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This is to certify that the

thesis entitled
CORN (Zea maxs L.) INBRED RESPONSE TO HERBICIDES

presented by

JOSEPH TODD SIMMONS

has been accepted towards fulfillment
of the requirements for

M.S. degree inCrOp and Soil Sciences

QAL/MJ

Mljor professor

 

 

 

 

Date

 

591;] 2?, 2000/
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11100 chIRC/D‘aDm.p65»p.t4

CORN (Zea mays L.) INBRED RESPONSE TO HERBICIDES
By

Joseph Todd Simmons

A THESIS

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

MASTERS OF SCIENCE
Department of Crop and Soil Sciences

2000

ABSTRACT
CORN (Zea mays L.) INBRED RESPONSE TO HERBICIDES
By

Joseph Todd Simmons

Seed corn production is a very important component of the agricultural economy in
southwest Michigan. The potential for weed growth in seed corn production fields following
detassseling and male row removal requires intensive weed management strategies including
the use of herbicides. Two inbred parents grown together in the same field create crop safety
concerns related to herbicide use in seed corn production fields. Corn inbreds are often more
sensitive to herbicides than corn hybrids. Therefore, many of the herbicides commonly used
in hybrid corn production cannot be used safely on corn inbreds. Field studies were
conducted to determine if antidotes could be used with acetarnide herbicides to reduce injury.
Benoxacor reduced corn injury fiom metolachlor, and MON-13900 and dichlorrnid reduced
com inbred injury from acetochlor. Greenhouse and field trials were conducted to determine
the response of commercially grown corn inbreds to four preemergence and four
postemergence herbicides. Environmental conditions was a major factor in the response of
corn inbreds to herbicides. Greenhouse trials were conducted to study the variation and
inheritance of isoxaflutole tolerance in com. Four Fl hybrids were produced from tolerant and
sensitive inbred lines from the B73 and C103 families. The results indicate that tolerance to
isoxaflutole is a heritable trait. The results of this research indicate that injury from
herbicides is often related to inherent differences in tolerance among corn inbreds. Therefore,

herbicides and corn inbreds must be matched carefully to assure crOp safety.

ACKNOWLEDGMENTS

I would like to sincerely thank my major advisor, Dr. James J. Kells, for his time,
guidance, and, most of all, his patience regarding my graduate studies at MSU. Being a
former Ag-Tech student made this masters degree very rewarding. I would also like to thank
my other committee members, Dr. Donald Penner, and Dr. Chris DiFonzo, for their
assistance and guidance in my research. I need to thank Herschel Wahls for being helpful as
my contact person with Great Lakes Hybrids.

Part of graduate school is meeting and working with great people. I was blessed to
have worked with some of the best. My research would not have been possible without the
help from Andy Chomas, Brent Tharp, Christy Sprague, Caleb Dalley, Matt Rinella,
Stephanie Eickolt, and Pat O’Boyle. Many other fiiendships were made that has made my
time at MSU enjoyable. Special thanks to Kyle Poling, Kelly Nelson, Sherry White, Chad
Lee, Gary Powell, Nate Kemp, Kyle “Biff” Fiebig, Gabe Corey, Amy Guza, Jeff Stachler,
Corey Ransom, Jason Fausey, and Frank Roggenbuck.

Finally, I have many great friends and family members that have made this degree
possible. I need to thank my parents, Richard and Arlene, for their many years of love and
support. I would also like to thank all my brothers and sisters for all their support and
encouragement. A special thank you goes to Laura Verona “LJV” for her encouragement

and, most of all, her friendship.

iii

TABLE OF CONTENTS

LIST OF TABLES ...................................................... v
LIST OF FIGURES ..................................................... x
CHAPTER 1
RESPONSE OF CORN (Zea mays L.) INBREDS B73 AND M017 TO ACETIMIDE
HERBICIDES AS INFLUENCED BY ANTIDOTES ......................... 1
ABSTRACT ...................................................... 1
INTRODUCTION ................................................. 3
MATERIAL AND METHODS ....................................... 4
RESULTS AND DISCUSSION ...................................... 5
LITERATURE CITED ............................................. 8
CHAPTER 2
RESPONSE OF CORN (Zea mays L.) INBREDS TO PREEMERGENCE AND
POSTEMERGENCE HERBICIDES ...................................... 13
ABSTRACT ..................................................... 13
INTRODUCTION ................................................ 1 5
MATERIAL AND METHODS ...................................... 16
Greenhouse Experiments ..................................... 16
Field Experiments .......................................... 18
Statistical Analysis .......................................... 20
RESULTS AND DISCUSSION ..................................... 21
Preemergence Herbicide Studies ............................... 21
Postemergence Herbicide Studies .............................. 22
LITERATURE CITED ............................................ 25
CHAPTER 3
VARIATION AND INHERITAN CE OF ISOXAFLUTOLE TOLERANCE IN
CORN (Zea mays L.) ................................................... 33
ABSTRACT ..................................................... 33
INTRODUCTION ................................................ 34
MATERIAL AND METHODS ...................................... 35
General Experimental Procedures .............................. 35
Isoxaflutole tolerance in corn inbreds within the B73 and C103 families 36
Inheritance of isoxaflutole tolerance ............................ 36
Statistical Analysis .......................................... 36
RESULTS AND DISCUSSION ..................................... 37
Isoxaflutole tolerance in corn inbreds within the B73 and C103 families 37
Inheritance of isoxaflutole tolerance ............................ 37
LITERATURE CITED ............................................ 40
APPENDIX ........................................................... 45

iv

LIST OF TABLES

CHAPTER 1
RESPONSE OF CORN (Zea mays L.) INBREDS B73 AND M017 TO ACETIMIDE
HERBICIDES AS INFLUENCED BY ANTIDOTES

Table 1. Rainfall accumulation for 14 days after herbicide application at the
research site ...................................................... 9

CHAPTER 2
RESPONSE OF CORN (Zea mays L.) INBREDS TO PREEMERGENCE AND
POSTEMERGENCE HERBICIDES

Table I. Inbred number, corresponding inbred family, and use in commercial
seed corn production .............................................. 27

Table 2. Rainfall accumulation for 14 days after herbicide application ....... 28

Table 3. Visual injury, plant height, and dry weight of corn inbreds 14 days
after preemergence herbicide application in the greenhouse ................ 29

Table 4. Visual injury and growing degree days to the initiation of tassel
emergence in corn inbreds after preemergence application of isoxaflutole
in 1998 and 1999 field trails ........................................ 30

Table 5. Visual injury, plant height, and dry weight of corn inbreds 14 days
after postemergence herbicide application of fluthiacet in the greenhouse ..... 31

Table 6. Visual injury to corn inbreds 14 days afier postemergence application
of herbicides in 1998 and 1999 field trials .............................. 32

APPENDIX

Table 1. Visual injury, plant height as % of the control, and dry weight as %
of the control to corn inbreds 14 days after preemergence application of
herbicides in a greenhouse applied at twice the typical use rate .............. 45

Table 2. Visual injury, plant height as % of the control, and dry weight as %
of the control to corn inbreds 14 days after preemergence application of
herbicides in a greenhouse applied at four times the typical use rate. ......... 46

LIST OF TABLES (cont)

Table 3. Visual injury to corn inbreds 28 days after preemergence application
of herbicides applied at twice the typical use rate in the 1998 field season. . . . . 47

Table 4. Visual injury to corn inbreds 35 days afier preemergence application
of herbicides applied at twice the typical use rate in the 1999 field season. . . . . 48

Table 5. Visual injury to corn inbreds 28 days after preemergence application
of herbicides applied at four times the typical use rate in the 1998 field season. 49

Table 6. Visual injury to corn inbreds 35 days after preemergence application
of herbicides applied at four times the typical use rate in the 1999 field season. 50

Table 7. Growing Degree Days as % of the control to corn inbreds after
preemergence application of herbicides applied at twice the typical use rate
in the 1998 field season ............................................. 51

Table 8. Growing Degree Days as % of the control to corn inbreds after
preemergence application of herbicides applied at twice the typical use rate
in the 1999 field season ............................................. 52

Table 9. Growing Degree Days as % of the control to corn inbreds after
preemergence application of herbicides applied at four times the typical use
rate in the 1998 field season. ........................................ 53

Table 10. Growing Degree Days as % of the control to corn inbreds afier
preemergence application of herbicides applied at four times the typical use
rate in the 1999 field season. ........................................ 54

Table 11. Visual injury to corn inbreds 3 and 7 days after postemergence
application of herbicides in a greenhouse applied at twice the typical use rate. . 55

Table 12. Visual injury to corn inbreds 3 and 7 days after postemergence
application of herbicides in a greenhouse applied at four times the typical
use rate. ........................................................ 56

Table 13. Visual injury to corn inbreds 14 days after postemergence
application of herbicides in a greenhouse for two runs applied at twice the
typical use rate. .................................................. 5 7

Table 14. Plant height as % of the control, and dry weight as % of the control

to corn inbreds 14 days after postemergence application of herbicides in a
greenhouse applied at twice the typical use rate. ......................... 58

vi

LIST OF TABLES (cont)

Table 15. Visual injury to corn inbreds 14 days after postemergence
application of herbicides in a greenhouse for two nms applied at four times
the typical use rate. ............................................... 59

Table 16. Plant height as % of the control to corn inbreds 14 days after
postemergence application of herbicides in a greenhouse applied at four times
the typical use rate. ............................................... 60

Table 1 7. Plant dry weight as % of the control to corn inbreds 14 days after
postemergence application of herbicides in a greenhouse applied at four times
the typical use rate. ............................................... 60

Table 18. Visual injury to corn inbreds 3 days after postemergence
application of herbicides applied at twice the typical use rate in the 1998
field season. ..................................................... 61

Table 19. Visual injury to corn inbreds 3 days after postemergence
application of herbicides applied at twice the typical use rate in the 1999
field season. ..................................................... 62

Table 20. Visual injury to corn inbreds 3 days after postemergence
application of herbicides applied at four times the typical use rate in the
1998 field season .................................................. 63

Table 21. Visual injury to corn inbreds 3 days after postemergence
application of herbicides applied at four times the typical use rate in the
1999 field season .................................................. 64

Table 22. Visual injury to corn inbreds 7 days after postemergence
application of herbicides applied at twice the typical use rate in the
1998 field season. ................................................ 65

Table 23. Visual injury to corn inbreds 7 days afier postemergence
application of herbicides applied at twice the typical use rate in the
1999 field season. ................................................ 66

Table 24. Visual injury to corn inbreds 7 days after postemergence
application of herbicides applied at four times the typical use rate in the
1998 field season. ................................................ 67

Table 25. Visual injury to corn inbreds 7 days after postemergence
application of herbicides applied at four times the typical use rate in the
1999 field season. ................................................ 68

vii

LIST OF TABLES (cont)

Table 26. Visual injury to corn inbreds 14 days after postemergence
application of herbicides applied at twice the typical use rate in the
1998 field season. ................................................ 69

Table 27. Visual injury to corn inbreds 14 days after postemergence
application of herbicides applied at twice the typical use rate in the
1999 field season .................................................. 70

Table 28. Visual injury to corn inbreds 14 days after postemergence
application of herbicides applied at four times the typical use rate in the
1998 field season .................................................. 71

Table 29. Visual injury to corn inbreds 14 days after postemergence
application of herbicides applied at four times the typical use rate in the
1999 field season .................................................. 72

Table 30. Growing Degree Days as % of the control to corn inbreds after
postemergence application of herbicides applied at twice the typical use rate
in the 1998 field season ............................................. 73

Table 31. Growing Degree Days as % of the control to corn inbreds afier
postemergence application of herbicides applied at twice the typical use rate
in the 1999 field season ............................................. 74

Table 32. Growing Degree Days as % of the control to corn inbreds afier
postemergence application of herbicides applied at four times the typical
use rate in the 1998 field season. ..................................... 75

Table 33. Growing Degree Days as % of the control to corn inbreds after
postemergence application of herbicides applied at four times the typical
use rate in the 1999 field season. ..................................... 76

Table 34. Visual injury to corn inbreds within the B73 family 14 days
afier preemergence application of herbicides in a greenhouse for two
runs applied at twice the typical use rate. .............................. 77

Table 35. Plant height as % of the control, and dry weight as % of the
control to corn inbreds within the B73 family 14 days after preemergence
application of herbicides in a greenhouse applied at twice the typical use rate. . 78

viii

LIST OF TABLES (cont)

Table 36. Visual injury, plant height as % of the control, and dry weight

as % of the control to corn inbreds within the B73 family 14 days after
preemergence application of herbicides in a greenhouse applied at four times

the typical use rate. ............................................... 79

Table 3 7. Visual injury, plant height as % of the control, and dry weight .

as % of the control to corn inbreds within the C103 family 14 days after
preemergence application of herbicides in a greenhouse applied at

twice the typical use rate. .......................................... 80

Table 38. Visual injury, plant height as % of the control, and dry weight

as % of the control to corn inbreds within the C103 family 14 days after
preemergence application of herbicides in a greenhouse applied at

four times the typical use rate. ....................................... 81

ix

LIST OF FIGURES

CHAPTER 1
RESPONSE OF CORN (Zea mays L.) INBREDS B73 AND M017 TO ACETIMIDE
HERBICIDES AS INFLUENCED BY ANTIDOTES

Figure 1. Response of inbred M017 to metolachlor at three times the typical
use rate with and without benoxacor .................................. 10

Figure 2. Response of inbred M017 to acetochlor at three times the typical
use rate affected by MON-13900 and dichlormid. Acetochlor without
safener was not included in 1997 ..................................... 1 1

Figure 3. Response of corn inbred M017 to commercially available
acetarnide herbicides applied at three times the typical use rate ............. 12

CHAPTER 3
VARIATION AND INHERITANCE OF ISOXAFLUTOLE TOLERANCE IN
CORN (Zea mays L.)

Figure I . Response of corn inbreds from the B73 and C103 families to
isoxaflutole at 314 g/ha, evaluated 14 days after treatment in the greenhouse . . 42

Figure 2. Distribution of isoxaflutole sensitivity within corn inbreds
from B73 and C103 families. Isoxaflutole was applied at 314 g/ha,
evaluated 14 days afier treatment in the greenhouse ...................... 43

Figure 3. Response of corn inbreds and F , hybrids to isoxaflutole
at 314 g/ha, evaluated 14 days after treatment in the greenhouse ............ 44

CHAPTER 1
Response of Com (Zea mays L.) Inbreds B73 and M017 to Acetamide Herbicides as
Influenced by Antidotes

Abstract Corn inbreds are often more sensitive to herbicides than corn hybrids. Therefore,
many of the herbicides commonly used in hybrid corn production cannot be used safely on
corn inbreds. Field studies were conducted in 1996 and 1997 to determine if antidotes could
be used with acetarnide herbicides to reduce injury to B73 and M017 corn inbreds. Visual
injury and number of injured plants per row were determined. Benoxacor reduced corn injury
from metolachlor, and MON-13900 and dichlonnid reduced corn inbred injury fi'om
acetochlor. Differences in corn injury were not apparent between MON-13900 and
dichlormid. Corn inbred injury was greater than 20% from flufenacet plus metribuzin,
dirnethenamid, metolachlor without safener, and acetochlor without safener. S-metolachlor
plus benoxacor, acetochlor plus dichlormid, acetochlor plus MON-13900, and alachlor
injured corn inbreds less than 20%. This research indicates that com inbreds vary in their
sensitivity to acetarnide herbicides.

Nomenclature: acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-
methylphenyl)acetamide; alachlor, 2-chloro-N-(2,6-diethylphenyl)-N-
(methoxymethyl)acetamide; benoxacor, (4-dichloroacetyl)-3,4-dihydro-3-methyl-2H-1,4-
benzoxazine; dichlormid, 2,2-dichloro-N,N-di-2-propenylacetamide; dirnethenamid, 2-
chloro—N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-y1)-acetamide; flufenacet,
N-(4-fluoropheny1)-N-(1-methy1ethyl)-2-[[5 -(trifluoromethyl)-1,3 ,4-thiadiazol-2-
yl]oxy]acetamide; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2—methoxy-1—

methylethyl)acetamide; S-metolachlor, 2-chloro-N-(2-ethy1—6—methylpheny1)~N-(2-methoxy-

1-methylethy1)acetamide, S—enantiomer; metribuzin, 4-amino-6-(1,l-dimethylethyl)-3-
(methylthio)-1,2,4-triazin-5(4H)-one; MON-13900, 3-dichloroacetyl-5-(2—furanyl)—2,2-
dimethyl-oxazolidine; corn, Zea mays L.;

Abbreviations: DAT, days after treatment.

INTRODUCTION

Acetamide herbicides are commonly used to control annual grasses in corn (Zea mays
L.) production. Acetamide herbicides rarely injure corn when used at rates recommended for
the soil type. However, under certain conditions injury can occur. Injury symptoms range
from twisting and curling of the leaves to more severe stunting and malformation of the
plant, which may decrease corn yield. Rowe and Penner (1990) reported that com injury
increased as rates of acetarnide herbicides were increased. Narsaiah and Harvey (1977) found
that alachlor at 10 kg/ha severely injured three corn inbreds, but two inbreds were not
affected by the herbicide, indicating that some inbreds are inherently more sensitive to this
herbicide than others. Environmental conditions also influence the response of com inbreds
to herbicides. Corn injury increased as soil moisture content increased (Rowe et a1. 1991).
Roggenbuck and Penner (1987) reported that air temperature influenced injury to trifluralin
[2,6-dinitro-N,N—dipropyl-4-(trifluoromethyl)benzenamine] more than soil moisture levels,
but both are important.

The concept of increasing crop selectivity to herbicides with antidotes (also known
as safeners) was introduced in 1962 (CL. Hoffinan 1962). Since this discovery, 3 number
of compounds have been identified as safeners (Hatzios 1984; Leavitt and Penner 1978). For
example, Winkle et a1. (1980) reported that dichlorrnid reduced corn injury from metolachlor
and alachlor. Most of the previous research on herbicide safeners has been conducted on
commercial hybrid corn. Inbreds typically lack the plant vigor associated with corn hybrids
(Biclmer 1993), which would likely make hybrid corn more tolerant to herbicides than corn
inbreds. More information is needed on inbred sensitivity to herbicides and how safeners
influence the response of inbreds to herbicides. The objective of this research was to evaluate

relative sensitivity of two corn inbreds to acetarnide herbicides as influence by safeners.

Material and Methods

Field trials were conducted in 1996 and 1997 at the Michigan State University Crop
and Soil Science Research Farm at East Lansing, MI. The soil was a Capac loam (fine-
loamy, mixed mesic Aeric Ochraqualf) with a pH of 7.5 and 2.9% organic matter in 1996 and
pH of 5.4 and 1.6% organic matter in 1997. Soybean [Glycine max (L.) Merr.] stubble was
spring chisel plowed, and field cultivated each year. Prior to the field cultivation in both
years, 305 kg/ha of 46-0-0 (N, P205, K20) fertilizer was broadcast. At planting 6-24-24 (N,
P205, K20) fertilizer at 319 kg/ha in 1996, and at 336 kg/ha in 1997 was applied as a banded
treatment 5 cm below and 5 cm beside the corn seed. Plots consisted of four rows spaced 76
cm apart with lengths of 12 m in 1996 and 10.6 m in 1997. The left two corn rows in all plots
were planted to the inbred B73 and the right two rows were planted to inbred M017. Corn
inbred seed were planted 3.8 cm deep at 51,900 seeds/ha on May 29, 1996, and 56,800
seeds/ha on May 12, 1997.

Herbicide treatments were applied at two rates, the first rate was treated at typical use
rate recommended for the soil type and the second rate was treated at three times the
recommended rate for the soil type. Herbicide treatments consisted of metolachlor at 2.23
kg/ha and 6.7 kg/ha; the ‘ S’ isomer ofmetolachlor plus benoxacor at 1.5 kg/ha and 4.5 kg/ha;
dimethenamid at 1.3 kg/ha and 3.9 kg/ha; flufenacet plus metribuzin at 0.87 kg/ha and 2.6
kg/ha in 1996, and at 0.7 kg/ha and 2.1 kg/ha in 1997; alachlor at 2.23 kg/ha and 6.7 kg/ha;
acetochlor at 1.8 kg/ha and 5.4 kg/ha; acetochlor plus dichlormid at 1.8 kg/ha and 5.4 kg/ha;
and acetochlor plus MON-13900 at 1.8 kg/ha and 5.4 kg/ha. Atrazine [6—chloro-N-ethyl-N’-
(1-methylethyl)—1,3,5-triazine-2,4—diamine] at 1.12 kg/ha was tank mixed with each herbicide

treatment to minimize annual weed competition. Treatments were compared against plots

 

treated with atrazine at 1.12 kg/ha. All herbicides were applied with a tractor mounted
compressed air sprayer calibrated to deliver 187 L/ha at 207 kPa using flat fan nozzles‘.
Applications of preemergence herbicides were on May 30, 1996 and May 13, 1997,
respectively. At least 1.34 cm of rainfall occurred within 14 days after treatment (DAT) in
both years (Table 1).

Experiments were conducted as randomized complete block designs with three
replications in 1996 and four replications in 1997. Each corn inbred was analyzed as an
independent trial. Corn injury was evaluated 28 DAT in 1996. Because of slow growing
conditions in 1997 injury was evaluated 42 DAT in 1997. Visual injury ratings were based
on a scale of 0 to 100, with 0 representing no effect and 100 representing plant death. The
number of plants showing typical acetarnide injury symptoms were counted in each row, and
are expressed as a percentage of the total plants in the row. Data from each year were
analyzed and reported separately. All data were subjected to analysis of variance (AN OVA)

and means were separated using the least significant difference procedure at the 0.05 level.

RESULTS AND DISCUSSION
Differences in injury to B73 at both application rates were small and consistently less
than 16% in 1996 and less than 10% in 1997 (data not shown). Injury to M017 at the typical
use rates of acetarnide herbicides never exceeded 16% (data not shown). Differences in
injury to M017 treated with acetarnide herbicides at three times the recommended rates for
soil type were apparent. In 1996 and 1997, M017 injury from metolachlor was reduced by

benoxacor (Figure 1). In 1996, visual injury to M017 was 60% for metolachlor alone, and

 

1TeeJet 8003, Spraying Systems Co., North Ave, Wheaton, IL 60188.

5

12% for metolachlor plus benoxacor. In 1997, visual injury to M017 was 23% for
metolachlor alone, and 1% for metolachlor plus benoxacor. However, not all plants showed
typical injury symptoms. The percentage of total plants showing typical injury symptoms in
1996 was 42% for metolachlor alone, and 8% for metolachlor plus benoxacor. In 1997, the
percentage of total plants showing injury symptoms was 25% and 4% for metolachlor alone
and metolachlor plus benoxacor, respectively. Rowe et a1. (1991) reported that benoxacor
does not influence the amount of metolachlor absorbed by com seedlings, and that the
mechanism by which benoxacor protects corn from metolachlor injury is by enhancement
of herbicide metabolism.

In 1996, M017 injury from unsafened acetochlor was reduced by safeners MON-
13900 and dichlormid, and differences between safeners were not apparent (Figure 2). The
percentage of total plants showing typical injury symptoms in 1996 was 27% for acetochlor
alone, and 2% and 5% for acetochlor plus MON-13900 and dichlormid, respectively. No
differences in visual injury were observed in 1997 between acetochlor plus dichlormid and
acetochlor plus MON-13900. Leavitt and Penner (1978) reported that dichlormid was the
most effective of six potential antidotes evaluated in protecting corn hybrids form alachlor
and metolachlor. Sprague et al. (1999) reported that MON-13900 reduced injury to corn
hybrids from isoxaflutole, [5-cyclopropyl-4-(2—methylsulfonyl-4-
trifluoromethylbenzoyl)isoxazole]. Data from these studies demonstrate that safeners
increase the tolerance of corn inbreds to acetarnide herbicides, and that com inbred injury
from acetarnide herbicides varies among herbicides.

In 1996 and 1997, corn inbred injury varied among commercially available acetarnide

herbicides (Figure 3). Dimethenarnid and flufenacet plus metribuzin injured M017 greater

than 20% in 1996 and 1997. In 1996 dimethenamid and flufenacet plus metribuzin visually
injured M017 more than metolachlor plus benoxacor, acetochlor plus MON-13900, and
acetochlor plus dichlormid. Herbicides that included safeners injured M017 less than 15%
both years. The percentage of injured plants was greatest fiom flufenacet plus metribuzin
both years. Metribuzin could be responsible for the increased injury. Olson et a1. (1979)
showed that metribuzin injured corn hybrids. The percentage of injured plants from
dimethenamid was greater than acetochlor plus MON-13900 in 1996 and metolachlor plus
benoxacor in 1997.

The results of this research indicate that herbicide application rate influences
acetarnide injury to corn. Injury to B73 and M017 was not observed when herbicides were
applied at rates recommended for the soil type. Safeners consistently decreased injury of
M017 to acetarnide herbicides. Injury to acetarnide herbicides varied between B73 and
M017, indicating that the inherent sensitivity of corn inbreds influences their response to
acetarnide herbicides. Inbreds also responded differently among acetarnide herbicides.
Therefore seed companies should screen all inbreds with commonly used corn herbicides,

and use herbicides that include safeners when possible.

 

LITERATURE CITED
Bickner, B. P. 1993. Hybrid Com, past, present, and future. Frontiers of Plant Sci. 4622-4.

Hatzios, K. K. 1984. Interactions between selected herbicides and protectants on corn
(Zea mays). Weed Sci. 32:51-58.

Hoffman, O. L. 1962. Chemical seed treatments as herbicide antidotes. Weeds. 10:322-
323.

Leavitt, J. R. C. and D. Penner. 1978. Protection of corn from acetanilide herbicide injury
with the antidote R-25788. Weed Sci. 26:653-659.

Narsaiah, D. B. and R. G. Harvey. 1977. Differential responses of corn inbreds and
hybrids to alachlor. Crop Sci. 17:65 7-659.

Olson, J. O. 1979. Factors affecting the tolerance of corn to metribuzin. Proc. North Cent.
Weed Control Conf. 34:54-55.

Roggenbuck, F. C. and D. Penner. 1987. Factors influencing corn (Zea mays) tolerance to
trifluralin. Weed Sci. 35:89-94.

Rowe, L., J. J. Kells, and D. Penner. 1991. Efficacy and mode of action of CGA-154281,
a protectant for corn (Zea mays) from metolachlor injury. Weed Sci. 39:78-82.

Rowe, L. and D. Penner. 1990. Factors affecting chloroacetanilide injury to corn. Weed
Technol. 4:904-906.

Sprague, C. L., D. Penner, and J. J. Kells. 1999. Enhancing the margin of selectivity of
RPA 201772 in Zea mays with antidotes. Weed Sci. 47:492-497.

Winkle, M. E., J. R. C. Leavitt, and O. C. Burnside. 1980. Acetamilide-antidote
combinations for weed control in corn and sorghum. Weed Sci. 28:699-704.

 

Table 1. Rainfall accumulation for 14 days after herbicide application at the research site.

 

 

 

 

Days after application 1996 1997
Rainfall (cm)

0-7 1.2 2.8

8-14 2.4 0.5

Total 3.6 3.3

 

Percent (%)

70

 

metolachlor without benoxacor I metolachlor with benoxacor

 

 

 

 

 

 

3‘.
J
g; .
.3. .
4'3
:3;
r;
1!
Ti.

1’34»-

1.».; i. 5“

 

 

 

1996 1997 1996 1997
Injury Injured plants

Figure 1. Response of inbred M017 to metolachlor at three times the typical use
rate with and without benoxacor.

70

 

- unsafened acetochlor

 

 

 

60 I acetochlor plus MON-13900 E] acetochlor plus dichlormid
LSDQOS = 26
50 _
r; 40 -
e
E
Q.)
8
a 30 .

 

 

 

 

 

 

 

 

 

 

 

 

1996 1997

l 996 1997
Injury Injured plants

Figure 2. Response of inbred M017 to acetochlor at three times the typical

use rate affected by MON-13900 and dichlormid. Acetochlor
without safener was not included in 1997.

11

 

acetochlor plus MON-13900

I dimethenamid
E] alachlor

I acetochlor plus dichlormid
flufenacet plus metribuzin

I metolachlor plus benoxacor

 

 

 

=6

..\ \
.A
1
(I.

LSD0.05

 

 

 

 

 

7

1

I
.c.

\ . .
I

LSDoos =

 

 

  

 

   
        

LSDODS

 

 

 

 

r .

m
0.
L

 

 

70

20
10 _
0

a m.

exp “808$

1996 1997
Injured plants

12

1997
acetarnide herbicides applied at three times the typical use

rate.

Injury
Figure 3. Response of corn inbred M017 to commercially available

1996

CHAPTER 2
Response of Com (Zea mays L.) Inbreds to Preemergence and Postemergence
Herbicides

Abstract. Weed growth in seed corn production fields after detasseling and male row
removal has made herbicide applications an important management practice. Two inbred
parents grown together in the same field creates crop safety concerns related to herbicide use
in seed com production fields. Greenhouse and field trials were conducted to determine the
response of eight corn inbreds to four preemergence and four postemergence herbicides.
Isoxaflutole and pendimethalin injured all corn inbreds in the greenhouse. Inbreds 3 (Iodent
family) and 24 (C103 family) were sensitive to all preemergence herbicides in the
greenhouse. Isoxaflutole was the only preemergence herbicide to delay initiation of tassel
emergence in field trials. Nicosulfuron did not injury corn inbreds in the greenhouse or in the
1998 field trials. However, injury to inbred 1 (Flint family) from nicosulfuron was observed
in the 1999 field trial. Fluthiacet injured inbreds 3 and 24 in the greenhouse. Bromoxynil
injury was less than 12% on any corn inbred in the greenhouse or field trial. Dicamba did not
injury corn inbreds in the greenhouse. However, dicamba injured certain inbreds in 1998 and
1999 field trials. Postemergence herbicides did not delay initiation of tassel emergence. Corn
inbreds vary in their sensitivity to preemergence and postemergence herbicides. Inbreds 3
and 24 were more sensitive to preemergence and postemergence herbicides than other
inbreds. Herbicides and corn inbreds must be matched carefully to assure crop safety.

Nomenclature: bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; dicamba, 3,6—dichloro-2-
methoxybenzoic acid; fluthiacet, [[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H, 3H-

[1,3,4]thiadiazolo[3,4—a]pyridazin-1-y1idene)amino]phenyl]thio]acetate; isoxaflutole, [5-

l3

cyclopropyl-4-(2-methylsulfony1-4-trifluoromethylbenzoyl)isoxazole]; nicosulfuron, 2-
[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-
pyridinecarboxamide; pendimethalin, N-( 1 -ethylpropyl)-3 ,4-dimethyl-2 ,6-
dinitrobenzenamine; corn, Zea mays L.

Abbreviations: DAT, days after treatment.

 

14

INTRODUCTION

Hybrid corn (Zea mays L.) is a cross of two or more unrelated lines of corn, known
as inbreds (Bickner 1993). Seed corn production is an important step in the production of
high yielding corn hybrids. Although agronomic practices for seed corn production are
similar to commercial com production, the production of seed corn requires more intense
management (Wych 1988). Weed control is one of the most challenging management
concerns in production of seed corn. Two practices that affect weed control in seed corn
production are detasseling and male row removal. Detasseling involves removal of the tassel
from the seed parent either manually or in combination with mechanical operations. The
male row is the pollen parent in seed corn production fields. The removal of the male row
eliminates the possibility of seed contamination, at harvest, from the pollen parent and can
also increase yield by reducing competition with developing seed parent for nutrients and
water (Craig 1977). Detasseling and removal of the pollen parent (male row) increases the
chance of weeds germinating and growing in seed corn production fields. Light transmission
through the crop canopy after detasseling and male row removal is a likely reason for
increased weed grth in seed corn fields. Harvey and McNevin (1990) reported that rows
spaced 102 centimeters apart are less competitive with weeds than rows spaced 76
centimeters apart. The potential for weed growth in seed corn fields has made herbicide
applications an important management practice in the production of seed corn (Craig 1977).

Crop safety is a concern when using herbicides in seed corn production fields. Seed
corn companies and growers are concerned about applying herbicides safely because inbreds
typically lack the plant vigor associated with corn hybrids (Bickner 1993). Two inbred

parents growing in the same field is another concern when using herbicides in seed com

15

 

production fields. Differences in herbicide tolerance between parent inbreds can result in
observed differences in corn injury. Green and Ulrich (1993), Penner et a1. (1986), and
Narsaiah and Harvey (1977) reported differences in corn inbred tolerance to herbicides. In
seed corn production it is essential that the female and male parents flower on the same date
(Craig 1977). Poor pollination results when the male and female inbreds fail to flower during
the same time frame. Poor pollination could result in reduced yield.

Seed corn production is very important to the agriculture economy in southwest
Michigan. Seed corn is considered a high value crop. Seed corn companies and farmers try
to obtain the highest economic return per acre as possible. Reducing weed competition and
crop damage are two important factors in managing seed corn to produce the highest
economic return. The objective of this research was to characterize the tolerance of eight
commercial corn inbreds to common preemergence and postemergence herbicides. The eight

inbreds used in all trials represent seven different inbred families (Table 1).

MATERIALS AND METHODS
Greenhouse Experiments. Greenhouse trials were conducted to determine tolerance of corn
inbreds to preemergence and postemergence herbicides under controlled environmental
conditions. All greenhouse trials were conducted at Michigan State University, East Lansing,
MI with a Spinks loamy sand (sand, mixed, Mesic Psarnmentic Hapludalfs) soil that had a
pH of 6.9 and 3% organic matter. Plants were grown at air temperature of 25 i 5 C with a
16-h photoperiod of natural lighting supplemented with sodium vapor lighting to provide a
total midday light intensity of 1,000 umol/mz/s photosynthetic photon flux at plant height.

Premergence trials had four seeds per pot and postemergence trials had one seed per pot

16

 

planted 2.5 cm deep in 910 ml plastic pots. Herbicides were applied at two and four times
the typical use rates using a continuous link-belt sprayer equipped with an even flat fan
nozzle‘ calibrated to deliver 234 L/ha at an operating pressure of 220 kPa.

Herbicide treatments for preemergence greenhouse experiments consisted of
untreated, isoxaflutole at 157 gm and 314 g/ha, acetochlor, 2-chloro-N-(ethoxymethyl)-N—
(2-ethy1-6-methy1phenyl)acetarnide; plus MON-4660, 4-(dichloroacetly-1-oxa—4-azaspiro-
(4,5)-decane; at 3.6 kg/ha and 7.2 kg/ha, and pendimethalin at 2.2 kg/ha and 4.4 kg/ha. To
incorporate preemergence treatments 125 m1 of water was added to each individual pot
immediately after herbicide application.

Herbicide treatments for postemergence greenhouse experiments consisted of
untreated, nicosulfuron at 70 g/ha and 140 g/ha with non-ionic surfactant at .25 % (v/v) and
28% nitrogen at 9 MM, fluthiacet at lOg/ha and 20 g/ha with crop oil concentrate at 2.4
L/ha, bromoxynil at 0.84 kg/ha and 1.68 kg/ha, and dicamba at 0.56 kg/ha and 1.12 kg/ha.
For the postemergence greenhouse trials extra pots were planted and used to select a turiform
population. Plants in postemergence trials were at V3 stage of development when treated
(Ritchie et a1. 1989).

All experiments were conducted as completely randomized design with four
replications and repeated. Corn injury, plant height, and plant dry weight 14 days after
treatment (DAT) were collected for all greenhouse studies. Visual injury ratings were based
on a scale of 0 to 100, with 0 representing no effect and 100 representing plant death. Corn
height and plant dry weight was calculated as a percentage of the nontreated plants, with 0
representing plant death and 100 representing height and dry weight equal to nontreated

plants.

 

'TeeJet 8001B, Spraying Systems Co., North Ave., Wheaton, IL 60188.

17

Field Experiments. Field trials were conducted in 1998 and 1999 to determine tolerance of
corn inbreds to preemergence and postemergence herbicides under field environmental
conditions. All field experiments were conducted at the Michigan State University Crop and
Soil Science Research Farm at East Lansing, MI on a Capac loam (fine-loamy, mixed mesic
Aerie Ochraqualf) soil. All field experiments were designed as split plots with three
replications. The main plots were herbicides and subplots were inbred varieties. Sub plots
were four 76 cm corn rows wide and 7.6 m long. Herbicide treatments were applied on the
center rows and the outside rows were untreated. One of the center rows was treated at two
times the typical use rate and the other row was treated at four times the typical use rate. All
herbicides were applied with a tractor mounted compressed air sprayer calibrated to deliver
a 51 cm band over the row at 187 L/ha at 207 kPa using even flat fan nozzlesz. The two rates
of herbicides were applied on the subplots at the same time using multiple tanks and nozzles
mounted on the tractor.

Preemergence Herbicide Experiments. In 1998 a fallow field with a soil pH of 7.7 and 2.3%
organic matter was spring moldboard plowed, disked two times, and field cultivated three
times. In 1999 soybean [Glycine max (L.) Merr.] stubble with a soil pH of 6.1 and 1.0%
organic matter was spring field cultivated three times. In both years prior to the last field
cultivation 318 kg/ha of 46-0-0 (N, P205, K20) fertilizer was broadcast. At planting 6-24-24
(N, P205, K20) fertilizer was applied as a banded neatment 5 cm below and 5 cm beside the
corn seed at 224 kg/ha in 1998 and 280 kg/ha in 1999. Corn inbred seed were planted 3.8
cm deep at 62,400 seeds/ha on June 17, 1998 and May 4, 1999, respectively.

Herbicide treatments for preemergence field experiments consisted of untreated,

 

2TeeJet 8003B, Spraying Systems Co., North Ave., Wheaton, IL 60188.

18

isoxaflutole at 157 g/ha and 314 g/ha, metolachlor, 2-chloro-N-(2-ethy1-6-methylphenyl)-N-
(2-methoxy-1-mehylethy)actamide; plus benoxacor, (4-dichloroacety1)-3,4-dihydro-3-
methyl-2H-1,4-benzoxazine; at 2.83 kg/ha and 5.66 kg/ha, acetochlor plus MON-13900, 3-
dichloroacetyl-S-(2-fi1ranyl)-2,2-dimethyl—oxazolidine; at 3.6kg/ha and 7.2 kg/ha, and
pendimethalin at 2.2 kg/ha and 4.4 kg/ha. Atrazine, [6-chloro-N-ethyl-N’-(l-methylethyl)-
1,3,5-triazine—2,4—diamine] at 1.68 kg/ha was applied preplant incorporated to the entire
study area to minimize annual weed competition. Applications of preemergence herbicides
were on June 18, 1998 and May 4, 1999, respectively. Rainfall in 1998 and 1999 was not
ideal for incorporation of herbicides into the soil. Efforts were made in 1998 to incorporate
herbicide treatments by applying 1.2 cm of over head irrigation on June 22, 1998. Rainfall
amounts 0-14 DAT in 1998 and 1999 are listed in Table 2.

Corn injury was evaluated 28 DAT in 1998 and 35 DAT in 1999. Other data collected
were number of days from planting to seedling emergence, and number of days from planting
to initiation of tassel emergence. Visual injury ratings were based on a scale of 0 to 100, with
0 indicating no effect and 100 indicating plant death.

Postemergence Herbicide Experiments. In 1998 corn stubble with a soil pH of 6.8 and 1.7%
organic matter was chisel plowed, in the fall of 1997, and spring field cultivated two times.
In 1999 soybean stubble with a soil pH 7.0 and 1.6% organic matter was spring field
cultivated two times. In both years prior to the last field cultivation 318 kg/ha 46-0-0 (N,
P205, K20) fertilizer was broadcast. At planting 6-24-24 (N, P205, K20) fertilizer was
applied as a banded treatment 5 cm below and 5 cm beside the corn seed at 302 kg/ha in
1998 and 280 kg/ha in 1999. Corn inbred seed were planted 3.8 cm deep at 62,400 seeds/ha

on May 15, 1998 and May 7, 1999, respectively. In 1998 the study was located in a field that

19

was com in 1997 so the insecticide tefluthrin [(2,3,5,6-tetrafluoro-4-methylphenyl) methyl-
(1a,3a)-(z)-(i)-3-(2-chloro-3,3 ,3-trif1uoro-1-propenyl)-2,2-
dimethylcyclopropanecarboxylate] at 0.35 kg/ha was T-banded over the row at planting.

Herbicide treatments consisted of untreated, nicosulfuron at 70 g/ha and 140 g/ha
with non-ionic surfactant at .25% (v/v) and 28% nitrogen at 9 L/ ha, fluthiacet at 10 g/ha and
20 g/hawith crop oil concentrate at 2.4 MM, bromoxynil at 0.84 kg/ha and 1.68 kg/ha, and
dicamba at 0.56 kg/ha and 1.12 kg/ha. Metolachlor plus benoxacor at 1.42 kg/ha, and
atrazine at 1.68 kg/ha were applied preplant incorporated to the entire study area to minimize
annual weed competition. Applications ofpostemergence herbicides were on June 15, 1998
and June 8, 1999, respectively. At time of herbicide application all inbreds were at V4-V5
stage of development (Richie et a1. 1989), averaged 6-7 visible leaves, and plant height
ranged from 7 to 11 inches.

Corn injury was evaluated 14 DAT both years, and number of days from planting to
initiation of tassel emergence was also recorded. Visual injury ratings were based on a scale
of 0 to 100, with 0 indicating no effect and 100 indicating plant death.

Statistical Analysis. Greenhouse data were subjected to the F-max test for homogeneity of
variance which indicated that the data could be combined over nms. The F-max test showed
that field data was non-homogenous. Therefore, data from each year were analyzed and
reported separately. All data were subjected to analysis of variance (ANOVA) and means
were separated using the least significant difference procedure at the 0.05 level. Arcsine
transformations were conducted. Transformations did not affect interpretation of the data,

therefore nontransformed means are presented.

20

RESULTS AND DISCUSSION

Preemergence Herbicide Studies. Herbicides applied at four times the typical use rates
provided the best representation of the effects for both greenhouse and field nials. Therefore,
data fiom herbicides applied at four times the typical use rates are presented for clarity. The
response of corn inbreds to preemergnce herbicides in the greenhouse is reported in Table
3. Pendimethalin and isoxaflutole severely injured all corn inbreds. Pendimethalin injury
ranged from 31% with inbred 1 to 88% with inbred 24. Isoxaflutole injury ranged from 12%
with inbreds 15 and 16 to 43% with inbred 24. Acetoclor plus MON-13900 severely injured
only two inbreds (3 and 24). With inbreds 3 and 24, visual injury was increased, and plant
height and dry weight were decreased by all three herbicides. This data demonstrates
differential tolerance among inbreds.

Isoxaflutole was the only preemergence herbicide in 1998 and 1999 field studies to
injure corn inbreds. Therefore, only corn inbred response to isoxaflutole is reported in Table
4. Preemergence herbicides did not delay crop emergence either year (data not shown).
Isoxaflutole caused visual injury and delayed the number of days to initiation of tassel
emergence both years. Luscombe et a1. (1994) reported that isoxaflutole is available for plant
uptake for six weeks after application. Corn inbred injury ranged from 78% with inbred 11
to 92% with inbred 15 in 1998. Injury in 1999 ranged from 13% with inbred 27 to 84% with
inbred 24. Initiation of tassel emergence was delayed by exposure to isoxaflutole with all
inbreds compared to untreated plants. For example, treated plants of inbred 26 took 26%
longer to tassel compared to the untreated plants in 1998. All inbreds except l6 and 27
required more growing degree days to tassel compared to untreated plants in 1999. Inbred

24 took 11% longer to tassel compared to untreated plants. Sprague et a1. (1999) reported

21

that the difference in corn hybrid tolerance to isoxaflutole was primarily due to differential
herbicide metabolism.

Environmental conditions influence inbred response to herbicides. Corn injury
increased as soil moisture content increased (Rowe et a1. 1991). Roggenbuck and Penner
(1987) reported that temperature influenced injury to trifluralin [2,6—dinitro—N,N-dipropyl-4-
(trifluoromethyl)benzenamine] more than soil moisture levels but both are important.
Environmental conditions may increase herbicidal activity or reduce the plants tolerance to
herbicide exposure. For example, pendimethalin caused 31-88% injury in greenhouse trials,
but caused no injury in field trials. Lack of corn injury from pendimethalin in 1998 or 1999
field studies is likely due to lack of exposure of the corn roots to the herbicide. In the
greenhouse, inigation applied at the time of herbicide application resulted in pendimethalin
migration through the soil to the roots, resulting in injury to corn inbreds. Lueschen and
Behrens (1977) reported that com hybrids exhibited a range of susceptibility to
pendimethalin but could not be easily grouped into tolerant and susceptible categories.
Postemergence Herbicide Studies. The response of corn inbreds in a greenhouse varied
between repeated trials of the experiment. No injury occurred in the first trial while herbicide
injury was observed in the second trial. Fluthiacet was the only herbicide to injure corn
inbreds. Therefore, only corn inbred response to fluthiacet from the second trial is reported
in Table 5. Fluthiacet injured only inbreds 3 and 24. Injury to each inbred was 19%, and
plant height and dry weight were decreased. No published data reports this variable response
among corn inbreds to fluthiacet. However, Fausey (1999) reported that decreased herbicide
retention, absorption, translocation, and increased metabolism contributed to corn tolerance

to fluthiacet.

22

The response of com inbreds to postemergnce herbicides in 1998 and 1999 field
studies are reported in Table '6. Herbicides did not delay growing degree days for initiation
of tassel emergence in any inbred (data not shown). Nicosulfuron did not injury any inbreds
in 1998, however in 1999, inbred 1 had 38% injury. Inbred 1 belongs to the flint family.
Green and Ulrich (1993) reported that flint inbreds varied widely in sensitivity to
sulfonylurea herbicides. However, inbred 1 is used as a female in seed production, and Green
and Ulrich (1993) reported that all female inbreds were tolerant of nicosulfuron Kang (1993)
reported that sensitivity to nicosulfuron is caused by a single recessive gene. In 1999, inbreds
15, 16, 24, and 27 exhibited intermediate sensitivity to nicosulfuron with injury ranging fiom
9 to 15%. Injury from fluthiacet was greatest on inbred 24 with 22% injury in 1998 and 12%
injury in 1999. Bromoxynil did not cause greater than 12% injury either year. Schafer and
Chilote (1970) reported susceptibility to bromoxynil is based on differential translocation
and degradation. Injury from dicamba was greatest on inbred 1 with 30% injury in 1998 and
12% injury in 1999. Inbred 16 had 23% injury from dicamba in 1998, but had no injury from
dicamba in 1999. Hansen and Buchholtz (1950) reported differences in com inbred tolerance
to 2,4-D, (2,4-dichlorophenoxy)acetic acid. The mode of action of dicamba is similar to that
of 2,4-D (Miller 1952). The exact sites of action of dicamba are not known and are believed
to be multiple (Gunsolus and Curran 1994). Dicamba alters the hormone balance and protein
synthesis in susceptible plants which results in abnormal growth.

The environment was a factor in the sensitivity of these inbreds. For example,
fluthiacet injured inbreds 3 and 24 in the greenhouse but injured only inbred 24 in the field.

Inbred 1 was injured by nicosulfuron and dicamba only under field conditions.

23

 

The response of corn inbreds to preemergence and postemergence herbicides is
variable. Inbreds 3 and 24 were more sensitive to preemergence and postemergence
herbicides than other inbreds. Inbred injury was not limited to herbicides that have the same
mode of action. For example, inbreds 3 and 24 were sensitive to isoxaflutole, acetochlor, and
fluthiacet in the greenhouse. These three herbicides have distinctly different modes of action.
The results of this research indicates that injury from herbicides is the result of inherent
differences among corn inbreds. Therefore, herbicides and corn inbreds must be matched

carefully to assure crop safety.

24

 

LITERATURE CITED
Bickner, B. P. 1993. Hybrid Corn, past, present, and future. Frontiers of Plant Sci. 46:2-4.

Craig, W. F. 1977. Production of hybrid seed corn. p. 671-719. In G. F. Sprague (ed.)
Corn and Corn Improvement. Agron. Monogr. 18. ASA, CSSA, and SSSA, Madison, WI.

Fausey, J. C. 1999. Enhancing postemergence weed control programs in corn and
soybean with fluthiacet and flurniclorac. Ph.D. Dissertation, Michigan State Univ., East
Lansing, MI. pp.2-29.

Green, J. M. and J. F. Ulrich. 1993. Response of corn (Zea mays L.) inbreds and hybrids
to sulfonylurea herbicides. Weed Sci. 41:508-516.

Gunsolus, J. L. and W. S. Curran. 1994. Herbicide mode of action and injury symptoms.
North Central Regional Extension Publication 377. pp. 4.

Hansen, J. R. and K. P. Buchholtz. 1950. Germination and seedling responses of inbred
lines of corn to 2,4-dichlorophenoxyacetic acid. Agron. J our. 42:452-455.

Harvey, R. G. and G. R. McNevin. 1990. Combining cultural practices and herbicides to
control wild-proso millet (Panicum miliaceum). Weed Tech. 4:433-439.

Kang, M. S. 1993. Inheritance of susceptibility to nicosulfirron herbicide in maize. J.
Heredity 84:216-217.

Lueschen, W. E. and R. Behrens. 1977. Corn hybrid response to preplant and
preemergence pendimethalin application. Proc. North Cent. Weed Control Conf. 32:78.

Luscombe, B. M., T. E. Vrabel, M. D. Paulsgroves, S. Cramp, P. Cain, A. Gamblin, and
J. C. Millet. 1994. RPA201772: A new broad spectrum preemergence herbicide for corn.
Proc. North Cent. Weed Sci. Soc. 49:57-58.

Miller, H. J. 1952. Plant hormone activity of substituted benzoic acids and related
compounds. Weeds 1:185-188.

Narsaiah, D. B. and R. G. Harvey. 1977. Differential responses of corn inbreds and
hybrids to alachlor. Crop Sci. 17:657-659.

Penner, D., F. C. Roggenbuck, and E. C. Rossman. 1986. Tolerance of corn inbreds and
hybrids to the herbicide trifluralin. Annual Corn and Sorghum Research Conf. 41 :155-
159.

25

Ritchie, S. W., J. J. Hanway, and G. O. Benson. 1989. How a corn plant develops.
Special Report No. 48, Iowa State University.

Roggenbuck, F. C. and D. Penner. 1987. Factors influencing corn (Zea mays) tolerance to
trifluralin. Weed Sci. 35:89-94.

Rowe, L., J. J. Kells, and D. Penner. 1991. Efficacy and mode of action of CGA-154281 ,
a protectant for corn (Zea mays) from metolachlor injury. Weed Sci. 39278-82.

Schafer, D. E. and D. O. Chilcote. 1970. Translocation and degradation of bromoxynil in
a resistant and a susceptible species. Weed Sci. 18:729-732.

Sprague, C. L., D. Penner, and J. J. Kells. 1999. Physiological basis for tolerance of four
Zea mays hybrids to RPA 201772. Weed Sci. 47:631-635.

Wych, R. D. 1988. Production of hybrid seed corn. p. 565-607. In G. F. Sprague and J.

W. Dudley (ed.) Corn and Corn Improvement. Agron. Monogr. 18. ASA, CSSA, and
SSSA, Madison, WI.

26

 

Table 1 . Inbred number, corresponding inbred family, and use in commercial seed corn

 

 

production.
Inbred No. Family Seed Parent Pollen Parent

1 Flint x -

3 Iodent x x

1 l SSS—B 14 x -

15 SSS-B73 x -

16 W153R x -
24 C 103 - x
26 SSS—B73 x -
27 SSS-B37 x -

 

27

Table 2. Rainfall accumulation for 14 days after preemergence herbicide application.

 

 

 

 

 

Days after
application 1998 1999
Irrigation Rainfall Rainfall
cm
0—7 1.27 0 0.25
8-14 - 3 .5 2.9
Total 1.27 3.5 3.15

 

28

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29

Table 4. Visual injury and growing degree days to the initiation of tassel emergence in
corn inbreds after preemergence application of isoxaflutole in 1998 and 1999 field trials‘.

 

 

 

 

 

 

 

 

Inbred Injury Growing degree days to tasseling
1998 1999 1998 1999
% —— % of untreated
1 80 43 113 104

3 82 38 111 104

1 1 78 40 112 104

15 92 47 116 107

16 80 68 109 100

24 87 84 112 111

26 88 63 126 106

27 85 13 112 100

 

 

‘ Isoxaflutole was applied at 314 g/ha. Injury was evaluated visually 28 DAT in 1998 and
35 DAT in 1999.

30

Table 5. Visual injury, plant height, and dry weight of corn inbreds 14 days after
postemergence herbicide application of fluthiacet in the greenhouse“.

 

 

 

 

 

Inbred Injury Plant height Dry weight
96 ————————-96cndunnuued
1 O 91 98
3 19 59 65
11 O 96 98
15 0 Q 105 102
16 O 83 71
24 19 77 72
26 0 97 94
27 0 95 121
LSDWOS, 5 24 — l6 —

 

aFluthiacet was applied at 20 gfha with crop oil concentrate at 2.4 L/ha. Data from one
trial only.

31

Table 6. Visual injury to corn inbreds 14 days after postemergence application of
herbicides in 1998 and 1999 field trials.
Inbred nicosulfurona fluthiacetb bromoxynilc dicambad

1998 1999 1998 1999 1998 1999 1998 1999

 

 

%

 

1 0 38 4 7 7 9 3o 12
3 0 3 3 5 5 9 0 0
11 0 2 3 7 6 6 3 o
15 2 9 7 7 5 7 2 3
16 0 15 4 3 6 12 23 0
24 2 15 22 12 8 9 8 5
26 0 0 5 3 4 3 0 0
27 0 11 8 6 11 2 3
LSDMOS) 7 6 7 6 7 6 7 6

 

aNicosulfuron was applied at 140 g/ha with non-ionic surfactant added at .25% (v/v)
and 28% nitrogen added at 9 L/ha.

b Fluthiacet was applied at 20 g/ha with crop oil concentrate added at 2.4 L/ha.

° Bromoxynil was applied at 1.68 kg/ha.

dDicamba was applied at 1.12 kg/ha.

32

CHAPTER 3

Variation and Inheritance of Isoxaflutole Tolerance in Corn (Zea mays L.)

Abstract. Corn injury from isoxaflutole has been reported in sites across the corn belt.
Variation in tolerance to isoxaflutole has been observed among corn hybrids. Greenhouse
trials were conducted to study the variation and inheritance of isoxaflutole tolerance in corn.
Inbreds from two families were treated with isoxaflutole applied preemergence to study plant
response. Injury to corn inbreds from isoxaflutole ranged from 2% to 44% among lines
within the C103 family and fiom 2% to 48% among lines within the B73 family. One
tolerant and one sensitive inbred line were selected from each family. The inbred lines were
crossed in the field to produce four F1 hybrids. The four hybrids were treated with
isoxaflutole in the greenhouse and tolerance of each hybrid was compared to the parent
inbred lines. Data indicate that sensitivity to isoxaflutole is a heritable trait. These results
suggest that sensitivity to isoxaflutole is mediated by nuclear genes. Tolerance of corn
hybrids to isoxaflutole can be predicted from the response of the parent inbreds.
Nomenclature: isoxaflutole, [5-cyclopropyl-4-(2-methylsu1fonyl-4-
trifluoromethylbenzoyl)isoxazole]; corn, Zea mays L.

Abbreviations: DAT, days after treatment.

33

INTRODUCTION

Isoxaflutole is a preemergence isoxazole herbicide that selectively controls annual
grass and broadleaf weeds in corn (Zea mays L.). Application rates for isoxaflutole are based
on soil texture. Bhowmik et al. (1999) and Young et a1. (1999) showed that com was not
injured after preemergence applications of isoxaflutole. However, Obermeier et a1. (1995),
and Sprague et a1. (1999’) observed injury to corn after preemergence applications of
isoxaflutole. Injury symptoms from isoxaflutole include bleaching of newly developed tissue
followed by necrosis. Luscombe et a1. ( 1994) reported that isoxaflutole is available for plant
uptake for six weeks after application. Corn injury from isoxaflutole is affected by several
factors including soils (Wicks et a1. 1999), environment (Wilson et a1. 1999), and application
technique (Klein et a1. 1999).

Corn inbreds and hybrids have demonstrated differential tolerance to herbicides
including alachlor (Narsaiah and Harvey 1977), trifluralin (Penner et a1. 1986), metolachlor
(Rowe and Penner 1990), and rimsulfuron (Green and Ulrich 1994). Differential tolerance
of isoxaflutole has also been documented in corn hybrids (Sprague et al. 1999’). However,
differences in tolerance to isoxaflutole among corn inbreds have not been reported. The use
of isoxaflutole on sensitive com inbreds could have a negative impact on the successful cross
pollenation and seed corn production in commercial fields. If corn inbreds used to produce
hybrids could be identified as tolerant or sensitive to isoxaflutole, sensitive corn hybrids
could possibly be predicted and thus risk of injury could be reduced. The objectives of this
research was to: 1) determine variation of isoxaflutole tolerance within the B73 and C103

families and 2) study the inheritance of isoxaflutole tolerance in F1 hybrids.

34

MATERIALS AND METHODS

General Experimental Procedures. Greenhouse trials were conducted to determine
variation and inheritance of isoxaflutole tolerance in corn under controlled environmental
conditions. All trials were conducted at Michigan State University, East Lansing, IVII with
a Spinks loamy sand (sand, mixed, Mesic Psammentic Hapludalfs) soil with a pH of 6.9 and
3% organic matter. Plants were grown at ambient air temperature of 25 d: 5 C with a 16-h
photoperiod of natural lighting supplemented with sodium vapor lights to provide a midday
light intensity of approximately 1,000 umol/mZ/s photosynthetic photon flux at plant height.
Four corn seeds were planted 2.5 cm deep in each 910 ml plastic pot. Isoxaflutole was
applied using a continuous link-belt sprayer equipped with an even flat fan nozzlel calibrated
to deliver 234 L/ha at an operating pressure of 220 kPa. Treatments for all greenhouse
experiments consisted of untreated and isoxaflutole preemergence at 314 g/ha, four times a
typical use rate. To incorporate preemergence treatments, 125 m1 of water was added to each
pot immediately after herbicide application.

All greenhouse experiments were conducted as completely randomized designs with
four replications and repeated. Corn injury, plant height, and plant dry weight 14 days after
treatment (DAT) were collected for all studies. Visual injury ratings were based on a scale
of 0 to 100, with 0 representing no effect and 100 representing plant death. Corn height and
plant dry weight were calculated as a percentage of the nontreated plants, with 0 representing
plant death and 100 representing height and dry weight equal to nontreated plants. Plant
height and plant dry weight supported the visual injury rating in all studies, therefore only

visual injury rating are shown.

 

lTeeJet 8001B, Spraying Systems Co., North Ave., Wheaton, IL 60188.

35

Isoxaflutole tolerance in corn inbreds within the B73 and C103 families.

Greenhouse trials were conducted to determine tolerance to isoxaflutole in corn
inbreds within the B73 and C103 families. Separate studies evaluated eight inbred lines
within the B7 3 family and Six inbred lines within the C103 family for tolerance to
isoxaflutole. After determining the variation within the two families, a separate greenhouse
trial was conducted to study the inheritance of isoxaflutole tolerance.

Inheritance of isoxaflutole tolerance.

One tolerant and one sensitive inbred line was selected from both the B73 and C103
families. The tolerant and sensitive inbred lines were crossed in the field, in 1999, to produce
four Fl hybrids. The four hybrids and the four parent inbreds were treated with isoxaflutole
and evaluated for injury.

Crossing Procedure. Tolerant and sensitive inbred lines were crossed in the field to produce
four hybrids. The crossing took place in 1999 at the Michigan State University Crop and Soil
Science Research F arm at East Lansing, MI on a Capac loam (fine-loamy, mixed mesic
Aerie Ochraqualf) soil. Each inbred was planted by hand in single rows. Each inbreds was
planted at three different times to assure synchronization of tassel and silk emergence.
During peak pollination, pollen was collected in color coded paper bags. Paper bags were
placed over ear shoots on female plants to prevent contamination prior to bags containing
pollen was placed over silks and stapled closed around each corn ear until harvest. F, hybrid
corn ears were hand harvested, air dried, and hand shelled.

Statistical Analysis. Statistical analysis revealed no experimental run interactions, so the
data were combined and are reported as means of the two experiments. All data were

subjected to analysis of variance (ANOVA) and means were separated using the least

36

significant difference procedure at the 0.05 level. Arcsine transformations were conducted
on all greenhouse trials. Transformations did not affect interpretation of the data, therefore

nontransformed means are presented for all trials.

RESULTS AND DISCUSSION
Isoxaflutole tolerance in corn inbreds within the B73 and C103 families.

Inbreds within the same family varied greatly in response to isoxaflutole (Figure 1).
Injury to corn inbreds from isoxaflutole ranged from 2% to 48% among lines within the B73
family and from 2% to 44% among lines within the C103 family. Sprague et al. (1999”)
observed differential tolerance in corn hybrids to isox'aflutole and determined that
metabolism rate is the primary basis for differences in tolerance to isoxaflutole.
Inheritance of isoxaflutole tolerance.

The distribution of isoxaflutole sensitivity within corn inbreds fi'om the B73 and
C103 families suggests that no previous selection for isoxaflutole tolerance has occurred
within the inbreds that were evaluated in this research (Figure 2). Five of the 14 inbreds
evaluated had 0-10% injury. Two inbreds had 11-20% injury. Four inbreds had 21-30%
injury. One inbred had 31-40% injury and two inbreds had 41-50% injury.

Inbreds from the B73 family are used as female (seed bearing) parents in commercial
seed corn production and inbreds from the C103 family are used as male (pollenator) parents.
Inbred 18 was selected as a sensitive inbred line in the B73 family with 48% injury. Inbred
23 had 2% injury and was selected as a tolerant inbred line in the B73 family. Inbred 22 had
44% injury from isoxaflutole and was selected as a sensitive inbred line in the C103 family.

Inbred 30 was injured 2% from isoxaflutole and was selected as a tolerant inbred line in the

37

C103 family. Four crosses were conducted using inbreds 18 and 23 as females and inbreds
22 and 30 as males.

The inheritance of isoxaflutole tolerance fiom inbreds to F, hybrids is reported in
Figure 3. The hybrid from inbreds 18x22 (sensitive x sensitive cross) was injured 48%. The
hybrid fi'om a sensitive female (18) and a tolerant male (30) had 9% injury. The hybrid from
a tolerant female (23) and a sensitive male (22) also had 9% injury. The hybrid from inbreds
23x30 (tolerant x tolerant cross) was injured only 2%. These results indicate that tolerance
to isoxaflutole is a heritable trait. All F, hybrids exhibited equal or less isoxaflutole injury
than either parent inbred suggesting heterosis. The characteristics that most commonly
distinguish hybrid corn plants from their inbred parents are more rapid growth, larger size,
greater yield potential, and greater tolerance to herbicides.

Tolerance to isoxaflutole was equally inherited from both the male and female
parents, suggesting that this trait is mediated by nuclear genes. Inheritance of isoxaflutole
does not appear to be influenced by maternal or cytoplasmic genes. Research has Shown that
sensitivity of corn inbreds to ALS-inhibiting herbicides can be caused by a single recessive
gene (Widstrom and Dowler 1995; Green and Ulrich 1993 and 1994; Kang 1993;).
Additional research is needed to determine the genetic basis for inheritance of isoxaflutole
tolerance.

Tolerance to isoxaflutole varies widely among com inbreds. An understanding of the
level of tolerance of corn inbreds would be valuable when isoxaflutole is used for weed
control in seed corn production fields.

Tolerance of corn hybrids to isoxaflutole can be predicted fiom the response of the

parent inbreds. Screening all important developmental corn inbreds for tolerance to

38

isoxaflutole should be conducted by com breeding programs so that sensitive inbreds can be
identified. Hybrids produced from two sensitive inbreds will likely be sensitive and thus
have a greater risk of injury form isoxaflutole. Information on the relative tolerance of corn

hybrids to herbicides is extremely useful in developing weed management strategies.

39

LITERATURE CITED

Bhowmik, P. C. S. Kushwaha, and S. Mitra. 1999. Response of various weed species and
corn (Zea mays) to RPA 201772. Weed Technol. 13:504-509.

Green, J. M. and J. F. Ulrich. 1993. Response of corn (Zea mays L.) inbreds and hybrids
to sulfonylurea herbicides. Weed Sci. 41 :508-516.

Green, J. M. and J. F. Ulrich. 1994. Response of maize (Zea mays) inbreds and hybrids to
rimsulfuron. Pestic Sci. 40:187-191.

Kang, M. S. 1993. Inheritance of susceptibility to nicosulfuron herbicide in maize. J.
Heredity 84:216-217.

Klein, R. N., G. A. Wicks, R. G. Wilson, A. R. Martin, F. W. Roeth, and S. Knezevic
1999. Factors affecting isoxaflutole injury to corn in Nebraska: Application. Proc. North
Cent. Weed Sci. Soc. 54:(In Press).

Narsaiah, D. B. and R. G. Harvey. 1977. Differential responses of corn inbreds and
hybrids to alachlor. Crop Sci. 172657-659.

Obermeier, M. R., C. H. Slack, J. R. Martin, and W. W. Witt. 1995. Evaluations of
EXP31130A-a new preemergence corn herbicide. Proc. N. Cent. Weed Sci. Soc. 50:25.

Penner, D., F. C. Roggenbuck, and E. C. Rossman. 1986. Tolerance of corn inbreds and
hybrids to the herbicide trifluralin. Annual Corn and Sorghum Research Conf. 41 :155-
159.

Rowe, L. and D. Penner. 1990. Factors affecting choloracetanilide injury to cOrn. Weed
Technol. 42904-906.

Sprague, C. L., J. J. Kells, and D. Penner. 1999a. Weed control and corn (Zea mays)
tolerance from soil-applied RPA 201772. Weed Technol. 13:713-725.

Sprague, C. L., D. Penner, and J. J. Kells. 1999’. Physiological basis for tolerance of four
Zea mays hybrids to RPA 201772. Weed Sci. 47:631-635.

Wicks, G. A., R. N. Klein, R. G. Wilson, F. W. Roeth, S. Knezevic, and A. R. Martin.
1999. Factors affecting isoxaflutole injury to corn in Nebraska: Soils. Proc. North Cent.
Weed Sci. Soc. 54:(In Press).

Widstrom, N. W. and C. D. Dowler. 1995. Sensitivity of selected field corn inbreds (Zea
mays) to nicosulfuron. Weed Technol. 92779-782.

40

Wilson, R. G., G. A. Wicks, R. N. Klein, F. W. Roeth, S. Knezevic, and A. R. Martin.
1999. Factors affecting isoxaflutole injury to corn in Nebraska: Environmental. Proc.
North Cent. Weed Sci. Soc. 54:(In Press).

Young, B. G., S. E. Hart, and F. W. Simmons. 1999. Preemergence weed control in
conventional-till corn (Zea mays) with RPA 201772. Weed Technol. 13:471-477.

41

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42

Number of inbreds

 

0-10 % injury
21—30 % injury

I 11-20 % injury
31-40 % injury

 

I 41-50 % injury

 

 

 

 

 

 

Figure 2. Distribution of isoxaflutole sensitivity within corn inbreds
from the B73 and C103 families. Isoxaflutole was applied
at 314 g/ha, evaluated 14 days after treatment in the greenhouse.

43

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44

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45

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46

Table 3. Visual injury to corn inbreds 28 days after preemergence application of
herbicides applied at twice the typical use rate in the 1998 field season.

 

 

 

 

Inbred Balancea Dual 11 Magnumb Harnessc ProwlCl
%

1 35 O O 0
3 50 O O O
6 55 0 O 0
1 1 42 O O 0
14 9O 0 O O
15 62 O 0 O
16 43 O O O
22 72 0 O O
24 62 O O O
26 50 O O 0
27 33 0 O 0
31 75 O 0 O
33 75 0 O O
37 67 0 O 0
38 6O 0 O O
39 47 0 O O

LSDQWDS) = 15

 

‘ Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).
bTypical use rate of Dual [1 Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i./A).
° Typical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

dTypical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

47

Table 4. Visual injury to corn inbreds 35 days afier preemergence application of
herbicides applied at twice the typical use rate in the 1999 field season.

 

 

 

 

Inbred Balancea Dual II Magnumb Harnessc Prowld
%

1 23 O O O
3 O O O O
6 17 O O O
1 l O O O 0
l4 3 5 O 0 O
1 5 3 O O O
l 6 23 O 0 0
22 40 O O 0
24 79 0 O O
26 13 O O O
27 O 0 0 O
3 1 28 O 0 O
33 0 O 0 O
3 7 70 O O O
3 8 5 O O O
3 9 0 O 0 O

LSD=(,,SO,05,= 13

 

aTypical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).

b Typical use rate of Dual 11 Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i./A).
cTypical use rate of Harness SL is 1.6 pt/A (1.6 lbs a.i./A).

dTypical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

‘ LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

48

Table 5. Visual injury to corn inbreds 28 days after preemergence application of
herbicides applied at four times the typical use rate in the 1998 field season.

 

 

 

 

Inbred Balancea Dual 11 Magnumb Harness“ Prowl“
%

l 80 0 O 0
3 82 0 O O
6 78 0 0 O
1 1 78 O O O
14 98 0 0 O
15 92 O 0 0
16 80 0 0 O
22 93 0 0 0
24 87 0 0 0
26 88 O O 0
27 85 O 0 0
31 92 0 0 O
33 93 0 0 0
37 97 O 0 0
38 89 0 0 0
39 88 O O O

LSDcmgoo» = 5
LSDf(p50DS) = 6

 

anTypical use rate of Balance 75DF is 1.5 071A (0.07 lbs a.i./A).
bTypical use rate of Dual 11 Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i.lA).
cTypical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

49

Table 6. Visual injury to corn inbreds 35 days after preemergence application of
herbicides applied at four times the typical use rate in the 1999 field season.

 

 

 

 

Inbred Balancea Dual H Magnumb Harnessc Prowl“
%
1 43 0 0 0
3 3 8 3 0 0
6 25 0 O 8
1 1 4O 0 0 0
14 50 O 0 3
15 47 O 0 O
16 68 O 0 O
22 83 O 0 0
24 84 0 O 0
26 63 0 0 0
27 13 O 2 O
31 73 3 0 0
33 48 O O O
37 83 O 0 O
3 8 8 O 0 O
39 7 O O O
Lspcugm= 18

 

3‘ Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).
bTypical use rate of Dual 11 Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i./A).
‘ Typical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i.lA).

° LSD to compare between inbred means within a herbicide.

‘ LSD to compare between herbicide means within an inbred.

50

Table 7. Growing Degree Days as % of the control to com inbreds afier preemergence
application of herbicides applied at twice the typical use rate in the 1998 field season.

 

 

 

 

Inbred Balance“ Dual H Magnum“ Harnessc Prowl“
96
l 106 98 99 101
3 105 100 101 99
6 107 100 101 101
11 103 100 100 100
14 110 99 100 101
15 107 99 101 101
16 106 100 100 100
22 107 98 100 101
24 105 98 101 99
26 106 99 102 99
27 105 99 100 100
31 109 99 100 100
33 105 99 101 100
37 108 99 100 99
38 107 99 100 100
39 104 98 100 101

LSDcwgoo» = 2

LSDfmgom) = 2
“Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).
“Typical use rate of Dual II Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i./A).
cTypical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).
“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).
“ LSD to compare between inbred means within a herbicide.
fLSD to compare between herbicide means within an inbred.

51

Table 8. Growing Degree Days as % of the control to corn inbreds after preemergence
application of herbicides applied at twice the typical use rate in the 1999 field season.

 

 

 

 

Inbred Balance“ Dual H Magnum“ Harnessc Prowl“
96
l 104 100 100 100
3 101 101 100 100
6 100 100 100 100
11 101 102 100 98
14 102 99 99 100
15 102 103 99 102
16 100 100 100 100
22 111 101 100 99
24 108 99 99 99
26 103 97 101 99
27 100 100 101 100
31 102 102 100 99
33 102 102 103 100
37 106 101 99 99
38 101 100 100 101
39 98 103 100 100
LSD‘GEQOS) = 6
LSDENDS) = 4

 

“Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).
“Typical use rate of Dual II Magnum 7.64L is 1.3 pt/A (1 .26 lbs a.i./A).
° Typical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

“ LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

52

Table 9. Growing Degree Days as % of the control to corn inbreds after preemergence
application of herbicides applied at four times the typical use rate in the 1998 field
season.

 

 

 

 

Inbred Balance“ Dual 11 Magnum“ Harnessc Prowf
96
1 113 98 99 100
3 111 100 100 100
6 110 100 101 101
11 112 100 100 101
14 143 99 100 101
15 116 100 101 101
16 109 100 100 100
22 113 98 100 101
24 112 99 102 100
26 126 99 101 99
27 112 99 100 101
31 143 99 100 100
33 124 99 101 100
37 131 99 100 99
38 129 99 100 99
39 110 98 100 101
LSDe(p50.05) = 6

 

“Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).

“ Typical use rate of Dual II Magnum 7.64L is 1.3 pt/A (1 .26 lbs a.i./A).
° Typical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

“ LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

53

Table 10. Grong Degree Days as % of the control to corn inbreds afier preemergence
application of herbicides applied at four times the typical use rate in the 1999 field
season.

 

 

 

 

Inbred Balance“ Dual 11 Magnum“ Harnessc Prowl“
96
l 104 100 100 100
3 104 100 100 100
6 100 100 100 100
11 104 102 100 100
14 103 99 100 102
15 107 102 101 102
16 100 100 100 100
22 115 100 101 100
24 111 99 99 104
26 106 98 101 99
27 100 100 102 100
31 104 101 100 100
33 103 102 103 101
37 113 100 99 99
38 104 100 101 101
39 100 102 101 100
LSDcmsoos) = 4

LSDfODSOOS) = 5

 

“ Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).

“ Typical use rate of Dual 11 Magnum 7.64L is 1.3 pt/A (1.26 lbs a.i./A).
“ Typical use rate of Harness 8L is 1.6 pt/A (1.6 lbs a.i./A).

“Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

“ LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

54

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55

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56

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57

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58

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59

Table 16. Plant height as % of the control to corn inbreds 14 days afier postemergence
application of herbicides in a greenhouse applied at four times the typical use rate.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“

96

1 101 102 90 94

3 104 77 91 101

1 1 100 91 89 94

15 99 102 88 97

16 90 86 87 89

24 95 85 94 82

26 103 101 91 100

27 100 103 88 98
LSDMO‘OS) 1 1

 

 

 

Table 17. Plant dry weight as % of the control to corn inbreds 14 days after
postemergence application of herbicides in a greenhouse applied at four times the
typical use rate.

 

 

 

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“ Mean“
%
1 89 99 69 75 83
3 95 75 69 76 79
1 1 97 86 62 72 79
15 1 12 97 63 78 88
16 79 76 61 75 73
24 91 77 68 61 74
26 124 99 75 100 100
27 127 128 82 83 105
LSDMDS, NS —1 1—
Mean“ 102 92 78 69
LSD(p50.05) 8

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action SWP is 1.2 oz/A (0.00375 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

“Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is 1/z pt/A (.25 lbs a.i./A).

° Mean of inbreds averaged over herbicides.

“ Mean of herbicides averaged over inbreds.

60

Table 18. Visual injury to corn inbreds 3 days after postemergence application of
herbicides applied at twice the typical use rate in the 1998 field season.

 

 

 

 

Inbred Accenta Actionb Buctrilc Clarityd
°/o
1 0 1 7 O
3 0 1 7 2
6 O 2 16 23
1 1 0 3 8 O
14 0 2 13 O
15 O 4 9 1
16 0 3 7 9
22 0 6 22 5
24 O 1 5 17 6
26 0 3 14 4
27 0 3 12 3
31 0 2 25 2
33 O 4 13 O
3 7 O 22 25 3
3 8 O 1 20 O
39 0 4 15 0
$137500.) = 7
LSD‘WDS) = 7

 

aTypical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i.lA). NIS was added at
25% (v/v) and 28% nitrogen was added at 4 qt/A.

bTypical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at l qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

dTypical use rate of Clarity 4L is ‘/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

61

Table 19. Visual injury to com inbreds 3 days after postemergence application of
herbicides applied at twice the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accenta Actionb Buctrilc Clarity“
%
1 0 10 12 20
3 0 10 7 15
6 O 8 20 28
1 1 O 7 5 7
14 0 12 10 7
15 O 6 10 15
16 O 4 17 15
22 0 7 15 7
24 O 15 9 8
26 O 7 7 7
27 0 10 13 9
31 0 5 20 8
33 0 7 7 O
37 O 17 18 7
38 0 10 10 15
39 O 10 10 13
LSDc(p§0.05) = 7

LSDQPQOS) = 7

3Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

bTypical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at l qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is 1/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

62

Table 20. Visual injury to corn inbreds 3 days after postemergence application of
herbicides applied at four times the typical use rate in the 1998 field season.

 

 

 

 

Inbred Accenta Action“ Buctrilc Clarity“
%
l 0 3 17 2
3 0 4 25 7
6 0 5 30 3 8
1 l O 5 17 2
14 O 7 22 2
15 0 7 22 13
16 O 4 13 22
22 O 22 30 27
24 0 42 32 13
26 0 5 28 10
27 0 8 3O 6
31 0 2 40 7
33 0 5 25 5
37 0 45 40 8
3 8 0 5 25 7
39 0 7 27 5
L81:)".(p5005) = 7
LSDfmom) = 8

 

IITypical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

cTypical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“ Typical use rate of Clarity 4L is ‘/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

63

Table 21 . Visual injury to corn inbreds 3 days after postemergence application of
herbicides applied at four times the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
96
1 0 13 18 30
3 O 12 11 15
6 0 15 23 4O
11 0 12 11 17
14 O 17 22 12
15 O 12 22 28
16 0 12 20 22
22 0 12 23 8
24 0 25 15 18
26 O 10 15 10
27 O 12 14 15
31 O 8 27 12
33 O 13 13 0
37 O 32 22 10
38 O 12 13 30
39 O 13 17 20
LSDflpSoos) = 8

LSDf(p<0.05) = 9

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i.lA). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is V2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

fLSD to compare between herbicide means within an inbred.

64

Table 22. Visual injury to corn inbreds 7 days after postemergence application of
herbicides applied at twice the typical use rate in the 1998 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
"/0

1 O 2 6 2
3 O 0 6 2
6 O 9 12 12
11 O 2 5 O
14 O 0 8 O
15 O 4 10 2
16 O 2 9 3
22 O 8 1 1 2
24 O 12 1 1 3
26 O 2 10 1
27 O 3 10 0
31 O 2 10 0
33 O 2 7 1
37 O 12 12 7
38 0 1 8 0
39 O O 1 1 0

LSDflpSQOS) = 4
LSDf(p<0.05) = 4

 

“ Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i.lA). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is 1/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

65

Table 23. Visual injury to corn inbreds 7 days afier postemergence application of
herbicides applied at twice the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctril“ Clarity“
°/o
1 22 2 4 6
3 2 3 3 2
6 2 2 8 9
1 1 0 4 5 6
14 O 4 5 2
1 5 4 4 4 3
16 1 O 3 6 2
22 3 6 6 0
24 7 5 5 5
26 0 4 3 O
27 2 4 4 5
3 1 2 4 6 0
33 2 3 4 0
37 1 2 4 1 0 2
3 8 2 3 4 6
39 0 3 4 3
LSD°(pgo.05) = 4

LSDf(p<0.05) = 4

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i.lA).

“Typical use rate of Clarity 4L is 1/2 pt/A (.25 lbs ai./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

66

Table 24. Visual injury to com inbreds 7 days after postemergence application of
herbicides applied at four times the typical use rate in the 1998 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
%
1 0 6 10 5
3 2 3 10 1
6 O 4 15 22
11 0 4 7 2
14 O 2 10 1
15 0 8 11 2
16 O 3 ll 12
22 O 12 14 22
24 0 37 12 8
26 2 4 10 3
27 2 6 13 1
31 2 6 12 O
33 3 6 10 2
37 0 33 17 12
38 5 11 12 4
39 O 8 11 2

LSDe(pSO.05) = 7
LSDfmo'os) = 7

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Cr0p oil concentrate
was added at 1 qt/A.

cTypical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs ai./A).

“Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

67

Table 25. Visual injury to corn inbreds 7 days after postemergence application of
herbicides applied at four times the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
"/0
1 38 2 7 12
3 6 3 4 2
6 4 3 10 25
1 l 0 5 6 7
14 O 7 6 4
15 10 5 7 7
16 17 4 7 7
22 8 10 9 2
24 20 14 6 20
26 0 4 6 2
27 7 7 5 7
31 2 4 12 O
33 2 4 7 0
37 17 7 12 3
38 4 5 6 9
39 0 3 7 4
LSDc(p$0.05) = 8

LSDfmoon = 8

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i.lA). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i.lA).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

68

Table 26. Visual injury to com inbreds 14 days after postemergence application of
herbicides applied at twice the typical use rate in the 1998 field season.

 

Inbred ' Accent“ Action“ Buctrilc Clarity“
%

 

 

l

3
6
ll
14
15
16
22
24
26
27
31
33
37
38
39

p...
O

OOOOOOOHOOOOOOOO
woothhhoowAh-oomom
##Qmamhomhmhkwhm
OOOOONOOONONNNO

LSDf(p<O.05) = 3

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“ Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i.lA).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

69

Table 27. Visual injury to corn inbreds 14 days after postemergence application of
herbicides applied at twice the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
%
1 23 5 7 O
3 O 5 8 O
6 5 3 1 1 2
1 1 O 5 6 O
14 O 4 6 O
15 7 6 6 O
16 10 3 8 O
22 7 7 7 O
24 10 9 5 O
26 O 3 3 O
27 6 4 7 2
3 1 15 4 9 O
33 2 3 4 O
37 3 5 1 l O
3 8 0 6 6 2
39 3 3 7 0
LSDc(p_<_0.05) = 3

LSDf(p<0.05) = 4

 

“ Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i.lA). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clan'ty 4L is “/2 pt/A (.25 lbs a.i.IA).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

7O

Table 28. Visual injury to corn inbreds 14 days afier postemergence application of
herbicides applied at four times the typical use rate in the 1998 field season.

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
%

1 O 4 7 3O
3 O 3 5 0
6 O 4 9 12
1 1 0 3 6 3
14 O 2 6 5
15 2 7 5 2
16 O 4 6 23
22 O 4 8 1 3
24 2 22 8 8
26 O 5 4 0
27 O 8 6 2
3 1 O 5 6 O
3 3 8 6 7 0
37 O 29 12 0
3 8 O 3 5 2
39 0 8 10 2

LSD°(pSo.05) = 7
LSDQKODS) = 7

“ Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“ Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

71

Table 29. Visual injury to corn inbreds 14 days after postemergence application of
herbicides applied at four times the typical use rate in the 1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
%
l 3 8 7 9 12
3 3 5 9 O
6 10 3 l4 7
1 1 2 7 6 O
14 O 5 10 O
1 5 9 7 7 3
1 6 1 5 3 12 O
22 1 l 1 0 10 0
24 1 5 12 9 5
26 0 3 3 O
27 1 1 5 11 3
31 25 8 13 0
33 3 10 6 O
37 3 8 17 O
3 8 2 8 9 9
39 5 3 7 0
LSDc(pfi0.05) = 6
Lsofwos) = 5

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at l qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“ Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

72

Table 30. Growing Degree Days as % of the control to corn inbreds after

‘postemergence application of herbicides applied at twice the typical use rate in the
1998 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
96

1 99 101 99 100
3 103 100 100 100
6 100 100 100 100,
11 99 99 99 100
14 100 101 100 101
15 101 100 99 101
16 100 101 101 101
22 99 101 100 101
24 100 100 100 101
26 101 102 100 98
27 100 98 98 100
31 100 99 100 99
33 100 101 98 100
37 97 100 103 99
38 99 102 98 103
39 100 101 99 103

LSDflpSom = NS
LSDQMDS) = NS

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i.IA). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i.lA).

“ Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

“ LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

73

Table 31. Growing Degree Days as % of the control to corn inbreds after
postemergence application of herbicides applied at twice the typical use rate in the
1999 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
96
1 101 99 100 100
3 100 100 100 100
6 101 101 100 100
11 100 100 100 100
14 99 99 100 102
15 99 102 100 100
16 100 100 100 100
22 95 99 102 101
24 97 98 102 101
26 101 101 102 101
27 100 100 100 100
31 100 98 101 101
33 100 99 101 103
37 99 100 102 100
38 100 100 100 101
39 102 102 104 92

Lsoapsm, = NS
LSDstm = NS

 

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at 1 qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

“ LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

74

Table 32. Growing Degree Days as % of the control to corn inbreds after

postemergence application of herbicides applied at four times the typical use rate in the
1998 field season.

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
96

1 99 100 100 102
3 100 100 100 102
6 100 100 101 101,
11 100 99 100 101
14 100 98 101 101
15 104 100 99 101
16 99 101 103 101
22 100 102 101 100
24 100 100 101 101
26 101 102 100 98
27 101 100 99 101
31 100 99 100 98
33 100 103 99 100
37 97 100 103 102
38 99 102 98 102
39 100 102 99 102

LSD°(p50_05) = NS
LSD“(p£0.05L= NS

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .9lEC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at l qt/A.

“ Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“ Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

75

Table 33. Growing Degree Days as % of the control to corn inbreds afier

postemergence application of herbicides applied at four times the typical use rate in the
1999 field season.

 

 

 

 

 

Inbred Accent“ Action“ Buctrilc Clarity“
96

1 101 99 100 101
3 100 111 100 100
6 101 101 100 100 ,
11 100 100 100 100
14 100 97 101 102
15 99 102 100 100
16 100 100 100 100
22 95 99 103 101
24 97 98 102 101
26 101 101 101 101
27 100 100 100 100
31 100 98 102 101
33 100 100 101 102
37 98 100 102 100
38 100 100 100 101
39 100 103 105 92

LSDflpsoos, = NS
LSDf(p50@ = NS

“Typical use rate of Accent 75DF is 2/3 oz/A (0.03125 lbs a.i./A). NIS was added at
.25% (v/v) and 28% nitrogen was added at 4 qt/A.

“ Typical use rate of Action .91EC is 0.6 oz/A (0.0044 lbs a.i./A). Crop oil concentrate
was added at l qt/A.

° Typical use rate of Buctril 2L is 1.5 pt/A (3/8 lbs a.i./A).

“Typical use rate of Clarity 4L is “/2 pt/A (.25 lbs a.i./A).

° LSD to compare between inbred means within a herbicide.

“LSD to compare between herbicide means within an inbred.

76

Table 34. Visual injury to corn inbreds within the B73 family 14 days afier
preemergence application of herbicides in a greenhouse for two runs applied at twice
the typical use rate.

 

 

 

 

 

 

 

 

 

Run I —— Run II
Inbred Balance“ Harness“ Prowl“ Balance“ Harness“ Prowl“
%
14 0 0 O 6 O O
1 5 O 0 10 0 O 0
1 8 3 1 O 1 5 25 O 0
23 0 O 3 1 O 0 O
25 0 O 0 0 O 0
26 1 8 0 0 8 O 0
28 O 0 O 0 8 O
34 7 0 O 4 O O
LSDWSODS, 9 6

 

“Typical use rate of Balance 75DF is 1.5 oz/A (0.07 lbs a.i./A).
“Typical use rate of Harness 7L is 1.8 pt/A (1.6 lbs a.i.lA).
“ Typical use rate of Prowl 3.3EC is 1.2 qt/A (0.99 lbs a.i./A).

77

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