damage on roots (Figure 3).

At Mason/Eaton Rapids, we anticipated high WCR densities based on prior
com-com rotation, but observed low overall root damage in 2004 and 2005 (Figure 3).
In 2004, delayed planting is the likely cause of low root damage (Hoffman et al. 2000).
The field site only had two years of corn prior to the establishment of the trial which
may not have been sufficient for the buildup of WCR larval densities capable of
producing a significant amount of damage to corn roots. Considerably higher root
damage was observed in 2006, and results were similar to those at Westphalia. In 2006,
all WCR treatments protected corn roots with the Bt-hybrid having the lowest amount

of damage (Figure 3). At both of these sites, in those years where WCR densities were

14

high, there were no differences in the amount of feeding between the LST and no
insecticide controls (Figure 3). This indicates that under high corn rootworm levels the
LST rate would not be sufficient to protect corn roots from damage. This is similar to
Steffey et al. (2005) who described that the performance of seed applied insecticide
treatments to be inconsistent under conditions of high WCR density and that these

products do not perform as well in protecting corn roots from injury as most SAI.

Corn Yield.

Low weed density locations. At MSU 1 , there were no differences in corn yield among
herbicide treatments in 2004 and 2005 (Table 5). In 2006, the corn yield obtained was
highest with the glyphosate-based PRE fb. POST and lowest with the conventional PRE
herbicide programs (Table 5). The corn yield with the conventional PRE herbicide
program did not differ from the glyphosate-based POST fb. POST or conventional PRE
fb. POST herbicide programs. At Westphalia, there were no differences in corn yield
among herbicide programs in 2005 and 2006 (Table 5). In 2004, the conventional PRE
herbicide program resulted in the highest corn yield and the conventional PRE fb. POST
herbicide program the lowest (Table 5). In most years, a single PRE herbicide
application may be sufficient to control weeds under low weed density. However, lack
of rainfall after PRE herbicide application may result in inadequate herbicide
incorporation and incomplete weed control. Similarly, a lack of weed control may occur
in the case of excess precipitation. The herbicide is activated but may be leached
beyond the weed seed germination zone (Walker and Roberts 1975). In both instances,

a POST herbicide application may be necessary to adequately control weeds. Under low

15

weed density, the glyphosate-based PRE fb. POST and POST fb. POST herbicide
programs resulted in corn yields not significantly different from the highest in six of six
environments (Table 5). Corn yields obtained with the conventional PRE and PRE fb.
POST herbicide programs were not different than the highest corn yields in five of six
environments (Table 5).

High weed density locations. At MSU2 there were differences in corn yield among
herbicide treatments in 2004 and 2005, but there were no consistent trends across years
(Table 5). In 2004, the glyphosate-based PRE fb. POST herbicide program resulted in
the highest corn yield (Table 5). There were no differences among herbicide programs
for corn yield at MSU2 in 2006 (Table 5). In 2004 and 2005 at Mason/Eaton Rapids,
there were no differences in corn yields among treatments. In 2006, the lowest corn
yields were obtained with the conventional PRE herbicide program. Corn receiving the
glyphosate-based PRE fb. POST herbicide program had yields similar to the highest
yields obtained in six of six environments. The conventional PRE fb. POST herbicide
program resulted in corn yields similar to the highest in five of six environments. Corn
receiving the glyphosate-based POST fb. POST herbicide program had yields equal to
the highest in four of six environments while corn that received the conventional PRE
herbicide program had yields similar to the highest in only three of six environments
(Table 5). The PRE fb. POST herbicide programs, regardless of whether the treatment
was glyphosate-based or conventional, most consistently resulted in high corn yields.
Low WCR density locations. In 2004, there were no differences in corn yield among
WCR control programs at both the MSU] and MSU2 locations (Table 6). These results

indicate what would be anticipated under low WCR density. In 2005, the corn variety

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receiving the high dose of clothianidin seed treatment had the lowest corn yields at all
locations (Table 6). This treatment, resulted in a significant reduction in corn population
at all locations in 2005 (Table 7). The lower corn yields were attributable to this
reduced population, which is likely related to the seed treatment process. In 2006, the Bt
corn hybrid had the highest and the SAI had the lowest corn yields at both low WCR
density locations (Table 6).

We saw an increase in overall damage to corn roots (Figure 1) and an increasing
effect of WCR on corn yield at MSU2 over the course of this three-year study (Table 6).
The MSU2 location was planted to corn after soybean to minimize WCR damage. This
increased level of feeding, as well as the increased density of WCR adults observed in
soybean on campus, indicates the presence of the WCR variant in central MI. In
summary, at the low WCR density sites, the Bt-hybrid had corn yields not different
from the highest in six of six environments. From both the conventional SA] and SA] +
LST programs corn yields were observed to be similar to the highest yielding treatments
in four of six environments. Corn receiving the HST treatment yields similar to the
highest in three of six environments. The variable corn yields with the HST was due to
the loss in corn population in 2005 (Table 7).
High WCR density locations. In 2004, there were no differences in corn yield observed
among WCR control programs at either the Westphalia or Mason/Eaton Rapids
locations, which is not the expected results at a high WCR density site. Both sites were
anticipated to have a high density of WCR, however neither did. Rainfall three times
above the monthly average (Table 4) in the Mid-Michigan area may have played a role

in the lack of WCR injury observed at Westphalia. Excess precipitation could have

17

compromised our anticipated high WCR density levels at Westphalia via larval
drowning during the 2004 growing season. Planting at both high WCR density sites was
delayed in 2004 (Table 1) and, as noted previously, delaying planting allows for the
avoidance of peak larval populations with the corn crop (Hoffman et al. 2000). In 2006,
there were no differences in corn yields observed among the various WCR control
programs at Mason/Eaton Rapids (Table 6). However, at Westphalia in 2006, there
were differences among treatments with the Bt-hybrid having the highest corn yield
(Table 6). There was no reduction in corn population associated with the HST at
Westphalia in 2006, however this treatment still resulted in corn yields lower than all
other control programs (Table 6). In summary, at the high WCR sites, the Bt-hybrid
had corn yields similar to the highest in six of six environments. The corn receiving
SAI, SAI + LST, and HST had yields similar to the highest corn yields in four, five, and
three environments, respectively. Overall, the Bt-hybrid was the most effective and
consistent system at protecting corn yield under high WCR density levels.

The presence of weeds had a considerable effect on corn yields at all locations,
including all low weed density sites (Table 8). At the low weed density sites, corn yield
losses associated with weeds ranged from 30 to 77 % and 22 to 48 % at MSUl and
Westphalia, respectively (Table 8). The effect of weeds on corn yield at MSU2 was 76
%, 89 %, and 95 % in 2004, 2005 and 2006, respectively (Table 8). The effect of weeds
on corn yield at Mason/Eaton Rapids was 36 %, 42 %, and 77 % in 2004, 2005, and
2006, respectively (Table 8). Corn yields were greatly increased with any weed control

program compared with uncontrolled weeds (Tables 5 and 8).

l8

WCR reduced corn yield less than 6% in five of six environments at the low
WCR density locations. In 2006 at MSU2, corn yield loss associated with WCR was 12
%, a noted increase from past years. At Westphalia, corn yield losses attributable to
WCR were 31% to 38% in 2005 and 2006, respectively. The Bt-hybrid had the greatest
corn yields at Westphalia in 2005 and 2006, however the conventional WCR control
programs still provided greater corn yields than no insect control (Table 6 and 8).
Overall corn yield loss associated with WCR at Mason/Eaton Rapids was low in 2004
and 2005 but reached nearly 23 % in 2006. At these anticipated high WCR density
locations, control of WCR significantly increased corn yields in three of six
environments. If the expected larval densities had not been compromised in 2004, WCR
control at these high WCR density locations may have increased corn yields at these
two locations as well. When compared to weed control, the effect of WCR on corn yield
was more variable in that WCR control did not increase corn yield at each site and each
year.

These results indicate that excellent weed control can be obtained in corn with
either glyphosate-based or with conventional herbicide programs. Control of annual
weeds is essential in preserving corn yields, even in low weed density sites. Regardless
of weed density, weed control was necessary at all sites in all years to avoid significant
corn yield loss from weeds. WCR control increased corn yields in one of six
environments at the low and three of six environments at the high WCR density
locations. The results from this field research indicate that the presence and larval
density of WCR should be an important factor for Michigan growers to consider

regarding the decision to adopt these stacked transgenic corn hybrids. However, the

19

main consideration for the adoption of these new pest management technologies will
likely be the cost of control and the economic return associated with the control of

weeds and WCR.

20

Source of Materials
' Dekalb Genetics Corp., Monsanto Company, St. Louis, MO 63167
2 Poncho 600, Bayer CropScience, Research Triangle Park, NC 27709
3 Roundup WeatherMax, Monsanto Company, St. Louis, MO 63167
4 Bicep 11 Magnum, Syngenta Crop Protection, Inc. Greensboro, NC 27409
5 Lumax, Syngenta Crop Protection, Inc. Greensboro, NC 27409
6 Dual 11 Magnum, Syngenta Crop Protection, Inc. Greensboro, NC 27409
7 TeeJet Spraying Systems Co., Wheaton, IL 60188
8 Force 3G, Syngenta Crop Protection, Inc. Greensboro, NC 27409

9 SAS Institute Inc., Cary, NC 27513

21

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24

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herbicide program. Each herbicide treatment n=96 and no weed control n=72.

Anticipated weed density based on field site history.

34

 

 

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37

CHAPTER II
Farm-Level Profitability of Transgenic Corn (Zea mays L.)
Resistant to Both Glyphosate and Western Corn Rootworm

(Diabrotica virgifera virgifera LeConte) in Michigan

38

ABSTRACT

The introduction of new transgenic traits offers com (Zea mays L.) producers
new options for weed and insect control. Many studies have investigated whether or
not common resistance traits are economically justified. However, there are no
records showing research results on the economic value of stacked or multiple
resistance traits. The objective of this study was to determine the profitability of
stacked trait corn hybrids by measuring the corn yield loss incurred from annual
weeds and western corn rootworm (Diabrotica virgifera virgifera LeConte) (WCR) in
comparison with conventional herbicide programs under varying corn rootworm and
weed densities. Weed control costs were economically justified under both low and
high weed densities. Gross margin gains relative to no weed control were reported for
all weed control programs at all locations all years. Gross margin gains for the
conventional herbicide programs were similar to the weed control programs based on
the herbicide glyphosate. The presence and intensity of WCR larvae feeding on corn
roots varied by year, and was less predictable than weed density. The overall gross
margin of the no WCR control at the low WCR sites was often higher than the gross
margins of the WCR control programs. This indicated that, unlike weed control, the
cost associated with the control of WCR in many instances was not justified. At the
high WCR Sites, the cost of WCR control via either Bt-hybrid or conventional
insecticide programs was justified in two of six site environments. In those two
environments, the Bt-hybrid consistently had the highest gross margin gains relative
to no WCR control. Gross margins were affected by com yield more than by

treatment costs. Gross margins were also greatly affected by commodity prices.

39

Planting corn hybrids that contain resistance traits for either glyphosate or corn
rootworm does not necessarily mean greater profits. Growers should focus on yield

potential by choosing high yielding corn hybrids adapted to local growing conditions.

Nomenclature: atrazine; glyphosate; mesotrione; s-metolachlor; clothianidin;
tefluthrin; European corn borer, Ostrinia nubilalis Hiibner; western corn rootworm,
Diabrotica virgifera virgifera LeConte; corn, Zea mays L. ‘DKC46-24’, ‘DKC46-

28’, ‘DKC46-22’, ‘DKC47-lO’.

Key Words: insect resistance, herbicide resistance, multiple resistance traits,

transgenic, western corn rootworm, corn, profitability, gross margins.

Abbreviations: PRE, preemergence; POST, postemergence; fb., followed by; R,
glyphosate resistant; WCR, corn rootworm; ECB, European corn borer; Bt, Bacillus
thuringiensis; HST, high seed treatment; LST, low seed treatment; SAI, soil-applied

insecticide.

4o

INTRODUCTION

Glyphosate-resistant (RR) corn (Zea mays L.) hybrids became commercially
available in the USA in 1998 (Duke 2005). Corn hybrids expressing an insecticidal
protein derived from the soil bacterium Bacillus thuringiensis spp. (BI) were
commercially introduced in the USA in 1996 to control the European corn borer
(Ostrinia nubilalis Hiibner) (ECB) (Ostlie et al. 1997). Corn hybrids expressing new
insecticidal toxins to control corn rootworm (WCR) (Diabrotica spp.), were
introduced in the United States in 2003 (Crowder et al. 2005). During the 2004
growing season, corn hybrids containing all three of the traits described above were
commercialized. In the industry, the insertion of more than one resistance trait in a
plant is commonly referred to as gene stacking. The development of stacked
transgenic corn hybrids gives producers new options for controlling weeds and
insects, but complicates hybrid selection.

Several economic studies have been published on weed control in glyphosate-
resistant crops, including soybean (Johnson et al. 1997; Reddy 2003; Reddy and
Whiting 2000; Webster et al. 1999), corn (Ferrell and Witt 2002; Hellwig et al. 2003;
Johnson et al. 2000; Nolte and Young 2002), cotton (Askew and Wilcut 1999; Bailey
et al. 2003; Culpepper and York 1999), sugarbeet (Kniss et al. 2004), and potato
(Hutchinson et al. 2003). The com studies concluded that net returns were Similar for
the glyphosate-based and conventional herbicide programs. Few researchers have
documented the costs and returns associated with Bt-WCR hybrids (Crowder et al.
2005, 2006). Results indicated that where WCR rotation-resistant phenotypes exist,

planting a Bt corn hybrid was the most economical strategy compared to conventional

41

insecticides (Crowder et al. 2006). To date, as noted in Chapter 1, no such study has
been conducted on corn hybrids containing multiple-resistance traits.

As with any new insect or weed management tactic, programs must be
evaluated for both pest efficacy and economic return. The adoption of new practices
is very dependent on economic considerations (Gianessi 2005). Growers choosing to
use transgenic crops face additional seed costs associated with technology fees. In a
survey conducted by Wilson et al. (2005), the technology fees associated with
transgenic crops were one of the top concerns that growers had when using
genetically modified corn.

Therefore, the objective of this study was to determine the profitability of
stacked trait corn hybrids by assessing the value of corn yield, inputs costs, and
refuge requirements and by measuring the corn yield loss incurred from weeds and
WCR in comparison with conventional pest management programs under varying

WCR and weed densities.

MATERIALS AND METHODS
Experimental Description. Field experiments were conducted in 2004, 2005 and
2006 at four locations each year as described in Chapter 1. There were two separate
sites on the Crop and Soil Sciences Research Farm at Michigan State University
(MSU) in East Lansing and two off-campus Sites on commercial farms within 50 km
of the MSU campus (Table 1). Sites were selected to reflect a range of weed density
and WCR pressures experienced by M1 producers. Experimental sites were chosen

based on past history of pest infestation. High WCR density sites had a history of

42

damage in corn planted afier corn. Low WCR density sites were planted to corn in
fields annually rotated between corn and soybean.

Near-isogenic corn hybrids1 were used throughout the experiment to minimize
agronomic differences. In 2004, two corn hybrids were used: 1) ‘DKC46-28’ with
glyphosate resistance (R) and 2) ‘DKC46-24’ with resistance to corn rootworm in
addition to RR (WCR/RR). In 2005, a three-way stacked hybrid with resistance to
ECB, WCR, R was approved for commercial production in the US. Thus, in 2005
and 2006, we used isogenic hybrid lines with RR/ECB (‘DKC47-10’) and
WCR/RR/ECB (‘DKC46-24’) to minimize experimental error attributable to ECB.
Corn hybrids with the rootworm resistance traits (‘DKC46-24’ and ‘DKC46-22’)
were available commercially only with a seed treatment of clothianidin2 at a low dose
(0.25 mg a.i./kemel) (LST) to control soil insects at planting. ‘DKC46-28’ and
‘DKC47-10’ were commercially available untreated or a low or high (1.25 mg
a.i./kernel) (HST) dose of clothianidin.

All corn hybrids were planted in rows 0.76 m apart at a seeding rate of
74,000 seed/ha. Plots were four rows wide by 10.7 m long. The experimental design
was a randomized complete block with four replications and 22 treatments (Table 2).
The middle two rows of each plot were harvested with a plot combine at maturity.
Corn grain yields were adjusted to 15.5% moisture. Treatments consisted of
combinations of conventional insecticide and herbicide programs and Bt-
corn/glyphosate-based weed and WCR management programs. Appropriate controls
were included in the design of the experiment and consisted of combinations of weed

(no weed control; weed free) and WCR (untreated; low dose of clothianidin (0.25 mg

43

a.i/kernel; Bt-hybrid expressing Cry3Bb1) control programs. The control program
with the low dose of clothianidin seed treatment was included because the Bt-hybrid
was commercially only available with a low dose of the clothianidin seed treatment.

A weed control program based on glyphosate resistant corn using
postemergence (POST) applications of glyphosate3 and a conventional weed control
program using selected herbicides to control weed Species present were used
throughout the study. Glyphosate-based weed management programs included (1) a
preemergence (PRE) herbicide application of atrazine (0.91 kg ai/ha) plus 8-
metolachlor4 (0.71 kg ai/ha) followed by a POST herbicide application of glyphosate
(0.87 kg/ha), and (2) two separate POST herbicide applications of glyphosate (0.87
kg/ha each). All glyphosate applications included 2% (w/w) ammonium sulfate.
Conventional management programs included (I) a PRE herbicide application of
mesotrione (0.19 kg ai/ha) plus S-metolachlor (1.88 kg tha) plus atrazine5 (0.70 kg
ai/ha), and (2) a PRE herbicide application of S-metolachlor6 (1.39 kg ai/ha) followed
by a POST herbicide application (determined by scouting for weed species and
density). Herbicide treatments were applied with a tractor mounted, compressed-air
sprayer calibrated to deliver 187 L/ha at 207 kPa through 8003 flat fan nozzles7.

WCR control programs included (1) a hybrid expressing Cry3Bb1 Bt, (2) the
conventional soil-applied granular insecticide (SAI) tefluthrin8 applied in-furrow at a
rate of 6.16 kg/ha, (3) a combination of the conventional SAI tefluthrin applied in-
fiirrow at a rate of 6.16 kg/ha + a commercially applied seed treatment of clothianidin
at a low rate (0.25 mg a.i.lkemel) (LST), and (4) a commercially applied seed

treatment of clothianidin at a high rate (1.25 mg a.i./keme1) (HST). The treatment

44

combining the SAI + LST was included because the Bt-hybrid was commercially only

available with a LST.

Profitability Analysis. The profitability analysis was based on gross margins over
weed and insect control costs. Total control costs included herbicide treatment,
insecticide treatment, application, and seed costs/technology fees. All other
production costs were assumed to be fixed across treatments. Gross margins over
total control costs were calculated by multiplying corn yield by com price and
subtracting total control costs.

Full suggested retail price for seed and pesticides (no discounts or promotional
pricing) were used. Average pesticide prices for June 2006 were obtained from two
major distributors within the state (Anonymous, 2006a). The technology fees were
included in seed costs (Table 3). A technology fee of $37.04/ha (equivalent to $1 S/A)
was subtracted from the treatments where no glyphosate was applied. Application
cost of $14.82/ha (equivalent to $6/A) was determined by communicating with
custom applicators throughout the state (Anonymous, 2006b). Application value was
substantiated by referring to published custom machine work rates in Michigan (Dartt
and Schwab 2002). The average rate for custom chemical application in Dartt and
Schwab (2002) was $15.19/ha (equivalent to $6.15/A) and ranged from $9.88/ha to
$41.98/ha (equivalent to $4/A to $17/A). All costs are summarized in Table 3. Gross
margins were not calculated for weed free treatments due to the difficulty in assessing

the value of hand-weeding.

45

Analysis per site per year. Historical corn prices from 1980-2005 were
obtained fiom the National Agricultural Statistics Service (NASS). These historical
values were discounted to adjust for inflation and the average of $ 0.10/kg (equivalent
to $2.60/bushel) used for the gross margin analysis. Gross margins over weed and
insect control costs for each site were statistically analyzed by year using ANOVA,
and means were compared using Fisher’s protected LSD (a = 0.05) in SAS (SAS
Institute 2007).

Sensitivity analysis by weed and WCR environment. The sensitivity analyses
were conducted for corn prices of $60/Mg (equivalent to $1 .SO/bu), $100/Mg
(equivalent to $2.50/bu), $140/Mg (equivalent to $3.50/bu), and $180/Mg (equivalent
to $4.50/bu). The sensitivity analysis for the weed environments consisted of
grouping the experimental Sites by low or high weed density characteristics. The
gross margin gains of the glyphosate-based weed control programs were evaluated
relative to no weed control at the various price assumptions. The gross margin gains
from the glyphosate-based and conventional weed control programs relative to no
weed control were evaluated at a corn selling price of $100/Mg. This value was
selected as it was the nearest to the historical discounted price. The sensitivity
analysis for the WCR environments consisted of grouping the experimental Sites by
low or high WCR density characteristics. The gross margin gains of the Bt-corn
hybrid were evaluated relative to no WCR control at the various price assumptions.
The gross margin gains of the Bt-corn hybrid were evaluated relative to no WCR
control for refuge requirements of 0%, 10%, and 20% at a corn selling price of

$lOO/Mg. The gross margin gains from the Bt-corn hybrid and conventional WCR

46

control programs relative to no WCR control were evaluated at a com selling price of
$100/Mg. Data were analyzed using the proc means statement in SAS (SAS Institute

2007) and gross margin gain means are presented with +/- 1 standard deviation.

RESULTS AND DISCUSSION
The gross margins for weed and WCR control treatments are presented in
Figures 1 and 2. The values in these figures were calculated relative to the gross
margins obtained when either no weed or no WCR control programs were utilized
(Table 4). The greatest factor affecting gross margins was com yield (r2 = 0.98, data

not shown) rather than treatment costs.

Gross margins affected by weed control. Gross margins increased for all weed
control programs at all locations for the duration of the study (Figure 1). The use and
cost of herbicides was economically justified (gain greater than 0) for all locations all
years.

At MSU], a low weed density site, there were no differences in gross margins
among weed control programs in 2004, 2005, and 2006. Higher gross margins were
noted in 2005 at MSU] relative to 2004 and 2006 (Figure 1). This was due to the
greater effect of uncontrolled weeds on corn yield (76.9%) in 2005, relative to 2004
and 2006 where the effect of weeds on corn yield was 30.2% and 38.1%, respectively
(data not Shown). This was also reflected in the lower gross margin value obtained for
the no weed control treatment in 2005 (Table 4). At Westphalia, there were no
differences in gross margins among weed control programs in 2005 and 2006 (Figure

1). In 2004, the plots receiving the conventional PRE herbicide program had

47

significantly higher gross margins gains than the plots receiving the conventional
PRE fb. POST herbicide program. The higher gross margin gains in the conventional
PRE herbicide program may be attributable to it being the only program that did not
include the costs associated with a second herbicide application. Overall, at the low
weed density sites, the glyphosate-based PRE fb. POST, POST fb. POST, and the
conventional PRE herbicide programs resulted in gross margins not significantly
different fiom the highest gross margins in six of six environments. The conventional
PRE fl). POST herbicide program had gross margins that were similar to the highest
gross margins in five of six environments.

The highest gross margin gains relative to no weed control were observed at
MSU2 (Figure 1). This is the site where the impact of uncontrolled weeds on corn
yields was the highest at 76%, 89%, and 95% in 2004, 2005, and 2006, respectively
(data not Shown). This is also reflected in the low and sometimes negative gross
margin of the no weed control treatments (Table 4). In 2004, the glyphosate-based
PRE fb. POST herbicide program and conventional PRE herbicide program had the
highest gross margins, followed by the conventional PRE fb. POST herbicide
program, and the glyphosate-based POST fb. POST herbicide program. However,
these differences were not consistent across years (Figure 1). In 2005, the only
treatment that had gross margins significantly lower than the highest gross margins
was the conventional PRE fl). POST herbicide program (Figure 1). At MSU2 in 2006,
there were no differences in gross margins among any of the weed control programs.
At Mason/Eaton Rapids in 2004, the conventional PRE herbicide program had the

highest gross margin and the glyphosate-based POST fl). POST herbicide program

48

resulted in the lowest gross margin gains. In 2005, there were no differences in gross
margins among weed control programs. In 2006, the conventional PRE herbicide
program had gross margins significantly lower than the other weed control programs,
which is what was anticipated for these high weed density sites. As described above,
there were inconsistencies in the gross margins of the conventional PRE herbicide
program from year to year. Preemergence soil applied herbicides allow for critical
early season weed control (Gonzini et al. 1999) but often the residual activity of these
products is not sufficient to provide adequate, season-long weed control, which has
the potential of jeopardizing corn yield (Rabaey and Harvey 1997; Spandl et al. 1997)
and inherent profitability. Soil-applied herbicides are highly dependent on rainfall
shortly after application in order to activate the herbicide (Walker and Roberts 1975).
Too little rainfall and the herbicides are not sufficiently activated and too much
rainfall causes the herbicide to leach past the critical weed seed germination zone. In
summary, at the high weed density sites, the glyphosate-based PRE fb. POST
herbicide program was the only weed control program to have gross margins similar
to the highest gross margins in all six of Six site environments. The conventional PRE
fb. POST herbicide program had gross margins that were similar to the highest gross
margins in five of six environments. The conventional PRE herbicide program had
high gross margins in five of Six environments.

Generic glyphosate products are widely available in the marketplace. An
analysis was conducted for weed control programs where the glyphosate-based
programs included glyphosate costs at either $2.64/L or $5.28/L (equivalent to

$10/gal and $20/gal, respectively). The use of generic glyphosate in lieu of more

49

expensive brand-name products did increase the GM of the glyphosate-based weed
control programs. The reduction in herbicide costs from using a generic glyphosate
product was not sufficient to create differences between the GM of the glyphosate-
based and conventional weed control programs (data not shown). Despite, there being
no differences between the GM of the glyphosate-based and conventional weed
control programs, growers would likely purchase the lower cost glyphosate product
assuming the efficacy of weed control was identical. For the PRE fb. POST (i.e. 1
application of glyphosate), the use of a generic glyphosate product would reduce
herbicide input costs by $8.12/ha and $12.52/ha for product prices of $5.28/L or
$2.64/L, respectively. For the glyphosate-based POST fb. POST herbicide program,
the use of a generic glyphosate product would reduce herbicide input costs by
$16.25/ha and $25.04/ha for product prices of $5.28/L or $2.64/L, respectively.
Furthermore, under low weed density environments, growers in Michigan often
employ a Single POST application of glyphosate to control weeds. This weed control
program would allow growers to further cut input costs by eliminating fees associated
with a second application of glyphosate.

The sensitivity analysis for both the PRE fb. POST and POST fb. POST
glyphosate-based weed control programs Showed similar results (Figures 3 and 4).
Gross margin gain means relative to no weed control were positive for all price
assumptions under both low and high weed environments. Also, as one would expect,
larger gains were noted with the higher corn prices. Similar gross margins gains were

achieved using the four weed control programs (Figure 5) and the additional cost of

50

weed control or technology fees were justified under both low and high weed

densities.

Gross margins affected by WCR control. The presence and intensity of WCR
larvae feeding on corn roots varied by Site and year and was less predictable than
weed density. The overall gross margins of the no WCR control treatments (Table 4)
at MSUI and MSU2, the rotated sites, were often higher than the gross margins of the
WCR control programs (Figure 2). This indicated that, unlike weed control, the cost
associated with the control of WCR in many instances was not justified. At MSU] in
2004 and 2005, all WCR control treatments incurred losses relative to no insect
control. These results were expected with the anticipated low WCR sites. There were
no difi'erences in gross margins from treatments in 2004 and 2005, with the exception
of the HST in 2005. In 2005, the HST resulted in the greatest losses relative to the
other treatments and the lowest gross margins of any treatment at all locations (Figure
2). This treatment resulted in a Significant stand reduction in corn population at all
locations in 2005. The lower gross margins observed with the HST may be a
reflection of lower yields due to the observed stand loss. The stand loss is likely
related to the seed treatment process. Even though MSU2 was a low WCR density
site, an increased effect of the insect on corn yield throughout the duration of the
study was observed (data not Shown). This increase in WCR density may explain why
use of the Bt-hybrid resulted in the largest gross margin gains relative to the
conventional WCR control programs in both 2005 and 2006 (Figure 2). In 2006,
losses were only incurred when the SA] was used. However, in 2004 and 2005 the

use of SAI resulted in gross margins that did not differ from the highest gross margins

51

(Figure 2). In summary, at the low WCR density sites, the Bt-hybrid resulted in gross
margin gains in three of six environments. However, the Bt-hybrid only had
significantly greater gross margins than the other control programs in one of six
environments. In most instances, the use of a WCR control program was not justified
as the gross margin with no control was often greater than the gross margins with the
WCR control programs.

Despite both Westphalia and Mason/Eaton Rapids being our anticipated high
WCR Sites, varying impacts of WCR on corn yields were observed, and consequently
on gross margins. In 2004 at Westphalia, there were no differences in gross margins
among WCR treatments (Figure 2). Furthermore, all WCR control methods recorded
losses relative to the no WCR control. This indicates that control of the insect was not
necessary at Westphalia in 2004. Spring rainfall three times above the monthly
average in the Mid-Michigan area may have played a role in the lack of WCR injury
at Westphalia. Excess precipitation could have possibly compromised the anticipated
high WCR density by drowning the larvae (MacDonald and Ellis 1990) at Westphalia
during the 2004 growing season. Planting was delayed at both Westphalia and
Mason/Eaton Rapids in 2004 (Table 1). Hoffrnann et al. (2000) found that delayed
planting dates may play a role in larval mortality due to the lack of com. This
circumvents a time period in which peak rootworm larval populations and the
younger, more susceptible, grth phase of corn typically coincide (Carlson and
Gauge 1989). However, there were clear economic advantages at Westphalia in 2005
and 2006 for utilizing any WCR control program (Figure 2). In both 2005 and 2006,

the highest gross margins relative to no WCR control were recorded with use of the

52

Bt-hybrid. The trend in gross margins was Similar in both 2005 and 2006, the Bt-
hybrid consistently had the highest gross margins gains, followed by the SAI and SAI
+ LST, and the HST. Among the conventional WCR control treatments, those
programs that included the SAI resulted in similar gross margins and both were
greater than the HST (Figure 2).

At Mason/Eaton Rapids the transgenic Bt-hybrid was the only WCR control
program that showed gains relative to no WCR control in 2004 and 2006, but there
were no differences in gross margins with the other WCR control programs (Figure
2). In 2005, the HST resulted in gross margins Significantly lower than the highest
gross margins (Figure 2) which may be attributable to the stand loss incurred from
this treatment. Although fields near Mason/Eaton Rapids had an anticipated high
WCR density, the additional costs associated with the control of the insect were not
justified because the actual WCR densities were much lower than anticipated. In
summary, at the anticipated high WCR density Sites, the cost of WCR control via
either the Bt-hybrid or conventional insecticide programs was justified in two of six
environments. In those two environments, use of the Bt-hybrid consistently resulted
in the highest gross margin gains relative to no WCR control.

The sensitivity analysis examined the value of Bt corn relative to no WCR
control which varied by WCR density (Figure 6). Regardless of corn price, the Bt GM
means were always negative at the low WCR density environments (Figure 6). At the
high WCR density, a negative GM mean for Bt was noted only for the $60/Mg corn
price. Positive GM gains, relative to no WCR control, were noted for $100/Mg,

$140/Mg, and $180/Mg corn prices at high WCR density (Figure 6). This follows the

53

fact that it becomes more manageable to cover input costs as commodity prices
increase. Currently, growers are required to plant a 20% refiige either within or
adjacent to a WCR-resistant corn field as a method to manage the development of
insect resistance. The application soil insecticides to control WCR larvae are
acceptable on refuge acres. At the $100/Mg corn price, the Bt GM means were
negative at the low and positive at the high WCR densities regardless of the Size of
the refuge (Figure 7). Under both low and high WCR densities the highest means
were for no refuge and the lowest for 20% refuge (Figure 7). Despite the inclusion of
costs associated with a 20% refuge, the Bt-corn hybrid had the highest mean gains of
all WCR control programs under high WCR density (Figure 8). Costs associated with
the use of Bt-corn were justified under high but not low WCR densities.

In conclusion, similar gross margins were achieved using the four weed
control programs and the additional cost of weed control or technology fees were
justified at all locations all years. In contrast, the cost associated with the control of
WCR was only justified in three of twelve environments, once at the low and twice at
the high WCR sites, respectively. In those three environments, use of the Bt-hybrid
resulted in significantly greater gross margins than using the conventional WCR
control programs. This indicated that, unlike weed control, the cost associated with
the control of WCR in many instances was not justified. It is important to consider
that the cost of technology fees associated with transgenic traits vary by region. The
profitability of corn hybrids resistant to glyphosate and WCR, assessed under realistic
field conditions, may be one of the key criteria for the adoption of these stacked traits.

However, non-pecuniary costs, such as pesticide applicator safety for example, may

54

also play a role in their adoption by certain corn growers. The use of a 20% refuge,
despite being treated with SAI, resulted in slightly lower profits for growers
compared to using only Bt corn. Relative to other WCR control programs, greater
gains were reported for the Bt-corn hybrid even when the latter included costs
associated with a 20% refuge. The use of refugia should be supported as the best
management practice in implementing a resistance management plan. The
implementation of refugia and resistance monitoring will become more and more
important as grower adoption increases and exposure of WCR larvae over multiple
growing seasons accrues. Furthermore, growers should be encouraged to scout for
WCR adults in fields (or land adjacent to fields) where corn will be planted the
following season and then base their management action on scouting observations
than relying solely on prophylactic pest control programs. From this study we
observed that gross margins reflected trends in corn yield rather than following costs
associated with specific treatments. Resistance to glyphosate or corn rootworm in a
corn hybrid does not necessarily mean greater profits. Growers should focus on the
yield potential of the crop by choosing high yielding hybrids adapted to local growing

conditions and closely monitor for the presence and density of pests.

55

Sources of Materials
1 Dekalb Genetics Corp., Monsanto Company, St. Louis, MO 63167
2 Poncho 600, Bayer CropScience, Research Triangle Park, NC 27709
3 Roundup WeatherMax, Monsanto Company, St. Louis, MO 63167
4 Bicep 11 Magnum, Syngenta Crop Protection, Inc. Greensboro, NC 27409
5 Lumax, Syngenta Crop Protection, Inc. Greensboro, NC 27409
6 Dual II Magnum, Syngenta Crop Protection, Inc. Greensboro, NC 27409
7 TeeJet Spraying Systems Co., Wheaton, IL 60188
8 Force 3G, Syngenta Crop Protection, Inc. Greensboro, NC 27409

9 SAS Institute Inc., Cary, NC 27513

56

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Gianessi, L. P. 2005. Economic and herbicide use impacts of glyphosate-resistant
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59

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72

APPENDIX

73

Table 1. Gross marginsl ($/ha) for no weed and no WCR control in 2004, 2005, and 2006

at all locations.

 

 

 

 

 

MSUl MSU2 Westphalia Mason/Eaton Rapids
S/ha
No weed control
2004 961.63 179.28 694.27 480.20
2005 141.21 2.17 347.65 469.60
2006 494.25 -97.31 754.64 125.28
No CRW control
2004 1418.94 1299.78 941.98 821.33
2005 1268.89 1284.74 539.01 101 1.91
2006 861.09 1052.17 614.72 859.11

 

“Gross margin values were used to make relative comparisons with the weed and insect control
treatments in Figures 1 and 2 (Chapter 2).

74

Table 2. Costs}r (S/unit) of additives, herbicides, and insecticides used in the weed and

insect control programs.

 

Product name Costs ($/unit)
28% nitrogen 1.37/gallon
Ammonium sulfate 0.19/lb
Activator 90 6.20/ gallon
Atrazine 4L 9.44/gallon
Atrazine 9ODF 2.17/1b

Bicep 11 Magnum 38.95/gallon
Buctril 2EC 64.35/gallon
Callisto 530.36/gallon
Clarity 89.89/gallon
Crop oil concentrate 6.20/gallon
Distinct 4| .13/lb

Dual 11 Magnum 95.59/gallon
Force 30 4.34/lb
Herbimax 6.20/gallon
Hornet WDG 52.04/1b
Lumax 43.40/gallon
Methylated seed oil 10.12/gallon
Option 9.27/02
Permit 16.27/02
Resource 163.31/gallon
Roundup Weathennax 39.17/gallon
Steadfast 21 08/02
Steadfast ATZ 20.59/lb

 

* June 2006 average price obtained from two distributors.

75

Table 3. Gross margins for insect control programs at MSU2 for varying refuge

requirements at a corn selling price of $60/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a’ NO refuge 10% refuge 20% refuge
WM

2004 Bt-hybrid (T) 622 a 619 a 616 3
SA] (C) 592 b 592 b 592 ab
SAI + LST(C) 588 b 588 b 588 b
HST (C) 584 b 584 b 584 b
Lso(o.05)° 26 25 25

2005 Bt-hybrid (T) 609 a 603 a 598 a
SAI (C) 550 b 550 b 550 b
SAI + LST (C) 526 b 526 b 526 b
HST (C) 436 c 436 c 436 c
LSD(0.05) 40 4O 40

2006 Bt-hybrid (T) 589 a 572 a 554 a
SAI (C) 440 c 440 c 440 c
SAI + LST (C) 495 b 495 b 495 b
HST(C) 5]] b 511 b 511 b
LSD(0.05) 35 35 35

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic 3! corn program for insect control; C, denotes a conventional
insecticide program.
bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.fkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i./kernel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

76

Table 4. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $100/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 8") No refiJge 10% refuge 20% refuge
S/ha

2004 Bt-hybrid (T) 1 192 a 1189 a 1186 a
SAI (C) 1161 ab 1161 ab 1161 ab
SAI + LST(C) 1165 ab 1165 ab 1 165 ab
HST (C) 1146 b 1146 b 1146 b
LSD(O.05)C 42 41 41

2005 Bt-hybrid (T) 1 176 a 1169 a 1163 a
SAI (C) 1110 b 1110 ab 1110 ab
SAI + LST (C) 1067 b 1067 b 1067 b
HST (C) 903 c 903 c 903 c
LSD(0.05) 64 64 63

2006 Bt-hybrid (T) 1 136 a 1108 a 1081 a
SAI (C) 805 c 805 b 805 b
SAI + LST (C) 1108 b 1108 a 1108 a
HST (C) 1020 ab 1020 a 1020 a
LSD(0.05) 123 122 122

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

77

Table 5. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $140/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control programEB N0 refuge 10% refiige 20% refiige
S/ha

2004 Bt-hybrid (T) 1762 a 1758 a 1756 a
SAI (C) 1730 a 1730 a 1730 a
SAI + LST(C) 1742 a 1 742 a 1742 a
HST (C) 1708 a 1708 a 1708 a
LSD(0.05)° 58 58 57

2005 Bt-hybrid (T) 1 742 a 1 735 a l 728 a
SAI (C) 1670 ab 1670 ab 1670 ab
SAI + LST (C) 1608 b 1608 b 1608 b
HST (C) 1371 c 1371 c 1371 c
LSD(0.05) 89 88 88

2006 Bt-hybrid (T) 1682 a 1645 a 1608 a
SAI (C) 1229 b 1229 b 1229 b
SAI + LST (C) 1521 a 1521 a 1521 a
HST (C) 1530 a 1530 a 1530 a
LSD(0.05) 172 172 171

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

SAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

78

Table 6. Gross margins for insect control programs at MSU2 for varying refuge
requirements at a corn selling price of $180/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 21,15 No refuge 10% refuge 20% refuge
$/ha

2004 Bt-hybrid (T) 2333 a 2329 a 2326 a
SAI (C) 2300 a 2300 a 2300 a
SAI + LST(C) 2319 a 2319 a 2319 a
HST (C) 2269 a 2269 a 2269 a
LSD(0.05)C 74 74 73

2005 Bt-hybrid (T) 2309 a 2301 a 2293 a
SAI (C) 2229 ab 2229 ab 2229 ab
SAI + LST (C) 2149 b 2149 b 2149 b
HST (C) 1838 c 1838 c 1838 c
LSD(0.05) 115 113 112

2006 Bt-hybrid (T) 2228 a 2182 a 2135 a
SAI (C) 1653 b 1653 b 1653 b
SAI + LST (C) 2034 a 2034 a 2034 a
HST (C) 2040 a 2040 a 2040 a
LSD(0.05) 222 221 221

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic BI corn program for insect control; C, denotes a conventional
insecticide program.

SAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.fkernel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different (a =
0.05) according to Fisher’s Protected LSD.

79

Table 7. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $60/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 3") No refuge 10% refuge 20% refuge
S/ha

2004 Bt-hybrid (T) 688 a 685 a 683 a
SAI (C) 662 a 662 a 662 a
SA1+ LST(C) 282 a 282 a 282 a
HST (C) 677 a 677 a 677 a
LSD(0.05)C 51 4s 46

2005 Bt-hybrid (T) 500 a 500 a 500 a
SAI (C) 499 a 662 a 662 a
SAI + LST (C) 464 a 282 a 282 a
HST (C) 369 b 677 b 677 b
LSD(0.05) 46 45 45

2006 Bt-hybrid (T) 426 a 416 a 406 a
SAI (C) 326 c 662 c 662 b
SAI + LST (C) 362 be 282 be 282 a
HST (C) 378 ab 677 ab 677 a
LSD(0.05) 49 49 49

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic BI corn program for insect control; C, denotes a conventional
insecticide program.

SAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i./kemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.fkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

80

Table 8. Gross margins for insect control programs at MSUI for varying refuge
requirements at a corn selling price of $100/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 3’1) NO refuge 10% refuge 20% refuge
S/ha

2004 Bt-hybrid (T) 1300 a 1297 a 1295 a
SAI (C) 1276 a 1276 a 1276 a
SAI + LST(C) 1320 a 1320 a 1320 a
HST (C) 1297 a 1297 a 1297 a
LSD(0.05)C 84 80 77

2005 Bt-hybrid (T) 989 a 991 a 992 a
SAI (C) 1007 a 1007 a 1007 a
SAI + LST (C) 960 a 960 a 960 a
HST (C) 787 b 787 b 787 b
LSD(0.05) 76 75 74

2006 Bt-hybrid (T) 864 a 849 a 835 8
SA] (C) 718 b 718 b 718 b
SAI + LST (C) 789 ab 789 ab 789 ab
HST (C) 800 a 800 a 800 a
LSD(0.05) 83 82 82

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

SAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.iJkernel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

81

Table 9. Gross margins for insect control programs at MSUl for varying refuge
requirements at a corn selling price of $140/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 8") No refuge 10% refirge 20% refuge
$/ha

2004 Bt-hybrid (T) 1911 a 1909 a 1907 a
SAI (C) 1 890 a 1 890 a 1890 a
SAI + LST(C) 1957 a 1957 a 1957 a
HST (C) 1918 a 1918 a 1918 a
LSD(0.05)c r 18 112 108

2005 Bt-hybrid (T) 1478 a 1481 a 1485 a
SAI (C) 1515 a 1515 a 1515 a
SAI + LST (C) 1455 a 1455 a 1455 a
HST (C) 1206 b 1206 b 1206 b
LSD(0.05) 105 104 103

2006 Bt-hybrid (T) 1302 a 1283 a 1263 a
SAI (C) 1109 b 1109 b 1109 b
SAl+LST (C) 1213 ab 1213 ab 1213 ab
HST (C) 1223 ab 1223 ab 1223 ab
LSD(0.05) 117 116 115

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkernel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkernel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

82

Table 10. Gross margins for insect control programs at MSU] for varying refuge
requirements at a corn selling price of $180/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 8’5 No refuge 10% refuge 20% refuge
$/ha

2004 Bt-hybrid (T) 2523 a 2521 a 2519 a
SAI (C) 2504 a 2504 a 2504 a
SAI + LST(C) 2595 a 2595 a 2595 a
HST (C) 2538 a 2538 a 2538 a
LSD(0.05)‘: 151 144 139

2005 Bt-hybrid (T) 1967 a 1973 a 1978 a
SAI (C) 2023 a 2023 a 2023 a
SAI + LST (C) 1950 a 1950 a 1950 a
HST (C) 1624 b 1624 b 1624 b
LSD(0.05) 136 134 133

2006 Bt-hybrid (T) 1740 a 1716 a 1692 a
SAI (C) 1500 b 1500 b 1500 b
SAI + LST (C) 1639 ab 1639 ab 1639 ab
HST (C) 1646 ab 1646 ab 1646 ab
LSD(0.05) 151 149 149

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

SAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i./kemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i./kernel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

83

Table 11. Gross margins for insect control programs at Mason/Eaton Rapids for varying
refuge requirements at a corn selling price of $60/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a’b No refuge 10% refuge 20% refuge
Slim

2004 Bt-hybrid (T) 405 a 400 a 394 a
SAI (C) 350 b 350 a 350 a
SAI + LST(C) 356 ab 356 a 356 a
HST (C) 361 ab 361 a 361 a
LSD(0.05)c 55 54 49

2005 Bt-hybrid (T) 433 a 429 a 425 a
SA] (C) 393 ab 393 ab 393 ab
SAI + LST (C) 351 b 351 b 351 be
HST (C) 325 b 325 b 325 c
LSD(0.05) 70 69 64

2006 Bt-hybrid (T) 386 a 373 a 360 3
SA] (C) 344 a 344 a 344 a
SAI+LST(C) 317 a 317 a 317 a
HST (C) 329 a 329 a 329 a
LSD(0.05) 101 96 88

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i./kemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i./kemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

84

Table 12. Gross margins for insect control programs at Mason/Eaton Rapids for varying
refuge requirements at a corn selling price of $100/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a‘b No refuge 10% refuge 20% refuge
S/ha

2004 Bt-hybrid (T) 829 a 821 a 814 a
SAI (C) 755 a 755 a 755 8
SA] + LST(C) 777 a 777 a 777 a
HST (C) 770 a 770 a 770 a
LSD(0.05)c 89 88 87

2005 Bt-hybrid (T) 878 a 873 a 868 a
SAI (C) 831 a 831 a 831 a
SAI + LST (C) 771 ab 771 ab 771 ab
HST (C) 714 b 714 b 714 b
LSD(0.05) 115 114 113

2006 Bt-hybrid (T) 799 a 779 a 759 a
SAI (C) 752 a 752 a 752 a
SAI+LST(C) 714 a 714 a 714 a
HST (C) 720 a 720 a 720 a
LSD(0.05) 171 163 157

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.iJkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.Ikemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

85

Table 13. Gross margins for insect control programs at Mason/Eaton Rapids for varying
refuge requirements at a corn selling price of $140/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 8’1) No refuge 10% refuge 20% refuge
S/ha

2004 Br-hybrid (T) 1252 a 1243 a 1234 8
SA] (C) 1161 a a 8
SA] + LST(C) 1198 a a a
HST (C) 1 180 a a a
LSD(0.05)° 120 122 121

2005 Bt-hybrid (T) 1322 a 1317 a 1312 a
SAI (C) 1269 a a a
SAI + LST (C) 1192 ab ab ab
HST (C) 1 103 b b b
LSD(0.05) 161 160 158

2006 Bt-hybrid (T) 1212 a 1185 a 1 158 a
SAI (C) 1160 a a a
SAI+LST(C) 1111 a a a
HST (C) 1 1 10 a a a
LSD(0.05) 241 23 1 221

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

86

Table 14. Gross margins for insect control programs at Mason/Eaton Rapids for varying
refuge requirements at a corn selling price of $180/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 3,5 N0 refuge 10% refuge 20% refuge
$/ha

2004 Bt-hybrid (T) 1675 a 1664 a 1653 a
SAI (C) 1566 a 1566 a 1566 a
SAI+LST(C) 1619 a 1619 a 1619 a
HST (C) 1589 a 1589 a 1589 a
LSD(0.05)° 159 156 155

2005 Bt-hybrid (T) 1767 a 1761 a 1755 a
SAI (C) 1707 a 1707 a 1707 a
SAI+LST (C) 1613 ab 1613 ab 1613 ab
HST (C) 1492 b 1492 b 1492 b
LSD(0.05) 202 205 203

2006 Bt-hybrid (T) 1624 a 1591 a 1557 a
SAI (C) 1568 a 1568 a 1568 a
SAI + LST (C) 1507 a 1507 a 1507 a
HST (C) 1501 a 1501 a 1501 a
LSD(0.05) 3 12 298 286

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.fkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

87

Table 15. Gross margins for insect control programs at Westphalia for varying refuge
requirements at a corn selling price of $60/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a,b No refuge 10% refuge 20% refiJge
$/ha

2004 Bt-hybrid (T) 378 a 375 a 372 a
SAI (C) 345 a 345 a 345 8
SA] + LST(C) 331 a 331 a 331 a
HST (C) 356 a 356 a 356 a
LSD(0.05)c 52 52 51

2005 Bt-hybrid (T) 368 a 354 a 340 8
SA] (C) 229 b 229 b 229 b
SAI + LST (C) 235 b 235 b 235 b
HST (C) 185 c 185 c 185 c
LSD(0.05) 43 42 41

2006 Bt-hybrid (T) 464 a 453 a 441 a
SAI (C) 350 bc 350 be 350 be
SAI + LST (C) 370 b 370 b 370 b
HST (C) 291 c 291 c 291 c
LSD(0.05) 62 61 60

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt com program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

88

Table 16. Gross margins for insect control programs at Westphalia for varying refuge
requirements at a corn selling price of $100/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a’b No refuge 10% refirge 20% refuge
$/ha

2004 Bt-hybrid (T) 788 a 784 a 781 a
SAI (C) 751 a 751 a 751 a
SAI + LST(C) 739 a 739 a 739 a
HST (C) 768 a 768 a 768 a
LSD(0.05)° 84 83 83

2005 Bt-hybrid (T) 769 a 748 a 727 8
SA] (C) 556 b 556 b 556 b
SAI + LST (C) 578 b 578 b 578 b
HST (C) 481 c 481 c 481 c
LSD(0.05) 72 70 69

2006 Bt-hybrid (T) 929 a 912 a 895 a
SAI (C) 759 be 759 b 759 ab
SAI + LST (C) 802 b 802 b 802
HST (C) 657 c 657 c 657 c
LSD(0.05) 103 101 99

 

alAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i./kemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

89

Table 17. Gross margins for insect control programs at Westphalia for varying refuge
requirements at a corn selling price of $140/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program 8") No refuge 10% refuge 20% refuge
S/ha

2004 Bt-hybrid (T) l 198 a l 194 a 1190 a
SAI (C) 1158 a 1158 a 1158 a
SAI + LST(C) 1148 a 1 148 a 1148 a
HST (C) 1179 a 1179 a 1179 a
LSD(0.05)c 1 17 1 16 115

2005 Bt-hybrid (T) 1171 a 1 142 a 1 l 14 a
SAI (C) 884 b 884 b 884 b
SAI + LST (C) 921 b 921 b 921 b
HST (C) 776 c 776 c 776 c
LSD(0.05) 101 99 96

2006 Bt-hybrid (T) 1395 a 1372 a 1350 a
SAI (C) 1168 b 1168 b 1168 b
SAI + LST (C) 1235 b 1235 ab 1235 ab
HST (C) 1023 c 1023 c 1023 c
LSD(0.05) 144 141 138

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i.lkemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i.lkemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

90

Table 18. Gross margins for insect control programs at Westphalia for varying refuge
requirements at a corn selling price of $180/Mg.

 

 

 

 

 

 

 

 

 

 

Year WCR control program a’B No refuge 10% refuge 20% refuge
$lha

2004 Bt-hybrid (T) 1608 a 1603 a 1599 a
SAl (C) 1565 a 1565 a 1565 8
SA] + LST(C) 1556 a 1556 a 1556 a
HST (C) 1591 a 1591 a 1591 a
LSD(0.05)C 149 148 147

2005 Bt-hybrid (T) 1572 a 1536 a 1500 a
SAI (C) 1212 b 1212 b 1212 b
SAI + LST (C) 1263 b 1263 b 1263 b
HST (C) 1072 c 1072 c 1072 c
LSD(0.05) 130 127 124

2006 Bt-hybrid (T) . 1860 a 1832 a 1804 a
SAI (C) 1577 b 1577 b 1577 b
SAI + LST (C) 1668 b 1668 ab 1668 ab
HST (C) 1390 c 1390 c 1390 c
LSD(0.05) 186 181 177

 

aAbbreviations: SAI, soil-applied insecticide; LST, low seed treatment; HST, high seed
treatment; T, denotes a transgenic Bt corn program for insect control; C, denotes a conventional
insecticide program.

bSAI was tefluthrin applied at planting; LST is a commercial seed coating of cothianidin at 0.25
mg a.i./kemel; HST is a commercial seed coating of clothianidin at 1.25 mg a.i./kemel.

cMeans within a column (per year) followed by the same letter are not significantly different
(a = 0.05) according to Fisher’s Protected LSD.

91

   

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