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This is to certify that the

dissertation entitled

ENHANCING POSTEMERGENCE WEED CONTROL PROGRAMS
IN CORN AND SOYBEAN WITH FLUTHIACET AND FLUMICLORAC

presented by

JASON C. FAUSEY

has been accepted towards fulﬁllment
of the requirements for

PhoDo degreein Crop and SOil Sciences

 

 

{51% a (WW

I Major professor

Date gZ/m / H99
L// J

MSU i: an Afﬁrmative Action/Equal Opportunity Institution 0-12771

 

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

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ma cane/0.03M“

 

 

 

ENHANCING POSTEMERGENCE WEED CONTROL PROGRAMS
IN CORN AND SOYBEAN WITH FLUTHIACET AND FLUMICLORAC

By

Jason C. Fausey

A DISSERTATION
Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY

Department of Crop and Soil Sciences

1999

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ABSTRACT

ENHANCING POSTEMERGENCE WEED CONTROL PROGRAMS
IN CORN AND SOYBEAN WITH FLUTHIACET AND F LUMICLORAC

BY

Jason C. Fausey

The recently developed cyclic imide herbicides ﬂuthiacet and ﬂumiclorac control one of
the most troublesome broadleaf weeds, velvetleaf. These herbicides selectively control
velvetleaf and other broadleaf weeds by inhibiting the protoporphyrinogen IX oxidase
enzyme. Studies examined the physiological basis for ﬂuthiacet and ﬂumiclorac
selectivity in ﬁve plant species. Enhanced herbicide metabolism contributed to the
tolerance of redroot pigweed to ﬂuthiacet and wild mustard to ﬂumiclorac. Decreased
herbicide retention, absorption, and translocation; and increased herbicide metabolism
contributed to com tolerance to these herbicides. Soybean tolerance resulted from
decreased herbicide retention and increased herbicide metabolism.

Experiments examined the effect temperature, light intensity, time to initial light
exposure, relative humidity, and the presence of dew have on ﬂuthiacet and flumiclorac
efficacy. Increasing temperature from 10 to 40 C and increasing light intensity from O to
1000 umol rn’2 3'1 increased herbicide activity. Time to initial light exposure and relative
humidity did not affect ﬂuthiacet and ﬂumiclorac activity. The presence of dew reduced
herbicide activity.

Studies evaluated broadleaf weed control with ﬂuthiacet and ﬂumiclorac applied alone

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and in tank mixtures. Velvetleaf, common lambsquarters, redroot pigweed, common
ragweed, common cocklebur, eastern black nightshade, and wild mustard growth in the
greenhouse were reduced by 50% from 0.1, 2.9, 0.9, 1.1, 0.8, 0.4, and 1.2 g ha'l of
ﬂuthiacet and 0.7, 3.0, 2.4, 3.3, 3.0, 3.4, and 74.1 g ha" of ﬂumiclorac, respectively.
Adjuvants enhanced common lambsquarters, redroot pigweed, common ragweed, and
velvetleaf control with ﬂuthiacet by 53, 57, 29, and 29% and with ﬂumiclorac by 36, 62,
41, and 34%, respectively, in the greenhouse. In ﬁeld studies, soybean injury and
broadleaf weed control were equivalent when ﬂuthiacet or ﬂumiclorac was applied with a
crop oil concentrate or a nonionic surfactant. Velvetleaf control with these herbicides
was greatest in the ﬁeld when applied to S cm tall plants. However, season-long
velvetleaf control with both herbicides was greatest when applied to 45 or 60 cm tall
plants. In ﬁeld studies, ﬂuthiacet and ﬂumiclorac tank mixtures with atrazine, dicamba,
2,4-D, and primisulfuron plus prosulfuron controlled common lambsquarters, redroot
pigweed, and velvetleaf season-long. Similarly, tank mixing ﬂuthiacet or ﬂumiclorac
with imazethapyr provided season-long common lambsquarters, redroot pigweed,
common ragweed, and eastern black nightshade control.

Field studies evaluated the performance of annual weed control programs that included
ﬂuthiacet and ﬂumiclorac. Experiments revealed these herbicides are effective applied in
a tank mixture with other postemergence herbicides. Alternatively, these herbicides
provide excellent weed control when applied postemergence following a preemergence

herbicide application.

 

USIOF

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CHAPTI

in
NI

TABLE OF CONTENTS

PAGE

LIST OF TABLES .................................................... vii

INTRODUCTION ...................................................... 1

CHAPTER 1. PHYSIOLOGICAL BASIS FOR

FLUTHIACET AND FLUMICLORAC SELECTIVITY.

Abstract ......................................................... 2

Introduction ..................................................... 4

Materials and Methods ............................................ 6

Electrolyte Leakage ......................................... 6

General Greenhouse Methods ................................ 6

Species Sensitivity .......................................... 7

Herbicide Retention ......................................... 8

Herbicide Absorption, Translocation, and Metabolism ............ 9

Statistical Analyses ......................................... 12

Results and Discussion ............................................ 12

Herbicide Effect on the Porphyrin Pathway .................... 12

Electrolyte Leakage .................................. 12

Fluthiacet and Flumiclorac Selectivity ......................... 14

Species Sensitivity ................................... 14

Herbicide Retention .................................. 14

Herbicide Absorption ................................ 15

Herbicide Translocation .............................. 16

Herbicide Metabolism ................................ 16

Acknowledgments ......................................... 19

Literature Cited ................................................. 20

CHAPTER 2. ENVIRONMENTAL EFFECTS ON F LUTHIACET AND
FLUMICLORAC EFFICACY AND SOYBEAN TOLERANCE.

Abstract ........................................................ 30
Introduction .................................................... 32
Materials and Methods ........................................... 34
General Methods for Laboratory Experiments ................. 34
Temperature ........................................ 35

Light Intensity ...................................... 35

Time to Initial Light Exposure ......................... 35

Relative Humidity ................................... 35

Inﬂuence of Dew on Efﬁcacy .......................... 36

iv

 

Cl

TABLE OF CONTENTS (cont.)

PAGE

Field Experiment .......................................... 37
Statistical Analyses ......................................... 38
Results and Discussion ............................................ 38
Laboratory Experiments .................................... 38
Temperature ........................................ 38

Light Intensity ...................................... 39

Time to Initial Light Exposure ......................... 39

Relative Humidity ................................... 40

Influence of Dew on Efﬁcacy .......................... 40

Field Experiment .......................................... 40
Acknowledgments ......................................... 43
Literature Cited ................................................. 44

CHAPTER 3. ADJUVANT EFFECTS ON FLUTHIACET AND
FLUMICLORAC EFFICACY AND SOYBEAN TOLERANCE.

Abstract ........................................................ 54
Introduction .................................................... 57
Materials and Methods ........................................... 59
General Methods for Laboratory Experiments ................. 59
Adjuvant Efﬁcacy ................................... 60

Tank Mixtures with Fluthiacet and Flumiclorac .......... 60

Field Experiments ......................................... 61
Species Sensitivity ................................... 61

Tank Mixtures with Fluthiacet and Flumiclorac .......... 62

Statistical Analyses ......................................... 63
Results and Discussion ............................................ 64
Adjuvant Efﬁcacy ................................... 64

Tank Mixtures with Fluthiacet and Flumiclorac ................ 66
Greenhouse ......................................... 66

Field ............................................... 66
Acknowledgments ......................................... 68
Literature Cited ................................................. 69

CHAPTER 4. BROADLEAF WEED CONTROL IN CORN AND
SOYBEAN WITH FLUTHIACET AND F LUMICLORAC
ALONE AND IN TANK MIXTURES.

Abstract ........................................................ 77
Introduction .................................................... 80
Materials and Methods ........................................... 82

 

IA

CH

TABLE OF CONTENTS (cont.)

PAGE
General Methods for Laboratory Experiments ................. 82
Species Sensitivity ................................... 83
Tank Mixtures with Fluthiacet and Flumiclorac .......... 84
Field Experiments ......................................... 85
Corn ............................................... 85
Soybean ............................................ 86
Statistical Analyses ......................................... 87
Results and Discussion ............................................ 88
Greenhouse Experiments ................................... 88
Species Sensitivity ................................... 88
Tank Mixtures with Fluthiacet and Flumiclorac .......... 89
Field Experiments ......................................... 91
Corn ............................................... 91
Soybean ............................................ 92
Acknowledgments ......................................... 95
Literature Cited ................................................. 96
CHAPTER 5. INCORPORATING FLUTHIACET AND FLUMICLORAC
INTO ANNUAL WEED CONTROL PROGRAMS FOR
CORN AND SOYBEAN.
Abstract ....................................................... 105
Introduction ................................................... 108
Materials and Methods .......................................... 109
Greenhouse Experiments .................................. 109
Annual Grass Control with
Fluthiacet and Flumiclorac Tank Mixtures ............. 109
Field Experiments ........................................ 1 1 1
Annual Grass Control with
Fluthiacet and Flumiclorac Tank Mixtures ............. 111
Velvetleaf Control .................................. l 11
Annual Weed Control in Corn ........................ 112
Annual Weed Control in Soybean ..................... 114
Statistical Analyses ........................................ 1 16
Results and Discussion ........................................... 116
Annual Grass Control with
Fluthiacet and Flumiclorac Tank Mixtures ............. 116
Weed Control Programs ................................... 117
Velvetleaf Control .................................. 117
Annual Weed Control in Corn ........................ 117
Annual Weed Control in Soybean ..................... 118
Acknowledgments ........................................ 121
Literature Cited ................................................ 122

vi

 

CHAP

CHAP

LIST OF TABLES

CHAPTER 1. PHYSIOLOGICAL BASIS FOR
FLUTHIACET AND FLUMICLORAC SELECTIVITY.

Table 1.
Table 2.

Table 3.

Table 4.

Table 5.
Table 6.

Table 7.

PAGE
Characterization of fluthiacet and flumiclorac metabolites ...... 23
Effect of 4,6-dioxoheptanoic acid (DA) on electrolyte leakage
24 h after ﬂuthiacet and ﬂumiclorac treatment ................ 24
Effect of aminolevulinic acid (ALA) on electrolyte leakage
24 h after fluthiacet and ﬂumiclorac treatment ................ 25
Species sensitivity to 2 g ha‘l fluthiacet and 15 g ha‘l ﬂumiclorac
in the greenhouse 14 d after treatment ....................... 26
Fluthiacet and ﬂumiclorac retention in ﬁve plant species ........ 27
Fluthiacet and ﬂumiclorac absorption, translocation, and
metabolism in ﬁve plant species ............................. 28
Factors affecting plant tolerance to ﬂuthiacet and flumiclorac
12 h after treatment ..................................... 29

CHAPTER 2. ENVIRONMENTAL EFFECTS ON F LUTHIACET AND
FLUMICLORAC EFFICACY AND SOYBEAN TOLERANCE.

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Effect of temperature on common lambsquarters and redroot
pigweed control with ﬂuthiacet and flumiclorac

72 h after treatment ...................................... 47
Effect of light intensity on common lambsquarters and redroot
pigweed control with fluthiacet and flumiclorac

72 h after treatment ...................................... 48
Effect of time to initial light exposure on common lambsquarters
and redroot pigweed control with fluthiacet and flumiclorac

72 h after treatment ...................................... 49
Effect of relative humidity on common lambsquarters and redroot
pigweed control with fluthiacet and flumiclorac

72 h after treatment ...................................... 50
Effect of dew on common lambsquarters and redroot pigweed
control with fluthiacet and ﬂumiclorac

72 h after treatment ...................................... 51
Herbicide application conditions in 1996, 1997,
and 1998 ﬁeld experiments ................................. 52

Effect of time of application on tolerance and efﬁcacy of
fluthiacet and flumiclorac applied at 0600, 1400, and 2000 h ..... 53

vii

LBT(

CHAP

CH!

 

 

Cl

LIST OF TABLES (Cont)

PAGE
CHAPTER 3. ADJUVANT EFFECTS ON F LUTHIACET AND

FLUMICLORAC EFFICACY AND SOYBEAN TOLERANCE.

Table 1. Adjuvant effect on fluthiacet efﬁcacy

in the greenhouse 14 d after treatment ....................... 72
Table 2. Adjuvant effect on ﬂumiclorac efﬁcacy

in the greenhouse 14 d after treatment ....................... 73
Table 3. Adjuvant effect on ﬂuthiacet or flumiclorac

soybean tolerance and efﬁcacy in the ﬁeld .................... 74

Table 4. Broadleaf weed control in the greenhouse with

fluthiacet and flumiclorac tank mixtures 14 d after treatment . . . 75
Table 5. Weed control and soybean yield in the ﬁeld with fluthiacet

and flumiclorac alone and in tank mixtures ................... 76

CHAPTER 4. BROADLEAF WEED CONTROL IN CORN AND
SOYBEAN WITH FLUTHIACET AND FLUMICLORAC
ALONE AND IN TANK MIXTURES.

Table l. Weed species sensitivity to fluthiacet and ﬂumiclorac

in the greenhouse ......................................... 99
Table 2. Corn injury 3 d after treatment (DAT) and broadleaf

weed control 14 DAT in the greenhouse with

fluthiacet or flumiclorac tank mixtures ..................... 100
Table 3. Soybean injury 3 d after treatment (DAT) and broadleaf

weed control 14 DAT in the greenhouse with

fluthiacet or ﬂumiclorac tank mixtures ..................... 101
Table 4. Corn injury, broadleaf weed control, and corn yield

in the ﬁeld with fluthiacet or flumiclorac tank mixtures ....... 102
Table 5. Soybean injury, broadleaf weed control, and soybean yield

In the ﬁeld with fluthiacet or ﬂumiclorac tank mixtures ....... 104

CHAPTER 5. INCORPORATING FLUTHIACET AND FLUMICLORAC
INTO ANNUAL WEED CONTROL PROGRAMS IN
CORN AND SOYBEAN.

Table 1. Giant foxtail and barnyardgrass control with

ﬂuthiacet and flumiclorac tank mixtures

in the greenhouse 14 d after treatment ...................... 124
Table 2. Giant foxtail and barnyardgrass control with

ﬂuthiacet and flumiclorac tank mixtures

in the ﬁeld 28 d after treatment ............................ 125
Table 3. Corn injury and velvetleaf control with

fluthiacet and ﬂumiclorac in the ﬁeld ....................... 126

viii

LIST OF TABLES (Cont.)

PAGE
Table 4. Corn injury, weed control, and corn yield with
fluthiacet and ﬂumiclorac alone and in tank mixtures ......... 127
Table 5. Soybean injury, weed control, and soybean yield in 1997 with
ﬂuthiacet and flumiclorac alone and in tank mixtures ......... 129

Table 6. Soybean injury, weed control, and soybean yield in 1998 with
ﬂuthiacet and ﬂumiclorac alone and in tank mixtures ......... 131

ix

INTRODUCTION

Velvetleaf (Abutilon theophrasti Medik.) is one of the most troublesome weeds in
agricultural crops. Acceptable postemergence velvetleaf control in corn (Zea mays L.)
and soybean (Glycine max (L.) Merr.) was difﬁcult before the development of ﬂuthiacet
and ﬂumiclorac. These herbicides provide unprecedented postemergence velvetleaf
control and offer several advantages over other commercial postemergence herbicides
including low use rates, short half-lives, rapid bumdown, resistance management, and the
ability to broaden the spectrum of other com and soybean herbicides when applied in a
tank mixture. Additionally, each herbicide provides a varying degree of activity on
common lambsquarters (Chenopodium album L), kochia (Kochia scoparia L.),
Amaranthus species, Solanaceae species, and other broadleaf weeds. Understanding the
mechanism of selectivity would provide information that may be used to maximize
ﬂuthiacet and ﬂumiclorac efﬁcacy of marginally controlled weeds.

To determine the most effective way to use ﬂuthiacet and ﬂumiclorac, research will
determine the basis of selectivity, evaluate the effect environmental conditions at
application have on efﬁcacy, examine the effect adjuvant selection has on efﬁcacy,
examine tank mixture interactions, and establish an optimal system that incorporates

these herbicides into corn and soybean weed control programs.

 

 

ﬂL

CHAPTER 1

Physiological Basis for Fluthiacet and Flumiclorac Selectivity
in Five Plant Species

ABSTRACT

Greenhouse and laboratory studies were conducted to determine the physiological basis
for ﬂuthiacet and ﬂumiclorac selectivity in ﬁve plant species. These herbicides
selectively control weeds postemergence by inhibiting protoporphyrinogen oxidase
(Protox). Injury symptoms include rapid desiccation and necrosis, Similar to diphenyl
ether and bipyridinium herbicide injury. Species sensitivity was evaluated by comparing
the dry weight reduction from postemergence ﬂuthiacet and ﬂumiclorac applications.
Velvetleaf was sensitive to both herbicides, redroot pigweed was more sensitive to
ﬂumiclorac than ﬂuthiacet, wild mustard was sensitive to ﬂuthiacet yet tolerant to
ﬂumiclorac, and corn and soybean were tolerant to both herbicides. Studies evaluated the
effects of herbicide retention, absorption, translocation, or metabolism on ﬂuthiacet and
ﬂumiclorac selectivity. Enhanced herbicide metabolism contributed to the tolerance of
redroot pigweed to ﬂuthiacet and wild mustard to ﬂumiclorac. Decreased herbicide
retention, absorption, and translocation; and increased metabolism contributed to corn

tolerance to ﬂuthiacet and ﬂumiclorac. Decreased herbicide retention and increased

.ah

herbicide metabolism provided soybean tolerance to these herbicides.

Nomenclature: Fluthiacet, [[2-chloro-4-ﬂuoro-5-[(tetrahydro-3-oxo-1H, 3H-

[1 ,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)arnino]phenyl]thio]acetate; ﬂumiclorac,
pentyl[2-chloro-4-ﬂuoro-5-(1 ,3,4,5 ,6,7-hexahydro- l ,3-dioxo-2H-isoindol-2—
yl)phenoxy]acetic acid; velvetleaf, Abutilon theophrasti Medik. #' ABUTH; redroot
pigweed, Amaranthus retroﬂexus L. # AMARE; wild mustard, Brassica kaber, (D.C.)
L.C. Wheeler # SINAR; corn, Zea mays L.‘Pioneer 3751’ # ZEAMA; soybean, Glycine
max (L.) Merr. ‘Conrad’ # GLYMA.

Key Words: Absorption, metabolism, protoporphyrin, retention, translocation, ABUTH,
AMARE, SINAR, ZEAMA, GLYMA.

Abbreviations: ALA, 6-aminolevulinic acid; DA, 4,6-dioxoheptanoic acid; DAT, days
after treatment; HAT, hours after treatment; LSS, liquid scintillation spectrometry; MES,
2-(N-morpholino) ethanesulfonic acid; NIS, nonionic surfactant; Proto, protoporphyrin
IX; Protogen, protoporphyrinogen IX; Protox, protoporphyrinogen oxidase; TLC, thin

layer chromatography; v/v volume per volume.

 

lLetters following this symbol are a WSSA-approved computer code from Composite List

of Weeds, Revised 1989. Available from WSSA, 810 East 10th Street, Lawrence, KA
66044-8897.

 

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INTRODUCTION

F luthiacet and ﬂumiclorac are recently developed cyclic irnide herbicides that
selectively control broadleaf weeds postemergence in corn and soybean (Porpiglia et a1.
1994; Kamoshita et a1. 1993). F luthiacet and ﬂumiclorac have a similar mode of action
to diphenyl ether, oxadiazole, and triazolinone herbicides despite their different chemical
structures (Sato et al. 1991). These herbicides inhibit the protoporphyrinogen oxidase
(Protox) enzyme in susceptible plant species which leads to an uncontrolled
nonenzymatic oxidation of protoporphyrinogen IX (Protogen) to protoporphyrin IX
(Proto) (Anonymous 1995; Duke et a1. 1991; Mito et al. 1991). Proto, a photodynamic
tetrapyrrole intermediate, is a potent photosensitizer generating singlet oxygen in the
presence of molecular oxygen and light (Duke et al. 1991). Injury in plants treated with
Protox-inhibiting herbicides includes rapid light-dependent chlorophyll bleaching,
desiccation, and necrosis (Wright et al. 1995). Although detectable in sensitive plant
species 30 minutes after herbicide exposure, Protox inhibition requires light to initiate
herbicidal activity (Duke et a1. 1990).

Predicting herbicide efﬁcacy is challenging. Environmental conditions at application
(Doran and Anderson 1976), herbicide rate (King and Oliver 1992), weed size (Kells et
al. 1984), interactions with other herbicides (Hatzios and Penner 1985), and the addition
of an adjuvant (Roggenbuck et al. 1990) inﬂuence herbicidal activity. Enhanced
herbicidal efﬁcacy generally reﬂects increased herbicide absorption (Harrison and Wax
1986); however, increased herbicide absorption does not always correlate with increased

efﬁcacy (Starke et al. 1996). Ritter and Coble (1981) reported that soybean tolerance to

 

 

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the diphenyl ether herbicide aciﬂuorfen (5-[2-chloro-4-(triﬂuoromethyl)phenoxy]-2-
nitrobenzoic acid) was explained by less rapid herbicide absorption and translocation
coupled with increased metabolism. Similarly, aciﬂuorfen caused widespread cell
membrane disruption decreasing weed control by reducing systemic herbicide absorption
and translocation (Westberg and Coble 1992).

Temperature and relative humidity inﬂuence Protox-inhibiting herbicides translocation
and efﬁcacy. Increasing relative humidity from 50 to 85% enhanced aciﬂuorfen,
fomesafen (5-[2-chloro-4-(triﬂuoromethyl)phenoxy] (methylsulfonyl)-2-nitrobenzamide),
and lactofen ((:)-2-ethoxy- 1 -methy1-2-oxoethyl-5-[2-chloro-4-(triﬂuoromethyl)phenoxy]
-2-nitrobenzoate) activity on prickly Sida (Sida spinosa L.), pitted momingglory
(Ipomoea lacunosa L.), entireleaf momingglory (Ipomoea hederacea var. integriuscula
L.), and common cocklebur (Xanthium strumarium L.) (Wichert et a1. 1992). However,
Higgins et al. (1988) reported that aciﬂuorfen and lactofen translocation and metabolism
in pitted momingglory was negligible.

Weeds prevent crops from reaching their yield potential. Fluthiacet and ﬂumiclorac
effectively control velvetleaf, one of the most troublesome broadleaf weeds in corn and
soybean. However, research investigating the physiological basis for ﬂuthiacet and
ﬂumiclorac selectivity is limited. Studies have not determined the mechanism of
selectivity for these herbicides. Conceivably, research could increase control of
marginally controlled weed species though crop tolerance may limit the potential to
increase ﬂuthiacet and ﬂumiclorac efﬁcacy. Therefore, the objective of this research was
to determine the physiological basis for ﬂuthiacet and ﬂumiclorac selectivity in

velvetleaf, redroot pigweed, wild mustard, corn, and soybean.

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MATERIALS AND METHODS

Herbicide Effect on the Porphyrin Pathway
Electrolyte Leakage. Experiments evaluating the effects ﬂuthiacet and ﬂumiclorac have
on membrane integrity of velvetleaf, redroot pigweed, wild mustard, corn, and soybean
leaf disks used the electrolyte leakage assay procedure described by Duke et al. (1984).
Treatments included technical grade ﬂuthiacet or ﬂumiclorac alone or with 4,6-
dioxoheptanoic acid2 (DA) or o-aminolevulinic acid2 (ALA). DA and ALA were used as
a herbicide antagonist and synergist, respectively. Five-mm diameter leaf disks were
excised and washed for 2 h in a 1% sucrose, 1 mM 2-(N-morpholino) ethanesulfonic acid2
(MES) solution with a pH of 6.8. Fifty leaf disks were placed in 13 by 100-mm test tubes
containing 3 ml of fresh sucrose/MES solution with various rates of herbicide, antagonist,
and synergist (see Tables 2 and 3). Leaf disks were added to the test tubes and incubated
at 25 C in darkness for 16 h followed by exposure to 1000 amol rn‘2 s‘1 at 25 C for 24 h.
The experiment was a completely randomized design with six replications and repeated.
Electrolyte leakage from the leaf disks was monitored 0, 12, and 24 h after initial light
exposure using a conductivity meter’. Results are expressed as the change in

conductivity from the 0 h light exposure.

General Greenhouse Methods

Velvetleaf and wild mustard seed were collected at the Michigan State University

 

2 Sigma Chemical Company, St. Louis, MO 63178.
3Omega Engineering Inc., Stamford, CT 06907-0047.

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Research Farm in East Lansing. Redroot pigweed seed was obtained from a commercial
seed supplier‘. The corn variety ‘Pioneer 3751 ’5 and soybean variety ‘Conrad’ were used
in the following studies.

Seeds were planted in BACCTO6 potting soil in 946-ml plastic pots. Environmental
conditions were maintained within a greenhouse at 27 i 5 C. Plants were grown under a
16-h photoperiod of natural and supplemental high pressure sodium lighting with a
photosynthetic photon ﬂux density of 1000 amol m2 5“. Plants were thinned to 1 plant
pot“, fertilized with 50 ml of a water-soluble fertilizer solution (400 ppm N, 400 ppm
P205, and 400 ppm K20), and watered as needed.

Species Sensitivity. Experiments compared velvetleaf, redroot pigweed, wild mustard,
corn, and soybean sensitivity to ﬂuthiacet and ﬂumiclorac. Treatments included an
untreated control, 2 g ha" ﬂuthiacet, and 15 g ha’l ﬂumiclorac. Herbicides were applied
with 0.25% (v/v) nonionic surfactant7 (NIS). At application, velvetleaf plants were 10 cm
tall with ﬁve to six leaves; redroot pigweed plants were 10 cm tall with seven to eight
leaves; wild mustard plants were 8 cm tall with four to ﬁve leaves; corn plants were 20
cm tall with four leaves; and soybean plants were 13 cm tall with two fully developed

trifoliolates. Herbicides were applied with a continuous belt-linked sprayer ﬁtted with an

 

4Seed, V & J Seed F arms, PO. Box 82, Woodstock, IL 60098.
SCorn, Pioneer Hi-Bred International, Inc., DeS Moines, IA 50301.

6BACCTO professional planting mix, Michigan Peat Co., PO. Box 98129, Houston, TX
77098.

7Activator-90, nonionic surfactant, a mixture of alkyl polyoxyethylene ether and fatty
acids, Loveland Industries Inc., PO. Box 1289, Greeley, CO 80632.

7

 

 

t“)

8001B ﬂat—fan nozzle8 traveling at 1.53 km h‘1 and delivering 234 L ha“ at 193 kPa of
pressure.

The experiment was a completely randomized design with four replications. Plants
were visually evaluated 3, 7, and 14 d aﬁer treatment (DAT). Visual ratings were based
on a scale from 0 to 100%, with 0 indicating no effect and 100 indicating plant death.
Evaluations represented visual stunting, chlorosis, and necrosis. Dry weight reduction
was determined 14 DAT by harvesting the aboveground plant material. Dry weight
reduction was calculated as 100[1 - (plant dry weight/untreated plant dry weight)].
Herbicide Retention. Experiments were conducted to determine ﬂuthiacet and
ﬂumiclorac foliar spray retention on velvetleaf, redroot pi gweed, wild mustard, corn, and
soybean using a modiﬁed Boldt and Putnam (1980) procedure. Treatments included 2 g
ha’l ﬂuthiacet or 15 g ha" ﬂumiclorac plus 0.25% (v/v) N187 and 2.5 g L'1 Chicago Sky
blue dyez. Herbicides were applied with a continuous belt-linked sprayer ﬁtted with an
8001E ﬂat-fan nozzle8 traveling at 1.53 km h" and delivering 234 L ha‘l at 193 kPa of
pressure. At application, velvetleaf plants were 10 cm tall with ﬁve to Six leaves; redroot
pigweed plants were 10 cm tall with seven to eight leaves; wild mustard plants were 8 cm
tall with four to ﬁve leaves; corn plants were 20 cm tall with four leaves; and soybean
plants were 13 cm tall with two trifoliolates.

The experiment was a completely randomized design with four replications. Following
herbicide application, aboveground plant segments were harvested and rinsed with

distilled water containing 0.25% (v/v) NIS7. Plant leaf area was determined while the

 

8Teejet ﬂat-fan nozzles, Spraying Systems Co., North Avenue and Schmale Road,
Wheaton, IL 60532.

 

 

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rinsate absorbance was measured with a spectrophotometer at 625 nm. Whole plant
retention was calculated from a standard curve, and results are expressed as a percent of
the theoretical maximum retention. Theoretical maximum retention was calculated as
100[1 - (herbicide concentration retained/maximum retention: based on the plant leaf
area)].

Herbicide Absorption, T ranslocation, and Metabolism. Experiments compared
ﬂuthiacet and ﬂumiclorac absorption, translocation, and metabolism in velvetleaf, redroot
pigweed, wild mustard, corn, and soybean. Herbicide absorption, translocation, and
metabolism were determined in a Single plant treated with l4C-radiolabeled ﬂuthiacet or
ﬂumiclorac. Plants were grown in the greenhouse as previously described to the growth
stages in the spray retention experiment. The youngest ﬁilly developed leaf was chosen
for the l‘lC-radiolabeled herbicide treatment; the 4th true velvetleaf and wild mustard leaf,
the 6th true redroot pigweed leaf, the 2“d true corn leaf, and the middle soybean leaﬂet of
the 1St trifoliolate.

Velvetleaf, redroot pigweed, wild mustard, corn, and soybean plants, except the leaf
chosen for 1“C treatment, were Sprayed with 2 g ha" ﬂuthiacet or 15 g ha" ﬂumiclorac
plus 0.25% (v/v) NIS7. Herbicides were applied as previously discussed in the Spray
retention experiment. The leaf chosen for 1“C treatment was covered with cellophane
during the broadcast herbicide application to prevent Spray interception. The cellophane
was removed immediately following herbicide application.

The spray retention study determined the quantity of spray solution intercepted during a
broadcast herbicide application. All hand-treated leaves received a herbicide treatment

that simulated a broadcast herbicide application. To ensure sufﬁcient radioactivity for the

 

 

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metabolism analysis, a minimum of 2.7 x 103 Bq was applied to the treated leaf.

The radiolabeled Spotting solution contained phenyl-labeled l“C-ﬂuthiacet (1.5 x 103
kBq mg'l speciﬁc activity, 95.4% purity) or tetrahydrophthaloyl-l, 2-labeled l“C-
ﬂumiclorac (9.5 x 103 kBq mg" speciﬁc activity, 94.9% purity) with the appropriate
formulation blank, NIS7, and water volumes. Treatments consisting of ﬁfteen, 2 ul
droplets of solution totaling 2.7 x 103 Bq were applied to the adaxial leaf surface.

Unabsorbed l“C ﬂuthiacet or ﬂumiclorac was removed by gently swirling the treated
leaf in a 20 ml liquid scintillation vial containing 3 ml of methanol : water (1:1) solution
for 60 seconds. Leaves were rinsed with an additional 0.5 ml of solvent as they were
removed ﬁom the scintillation vial. The rinse solution was radioassayed by liquid
scintillation spectrometry (LSS). Fluthiacet and ﬂumiclorac absorption was calculated by
dividing the recovered l“C-herbicide by the quantity of I“C-herbicide applied.

Radiolabeled plants were harvested 2, 4, and 12 h after treatment (HAT) and divided
into three sections; the treated leaf, above the treated leaf, and below the treated leaf.
These parts were immediately frozen and stored at -30 C until further analysis.
Preliminary experiments found that only treated leaves contained sufﬁcient l4C herbicide
concentrations to conduct metabolism analysis; therefore, the other leaf sections were
separately combusted in a biological sample oxidizer", and the evolved radiolabeled
herbicide was sustained within a MC trapping cocktail. Cocktail samples were assayed
with LSS to quantify herbicide translocation above and below the treated leaf. l“C
translocation out of the treated leaf was calculated as the 14C recovered above and below

the treated leaf divided by the total 14C recovered in the plant.

 

9 R. J. Harvey Instruments Corp., 123 Patterson St., Hillsdale, NJ 07642.

10

 

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Fluthiacet and ﬂumiclorac metabolism was investigated in the 1“C treated leaf. Leaves
were ground in a tissue homogenizerlo with 20 ml of an acetonitrile : water (6:4) solution.
The homogenate was vacuum-ﬁltered, and the residue was rinsed with an additional 20
ml of solvent. Rinsate volumes were recorded and two, 1 ml aliquots were radioassayed
with LSS to determine the extractable MC. The ﬁlter paper and residue were air dried and
combusted to determine the unextractable 1“C. Total radioactivity within the treated leaf
was calculated by adding the extractable and unextractable l“C.

The ﬁltrate was evaporated to 2 ml with a rotary evaporator at 35 C, and the solution
was transferred to a 13 by 100 mm test tube and concentrated to 100 to 150 it] under an
air stream in a 40 C water bath. Fifty pl of the concentrated extract were Spotted on 20
by 20 cm Silica gel (60 F 254) thin layer chromatography (TLC) plates” for metabolite
separation. Plates were developed in a 13 cm solvent front in toluene : ethyl acetate :
acetic acid (5:7:1 v/v/v). Radioactive positions, proportions, and their corresponding R,
values were determined by scanning TLC plates with a radiochromatogram scanner”.

TLC separations revealed parent ﬂuthiacet, ﬂumiclorac, and three metabolites for each
herbicide (Table 1). To determine metabolite biological activity, the previously discussed
procedures were followed using nonradioactive herbicide treated plants. Nomadioactive
metabolites were separated on the TLC plates, and their location was conﬁrmed using
ultraviolet lighting. The parent herbicides and their metabolites were scraped from the

silica gel plates and placed in 13 by 100 mm test tubes. The modiﬁed Duke et al. (1984)

 

'0 Sorvall Omni-mixer, Sorvall Inc., Newton, CT 06470.
” Whatrnan Inc., Clifton, NJ 07011.
‘2 Ambis Systems, Inc., 3939 Rufﬁn Road, San Diego, CA 92123.

11

 

was
total

four

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E184
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electrolyte leakage assay procedures established biological activity of the parent
herbicides and the metabolites. Fluthiacet, two ﬂuthiacet metabolites, ﬂumiclorac, and
one ﬂumiclorac metabolite were biologically active (data not presented). Metabolism
was calculated in the treated leaf by dividing the remaining biologically active 14C by the
total 1“C in the treated leaf. The experiment was a completely randomized design with

four replications.

Statistical Analyses

All experiments were repeated over time, and data were analyzed using analysis of
variance (ANOVA). Data for individual experiments were combined as analyses
revealed no treatment by time interaction. Means were separated by Fisher’s protected

least signiﬁcant difference test (LSD) at the 5% level.

RESULTS AND DISCUSSION

Herbicide Effect on the Porphyrin Pathway

Electrolyte Leakage. Several herbicide classes, including cyclic imides, diphenyl ethers,
and oxadiazoles, initiate light-dependent chlorosis resulting from an accumulation of the
photodynamic tetrapyrrole, protoporphyrin IX (Proto) (Duke et al. 1990). These
herbicides also inhibit protoporphyrinogen oxidase (Protox), the last common enzyme in
the heme and chlorophyll biosynthesis pathways (Duke et al. 1991). Protox iS present in
plant plastids and mitochondria and catalyzes the oxidation of protoporphyrinogen IX

(Protogen) to protoporphyrin IX (Proto) (Jacobs et al. 1991). Reports suggest Protox-

12

 

 

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inhibiting herbicides induce Protogen accumulation that diffuses into the cytoplasm and
is oxidized to Proto by an unidentiﬁed oxidase in the plasma membrane (Jacobs et al.
1991). Once outside the normal porphyrin pathway, Proto induces the formation of
membrane and chlorophyll-destroying singlet oxygen (Lydon and Duke 1988). Singlet
oxygen is highly toxic to plants and results in a measurable increase in cellular
conductivity. Herbicide initiated electrolyte efﬂux was assessed by monitoring the
herbicide treated bathing medium conductivity (Duke et a1. 1984). However, the bathing
medium conductivity did not increase when Protox-inhibiting herbicides were applied in
darkness (Wright et al. 1995). Similarly, preliminary experiments revealed ﬂuthiacet and
ﬂumiclorac require light to initiate herbicidal activity (data not presented).

The herbicidal effects evident by electrolyte leakage from 1 HM ﬂuthiacet and 1 aM
ﬂumiclorac on velvetleaf, redroot pigweed, corn, and soybean leaf disks were equivalent
(Table 2). However, herbicidal effects on wild mustard leaf disks were greater with
ﬂuthiacet when compared with ﬂumiclorac. One mM 4,6-dioxoheptanoic acid (DA)
alone did not induce electrolyte leakage compared with an untreated control. Yet, adding
DA to ﬂuthiacet or ﬂumiclorac reduced herbicidal activity compared with ﬂuthiacet and
ﬂumiclorac applied without DA. Duke et al. (1991) reported that the addition of DA to
Protox-inhibiting herbicides reduces their herbicidal activity by inhibiting an early
enzyme in the prophyrin synthesis pathway, 5-aminolevulinic acid (ALA) dehydratase.

ALA is an early intermediate in the prophyrin synthesis pathway (Lydon and Duke
1988). Exogenous ALA applications may result in herbicidal effects by initiating the
accumulation of photodynamic porphyrin compounds (Lydon and Duke 1988). Wright et

al. (1995) reported treating cucumber (Cueumis sativus L.) leaf disks with 50 MM ALA

l3

 

increased

redroot p:
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and soyh.
.51 ALA I

redroot p;

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Fluthiace
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increased the bathing medium conductivity. However, in our experiments, velvetleaf,
redroot pigweed, wild mustard, corn, and soybean leaf disks were not affected by the
addition of 50 aM ALA (Table 3). Conductivity in the velvetleaf, wild mustard, corn,
and soybean assay tubes was equivalent between ﬂuthiacet and ﬂumiclorac. Applying 50
aM ALA to ﬂuthiacet or ﬂumiclorac increased herbicidal activity except for ﬂuthiacet on
redroot pigweed. All data suggest ﬂuthiacet and ﬂumiclorac exert their light-dependent

herbicidal effects by inhibiting Protox.

Fluthiacet and Flumiclorac Selectivity

Species Sensitivity. The ﬁeld use rate for ﬂuthiacet is 4 to 5 g ha" (Anonymous 1995),
whereas ﬂumiclorac is used at rates of 30 to 60 g ha’l (Kurtz and Pawlak 1993).
Velvetleaf, redroot pigweed, wild mustard, corn, and soybean sensitivities to 2 g ha‘l
ﬂuthiacet or 15 g ha‘l ﬂumiclorac were determined for greenhouse grown plants (Table
4). Velvetleaf was sensitive to both herbicides, as a postemergence herbicide application
reduced velvetleaf dry weight by 96% (Table 4). Similarly, ﬂuthiacet and ﬂumiclorac
reduced redroot pigweed dry weight by at least 90%. However, redroot pigweed was
more sensitive to ﬂumiclorac when compared with ﬂuthiacet. Fluthiacet provided a 91%
reduction in wild mustard dry weight, yet ﬂumiclorac only reduced wild mustard dry
weight by 53%. Corn and soybean were tolerant to ﬂuthiacet and ﬂumiclorac as dry
weight reduction was less than 5%.

Herbicide Retention. Species susceptibility to a postemergence herbicide application is
affected by herbicide retention (Gillespie 1994). Sprague et al. (1997) reported a ﬁvefold

increase in isoxaﬂutole (5-cyclopropyl isoxazol-4-yl-2-mesyl-4-triﬂuoromethylphenyl

l4

ketone) retention when metolachlor/benoxacor (2-chloro-N-(2-ethyl-6-methylphenyl)-‘(2-
methoxy-l -methylethyl)acetamide/(4-dichloroacetyl)-3 ,1dihydro-3-methyl-2H-l ,4-
benzoxazine) was added which resulted in enhanced corn injury compared with
isoxaﬂutole alone.

Fluthiacet and ﬂumiclorac retention on leaves varied among test species with the
greatest differences occurring between the crop and weed species (Table 5). Fluthiacet
and ﬂumiclorac retention by redroot pigweed was eightfold greater than soybean. Thus,
for each square leaf area unit, eight times more herbicide was present on a redroot
pigweed leaf than a soybean leaf. Velvetleaf and wild mustard retained less ﬂuthiacet
and ﬂumiclorac than redroot pigweed; however, herbicide retention by these species was
twice that of corn or soybean. Differences in redroot pigweed and soybean epicuticular
wax structure could explain differences in herbicide retention of these species. Harr et al.
(1991) reported 54 and 75° leaf contact angles for redroot pigweed and soybean,
respectively, conﬁrming differences in the epicuticular wax of these two Species.
Herbicide Absorption. Fluthiacet and ﬂumiclorac both provide excellent postemergence
velvetleaf control (Table 4). However, ﬂuthiacet absorption by velvetleaf foliage was
greater than ﬂumiclorac 12 HAT (Table 6). Although soybean is tolerant to both
herbicides, foliar absorption of ﬂuthiacet and ﬂumiclorac was greater in soybean than
velvetleaf. However, corn absorbed less ﬂuthiacet than velvetleaf.

Fluthiacet absorption was greater by redroot pigweed, wild mustard, and corn when
compared with absorption of ﬂumiclorac 12 HAT. Increased ﬂuthiacet absorption in
wild mustard may explain greater sensitivity of wild mustard to ﬂuthiacet than

ﬂumiclorac. However, redroot pigweed absorbed more ﬂuthiacet than ﬂumiclorac, yet

15

redroot pigweed is more tolerant of ﬂuthiacet than ﬂumiclorac. Corn is equally sensitive
to both herbicides; and ﬂuthiacet and ﬂumiclorac foliar absorption was Similar in corn 2
HAT. Foliar absorption of ﬂuthiacet and ﬂumiclorac alone cannot account for
differences in herbicide sensitivity or selectivity.

Herbicide T ranslocation. Protox-inhibiting herbicides are regarded as contact herbicides
because of limited translocation (Scalla and Matringe 1994). F luthiacet and ﬂumiclorac
movement within plants was evaluated by measuring l“C translocation out of the l"C
treated leaf. Herbicide translocation was limited as less than 29% of the MC herbicide
was translocated out of the treated leaves (Table 6). Relative herbicide translocation did
not vary between species and herbicides 2 and 12 HAT. This was not surprising Since
herbicidal injury symptoms from ﬂuthiacet or ﬂumiclorac were present within 3 h after
treatment (data not presented). Differences in species sensitivity to ﬂuthiacet and
ﬂumiclorac are not explained by differential herbicide translocation.

Translocation of ﬂuthiacet and ﬂumiclorac 12 HAT was greater in wild mustard and
corn compared with velvetleaf. However, translocation did not correlate with ﬂuthiacet
and ﬂumiclorac selectivity. Wild mustard is tolerant to ﬂumiclorac yet susceptible to
ﬂuthiacet, while corn is tolerant to both herbicides (Table 4). Fluthiacet and ﬂumiclorac
tolerant Species translocated similar or greater amounts of herbicide compared with plants
susceptible to these herbicides. Thus, herbicide translocation did not appear to contribute
to ﬂuthiacet or ﬂumiclorac selectivity.

Herbicide Metabolism. Research evaluated differences in ﬂuthiacet and ﬂumiclorac
metabolism to a nonbiologically active metabolite. Although both herbicides were

metabolized, the structural characterization of these metabolites was beyond the scope of

16

this study.

Velvetleaf, redroot pigweed, and corn metabolized more ﬂuthiacet than ﬂumiclorac 12
HAT to nonbiologically active metabolites (Table 6). However, redroot pigweed was the
only species more sensitive to ﬂumiclorac than ﬂuthiacet. Fluthiacet metabolism to a
nonbiologically active metabolite was greater in redroot pi gweed, corn, and soybean 12
HAT when compared with velvetleaf and wild mustard (Table 6). Metabolism results
support the species sensitivity experiment where redroot pigweed, corn, and soybean
were more tolerant to ﬂuthiacet than velvetleaf (Table 4). Likewise, there were more of
the biologically active forms of ﬂumiclorac present in the most sensitive Species,
velvetleaf and redroot pigweed. Flumiclorac metabolism to a nonactive form was greater
in wild mustard, corn, and soybean than velvetleaf and redroot pigweed. Fluthiacet and
ﬂumiclorac tolerant species metabolize these herbicides more rapidly than sensitive
species.

Fluthiacet and ﬂumiclorac exert their light-dependent herbicidal effects by inhibiting
Protox. However, the selectivity mechanisms plants use to protect against these
herbicides varies by species. Table 7 identiﬁes the factors that Si gniﬁcantly contribute to
species tolerance to these herbicides when compared with velvetleaf. Differential
herbicide metabolism and differential foliar herbicide retention, absorption, and
translocation contribute to ﬂuthiacet and ﬂumiclorac selectivity. However, the
differences in foliar absorption and metabolism in wild mustard treated with ﬂuthiacet
compared with ﬂumiclorac does not account for the dramatic differences in the whole
plant sensitivity to these herbicides. Sherman et al. (1991) reported that mustard, which

is tolerant to aciﬂuorfen, produced limited Proto in response to aciﬂuorfen despite having

17

susceptible Protox. Jacobs et al. (1990) reported tolerant soybean root mitochondria are
insensitive to aciﬂuorfen, thus suggesting aciﬂuorfen selectivity may be explained by
differences in Protox sensitivity. However, further investigations by Sherman et al.
(1991) found no correlation between Protox sensitivity and herbicidal effects from
aciﬂuorfen. Thus, species selectivity to Protox-inhibiting herbicides may be explained by
less Proto accumulation, decreased absorption, increased translocation, rapid metabolism,
and other mechanisms; but apparently, it is not due to differences in Protox sensitivity
(Scalla and Matringe 1994).

Another explanation for tolerance to Protox-inhibiting herbicides is an enhanced
capacity to detoxify singlet oxygen. Plants contain natural defense mechanisms that
provide protection from damaging oxygen radicals. The reductant, ascorbate, is one such
molecule. Sandmann and Boger (1990) reported ﬁfteenfold greater ascorbate levels in
Protox-inhibiting herbicide tolerant Bumilleriopsis microalgae when compared with
susceptible Scendesmus. Similarly, tobacco (Nicotiana tabacum L.)) susceptibility to
ﬂumiclorac and aciﬂuorfen was attributed to an enhanced antioxidant system in tolerant
biotypes (Gullner et al. 1991). Antioxidant systems that can protect plants from Protox-
inhibiting herbicides are one selectivity mechanism. However, their impact on Protox-
inhibiting herbicide efﬁcacy is unclear. Plant tolerance to Protox-inhibiting herbicides is
a complex process, and factors not examined in these experiments may contribute to
ﬂuthiacet and ﬂumiclorac selectivity. A complex interaction of factors including
herbicide retention, absorption, translocation, and metabolism ultimately determine

Species sensitivity to a particular Protox-inhibiting herbicide.

18

ACKNOWLEDGMENTS

The authors thank Jason Simon for his assistance in this research. Appreciation is
extended to Valent U.S.A. Corporation and Novartis Crop Protection, Inc. for their

ﬁnancial support.

19

10.

11.

12.

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Jacobs, and S. 0. Duke. 1991. Physiological basis for differential sensitivities of
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adj uvants and desmedipham plus phenmedipham on velvetleaf (Abutilon
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Westberg D. E. and H. D. Coble. 1992. Effect of aciﬂuorfen on the absorption,
translocation, and metabolism of chlorimuron in certain weeds. Weed Technol.
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Herbicidal activity of UCC-C4243 and aciﬂuorfen is due to inhibition of
protoporphyrinogen oxidase. Weed Sci. 43:47-54.

22

Table 1. Characterization of ﬂuthiacet and ﬂumiclorac metabolites.a

 

 

Herbicide Metabolite Rf Biologically activeb
Fluthiacet Parent 0.75 Yes

A 0.52 Yes

B 0.3 1 Yes

C 0. 1 3 No
Flumiclorac Parent 0.88 Yes

A 0.44 Yes

B 0.27 No

C O. 1 3 No

 

‘ Quantiﬁed parent herbicide and metabolites from Thin Layer Chromatography (TLC)
separation using 20 by 20 cm Silica gel (60 F 254) TLC plates. Plates were developed in
a 13 cm solvent front in toluene : ethyl acetate : acetic acid (5:7:1 v/v/v).

b Electrolyte leakage assay indicated biological activity equivalent to the parent herbicide.

23

Table 2. Effect of 4,6-dioxoheptanoic acid (DA) on electrolyte leakage 24 h after
ﬂuthiacet and ﬂumiclorac treatment.a

 

 

 

 

Species
Redroot Wild
Treatment Rate Velvetleaf pigweed mustard Corn Soybean
aM —— amhos" cm" assay tube"

Fluthiacet 1 194 144 291 73 255
Flumiclorac 1 181 139 208 75 213
DA 1000 3 28 2 4 11
Fluthiacet + DA 1000 + 1 56 9 89 33 166

F lumiclorac + DA 1000 + 1 82 3O 74 36 155

LSD (0.05) 43

 

 

 

‘ Means may be compared within or across columns within herbicides and within Species.

24

Table 3. Effect of 6-aminolevulinic acid (ALA) on electrolyte leakage 24 h aﬁer
ﬂuthiacet and ﬂumiclorac treatment.al

 

 

 

 

 

 

 

Species
Redroot Wild
Treatment Rate Velvetleaf pigweed mustard Corn Soybean
aM amhos" cm" assay tube"
Fluthiacet 0.2 155 171 175 73 138
Flumiclorac 0.2 126 129 144 42 157
ALA 50 27 9 15 4 3
Fluthiacet + ALA 0.2 +50 206 182 226 127 201
Flumiclorac + ALA 0.2 + 50 210 196 240 94 229
LSD (0.05) 41

 

 

“ Means may be compared within or across columns within herbicides and within Species.

25

Table 4. Species sensitivity to 2 g ha" ﬂuthiacet and 15 g ha" ﬂumiclorac in the
greenhouse 14 d after treatment.“

 

 

 

 

 

Herbicide
Species Fluthiacet Flumiclorac
% dry weight reduction
Velvetleaf 96 a 96 a
Redroot pigweed 90 b 97 a
Wild mustard 91 b 53 0
Corn 5 d 2 d
Soybean 5 d 5 d

 

‘ Means may be compared within or across columns within herbicides and within species.
Means followed by the same letter are not signiﬁcantly different according to Fisher’s
Protected LSD (or= 0.05). All treatments included nonionic surfactant at 0.25% v/v.

26

Table 5. F luthiacet and ﬂumiclorac retention in ﬁve plant species.“

 

Herbicide
Species Fluthiacet Flumiclorac

% of theoretical maximum retention

Velvetleaf 45 c 42 c
Redroot pigweed 78 a 66 b
Wild mustard 37 c 42 c
Corn 17 d 17 d
Soybean 8 d 8 d

 

" Means may be compared within or across columns within herbicides and within species.
Means followed by the same letter are not signiﬁcantly different according to Fisher’s
Protected LSD (th= 0.05). All treatments included nonionic surfactant at 0.25% WV.

27

Table 6. Fluthiacet and ﬂumiclorac absorption, translocation, and metabolism in 5 plant

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

species.ll
Harvest time
12 h

Species F luthiacet Flumiclorac Fluthiacet Flumiclorac

Foliar absorption

% of applied l"C
Velvetleaf 64 c 44 d 81 c 56 f
Redroot pigweed 79 a 42 d 93 a 66 e
Wild mustard 79 a 68 be 95 a 85 bc
Corn 50 d 43 d 73 d 60 f
Soybean 75 ab 70 abc 90 ab 87 b

Translocationb

% of applied l“C
Velvetleaf 99 a 99 a 96 a 98 a
Redroot pigweed 96 ab 86 b 98 a 92 ab
Wild mustard 89 ab 90 ab 82 be 84 b
Corn 76 c 74 c 73 c 71 c
Soybean 99 a 99 a 96 a 99 a

Metabolismc

% of applied 1“C
Velvetleaf 83 a 77 ab 49 be 63 a
Redroot pigweed 68 b 70 b 35 de 54 ab
Wild mustard 80 ab 72 ab 39 cde 46 bed
Corn 78 ab 46 c 36 de 30 e
Soybean 40 c 72 ab 15 f 40 cde

 

“ Means may be compared within or across columns within factors and within harvest
time. Means followed by the same letter are not Signiﬁcantly different according to

Fisher’s Protected LSD (or = 0.05).
b Radioactive herbicide remaining in the treated leaf.

° Metabolism expressed as percentage remaining biologically active within the treated

leaf.

28

 

1a

116

Table 7. Factors affecting plant tolerance to ﬂuthiacet and ﬂumiclorac 12 h after
treatment.3

 

Herbicide

 

Herbicide Species Toleranceb Retention Absorption Translocation Metabolism

 

 

Fluthiacet velvetleaf S — — _ _
redroot S _ _ _ X
pigweed
wild
mustard S X
corn T X X X X
soybean T X — _ X

Flumiclorac velvetleaf S — — ._ _
redroot

. S — —— _ _
pigweed
wrld ST __ _ X X
mustard
corn T X — X X
soybean T X — _ X
‘X = signiﬁcantly contributes, — = does not signiﬁcantly contribute to Species tolerance.

b S= sensitive, T= tolerant based on Table 4.

29

CHAPTER 2

Environmental Effects on Fluthiacet and Flumiclorac
Efﬁcacy and Soybean Tolerance

ABSTRACT

Laboratory and ﬁeld experiments were designed to examine the effect temperature,
light intensity, time to initial light exposure, relative humidity, and the presence of dew
had on ﬂuthiacet and ﬂumiclorac efﬁcacy. Increasing temperature ﬁom 10 to 40 C and
light intensity ﬁom 0 to 1000 mm] m‘2 S" increased ﬂuthiacet and ﬂumiclorac activity on
redroot pigweed and common lambsquarters. Time to initial light exposure and relative
humidity did not affect ﬂuthiacet and ﬂumiclorac activity on redroot pigweed and
common lambsquarters. The presence of dew reduced herbicide activity on redroot
pigweed and common lambsquarters. A ﬁeld study was conducted to determine if
ﬂuthiacet or ﬂtuniclorac applications at 0600 h, 1400 h, or 2200 h inﬂuenced soybean
tolerance and weed control. The greatest soybean injury occurred from ﬂuthiacet or
ﬂumiclorac applications at 0600 h compared with 1400 or 2200 h. Common
lambsquarters control was greatest when ﬂuthiacet or ﬂumiclorac was applied at 0600 h
or 1400 h compared with 2200 h. However, redroot pigweed control was greatest when

ﬂuthiacet or ﬂumiclorac was applied at 1400 h. Application time of day did not effect

30

velvetleaf control with either herbicide. Results suggest environmental conditions at
application inﬂuence soybean tolerance and weed control with ﬂuthiacet and ﬂumiclorac.
Nomenclature: F luthiacet, [[2-chloro-4-ﬂuoro-5-[(tetrahydro-3-oxo-1H, 3H-

[1 ,3 ,4]thiadiazolo[3 ,4-a]pyridazin— 1 -ylidene)amino]phenyl]thio]aceate; ﬂumiclorac,
pentyl[2-chloro-4-ﬂuoro-5-(1 ,3,4,5 ,6,7-hexahydro-1 ,3-dioxo-2H-isoindol-2-
yl)phenoxy]acetic acid; common lambsquarters, Chenopodium album L. #‘ CHEAL;
redroot pigweed, Amaranthus retroﬂexus # AMARE; velvetleaf, Abutilon theophrasti
Medik. # ABUTH; soybean Glycine max (L.) Merr. ‘Conrad’ # GLYMA.

Key Words: Application time of day, temperature, relative humidity, light intensity,
dew, CHEAL, AMARE, ABUTH, GLYMA.

Abbreviations: COC, crop oil concentrate; DAT days after treatment; HAT, hours after
treatment; NTS, nonionic surfactant; Protox, protoporphyrinogen oxidase; UAN, 28%

urea ammonium nitrate; v/v, volume per volume.

 

'Letters following this symbol are a WSSA-approved computer code from Composite
List of Weed, Revised 1989. Available from WSSA.

31

INTRODUCTION

Environmental conditions at application such as temperature, light, relative
humidity, rainfall, and soil moisture inﬂuence herbicide efﬁcacy (Coupland 1983; Kudsk
et al. 1990). Because environmental conditions vary within the day, application time may
influence the herbicidal activity of cyclic imide herbicides such as ﬂuthiacet and
ﬂumiclorac.

Several classes of photodynamic herbicides including cyclic imides, diphenyl ethers,
and oxadiazoles block the enzymatic oxidation of protoporphyrinogen IX to
protoporphyrin IX by protoporphyrinogen oxidase (Protox) (Duke et al. 1991).
Protoporphyrin IX rapidly generates singlet oxygen in the presence of light and molecular
oxygen, subsequently causing lipid peroxidation and immediate cellular death in sensitive
plant species (Lee and Duke 1994).

Research investigating environmental effects on soybean tolerance and efﬁcacy of
photodynamic herbicides is limited. Common cocklebur (Xanthium strumarium L.) and
velvetleaf control with bentazon (3-(l-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-
one 2,2-dioxide) were reduced when bentazon was applied early morning, late evening, or
at night (Doran and Anderson 1976). Paraquat (l ,1'-dimethyl-4,4'-bipyridinium ion)
provided greater quackgrass (Elyitrigia repens L.) control when applied at 2000 h
compared with an application at 1400 h (Putnam and Ries 1968). Yet, common
lambsquarters and redroot pigweed control with paraquat and aciﬂuorfen (5-[2-chloro-4-
(triﬂuoromethyl)phenoxy]-2-nitrobenzoic acid) increased when applied at 0900 h or 1500

h compared with 0300 h or 2100 h (Zhou and Ahrens 1995). Hemp sesbania (Sesbania

32

exaltata (Raf) Cory) control with aciﬂuorfen increased when applied at 2100 h compared
with 0600 h or 1200 h (Lee and Oliver 1982).

Temperature and relative humidity inﬂuence the translocation and efﬁcacy of
diphenyl ether herbicides. Aciﬂuorfen translocation in showy crotalaria (Crotalaria
spectabilis Roth) increased fourfold when relative humidity increased from 40 to 100%
(Wills and McWhorter 1981). Common cocklebur and common ragweed (Ambrosia
artemisiifolia L.) control with aciﬂuorfen was 10 to 30% greater when aciﬂuorfen was
applied at 85% relative humidity compared with 50% relative humidity (Ritter and Coble
1981). Similarly, increasing relative humidity from 50 to 85% enhanced aciﬂuorfen,
fomesafen (5-[2-chloro-4-(triﬂuoromethyl)phenoxy](methylsulfonyl)-2-nitrobenzamide),
and lactofen ((:)-2-ethoxy- l -methyl-2-oxoethyl-5-[2-chloro-4-
(triﬂuoromethyl)phenoxy]-2-nitrobenzoate) activity on prickly Sida (Sida spinosa L.),
pitted momingglory, (Ipomoea lacunosa L.), entireleaf momingglory (Ipomoea
hederacea var. integriuscula L.), and common cocklebur (Wichert et al. 1992).

Inconsistent weed control with ﬂumiclorac was reported in 1995 (K. A. Renner,
personal communication). The effect environmental conditions have on soybean tolerance
and weed control with ﬂuthiacet or ﬂumiclorac has not been documented. Therefore, the
objectives of this research were to evaluate the effect temperature, light intensity, time to
initial light exposure, relative humidity, the presence of dew, and the application time of

day has on ﬂuthiacet or ﬂumiclorac efﬁcacy and soybean tolerance.

33

MATERIALS AND METHODS
General methods for laboratory experiments. Experiments were conducted to
determine the effect temperature, light intensity, time to initial light exposure, and
relative humidity have on ﬂuthiacet and ﬂumiclorac efﬁcacy. Uniform, fully expanded
leaves from natural populations of ﬁeld-grown common lambsquarters and redroot
pigweed were harvested at the Michigan State University Research Farm in East Lansing,
MI, in August 1998. Leaf sections of 1.5 by 1.5 cm were excised and placed in 20 by
lOO-mm petri dishes containing No. 2 Whatrnan ﬁlter paper2 and 5 ml of distilled water.
Distilled water was added throughout the experiment to maintain leaf turgor.

Herbicide application consisted of ﬁve, 1 ul droplets of solution applied to the
adaxial leaf surface. Treatments included 4 g ha" ﬂuthiacet, 30 g ha" ﬂumiclorac, and an
untreated control. Herbicide treatments were applied with 0.25% (v/v) nonionic
surfactant3 (NIS).

F luthiacet and ﬂumiclorac activity on common lambsquarters and redroot pigweed
leaf sections were visually evaluated 72 h after treatment (HAT). Visual ratings were
based on a scale from 0 (no effect) to 100% (complete dessication). Values represent leaf
discoloration and necrosis.

Each experiment was a completely randomized design with Six replications.
Experiments were conducted twice, and the data presented are the means of the two

experiments. Unless otherwise indicated, the following conditions were standardized:

 

2Filter paper, Whatrnan #2. Whatman International Ltd., Maidstone, England.

3Activator-90, nonionic surfactant, a mixture of alkyl polyoxyethylene ether and fatty
acids. Loveland Industries, Inc., PO. Box 1289, Greeley, CO 80632.

34

temperature at 30 C, 24-h illumination at 40 amol m’2 s", and 6 leaf sections per
treatment.

Temperature. Petri dishes containing hydrated leaf sections were placed in water baths
calibrated to 10, 20, 30, or 40 C. Leaf sections were equilibrated to the water temperature
for 45 min before herbicide application.

Light intensity. Light intensity was examined by comparing herbicidal activity on
hydrated leaf sections exposed to 0, 4, 40, or 1,000 amol In2 S" for 72 h.

Time to initial light exposure. Leaf sections were equilibrated for l h at 30 C in darkness
before herbicide application. Leaf sections were removed from darkness at 0, 2, 4, 6, 8, or
12 HAT and exposed to 24-h illumination at 40 amol rn'2 3".

Relative humidity. A continuous ﬂow system consisting of a vapor generator and three
9.3 L glass chambers connected with 3 mm id. teﬂon tubing was designed. In-line
microbial ﬁlters4 ﬁltered incoming air. Flow rate of 150 ml per min was regulated with
glass microbore capillary tubes and a pressure regulators. Humidity was established
within the chambers by directing air ﬂow through 1) sterilized water (90% relative
humidity), 2) saturated calcium nitrate solution (50% relative humidity), or 3) by directly
transferring air into the chamber (10% relative humidity). The glass chambers were
equilibrated for 24 h before leaf sections were treated with herbicide. Treated leaf
sections were placed in the chambers for 8 h and exposed to 4 amol rn‘2 5". Leaf sections

were removed from the glass chambers and exposed to 40 amol m2 s" for 64 h.

 

4Microbial ﬁlter, Alltech Associates, Inc., Deerﬁeld, IL 60015.
5Scientiﬁc pressure regulator, South Plainﬁeld, NJ 07080.

35

Inﬂuence of dew on efﬁcacy. Experiments were conducted at the Michigan State
University Research Farm in East Lansing, MI, in 1998. Locally collected common
lambsquarters and redroot pigweed seeds were planted in BACCTO" potting soil in 946-
ml plastic pots. Initial environmental conditions were maintained within a greenhouse at
27 d: 5 C. Following emergence, seedlings were transferred to outdoor environmental
conditions. Plants were thinned to 1 plant pot", fertilized with 50 ml of a water—soluble
fertilizer solution (400 ppm N, 400 ppm P205, and 400 ppm K20), and watered as needed.
Plants were split into two groups the evening prior to herbicide application, dew or no
dew. Dew designated plants were left uncovered while the no dew plants were loosely
covered with burlap to inhibit natural dew formation. Plants were treated with ﬂuthiacet
or ﬂumiclorac 30 min after burlap removal.

The experiment was a completely randomized design with four replications.
Treatments included 4 g ha" ﬂuthiacet, 30 g ha" ﬂumiclorac, and an untreated control.
All treatments were applied in combination with 0.25% (v/v) NIS.

Herbicides were applied on July 4, 1998 and July 6, 1998 with a carbon dioxide
backpack sprayer traveling at 6.3 km h" and delivering 178 L ha" at 207 kPa of pressure.
Treatments were applied with 8003 ﬂat-fan nozzles7 spaced 51 cm apart and 48 cm above
the canopy. At application, common lambsquarters plants were 1 to 6 cm tall with two to

ten leaves; and redroot pigweed plants were 1 to 10 cm tall with two to twelve leaves.

 

6BACCTO professional planting mix, Michigan Peat Co., Houston, TX 77098.

7Teejet ﬂat-fan tips, Spraying Systems Co., North Avenue and Schmale Road, Wheaton,
IL 60188.

36

Common lambsquarters and redroot pigweed control was visually evaluated for
phytotoxicity 7 and 14 d after treatment (DAT). Visual ratings were based on a scale from
0 to 100%, with 0 indicating no effect and 100 indicating plant death. Evaluations
represented visual stunting, chlorosis, and necrosis.

Field experiment. Experiments were conducted at the Michigan State University
Research Farm at East Lansing, MI, in 1996 and 1998 and at the Michigan State
University Horticulture Research Station at Clarksville, MI, in 1997. The East Lansing
soil was a Capac sandy clay loam (ﬁne-loamy, mixed mesic Aerie Ochraqualfs) with 3.3
and 2.2% organic matter in 1996 and 1998, respectively. The Clarksville soil was a
Lapeer sandy loam (coarse-loamy, mixed, mesic Mollic Haplaquepts) with 1.9% organic
matter. The soil pH was 7.0, 6.8, and 7.1 in 1996, 1997, and 1998, respectively. The 1996
and 1998 Sites were fall chisel plowed with secondary tillage consisting of two ﬁeld
cultivations at planting. The 1997 Site was spring moldboard plowed, and secondary
tillage consisted of two ﬁeld cultivations at planting. ‘Conrad’ soybean was planted in
76-cm rows at 395,000 seed ha". Plots were 3 m wide by 9.1 m in length.

The experimental design was a split plot with four replications. Main plots were
herbicide. Subplots were time of application. Main plots included either 4 g ha" ﬂuthiacet
or 30 g ha" ﬂumiclorac. Each herbicide treatment was applied within a 24 h time period
at 0600 h, 1400 h, and 2200 h (Table 6). All treatments included either 0.25% (v/v) NIS
plus 1.0% (v/v) 28% urea ammonium nitrate (UAN) or 0.5% (v/v) crop oil concentrate8

(COC).

 

8Herbirnax, crop oil concentrate, 83% petroleum oil, 17% surfactant, Loveland Industries,
Inc., PO. Box 1289, Greeley, CO 80632.

37

Herbicides were applied June 13, 1996, June 24, 1997, and June 9, 1998, 26, 31, and
27 d after planting, with a compressed air tractor-mounted sprayer traveling at 6.3 km h"
and delivering 178 L ha" at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-
fan nozzles Spaced 51 cm apart and 48 cm above the weed canopy. At application,
soybean plants were 10 to 12 cm tall with two fully developed trifoliolates, common
lambsquarters plants were 1 to 10 cm tall with 2 to 24 leaves, redroot pigweed plants
were 1 to 10 cm tall with 2 to 12 leaves, and velvetleaf plants were 1 to 10 cm tall with l
to 7 leaves.

Soybean injury was visually evaluated 3, 7, l4, and 21 DAT. Weed control was
evaluated for each Species 7, 14, and 21 DAT. Visual ratings were based on a scale from
0 to 100%, with 0 indicating no effect and 100 signifying plant death. Soybean injury and
weed control evaluations represent visual stunting, chlorosis, and necrosis.

Statistical analyses. All experiments were repeated over time, and data were analyzed
using analysis of variance (ANOVA). Data for individual experiments were combined as
analyses revealed no treatment by time interaction. Means were separated by Fisher’s

protected least signiﬁcant difference (LSD) at the 5% level.

RESULTS AND DISCUSSION
Laboratory experiments.
Temperature. F luthiacet and ﬂumiclorac activity on common lambsquarters increased
four and sevenfold, respectively, when temperature increased from 10 to 40 C (Table 1).
Similarly, when temperature increased from 10 to 40 C, activity of both herbicides

increased threefold on redroot pigweed. However, ﬂuthiacet and ﬂumiclorac activity on

38

x _2.

redroot pigweed increased, while activity on common lambsquarters did not increase
when temperature increased from 30 to 40 C.

Eckl and Gruler (1980) found species dependent phase changes in plant cuticles were
associated with changes in temperature. The composition and structure of epicuticular
wax affects herbicide efﬁcacy (Flore and Bukovac 197 8). Harr et a1. (1991) reported
nonpolar fractions of common lambsquarters and redroot pigweed cuticles were 30 and
42%, respectively, conﬁrming natural differences exist in the epicuticular wax of these
species. Differences in phase changes or the epicuticular wax structure of common
lambsquarters and redroot pigweed cuticles may explain differences in herbicidal
response of these weed species at 30 and 40 C.

Light intensity. Increasing light intensity from 4 to 1,000 amol m'2 5" increased ﬂuthiacet
and ﬂurrriclorac activity on common lambsquarters and redroot pigweed 4 to 15 fold
(Table 2). Light and molecular oxygen combine with protoporphyrin IX to generate
Singlet oxygen, which initiates lipid peroxidation and cellular death in Protox susceptible
plant species (Lee and Duke 1994). Thus, increased herbicidal activity on common
lambsquarters and redroot pigweed was observed with increasing light intensity.

Time to initial light exposure. Time to initial light exposure did not affect ﬂuthiacet and
ﬂumiclorac activity on common lambsquarters or redroot pigweed 72 HAT (Table 3).
Fluthiacet and ﬂumiclorac activity is evident within 3 h after application if light is present
at application (data not presented). Thus, the mechanism of ﬂuthiacet or ﬂumiclorac
selectivity must occur rapidly in tolerant Species. Ritter and Coble (1981) reported that
soybean tolerance to aciﬂuorfen was explained by less rapid herbicide penetration and

translocation coupled with increased metabolism rates. Less rapid absorption and

39

decreased translocation rates of ﬂuthiacet and ﬂumiclorac may account for differences in
herbicidal response of common lambsquarters and redroot pigweed.
Relative humidity. Increased relative humidity can enhance herbicidal activity by
prolonging the drying time and increasing cuticle hydration (Caseley 1989; Ritter and
Coble 1981). Wichert et al. (1992) reported increased relative humidity enhanced Protox-
inhibiting herbicide activity on prickly Sida, pitted and entireleaf momingglory, and
common cocklebur. In our research, increased relative humidity prolonged drying time
(personal observation), but did not affect ﬂuthiacet or ﬂumiclorac activity on common
lambsquarters and redroot pigweed 72 HAT (Table 4). The lack of response to relative
humidity may result from factors such as temperature and light masking the subtle effects
of relative humidity.
Inﬂuence of dew on efﬁcacy. The presence of dew at application may increase or
decrease herbicide performance depending upon the herbicide and species involved
(Caseley 1989; Wanamarta and Penner 1989). The presence of dew at application reduced
common lambsquarters and redroot pigweed control with ﬂuthiacet or ﬂumiclorac l4
DAT (Table 5).
Field experiment. Preliminary experiments revealed soybean tolerance and weed control
with lactofen, oxasulfuron, and tank mixtures of lactofen or oxasulfuron with ﬂuthiacet or
ﬂumiclorac were unaffected by application time of day (data not presented). However,
application time of day affected soybean tolerance and weed control with ﬂuthiacet or
ﬂumiclorac applied alone (Table 7).

Soybean injury was greatest 7 DAT for both herbicides applied at 0600 h (Table 7).

Fluthiacet or ﬂumiclorac applied at 0600 h and 1400 h provided greater common

40

lambsquarters control compared with herbicides applied at 2200 h (Table 7). Either
herbicide applied at 1400 h provided greater redroot pigweed control compared with
applications at 0600 h or 2200 h. Velvetleaf control 14 DAT with ﬂuthiacet or
ﬂumiclorac was unaffected by application time of day (Table 7).

Fluthiacet or ﬂumiclorac applied at 1400 h provided the greatest broad-spectrum
broadleaf weed control. At 1400 h, air temperature and light intensity in the ﬁeld were
greatest (Table 6). Interestingly, soybean injury did not increase with increasing
temperature or light intensity. Therefore, soybean tolerance to ﬂuthiacet and ﬂumiclorac
must be inﬂuenced by other factors. Common lambsquarters and redroot pigweed control
decreased in the ﬁeld when initial light exposure occurred 8 h after ﬂuthiacet or
ﬂumiclorac applications. Laboratory experiments suggest reduced weed control with
evening applications of fluthiacet or ﬂumiclorac is not related to a delay in light
exposure. However, laboratory experiments were conducted at 30 C, whereas the air
temperature in the ﬁeld was 526 C and decreased following herbicide application (Table
6). Thus, at low temperatures time to initial light exposure may inﬂuence ﬂuthiacet or
ﬂumiclorac activity. Dew was only present at 0600 h in 1996 (Table 6), and weed control
was not reduced compared with other years (data not presented).

Herbicide absorption is a complex process with no single controlling factor. Spray
solution, plant foliage, and environmental conditions before, at, and following application
determine herbicide response (Holen and Dexter 1993; Wanamarta and Penner 1989).
Leaf movements have important implications on herbicide efﬁcacy (Anderson and
Koukkari 1979). Rhythmic leaf movements allow leaves to maximize the capture of light

(Akey et al. 1990). Daily leaf oscillations in velvetleaf account for decreased velvetleaf

41

control with bentazon by reducing spray interception when leaves are positioned
vertically (Anderson and Koukkari 1978; Doran and Anderson 1979). However,
Koukkari and Johnson (1979) reported the physical orientation of velvetleaf leaves did
not affect bentazon retention, thus concluding plant susceptibility was due to diurnal
changes in the plants physiological ability to detoxify the herbicide. Similarly, velvetleaf
control with ﬂuthiacet or ﬂumiclorac did not decrease at 2200 h although the leaves had a
vertical orientation. Weaver and Nylund (1963) reported increased carbohydrate
concentrations at application were associated with the susceptibility of ﬁeld pea to
MCPA (2-methyl-4-chlorophenoxyacetic acid). These aspects and others ultimately
combine to inﬂuence herbicide tolerance and efﬁcacy in the ﬁeld.

Laboratory results suggest a herbicide application at high temperature, high light
intensity, and in the absence of dew would increase ﬂuthiacet or ﬂumiclorac activity on
common lambsquarters and redroot pigweed. Field studies conﬁrmed these observations
for redroot pigweed as maximum control was obtained from an application of ﬂuthiacet
or ﬂumiclorac at 1400 h. The greatest common lambsquarters control in the ﬁeld was
achieved with ﬂuthiacet or ﬂumiclorac applications at 0600 h or 1400 h. Equivalent
common lambsquarters susceptibility to ﬂuthiacet or ﬂumiclorac applied in the ﬁeld early
morning and aﬁemoon illustrates the complex nature of herbicide selectivity. A reduction
in herbicide retention or absorption may not be relevant for velvetleaf control with
ﬂuthiacet or ﬂumiclorac because of high velvetleaf sensitivity to these herbicides (Fausey
and Renner 1998). Greater soybean tolerance to ﬂuthiacet or ﬂumiclorac at 1400 h or

2200 h applications compared with 0600 h applications could be due to more rapid

42

herbicide drying, less herbicide uptake, or an increase in the detoxifying capabilities of
soybean.

Beyers and Smeda (1997) reported reduced weed control with a late evening
glufosinate (2-amino-4-(hydroxymethylphosphinyl)butanoic acid) application. The
presence of dew, lower air temperature, or a lack of light may explain ineffective weed
control with an evening glufosinate application. A further understanding of the direct and
indirect effect environmental conditions at and following herbicide application is needed

to identify the ideal application time of day for photodynamic herbicides.

ACKNOWLEDGMENTS
The authors thank Gary Powell and Dr. Randy Beaudry for their assistance in this

research. Appreciation is extended to Valent U.S.A. Corporation and Novartis Crop

Protection, Inc. for their ﬁnancial support.

43

10.

11.

12.

LITERATURE CITED

Akey, W. C., T. W. Jurik, and J. Dekker. 1990. Competition for light between
velvetleaf (Abutilon theophrasti) and soybean (Glycine max). Weed Res. 30:403-
41 1.

Anderson, R. N. and W. L. Koukkari. 1978. Response of velvetleaf (Abutilon
theophrasti) to bentazon as affected by leaf orientation. Weed Sci. 26:393-395.

Anderson, R. N. and W. L. Koukkari. 1979. Rhythmic movements of some common
weeds. Weed Sci. 27:401-415.

Beyers, J. T. and R. J. Smeda. 1997. Inﬂuence of time of day on glufosinate activity.
Proc. N. Cent. Weed Sci. Soc. 52:123.

Black, F. S. and H. P. Wilson. 1969. Performance of herbicide adjuvant-sprays as
effected by the time of day, by the ratio of herbicide adjuvant, and by the chemical
type of the adjuvant. Abstr. Weed Sci. Soc. Am. p. l.

Caseley, J. C. 1989. Variations in foliar pesticide performance attributable to
humidity, dew, and rain effects. Aspects of App. Biol. 215-225.

Coupland, D. 1983. Inﬂuence of light, temperature and humidity on the translocation
and activity of glyphosate in Elymus repens (=Agropyr0n repens). Weed Res.
23:347-355.

Doran, D. L. and R. N. Andersen. 1976. Effectiveness of bentazon applied at various
times of day. Weed Sci. 24:567-570.

Duke, S. O., J. Lydon, J. M. Becerril, T. D. Sherman, L. P. Lehnen, Jr., and H.
Matsumoto. 1991. Protoporphyrinogen oxidase-inhibiting herbicides. Weed Sci.
39:465-473.

Eckl, K. and H. Gruler. 1980. Phase transitions in plant cuticle. Planta 150:102-113.
Fausey, J. C. and K. A. Renner. 1998. Broadleaf weed control in soybean with
ﬂumiclorac and CGA-248757 alone and in tank mixtures. Abstr. Weed Sci. Soc.
Am. 38:9.

Flore, J. A. and M. J. Bukovac. 1978. Pesticide effects on the plant cuticle: HI. EPTC

effects on the qualitative composition of Brassica oleracea L. leaf cuticles. J. Amer.
Soc. Hort. Sci. 103:297-301.

44

13.

14.

15.

16.

17.

18.

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22.

23.

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25.

Gossett, B. J. and C. E. Rieck. 1970. Performance of chloroxuron as inﬂuenced by
spray additives, spray volumes, and early morning versus late afternoon applications.
Proc. South. Weed Sci. Soc. 23:163.

Harr J ., R. Guggenheim, G. Schulke, and R. H. Falk. 1991. The leaf surface of major
weeds. Basel: Sandoz Agro Ltd.

Holen, C. D. and A. G. Dexter. 1993. Effect of increased temperature before and
after desmedipham application. Proc. N. Cent. Weed Sci. Soc. 48:86-87.

Koukkari, W. L. and M. A. Johnson. 1979. Oscillations of leaves of Abutilon
theophrasti (velvetleaf) and their sensitivity to bentazon in relation to low and high
humidity. Physiol. Plant. 47:158-162.

KudSk, P., T. Olsen, and K. E. Thonke. 1990. The inﬂuence of temperature,
humidity and simulated rain on the performance of thiarneturon-methyl. Weed Res.
30:261 -269.

Lee, H. J. and S. 0. Duke. 1994. Protoporphyrinogen IX-oxidizing activities
involved in the mode of ﬂuthiacet of peroxidizing herbicides. J. Agric. Food Chem.

42:2610-2618.

Lee, S. D. and L. R. Oliver. 1982. Efﬁcacy of aciﬂuorfen on broadleaf weeds. Times
and methods for application. Weed Sci. 30:520-526.

Putman, A. R. and S. K. Ries. 1968. Factors inﬂuencing the phytotoxicity and
movement of paraquat in quackgrass. Weed Sci. 16:80-83.

Ritter, R. L. and H. D. Coble. 1981. Inﬂuence of temperature and relative humidity
on the activity of aciﬂuorfen. Weed Sci. 29:480-485.

Wanamarta, G. and D. Penner. 1989. Foliar absorption of herbicides. Rev. Weed Sci.
42215-231 .

Weaver, M. L. and R. E. Nylund. 1963. Factors inﬂuencing the tolerance of peas to
MCPA. Weed Sci. 11:142-148

Weaver, M. L. and R. E. Nylund. 1965. The susceptibility of annual weeds and
Canada thistle to MCPA applied at different times of day. Weed Sci. 13:110-113.

Wichert, R. A., R. Bozsa, R. E. Talbert, and L. R. Oliver. 1992. Temperature and
relative humidity effects on diphenylether herbicides. Weed Technol. 6: 19-24.

45

26. Wills, G. D. and C. G. McWhorter. 1981. Effect of environment on the translocation
and toxicity of aciﬂuorfen to showy crotalaria (Crotalaria spectabilis). Weed Sci.
29:397-401.

27. Zhou, P. and W. H. Ahrens. 1995. The effect of time of day of application on
herbicide efﬁcacy. Proc. N. Cent. Weed Sci. Soc. 50:90-91.

46

Table 1. Effect of temperature on common lambsquarters and redroot pigweed control

with ﬂuthiacet and ﬂumiclorac 72 h after treatment.

 

 

 

 

 

Treatmenta Rate Temperature Common lambsquarters Redroot pigweed
g ha" C % control
Fluthiacet 4 10 6 20
4 20 14 36
4 30 24 53
4 40 28 63
F lumiclorac 30 1 0 4 23
30 20 16 32
30 3O 29 41
30 40 31 58
LSD (0.05) 7 10

 

‘All treatments were applied with 0.25% nonionic surfactant (NIS).

47

Table 2. Effect of light intensity on common lambsquarters and redroot pigweed control
with ﬂuthiacet and ﬂumiclorac 72 h after treatment.

 

Treatment"I Rate Light intensity Common lambsquarters Redroot pigweed

 

 

 

 

g ha" amol m'2 S" % control
Fluthiacet 4 0 3 4
4 4 9 8
4 40 23 43
4 1000 38 56
Flumiclorac 30 0 4 1
30 4 5 5
30 40 20 49
30 1000 46 75
LSD (0.05) 5 4

 

aAll treatments were applied with 0.25% nonionic surfactant (NIS).

48

Table 3. Effect of time to initial light exposure on common lambsquarters and redroot
pigweed control with ﬂuthiacet and ﬂumiclorac 72 h after treatment.

 

Time to initial
Treatment“ Rate light exposure Common lambsquarters Redroot pi gweed

 

 

 

 

g ha" h % control
Fluthiacet 4 0 21 33
4 2 21 33
4 4 21 33
4 6 19 32
4 8 19 31
4 12 19 32
Flumiclorac 30 0 24 42
30 2 23 41
30 4 24 43
30 6 24 43
30 8 23 41
30 12 23 42
LSD (0.05) 3 4

 

2'All treatments were applied with 0.25% nonionic surfactant (NIS).

49

Table 4. Effect of relative humidity on common lambsquarters and redroot pigweed
control with ﬂuthiacet and ﬂumiclorac 72 h after treatment.

 

Treatmenta Rate Relative humidity Commonlambsquarters Redroot pigweed

 

 

 

 

g ha" % % control
Fluthiacet 4 10 38 45
4 50 36 44
4 90 38 45
Flumiclorac 30 10 40 48
30 50 39 48
30 90 36 50
LSD (0.05) 7 6

 

2‘All treatments were applied with 0.25% nonionic surfactant (NIS).

50

Table 5. Effect of dew on common lambsquarters and redroot pi gweed control with
ﬂuthiacet and ﬂumiclorac 14 d after treatment.

 

Treatment“ Rate Leaf surface Commonlambsquarters Redroot pigweed

 

 

 

 

g ha" % control
F luthiacet 4 dew 92 69
4 no dew 97 87
Flumiclorac 30 dew 91 76
30 no dew 96 95
LSD (0.05) 3 8

 

“All treatments were applied with 0.25% nonionic surfactant (NIS).

51

Table 6. Herbicide application conditions in 1996, 1997, and 1998 ﬁeld experiments.

 

 

Application Air Relative Leaf surface
Date treated time Cloud cover temperature humidity moisture“
h % C %
6/13/96 0600 90 19 95 1
1400 30 29 62 5
2200 100 26 88 4
6/24/97 0600 80 26 65 5
1400 20 33 47 5
2200 90 29 62 5
6/9/98 0600 95 14 70 5
1400 30 21 26 5
2200 100 16 55 5

 

“Visual l to 5 rating with 1 signifying wet and 5 dry.

52

Table 7. Effect of time of application on tolerance and efﬁcacy of ﬂuthiacet and
ﬂumiclorac applied at 0600, 1400, and 2000 h.“

 

 

 

 

 

Application Common Redroot
Treatmentb Rate time Soybean lambsquarters pigweed Velvetleaf

g ha" h % injuryc % controld

F luthiacet 4 0600 14 74 51 98

4 1400 11 73 74 99

4 2200 12 61 52 98

Flumiclorac 30 0600 16 71 60 94

30 1400 11 68 77 94

30 2200 12 53 60 90

LSD (0.05) 2 7 7 6

 

“Data averaged over 1996, 1997, and 1998.

bAll treatments included either 0.25% (v/v) nonionic surfactant (N18) plus 1.0% (WV)
28% urea ammonium nitrate (UAN) or 0.5% (v/v) crop oil concentrate (COC).
cPercent injury 7 d after treatment (DAT).

dPercent control 14 DAT.

53

CHAPTER 3

Adjuvant Effects on Fluthiacet and Flumiclorac Efﬁcacy
and Soybean Tolerance

ABSTRACT

Greenhouse and ﬁeld studies evaluated adj uvant effects on weed control and soybean
tolerance with ﬂuthiacet or ﬂumiclorac applied alone and in combination with
imazethapyr and oxasulfuron. Adjuvants enhanced common lambsquarters, redroot
pigweed, common ragweed, and velvetleaf control with ﬂuthiacet by 53, 57, 29, and 29%
and ﬂumiclorac by 36, 62, 41, and 34%, respectively, in the greenhouse. In ﬁeld studies,
soybean injury and common lambsquarters, redroot pi gweed, and common ragweed
control were equivalent when ﬂuthiacet or ﬂumiclorac was applied with a cr0p oil
concentratel (0.5 or 1.0% v/v) or a nonionic surfactant2 plus 28% urea ammonium nitrate
(UAN) (0.25 + 1.0% v/v). In greenhouse studies, a tank mixture of ﬂuthiacet and
imazethapyr with a methylated seed oil3 or an organosilicone4 adjuvant enhanced
common lambsquarters and velvetleaf control compared with a nonionic surfactant.
Redroot pigweed control with ﬂuthiacet plus imazethapyr; and common lambsquarters
and velvetleaf control with ﬂumiclorac plus imazethapyr increased by the addition of an

organosilicone adjuvant compared with a nonionic surfactant. Redroot pigweed and

54

common ragweed control with tank mixtures of ﬂuthiacet or ﬂumiclorac plus oxasulfuron
were enhanced by adding an organosilicone adj uvant compared with a nonionic
surfactant. In ﬁeld evaluations of ﬂuthiacet or ﬂumiclorac plus imazethapyr, adding a
nonionic surfactant or an organosilicone adjuvant resulted in equivalent soybean injury
and giant foxtail, common lambsquarters, and redroot pi gweed control. The addition of
an organosilicone adjuvant increased redroot pigweed control and soybean yield in tank
mixtures of ﬂuthiacet or ﬂumiclorac plus oxasulfuron compared with a nonionic
surfactant.

Nomenclature: Fluthiacet, [[2-chloro-4-ﬂuoro-5-[(tetrahydro-3-oxo-1H, 3H-

[1 ,3,4]thiadiazolo[3 ,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; ﬂumiclorac,
pentyl[2-chloro-4-fluoro-5-(l ,3 ,4,5,6,7-hexahydro-1 ,3-dioxo-2H-isoindol-2-
yl)phenoxy]acetic acid; imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-
1H—imidazol-Z-yl]-5-ethyl-3-pyridinecarboxylic acid; oxasulfuron, 2-[[[[(4,6-dimethyl-2-
pyrimidinyl)-amino]carbonyl]aminojsulfonyl] benzoic acid, 3-oxetanyl ester; velvetleaf,
Abutilon theophrasti Medik. #' ABUTH; redroot pigweed, Amaranthus retroﬂexus L. #
AMARE; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common
lambsquarters, Chenopodium album L. # CHEAL; giant foxtail, Setariafaberi Henm. #
SETFA; soybean, Glycine max (L.) Merr. ‘Conrad’ # GLYMA.

Key Words: Herbicide additive, surfactant, ABUTH, AMARE, AMBEL, CHEAL,
GLYMA.

Abbreviations: COC, crop oil concentrate; DAT, days after treatment; MSO, methylated

 

‘Letters following this symbol are a WSSA-approved computer code from Composite List

of Weeds, Revised 1989. Available from WSSA, 810 East 10th Street, Lawrence, KA
66044-8897.

55

seed oil; NIS, nonionic surfactant; Protox, protoporphyrinogen oxidase; UAN, 28% urea

ammonium nitrate; v/v, volume per volume.

56

INTRODUCTION

Predicting herbicide efﬁcacy is challenging. Environmental conditions at application
(Doran and Anderson 1976), herbicide rate (King and Oliver 1992), weed size (Kells et
al. 1984), interactions with other herbicides (Hatzios and Penner 1985), and the addition
of an adjuvant (Roggenbuck et al. 1990) inﬂuence herbicidal response. Adjuvants
optimize herbicide penetration and efﬁcacy under adverse environmental conditions (Sun
et al. 1996) and provide more consistent control of marginally controlled species (Wills
and McWhorter 1981). Enhanced herbicidal efﬁcacy generally reﬂects increased
herbicide absorption (Harrison and Wax 1986); however, increased herbicide absorption
does not always correlate with increased efﬁcacy (Starke et al. 1996).

The recently developed cyclic imide herbicides ﬂuthiacet and ﬂumiclorac control
broadleaf weeds postemergence in corn (Zea mays L.) and soybean (Porpiglia et al. 1994;
Kamoshita et al. 1993). The mode of action of cyclic imide, diphenyl ether, oxadiazole,
and triazolinone herbicides is protoporphyrinogen oxidase (Protox) inhibition
(Anonymous 1995; Duke et a1. 1991; Mito et al. 1991). Protox inhibition leads to an
uncontrolled nonenzymatic oxidation of protoporphyrinogen IX to protoporphyrin IX in
sensitive plant species. Herbicidal activity of these herbicide classes is light-dependent
and closely associated with the concentration of accumulated protoporphyrin IX (Duke et
al. 1990).

F luthiacet and ﬂumiclorac provide exceptional postemergence velvetleaf control
(Brown et al. 1991; Fausey and Renner 1998; Kapusta et al. 1995). Roeth and Schleufer
(1994) reported that velvetleaf control with ﬂumiclorac was not affected when

ﬂumiclorac was applied with a crop oil concentrate (COC) or a COC plus 28% urea

57

ammonium nitrate (U AN). However, Dill et al. (1994) reported that a COC or an
organosilicone spray additive provided more consistent weed control with ﬂuthiacet than
a nonionic spray additive.

Weed control programs must provide acceptable season-long weed control for each
weed species present. This is commonly achieved by tank mixing herbicides.
Understanding the potential interactions between herbicides used in tank mixtures is
important when developing weed management systems (Young et al. 1996). Tank
mixtures of ﬂuthiacet or ﬂumiclorac with imazethapyr or oxasulfuron provide more
consistent broad-spectrum weed control compared with ﬂuthiacet or ﬂumiclorac alone
(Dill et al. 1994; James et al. 1994; Krutz and Pawlak 1992). Potentially, tank mixtures
of ﬂuthiacet or ﬂumiclorac with imazethapyr or oxasulfuron may enhance velvetleaf
control and provide consistent broad-Spectrum broadleaf weed control (Dill et al. 1994;
James et al. 1994; Kurtz and Pawlak 1992). However, Nelson and Renner (1998)
reported that adding ﬂuthiacet to oxasulfuron reduced common ragweed control
compared with oxasulfuron alone.

Research investigating adjuvant effects on ﬂuthiacet or ﬂumiclorac efﬁcacy and
soybean tolerance is limited. Conceivably, adjuvant selection may enhance or reduce
efﬁcacy and affect soybean tolerance in tank mixtures with ﬂuthiacet or ﬂumiclorac.
Therefore, the objectives of this research were to determine the inﬂuence adjuvant
selection has on efficacy and soybean tolerance with ﬂuthiacet or ﬂumiclorac applied

alone and in tank mixtures with imazethapyr and oxasulfuron.

58

MATERIALS AND METHODS

General Methods for Greenhouse Experiments

Velvetleaf and common lambsquarters seed was collected at the Michigan State
University Crop and Soil Sciences Research Farm in East Lansing, Michigan. Redroot
pigweed and common ragweed seed was obtained from a commercial seed supplierz.
Seeds were planted in BACCTO3 potting soil in 946 ml plastic pots. Environmental
conditions were maintained within a greenhouse at 27 i: 5 C. Plants were grown under a
16-h photoperiod of natural and supplemental high pressure sodium lighting with a
photosynthetic photon ﬂux density of 1000 umol m'2 3". Plants were thinned to 1 plant
pot", fertilized with 50 ml of a water-soluble fertilizer solution (400 ppm N, 400 ppm
P205, and 400 ppm K20), and watered as needed. Herbicides were applied with a
continuous belt-linked sprayer ﬁtted with an 8001B ﬂat-fan nozzle4 traveling at 1.53 km
h" and delivering 234 L ha‘l at 193 kPa of pressure.

Each experiment was a completely randomized design with four replications. Weed
control was visually evaluated in each experiment 3, 7 and 14 d after treatment (DAT).
Visual ratings were based on a scale from 0 to 100%, with 0 indicating no effect and 100
indicating plant death. Evaluations represented visual stunting, chlorosis, and necrosis.

Dry weight reduction was determined in each experiment 14 DAT by harvesting the

 

2Seed, V & J Seed Farms, PO. Box 82, Woodstock, IL 60098.

3BACCTO professional planting mix, Michigan Peat Co., PO. Box 98129, Houston, TX
77098.

”Teejet ﬂat-fan nozzles, Spraying Systems Co., North Avenue and Schmale Road,
Wheaton, IL 60532.

59

aboveground plant material. Percent dry weight reduction was calculated as 100[1 -
(plant dry weight/untreated plant dry weight)].

Adjuvant Efﬁcacy. Experiments were conducted to evaluate adjuvant effects on
ﬂuthiacet and ﬂumiclorac efﬁcacy. Commercial formulations of ﬂuthiacet or ﬂumiclorac
were applied at 2 g ha" and 15 g ha", respectively. Herbicides were applied with: no
adjuvant; UAN (1.0% v/v); Activator 905 (0.25% v/v), Activator 90 plus UAN (0.25 +
1.0% v/v); Herbimax6 (05,10, and 2.0% v/v); Herbimax plus UAN (0.5 + 1.0% v/v);
Dash7 (1.0% v/v); Scoil8 (1.0% v/v); Scoil plus UAN (1.0 + 1.0% v/v); Sylgard 3099
(0.25% v/v); and Sylgard 309 plus UAN (0.25 + 1.0% v/v).

Separate experiments were conducted for velvetleaf, common lambsquarters, redroot
pigweed, and common ragweed. At application, velvetleaf plants were 10 to 11 cm tall
with six leaves; common lambsquarters plants were 6 cm tall with six to eight leaves;
redroot pi gweed plants were 6 cm tall with four to six leaves; and common ragweed
plants were 6 cm tall with Six leaves. Herbicide injury was visually evaluated, and
aboveground biomass was harvested 14 DAT, oven dried, and weighed.

Tank Mixtures with Fluthiacet and Flumiclorac. Experiments were conducted to

 

5Activator-90, nonionic surfactant, a mixture of alkyl poloxyethlene ether and free fatty
acids, Loveland Industries Inc., PO. Box 1289, Greeley, CO 80632.

6Herbimax, 83% petroleum oil, 17% surfactant, Loveland Industries Inc., PO. Box 1289,
Greeley, CO 80632.

7Dash, 45% petroleum hydrocarbons, 5% naphthalene, 1.5% phosphoric acid, and 48.5%
mixture of alkyl esters and anionic surfactant. BASF Corp., RTP, NC 27709.

8Scoil, methylated seed oil, AGSCO. Inc., PO. Box 458 Grand Forks, ND 58206.

9Sylgard 309, organosilicone adjuvant, 2-(3-hydroxy-propyl)-heptamethyl-triSiloxane,
ethoxylated acetate, Dow Corning Corp., Midland, MI 48686-0944.

60

evaluate adjuvant effect on weed control with tank mixtures of ﬂuthiacet or ﬂumiclorac
with imazethapyr and oxasulfuron (Table 4). Treatments included 18 g ha" imazethapyr
or 16 g ha" oxasulfuron applied in combination with 1 g ha" ﬂuthiacet or 8 g ha"
ﬂumiclorac. All treatments were applied with Activator 90 plus UAN (0.25 + 0.1% v/v),
Scoil plus UAN (1.0 + 1.0% v/v), and Sylgard 309 plus UAN (0.25 + 1.0% v/v). At
application, velvetleaf plants were 12 cm tall with four to Six leaves; common
lambsquarters plants were 9 cm tall with ten to 12 leaves; redroot pigweed plants were 10
cm tall with eight to ten leaves; and common ragweed plants were 6 cm tall with eight to
10 leaves. Herbicide injury was visually evaluated, and aboveground biomass was

harvested 14 DAT, oven dried, and weighed.

Field Experiments
Species Sensitivity. Experiments were conducted at the Michigan State University
Research Farm in East Lansing, MI in 1996 and 1997. The soil was a Capac sandy clay
loam (ﬁne-loamy, mixed mesic Aerie Ochraqualfs) with 2.4% organic matter in 1996 and
a sandy loam with 2.5% organic matter in 1997. The soil pH was 7.9 and 6.7 in 1996 and
1997, respectively. Sites were fall chisel plowed with secondary tillage consisting of two
ﬁeld cultivations at planting. ‘Conrad’ soybean was planted in 76-cm rows at 395,000
seed ha". Plots were 3 m wide by 12.2 m in length in 1996 and 3 m wide by 9.1 m in
length in 1997.

The experiment was a randomized complete block with four replications. Treatments
included 4 g ha" ﬂuthiacet or 30 g ha" ﬂumiclorac applied with Herbimax (0.5 and 1.0%

v/v) or Activator 90 plus UAN (0.25 + 1.0% v/v).

61

Herbicides were applied on June 10, 1996 and June 17, 1997, 24 and 26 d after planting
(DAP), with a compressed air tractor-mounted sprayer traveling at 6.3 km h" and
delivering 178 L ha" at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-fan
nozzles4 spaced 51 cm apart and 48 cm above the weed canOpy. At application, soybean
plants were 8 to 10 cm tall with one fully developed trifoliolate; common lambsquarters
plants were 1 to 10 cm tall with two to 24 leaves; redroot pigweed plants were 1 to 8 cm
tall and from cotyledon to eight leaves; and common ragweed plants were 1 to 7 cm tall
and from cotyledon to eight leaves.

Soybean injury and weed control were visually evaluated 7, 14, and 28 DAT. Visual
ratings were based on a scale from 0 to 100%, with 0 indicating no effect and 100
signifying plant death. Soybean injury and weed control evaluations represented visual
stunting, chlorosis, and necrosis.

Tank Mixtures with Fluthiacet and Flumiclorac. Experiments were conducted at the
Michigan State University Research Farm at East Lansing, MI in 1997 and 1998. The
soil was a Capac sandy clay loam (ﬁne-loamy, mixed mesic Aerie Ochraqualfs) with 2.8
and 4.2% organic matter in 1997 and 1998, respectively. The soil pH was 6.6 and 6.3 in
1997 and 1998, respectively. Sites were fall chisel plowed with secondary tillage
consisting of two ﬁeld cultivations at planting. Asgrowl0 ‘2701 RR’ soybean was
planted in 76-cm rows at 345,000 seed ha". Plots were 3 m wide by 10.6 min length.

The experiment was a randomized complete block with four replications. Treatments
included 2240 g ha" metolachlor preemergence (PRE) followed by 4 g ha" ﬂuthiacet or

30 g ha" ﬂumiclorac postemergence (POST); and tank mixtures of 4 g ha" ﬂuthiacet or

 

10Soybean, Asgrow Seed Company, PO. Box 7570, Des Moines, IA 50322.

62

30 g ha" ﬂumiclorac with 70 g ha" imazethapyr or 65 g ha" oxasulfuron plus 60 g ha"
quizalofop (POST). All POST herbicide treatments were applied with Activator 90 plus
UAN (0.25 + 1.0% v/v) or Sylgard 309 plus UAN (0.25 + 1.0% v/v).

PRE herbicide applications were applied on May 13, 1997 and 1998. POST herbicide
applications were applied on June 17, 1997, and June 8, 1998, 35 and 26 DAP. All
herbicide treatments were applied with a compressed air tractor-mounted sprayer
traveling at 6.3 km h" and delivering 178 L ha" at 207 kPa of pressure. Treatments were
applied with 8003 ﬂat-fan nozzles“ spaced 51 cm apart and 48 cm above the weed
canopy. At application, soybean plants were 10 to 14 cm tall with two fully developed
trifoliolates; giant foxtail plants were 1 to 15 cm tall with one to four leaves; common
lambsquarters plants were 1 to 10 cm tall with two to 22 leaves; and redroot pigweed
plants were 1 to 8 cm tall and from cotyledon to ten leaves.

Soybean injury was visually evaluated 3, 7, and 14 DAT. Weed control was evaluated
for each species 7, 14, 21, 35, and 56 DAT. Visual ratings were based on a scale ﬁom 0
to 100%, with 0 indicating no effect and 100 Signifying plant death. Soybean injury and
weed control evaluations represented visual stunting, chlorosis, and necrosis. The two
middle rows from each plot were harvested with a Massey 10” small-plot combine.
Soybean yield was adjusted to 13% moisture.

Statistical Analyses

All experiments were repeated overtime, and data were analyzed using analysis of

variance (ANOVA). Data for individual experiments were combined as analyses

revealed no treatment by time interaction. Means were separated by Fisher’s protected

 

l‘Kincaid Equipment Manufacturing, PO. Box 400, Haven, KS 47543.

63

least Signiﬁcant difference test (LSD) at the 5% level.

RESULTS AND DISCUSSION

Adjuvant Efﬁcacy. Selected adjuvants increased velvetleaf, common lambsquarters,
redroot pigweed, and common ragweed control by ﬂuthiacet in the greenhouse, however,
enhancement varied by species (Table 1). All adjuvants, except UAN alone, increased
velvetleaf, common lambsquarters, redroot pigweed, and common ragweed control by
ﬂuthiacet compared with ﬂuthiacet applied without an adjuvant. Velvetleaf control with
ﬂuthiacet was greatest when applied with Herbimax (0.5, 1.0, 2.0% v/v), Herbimax plus
UAN, Dash, Scoil, or Scoil plus UAN. Maximum common lambsquarters control with
ﬂuthiacet was obtained with Scoil plus UAN, while common ragweed control with
ﬂuthiacet was greatest with Sylgard 309 plus UAN. Redroot pigweed control with
ﬂuthiacet was greatest with Dash, Scoil plus UAN, Sylgard 309, or Sylgard 309 plus
UAN. Although other adjuvants provided maximum control of a single Species, adding
Scoil plus UAN to ﬂuthiacet provided the most effective velvetleaf, common
lambsquarters, and redroot pigweed control.

Velvetleaf, common lambsquarters, redroot pigweed, and common ragweed control
with ﬂumiclorac was enhanced in the greenhouse with all adjuvants but UAN alone
(Table 2). Maximum velvetleaf control was obtained with ﬂumiclorac plus Herbimax
plus UAN or ﬂumiclorac plus Sylgard 309 plus UAN. Adding Sylgard 309 plus UAN
provided the greatest redroot pigweed control with ﬂumiclorac. Maximum common

lambsquarters control with ﬂumiclorac was achieved by adding Activator 90 plus UAN,

64

Herbimax (2.0% v/v), Dash, Scoil plus UAN, or Sylgard 309 plus UAN. Herbimax
(2.0% v/v), Herbimax plus UAN, Scoil plus UAN, or Sylgard 309 plus UAN provided
the greatest common ragweed control with ﬂumiclorac. Adjuvants enhanced ﬂumiclorac
activity on a Single Species, however, Sylgard 309 plus UAN provided the most effective
velvetleaf, common lambsquarters, redroot pigweed, and common ragweed control with
ﬂumiclorac.

Adding an adjuvant to ﬂuthiacet or ﬂumiclorac increased soybean injury and common
lambsquarters, redroot pigweed, and common ragweed control in the ﬁeld compared with
these herbicides applied without an adjuvant (Table 3). Adding Herbimax (0.5 or 1.0%
v/v) or Activator 90 plus UAN to ﬂuthiacet or ﬂumiclorac resulted in equivalent soybean
tolerance and weed control in the ﬁeld. This differed from greenhouse studies where
common lambsquarters control with ﬂuthiacet or ﬂumiclorac increased when Activator
90 plus UAN was added compared with 0.5% (v/v) Herbimax. In a second ﬁeld
experiment, weed control with ﬂuthiacet or ﬂumiclorac did not increase by adding
Sylgard 309 plus UAN or Activator 90 plus UAN when compared with Activator 90 plus
UAN (Table 5). Field results were contrary to the greenhouse results where redroot
pigweed control with these herbicides increased when applied with Sylgard 309 plus
UAN compared with Activator 90 plus UAN. Differences in the greenhouse and ﬁeld
application rates of ﬂuthiacet or ﬂumiclorac may explain these conﬂicting results.
Fluthiacet and ﬂumiclorac were applied in the greenhouse at one-half the ﬁeld application
rate. Thus, weed control in the ﬁeld may increase by adding Sylgard 309 plus UAN
compared with Activator 90 plus UAN if ﬂuthiacet or ﬂumiclorac are applied at reduced

rates. Altematively, a change in cuticle development may explain the differences in

65

efﬁcacy between greenhouse and ﬁeld grown plants. Regardless, ﬁeld results indicated
adjuvant selection did not affect soybean tolerance or weed control with 4 g ha" ﬂuthiacet

or 15 g ha" ﬂumiclorac.

Tank Mixtures with Fluthiacet and Flumiclorac.

Greenhouse. Velvetleaf and common lambsquarters control with ﬂuthiacet plus
imazethapyr increased when Scoil plus UAN or Sylgard 309 plus UAN was added.
Sylgard 309 plus UAN provided the greatest velvetleaf and common lambsquarters
control with ﬂumiclorac plus imazethapyr (Table 4). Redroot pigweed control with
ﬂuthiacet plus imazethapyr was greatest with Sylgard 309 plus UAN. Scoil plus UAN or
Sylgard 309 plus UAN increased redroot pigweed control with ﬂuthiacet plus
oxasulfuron compared with Activator 90 plus UAN. Adding Sylgard 309 plus UAN to
ﬂumiclorac plus oxasulfuron maximized redroot pigweed control while common ragweed

control was greatest with Sylgard 309 plus UAN (Table 4).

Field. Soybean exhibited leaf necrosis from tank mixtures with ﬂuthiacet or ﬂumiclorac,
but this was not apparent 21 DAT (data not presented). Kapusta et al. (1986) and Wichert
and Talbert (1993) reported that leaf necrosis from Protox-inhibiting herbicides does not
affect soybean yield. In contrast to our greenhouse results, common lambsquarters and
redroot pigweed control in the ﬁeld with tank mixtures of ﬂuthiacet or ﬂumiclorac plus
imazethapyr and Activator 90 plus UAN equaled that of Sylgard 309 plus UAN (Table
5). Adjuvant selection did not affect soybean injury, weed control, and soybean yield

with tank mixtures of ﬂuthiacet or ﬂumiclorac with imazethapyr in the ﬁeld.

66

Adding Sylgard 309 plus UAN to ﬂuthiacet plus oxasulfuron plus quizalofop increased
common lambsquarters and redroot pi gweed control which was reﬂected as a 14%
increase in soybean yield when compared with adding Activator 90 plus UAN. Similarly,
redroot pigweed control and soybean yield with ﬂumiclorac plus oxasulfuron plus
quizalofop increased by 12 and 16%, respectively, by adding Sylgard 309 plus UAN
compared with Activator 90 plus UAN.

Field results suggest adj uvant selection does affect the efﬁcacy of ﬂuthiacet or
ﬂumiclorac tank mixtures in the ﬁeld. Thus, careful consideration must be given when
choosing an adjuvant for ﬂuthiacet and ﬂumiclorac tank mixtures. Cantwell et al. (1989)
and Wesley and Shaw (1992) reported that tank mixtures with Protox-inhibiting
herbicides may increase or decrease weed control. Nelson and Renner (1998) observed
decreased common ragweed control with a tank mixture of ﬂuthiacet plus oxasulfuron
compared with oxasulfuron alone. An alternate adjuvant choice may eliminate
antagonism between ﬂuthiacet and oxasulfuron when applied in a tank mixture.

Fluthiacet and ﬂumiclorac activity on velvetleaf, common lambsquarters, redroot
pi gweed, and common ragweed was enhanced by selected adjuvants. However, a Single
application of ﬂuthiacet or ﬂumiclorac provided insufﬁcient broad-Spectrum broadleaf
weed control in the ﬁeld (Fausey and Renner 1998). James et al. (1994) and Kurtz and
Pawlak (1993) reported enhanced broadleaf weed control by adding ﬂuthiacet or
ﬂumiclorac to several postemergence broadleaf herbicides. With the appropriate
adjuvant, tank mixtures of imazethapyr or oxasulfuron plus quizalofop with ﬂuthiacet or

ﬂumiclorac may provide season-long broad-spectrum weed control in the ﬁeld.

67

ACKNOWLEDGMENTS
The authors thank Gary Powell and Jason Simon for their assistance in this research.
Appreciation is extended to Valent U.S.A. Corporation and Novartis Crop Protection,

Inc. for their ﬁnancial support.

68

10.

11.

12.

LITERATURE CITED

Anonymous. 1995. F luthiacet herbicide technical information bulletin.
Greensboro, NC: CIBA-GEIGY Corp., Agricultural Division.

Brown, W. B., M. S. DeFelice, and C. S. Holman. 1991. Weed control in corn and
soybeans with V-23031. Proc. N. Cent. Weed Sci. Soc. 46:40.

Cantwell, J. R., R. A. Liebl, and F. W. Slife. 1989. Irnazethapyr for weed control
in soybean (Glycine max). Weed Technol. 7:345-351.

Doran, D. L. and R. N. Anderson. 1976. Effectiveness of bentazon applied at
various times of day. Weed Sci. 24:567-570.

Dill, T. R., J. R. James, L. Stahlberg, and E. R. Hill. 1994. Update on the
herbicidal activity of CGA-248757 in corn in the Midwest. Proc. N. Cent. Weed
Sci. Soc. 49:58.

Duke, S. O., J. M. Becerril, T. D. Sherman, J. Lydon, and H. Matsumoto. 1990.
The role of protoporphyrin IX in the mechanism of action of diphenyl ether
herbicides. Pestic. Sci. 30:367-378.

Fausey, J. C. and K. A. Renner. 1998. Broadleaf weed control in soybeans with
ﬂumiclorac and CGA-248757 alone and in tank mixtures. Abstr. Weed Sci. Soc.
Am. 38:9.

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

Harrison, S. K. and L. M. Wax. 1986. Adjuvant effects on absorption,
translocation, and metabolism of haloxyfop-methyl in corn (Zea mays). Weed Sci.
34: 1 85-195.

James, J. R., L. Stahlberg, T. R. Dill, and G. Hill. 1994. Update on the herbicidal
activity of CGA-248757 in soybeans in the Midwest. Proc. N. Cent. Weed Sci.
Soc. 49:129.

Kamoshita, K., E. Nagano, S. Hashimoto, R. Sato, R. Yoshida, and H. Oshio.
1993. V-23031-A new herbicide for postemergence weed control in soybeans and
ﬁeld corn. Abstr. Weed Sci. Soc. Am. 53:3.

Kapusta, G., S. E. Curvey, and S. T. Autrnan. 1995. Soybean weed control with

CGA-248757 and CGA-277476 at three weed growth stages. Research Report N.
Cent. Weed Sci. Soc. 52:253-255.

69

l3.

14.

15.

16.

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19.

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21.

22.

23.

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25.

Kells, J. J ., W. F. Meggitt, and D. Penner. 1984. Absorption, translocation, and
activity of ﬂuazifop-butyl as inﬂuenced by plant growth stage and environment.
Weed Sci. 32: 143-149.

King, C. A. and L. R. Oliver. 1992. Application rate and timing of aciﬂuorfen,
bentazon, chlorimuron, and imazaquin. Weed Technol. 6:526-534.

Kurtz, A. R. and J. A. Pawlak. 1992. Postemergence weed control in ﬁeld corn
with V-23031 herbicide. Proc. N. Cent. Weed Sci. Soc. 47:47.

Mito, N., R. Sato, M. Miyakado, H. Oshio, and S. Tanaka. 1991. In vitro mode of
ﬂuthiacet of N—Phenylimide photobleaching herbicides. Pestic. Biochem. Physiol.
40:128-135.

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

Porpiglia, P. J ., E. R. Hill, and A. Tally. 1994. CGA-248757 for postemergence
broadleaf weed control in corn (Zea mays L.) and soybeans (Glycine max (L.)
Merr.). Abstr. Weed Sci. Soc. Am. 34:2.

Roggenbuck, F. C., L. Rowe, D. Penner, L. Petroff, and R. Burrow. 1990.
Increasing postemergence herbicide efﬁcacy and rainfastness with silicone
adjuvants. Weed Technol. 4:576-580.

Roeth, F. W. and I. Schleufer. 1994. Postemergence velvetleaf control in
soybeans. Proc. N. Cent. Weed Sci. Soc. 49:36-41.

Sander, K. W. and P. J. Porpiglia. 1996. CGA-248757 combinations for broadleaf
weed control in soybeans. Proc. N. Cent. Weed Sci. Soc. 51:132.

Starke, R. J ., K. A. Renner, D. Penner, and F. C. Roggenbuck. 1996. Inﬂuence of
adjuvants and desmedipham plus phenmedipham on velvetleaf (Abutilon
theophrasti) and sugarbeet response to triﬂusulfuron. Wed Sci. 442489-495.

Sun J ., C. L. Foy, and H. L. Witt. 1996. Effect of organosilicone surfactants on
the rainfastness of primisulfuron in velvetleaf (Abutilon theophrasti). Weed
Technol. 10:263-267.

Wesley, T. M. and D. R. Shaw. 1992. Interactions of diphenylether herbicides
with chlorimuron and imazaquin. Weed Technol. 62345-351.

Wills, G. D. and C. G. McWhorter. 1981. Effect of environment on the
translocation and toxicity of aciﬂuorfen to showy crotalaria (Crotalaria

70

26.

spectabilis). Weed Sci. 29:397-401.

Young, B. G., S. E. Hart, and L. M. Wax. 1996. Interactions of sethoxydim and

corn (Zea mays) postemergence broadleaf herbicides on three annual grasses.
Weed Technol. 10:914-922.

71

Table I. Adjuvant effect on ﬂuthiacet efﬁcacy in the greenhouse 14 d after treatment.“

 

 

 

 

 

Adjuvant Rate ABUTH CHEAL AMARE AMBEL
% v/v % control

No adjuvant — 69 18 16 12
UANb 1.0 93 14 48 19
Activator 90 0.25 52 34 37 19
Activator 90 + UAN 0.25 + 1.0 83 41 48 20
Herbimax 0.5 91 28 46 19
Herbimax 1 .0 95 36 46 24
Herbimax 2.0 97 44 57 24
Herbimax + UAN 0.5 + 1.0 97 25 45 24
Dash 1.0 96 56 64 29
Scoil 1.0 96 53 45 24
Scoil + UAN 1.0 + 1.0 98 71 63 30
Sylgard 309 0.25 76 35 68 19
Sylgard 309 + UAN 0.25 + 1.0 90 45 73 41
Untreated control — 0 0 0

LSD (0.05) 7 5 ll 4

 

“All treatments received 2 g ha" ﬂuthiacet.
bUAN, 28% urea ammonium nitrate.

72

Table 2. Adjuvant effect on ﬂumiclorac efﬁcacy in the greenhouse 14 d after treatment.“

 

 

 

 

 

Adjuvant Rate ABUTH CHEAL AMARE AMBEL
% v/v % control
No adjuvant — 51 20 28 25
UAN“ 1.0 54 21 37 28
Activator 90 0.25 66 48 49 36
Activator 90 + UAN 0.25 + 1.0 73 54 57 52
Herbimax 0.5 66 30 63 44
Herbimax 1.0 66 48 74 53
Herbimax 2.0 62 54 61 61
Herbimax + UAN 0.5 + 1.0 85 43 66 63
Dash 1 .0 71 51 73 58
Scoil 1.0 68 48 54 46
Scoil + UAN 1.0 + 1.0 63 54 71 64
Sylgard 309 0.25 59 49 71 51
Sylgard 309 + UAN 0.25 + 1.0 78 56 90 66
Untreated control — 0 0 0 0
LSD (0.05) 7 5 14 7

 

“All treatments received 15 g ha" ﬂumiclorac.
bUAN, 28% urea ammonium nitrate.

73

Table 3. Adjuvant effect on ﬂuthiacet or ﬂumiclorac soybean tolerance and efﬁcacy in
the ﬁeld.“

 

 

 

 

 

Herbicide“ Adjuvantc Rate GLYMA CHEAL AMARE AMBEL
% v/v % injury % control
F luthiacet no adjuvant — 5 24 57 65
Herbimax 0.5 14 98 76 97
Herbimax 1.0 1 5 91 77 92
Activator 90 + UAN 0.25 + 1.0 16 95 80 92
Flumiclorac no adjuvant —— 7 52 74 78
Herbimax 0.5 13 90 97 98
Herbimax l .0 1 5 99 99 99
Activator 90 + UAN 0.25 + 1.0 15 89 99 98
LSD (0.05) 2 19 17 12

 

“ Soybean injury 7 d after treatment (DAT) and weed control 14 DAT.
l’I‘reatrnents applied with either 4 g ha" ﬂuthiacet or 30 g ha" ﬂumiclorac.
cUAN, 28% urea ammonium nitrate.

74

Table 4. Broadleaf weed control in the greenhouse with ﬂuthiacet and ﬂumiclorac tank
mixtures 14 d after treatment.

 

 

 

 

 

Treatment Rate Adjuvant“ ABUTH CHEAL AMARE AMBEL
g ha" % control
Imazethapyr + ﬂuthiacet 18 + 1 Activator 90 87 25 81 56
Imazethapyr + ﬂuthiacet 18 + 1 Scoil 97 43 77 63
Imazethapyr + ﬂuthiacet 18 + 1 Sylgard 309 96 48 92 54
Imazethapyr + ﬂumiclorac 18 + 8 Activator 90 68 44 85 66
Imazethapyr + ﬂumiclorac 18 + 8 Scoil 69 33 87 57
Imazethapyr + ﬂumiclorac 18 + 8 Sylgard 309 91 53 92 58
Oxasulﬁiron + ﬂuthiacet 16 + l Activator 90 91 48 67 57
Oxasulfuron + ﬂuthiacet 16 + l Scoil 98 56 80 54
Oxasulfuron + ﬂuthiacet 16 + 1 Sylgard 309 96 55 88 68
Oxasulfuron + ﬂumiclorac 16 + 8 Activator 90 83 53 68 46
Oxasulfuron + ﬂumiclorac 16 + 8 Scoil 83 54 71 57
Oxasulfuron + ﬂumiclorac 16 + 8 Sylgard 309 90 60 93 59
LSD (0.05) 8 9 10 10

 

“Activator 90 and Sylgard 309 treatments were applied at 0.25% v/v. Scoil treatments
were applied at 1.0% v/v. All treatments included 28% urea ammonium nitrate (U AN) at
1.0% WV.

75

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76

CHAPTER 4

Broadleaf Weed Control in Corn (Zea mays) and Soybean (Glycine max)
with Fluthiacet and Flumiclorac Alone and in Tank Mixtures

ABSTRACT

Greenhouse and ﬁeld studies evaluated broadleaf weed control with ﬂuthiacet and
ﬂumiclorac applied alone and in tank mixtures. Velvetleaf, common lambsquarters,
redroot pi gweed, common ragweed, common cocklebur, eastern black nightshade, and
wild mustard growth in the greenhouse were reduced by 50% from 0.1, 2.9, 0.9, 1.1, 0.8,
0.4, and 1.2 g ha" of ﬂuthiacet and 0.7, 3.0, 2.4, 3.3, 3.0, 3.4, and 74.1 g ha“ of
ﬂumiclorac, respectively. Fluthiacet or ﬂumiclorac tank mixtures with atrazine,
bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, primisulfuron plus
prosulfuron, or 2,4-D increased velvetleaf, common lambsquarters, redroot pigweed, or
common ragweed control in the greenhouse 14 d after treatment (DAT) when compared
with the control provided by the tank mix partner alone. Redroot pigweed control
increased when ﬂumiclorac was tank mixed with oxasulfuron compared with oxasulfuron
alone. However, adding ﬂuthiacet to oxasulfuron did not increase velvetleaf, common
lambsquarters, redroot pigweed, or common ragweed control in the greenhouse. In ﬁeld

studies, tank mixtures of ﬂuthiacet or ﬂumiclorac plus atrazine, dicamba, and 2,4-D

77

increased velvetleaf control compared with control by atrazine, dicamba, and 2,4-D alone.
Fluthiacet or ﬂumiclorac tank mixtures with primisulfuron plus prosulfuron increased
common lambsquarters control compared with primisulfuron plus prosulﬁnon alone.
Fluthiacet or ﬂumiclorac tank mixtures with bentazon, lactofen, or oxasulfuron increased
weed control in the ﬁeld 14 DAT; however, season-long control of redroot pigweed,
common ragweed, and eastern black nightshade with bentazon tank mixtures; common
ragweed and eastern black nightshade with oxasulfuron tank mixtures; and common
lambsquarters with lactofen tank mixtures was less than 80%. Tank mixing ﬂumiclorac
with imazethapyr provided season-long common lambsquarters, redroot pigweed,
common ragweed, and eastern black nightshade control.

Nomenclature: Atrazine, 6-chloro-N-ethyl-N’ -( 1-methylethyl)—1,3 ,5-triazine-2,4—
diamine; bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin—4(3H)-one 2,2-dioxide;
bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; 2,4-D, (2,4-dichlorophenoxy)acetic
acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; ﬂuthiacet, methy1[[2-chloro-4-
ﬂuoro-S-[(tetrahydro-3-oxo-1H, 3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-
ylidene)amino]phenyl]thio]acetate; ﬂumiclorac, pentyl[2-chloro-4-ﬂuoro-5-(1,3,4,5,6,7-
hexahydro-l,3-dioxo-2H-isoindol-2-yl)phenoxy]acetic acid; halosulfuron, methyl 5-
[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonylaminosulfonyl]-3-chloro-1-methyl- 1 -H—
pyrazole-4-carboxylate; imazethapyr, 2-[4,5-dihydro-4-methyl—4-(1-methylethyl)-5-oxo-
1H—imidazol-Z-yl]-5-ethyl-3-pyridinecarboxylic acid; lactofen, (ﬁ-Z-ethoxy-l-methyl-Z-
oxoethyl 5-[2-chloro—4-(triﬂuoromethyl)phenoxy]-2-nitrobenzoate; oxasulﬁiron, 2-
[[[[(4,6-dimethyl-2-pyrimidinyl)-amino]carbonyl]amino]sulfonyl] benzoic acid, 3-

oxetanyl ester; primisulfuron, 2-[[[[[4,6-bis(diﬂuoromethoxy)—2-

78

pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; prosulfuron, 1-(4-methoxy-6-
methyl-triazin-Z-yl)-3-[2-(3,3,3-triﬂuoropropyl)-phenylsulfonyl]-urea; common
cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium
album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; eastern
black nightshade, Solanum ptycanthum Dun. # SOLPT; Pennsylvania smartweed,
Polygonum pensylvanicum L. # POLPY; redroot pigweed, Amaranthus retroﬂexus L. #
AMARE; velvetleaf, Abutilon theophrasti Medik. #1 ABUTH; wild mustard, Brassica
kaber (D.C.) L.C. Wheeler # SINAR; corn, Zea mays L. ‘Pioneer 3751’, ‘Dekalb 404SR’,
and ‘Dekalb 493 SR’ # ZEAMA; soybean, Glycine max (L.) Merr. ‘Conrad’ # GLYMA.
Key Words: Antagonism, herbicide interaction, Protox, ABUTH, AMARE, AMBEL,
CHEAL, POLPY, SINAR, SOLPT, XAN ST, GLYMA, ZEAMA.

Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAT, days after
treatment; NIS, nonionic surfactant; Protox, protoporphyrinogen oxidase; UAN, 28%

urea ammonium nitrate; v/v, volume per volume.

 

‘Letters following this symbol are a WSSA-approved computer code from Composite List

of Weeds, Revised 1989. Available from WSSA, 810 East 10th Street, Lawrence, KA
66044-8897.

79

INTRODUCTION

Several commercial and experimental herbicides including cyclic imides, diphenyl
ethers, oxadiazoles, and triazolinones inhibit protoporphyrinogen oxidase (Protox), the
enzyme that converts protoporphyrinogen IX to protoporphyrin IX (Anonymous 1995;
Duke et a1. 1991; Mito et al. 1991). Protox inhibition, although detectable in sensitive
plant species 30 minutes after herbicide exposure, requires light to initiate herbicidal
activity (Duke et al. 1990; Lehnen et al. 1990).

Fluthiacet and ﬂumiclorac are cyclic imide herbicides used in corn and soybean to
control broadleaf weeds postemergence (Porpiglia et al. 1994; Kamoshita et al. 1993).
F luthiacet and ﬂumiclorac provided greater than 96% season-long velvetleaf control
(Brown et al. 1991; F ausey and Renner 1998; Kapusta et al. 1995). However, season-
long common cocklebur control with ﬂuthiacet was 83% (Kapusta et al. 1995), and
Pennsylvania smartweed control with ﬂumiclorac was 60% (Brown et al. 1991). Tank
mixtures with ﬂuthiacet or ﬂumiclorac provided more consistent broad-spectrum weed
control when compared with ﬂuthiacet or ﬂumiclorac alone (Dill et a1. 1994; James et al.
1994; Kurtz and Pawlak 1992). Fluthiacet or ﬂumiclorac tank mixtures with aciﬂuorfen
(5-[2-chloro-4-(triﬂuoromethyl)phenoxy]-2-nitrobenzoic acid), atrazine, bentazon,
chlorimuron (2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]
benzoic acid), dicamba, imazethapyr, nicosulfuron (2-[[[[(4,6-dimethoxy-2-
pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N—dimethyl-3-pyridinecarboxamide),
primisulfuron, prosulfuron, or 2,4-D may enhance velvetleaf control and provide more
consistent broadleaf weed control compared with these herbicides applied alone (Dill et

al. 1994; James et al. 1994; Kurtz and Pawlak 1992).

80

Understanding interactions between herbicides used in tank mixtures is important for
the development of effective weed control programs. Giant foxtail (Setariafaberi
Herrm.) control with sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-
hydroxy-Z-cyclohexen-l-one) was not affected by adding ﬂuthiacet or ﬂumiclorac (James
et al. 1994; Young et al. 1996); yet, shattercane (Sorghum bicolor (L.) Moench) control
was reduced (Young et al. 1996). Large crabgrass (Digitaria sanguinalis (L.) Scop.)
control with sethoxydim was not affected by the addition of ﬂuthiacet, however, control
was reduced when flumiclorac was added. Fluthiacet or ﬂumiclorac tank mixtures with
glyphosate (N-(phosphonomethy1)glycine) increased velvetleaf and common ragweed
control compared with glyphosate alone (Lich et a1. 1997). In contrast, tank mixing
ﬂuthiacet with oxasulfuron decreased common ragweed control compared with
oxasulfuron alone (Nelson and Renner 1998).

Potential beneﬁts of ﬂuthiacet and ﬂumiclorac include low use rates, short-half lives,
resistance management, and the ability to broaden the spectrum of other herbicides
(Anonymous 1995). Research investigating corn and soybean tolerance and weed control
with ﬂuthiacet or ﬂumiclorac is limited. Tank mixtures including ﬂuthiacet or
ﬂumiclorac may increase broadleaf weed control, however, affects on crop tolerance have
not been reported. Therefore, the objective of this research was to evaluate corn and
soybean tolerance and broadleaf weed control with ﬂuthiacet and ﬂumiclorac applied

alone and in tank mixtures.

81

MATERIALS AND METHODS

General Methods for Greenhouse Experiments

Velvetleaf, common lambsquarters, common cocklebur, and eastern black nightshade
seed were collected at the Michigan State University Research Farm in East Lansing.
Redroot pigweed and common ragweed seed was obtained from a commercial seed
supplier’. The corn variety ‘Pioneer 3751’3 and soybean variety ‘Conrad’ were evaluated.

Seeds were planted in BACCTO‘1 potting soil in 946 ml plastic pots. Environmental
conditions were maintained within a greenhouse at 27 i 5 C. Plants were grown under a
16-h photoperiod of natural and supplemental high pressure sodium lighting with a
photosynthetic photon ﬂux density of 1000 amol m2 5". Plants were thinned to 1 plant
pot", fertilized with 50 ml of a water-soluble fertilizer solution (400 ppm N, 400 ppm
P205, and 400 ppm K20), and watered as needed. Herbicides were applied with a
continuous belt-linked sprayer ﬁtted with an 8001B ﬂat-fan nozzles traveling at 1.53 km
h" and delivering 234 L ha‘l at 193 kPa of pressure.

Each experiment was a completely randomized design with four replications. Crop
tolerance and weed control were visually evaluated in each experiment 3, 7 and 14 d after
treatment (DAT). Visual ratings were based on a scale from O to 100%, with 0 indicating

no effect and 100 indicating plant death. Evaluations represented visual stunting,

 

2Seed, V & J Seed Farms, PO. Box 82, Woodstock, IL 60098.
3Corn, Pioneer Hi-Bred International, Inc., Des Moines, IA 50301.

‘BACCTO professional planting mix, Michigan Peat Co., PO. Box 98129, Houston, TX
77098.

5Teej et ﬂat-fan nozzles, Spraying Systems Co., North Avenue and Schmale Road,
Wheaton, IL 60532.

82

chlorosis, and necrosis. Dry weight reduction was determined in each experiment 14
DAT by harvesting the aboveground plant material. Percent dry weight reduction was
calculated as 100[1 - (plant dry weight/untreated plant dry weight)].

Species Sensitivity. Experiments compared weed sensitivity to ﬂuthiacet and
ﬂumiclorac. Commercial formulations of each herbicide were applied at various rates.
Herbicides were applied with 0.25% (v/v) nonionic surfactant6 (NIS) and 1.0% (v/v) 28%
urea ammonium nitrate (U AN). At application, velvetleaf plants were 5 cm tall with two
leaves, 7.5 cm tall with four leaves, and 11 cm tall with six to seven leaves; common
lambsquarters plants were 6 cm tall with six to eight leaves; redroot pi gweed plants were
6 cm tall with four to six leaves; common ragweed plants were 6 cm tall with six to eight
leaves; common cocklebur plants were 9 cm tall with four to ﬁve leaves; eastern black
nightshade plants were 5 cm tall with ﬁve to seven leaves; and wild mustard plants were
6 cm tall with ﬁve to six leaves. Herbicide injury was visually evaluated, and
aboveground biomass was harvested 14 DAT, oven dried, and weighed.

Separate experiments were conducted for each weed species. Data were ﬁt to the log
logistic model as described by Seefeldt et al. (1995). Nonlinear regression was conducted
with SAS7, and GR50 values were calculated for both plant dry weight reduction and the
percent of the ﬁeld use rate required to reduce plant growth by 50% (Table 1). Dry
weight reduction represents the g ha‘l required to reduce plant grth by 50%, whereas

percent of the ﬁeld use rate represents the percent of either 4 g ha'l ﬂuthiacet or 30 g ha"

 

6Activator-9O, nonionic surfactant, a mixture of alkyl polyoxyethylene ether and fatty
acids, Loveland Industries Inc., PO. Box 1289, Greeley, CO 80632.

7SAS Institute Inc., SAS Circle, Box 8000, Cary, NC 27512-8000.

83

ﬂumiclorac required to reduce plant growth by 50%.

Tank Mixtures with Fluthiacet and Flumiclorac. Experiments evaluated corn tolerance
and weed control with tank mixtures including ﬂuthiacet or ﬂumiclorac. Treatments
included an untreated control, 210 g ha'l atrazine, 70 g ha" bromoxynil, 70 g ha"
dicamba, 9 g ha‘l halosulfuron, 10 g ha" primisulfuron plus prosulﬁrron (6:4), and 140 g
ha" 2,4-D amine applied alone and in a tank mixture with 1 g ha'l ﬂuthiacet or 8 g ha"
ﬂumiclorac. All atrazine treatments were applied with 1.0% (v/v) crop oil concentrate8
(COC); and bromoxynil, dicamba, halosulfuron, primisulfuron plus prosulfuron, and 2,4-
D treatments included 0.25% (v/v) NIS“. Corn plants were 16 cm tall with four leaves;
velvetleaf plants were 11 cm tall with four to ﬁve leaves; common lambsquarters plants
were 9 cm tall with 10 to 12 leaves; redroot pigweed plants were 10 cm tall with eight to
ten leaves; and common ragweed plants were 10 cm tall with eight to 12 leaves.
Herbicide injury was visually evaluated, and aboveground biomass was harvested 14
DAT, oven dried, and weighed.

Experiments evaluated soybean tolerance and weed control in the greenhouse with
ﬂuthiacet or ﬂumiclorac tank mixtures. Treatments included an untreated control, 210 g
ha’l bentazon, 18 g ha‘l imazethapyr, 26 g ha" lactofen, and 16 g ha" oxasulfuron applied
alone and in a tank mixture with 1 g ha" ﬂuthiacet or 8 g ha'1 ﬂumiclorac. All bentazon
treatments were applied with 1.0% (v/v) COC“; imazethapyr and oxasulfuron treatments
included 0.25% (v/v) NIS" plus 1.0% (v/v) UAN; and lactofen treatments included 0.5%

COCB. At application, soybean plants were 10 cm tall with two trifoliolates, and weed

 

8Herbimax, 83% petroleum oil, 17% surfactant, Loveland Industries Inc., PO. Box 1289,
Greeley, CO 80632.

84

sizes were as previously described. Herbicide injury was visually evaluated, and

aboveground biomass was harvested 14 DAT, oven dried, and weighed.

Field Experiments

Corn. Experiments were conducted at the Michigan State University Research Farm in
East Lansing, MI in 1996 and 1997. The soil was a Capac sandy clay loam (ﬁne-loamy,
mixed mesic Aeric Ochraqualfs) with 3.1 and 3.2% organic matter in 1996 and 1997,
respectively. The soil pH was 6.5 and 7.2 in 1996 and 1997, respectively. Sites were fall
moldboard plowed with secondary tillage consisting of two ﬁeld cultivations at planting.
‘DK 404 SR’9 corn was planted in 76-cm rows at 62,000 seed ha‘1 in 1996, and ‘DK 493
SR’9 corn was planted in 76-cm rows at 56,000 seed ha" in 1997. Plots were 3 m wide by
9.1 m in length.

The experiment was a randomized complete block with three replications. Treatments
included 840 g ha‘l atrazine, 280 g ha" bromoxynil, 208 g ha'l dicamba, 35 g ha"
halosulfuron, 40 g ha‘l primisulfuron plus prosulﬁiron (6:4), and 560 g ha'l 2,4-D amine
applied alone and in a tank mixture with 4 g ha‘1 ﬂuthiacet or 30 g ha'l ﬂumiclorac. A
weed-free control and an untreated control were included. All atrazine treatments
included 1.0% (v/v) COCS; and bromoxynil, dicamba, halosulfuron, primisulfuron plus
prosulfuron, and 2,4—D treatments included 0.25% (v/v) NIS". Sethoxydim was applied
broadcast for annual grass control June 3, 1996 and June 9, 1997.

Herbicides were applied on June 14, 1996 and June 13, 1997, 28 and 30 d after planting

(DAP), with a compressed air tractor-mounted sprayer traveling at 5.7 km h" and

 

9Corn, DEKALB Genetics Corporation, 3100 Sycamore Road Dekalb, IL 60115.

85

delivering 187 L ha“l at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-fan
nozzles spaced 51 cm apart and 48 cm above the weed canopy. At application, corn
plants were 13 to 20 cm tall with ﬁve to six leaves; Pennsylvania smartweed plants were
1 to 3 cm tall and from cotyledon to three leaves; velvetleaf plants were 1 to 10 cm tall
and from cotyledon to ﬁve leaves; common lambsquarters plants were 1 to 7 cm tall with
two to ten leaves; and redroot pigweed plants were 1 to 8 cm tall and from cotyledon to
eight leaves.

Corn injury was visually evaluated 3, 7, and 14 DAT. Weed control was evaluated for
each species 7, 14, 21, 3S, and 56 DAT. Visual ratings were based on a scale from O to
100%, with 0 indicating no effect and 100 signifying plant death. Corn injury and weed
control evaluations represented visual stunting, chlorosis, and necrosis. The two middle
rows from each plot were harvested with a Massey 10IO small-plot combine. Corn yield
was adjusted to 15.5% moisture.

Soybean. Experiments were conducted at the Michigan State University Research Farm
in East Lansing, MI in 1996 and 1997. The soil was a Capac sandy clay loam (ﬁne-
loamy, mixed mesic Aeric Ochraqualfs) with 2.4% organic matter in 1996 and a sandy
loam with 2.5% organic matter in 1997. The soil pH was 7.9 and 6.7 in 1996 and 1997,
respectively. The 1996 and 1997 sites were fall chisel plowed with secondary tillage
consisting of two ﬁeld cultivations at planting. ‘Conrad’ soybean was planted in 76-cm
rows at 395,000 seed ha". Plots were 3 m wide by 12.2 m in length in 1996, and 3 m
wide by 9.1 m in length in 1997.

The experiment was a randomized complete block with four replications. Treatments

 

loKincaid Equipment Manufacturing, PO. Box 400, Haven, KS 47543.

86

included 840 g ha" bentazon, 105 g ha‘l lactofen, 70 g ha'l imazethapyr, 65 g ha"
oxasulfuron applied alone and in a tank mixture with 4 g ha‘l ﬂuthiacet or 30 g ha‘l
ﬂumiclorac, a weed-free control, and an untreated control. All bentazon treatments were
applied in combination with 1.0% (v/v) COCs; imazethapyr and oxasulfuron treatments
included 0.25% (v/v) NIS" plus 1.0% (v/v) UAN; and lactofen treatments included 0.5%
(v/v) COC”.

Herbicides were applied on June 10, 1996 and June 17, 1997, 24 and 26 DAP, with a
compressed air tractor-mounted sprayer traveling at 6.3 km h'1 and delivering 178 L ha'l
at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-fan nozzles spaced 51 cm
apart and 48 cm above the weed canopy. At application, soybean plants were 8 to 10 cm
tall with one ﬁilly developed trifoliolate; eastern black nightshade plants were 1 to 4 cm
tall and from cotyledon to ﬁve leaves; common lambsquarters plants were 1 to 10 cm tall
with two to 24 leaves; redroot pi gweed plants were 1 to 8 cm tall and ﬁ'om cotyledon to
eight leaves; and common ragweed plants were l to 7 cm tall and from cotyledon to eight
leaves.

Soybean injury was visually evaluated 3, 7, and 14 DAT. Weed control was evaluated
for each species 7, 14, 21, 35, and 56 DAT. Visual ratings were based on a scale from 0
to 100%, with 0 indicating no effect and 100 signifying plant death. Soybean injury and
weed control evaluations represented visual stunting, chlorosis, and necrosis. The two
middle rows from each plot were harvested with a Massey 10lo small-plot combine.
Soybean yield was adjusted to 13% moisture.

Statistical Analyses

All experiments were repeated over time, and data were analyzed using analysis of

87

variance (AN OVA). Data for individual experiments were combined as analyses
revealed no treatment by time interaction. Means were separated by Fisher’s protected

least signiﬁcant difference test (LSD) at the 5% level.

RESULTS AND DISCUSSION

Greenhouse Experiments

Species Sensitivity. Species sensitivities to ﬂuthiacet or ﬂumiclorac were calculated as
GR50 values based on a percent dry weight reduction and converted to the percent of the
ﬁeld use rate (Table 1). The ﬁeld use rate for ﬂuthiacet is 4 to 5 g ha" (Anonymous
1995), whereas ﬂumiclorac is used at rates of 30 to 60 g ha" (Kurtz and Pawlak 1993).
Calculated values for the percent of the ﬁeld use rate of ﬂuthiacet or ﬂumiclorac required
to reduce plant growth by 50% are based on application rates used in our ﬁeld research; 4
and 30 g ha", respectively.

Velvetleaf was sensitive to both herbicides. GR50 values were below 10% of the ﬁeld
use rate for either herbicide (Table 1). Two, four, and six to seven-leaf velvetleaf were
more sensitive to ﬂuthiacet when compared with ﬂumiclorac. GR50 values calculated on
the percent of the ﬁeld use rate required to reduce the growth of four and six to seven leaf
velvetleaf by 50% revealed greater sensitivity to ﬂuthiacet compared with ﬂumiclorac.
However, GR50 values calculated on the percent of the ﬁeld use rate revealed two leaf
velvetleaf were more sensitive to ﬂumiclorac than ﬂuthiacet.

The quantity of active ingredient required to reduce common lambsquarters dry weight

by 50% did not differ between ﬂuthiacet and ﬂumiclorac (Table 1). However, based on

88

the percent of the ﬁeld rate required for a 50% reduction in growth, common
lambsquarters had greater tolerance to ﬂuthiacet compared with ﬂumiclorac.

GRso values calculated on redroot pi gweed, common ragweed, and common cocklebur
dry weight reduction indicated these species were more sensitive to ﬂuthiacet than
ﬂumiclorac. When the GR50 values were converted to a percent of the ﬁeld use rate,
values revealed redroot pigweed, common ragweed, and cormnon cocklebur were more
sensitive to ﬂumiclorac than ﬂuthiacet. These data support Kapusta et al. (1995) and
Brown et al. (1991) that common ragweed is more sensitive to ﬂumiclorac when
compared with ﬂuthiacet.

Eastern black nightshade and wild mustard required less active ingredient and a lower
percent of the ﬁeld use rate of ﬂuthiacet to reduce growth by 50% when compared with
ﬂumiclorac. GR50 values for eastern black nightshade were below 12% of the ﬁeld use
rate for either herbicide, while GR,0 values for wild mustard were 30% of the ﬁeld use
rate for ﬂuthiacet and 245% for ﬂumiclorac. Thus, our results suggest broadleaf weed
sensitivity to ﬂuthiacet and ﬂumiclorac varies by species.

Tank Mixtures with Fluthiacet and Flumiclorac. Adding ﬂuthiacet or ﬂumiclorac to
atrazine, dicamba, 2,4-D, bromoxynil, halosulfuron, or primisulfuron plus prosulfuron
increased corn injury 3 DAT compared with these herbicides applied alone (Table 2).
Tank mixtures with ﬂumiclorac resulted in greater corn injury compared with ﬂuthiacet
tank mixtures.

Cantwell et al. (1989) and Wesley and Shaw (1992) reported that tank mixtures with
Protox-inhibiting herbicides may increase or decrease weed control. Fluthiacet or

ﬂumiclorac tank mixtures with atrazine or dicamba increased velvetleaf and common

89

lambsquarters control 14 DAT compared with atrazine or dicamba alone (Table 2).
Redroot pigweed and common ragweed control increased when ﬂumiclorac, but not when
ﬂuthiacet was tank mixed with atrazine or dicamba. Fluthiacet or ﬂumiclorac tank
mixtures with 2,4-D increased velvetleaf, redroot pi gweed, and cormnon ragweed control
compared with 2,4-D alone. Velvetleaf, common lambsquarters, and redroot pigweed
control with bromoxynil increased by adding ﬂuthiacet or ﬂumiclorac. Common
lambsquarters control increased, but common ragweed control decreased with ﬂuthiacet
or ﬂumiclorac plus halosulfuron compared with halosulfuron alone. Redroot pigweed
control with primisulfuron plus prosulfuron increased by adding ﬂuthiacet or ﬂumiclorac.
Fluthiacet or ﬂumiclorac tank mixtures with halosulfuron or primisulfuron plus
prosulfuron did not reduce velvetleaf control as previously reported (Hart 1997). With
the exception of halosulfuron, the addition of ﬂuthiacet or ﬂumiclorac did not decrease
broadleaf weed control in these greenhouse studies.

Adding ﬂuthiacet or ﬂumiclorac to bentazon, imazethapyr, lactofen, or oxasulfuron
increased soybean injury 3 DAT compared with bentazon, imazethapyr, lactofen, or
oxasulfuron alone (Table 3). Fluthiacet or ﬂumiclorac tank mixtures with bentazon
increased velvetleaf, common lambsquarters, and redroot pigweed control compared with
bentazon alone 14 DAT. Common lambsquarters, redroot pigweed, and common
ragweed control with imazethapyr increased by adding ﬂumiclorac. However, adding
ﬂuthiacet to imazethapyr only increased common lambsquarters control. Adding
ﬂuthiacet or ﬂumiclorac to lactofen increased velvetleaf, common lambsquarters, and
common ragweed control. However, redroot pigweed control with lactofen increased

only when ﬂumiclorac was added. Fluthiacet or ﬂumiclorac tank mixtures with

90

oxasulfuron decreased common ragweed control compared with oxasulfuron alone.
Similarly, Nelson and Renner (1998) observed decreased common ragweed control in a
tank mixture of oxasulfuron plus ﬂuthiacet. Greenhouse results conﬁrm reports that tank
mixtures with Protox-inhibiting herbicides, such as ﬂuthiacet and ﬂumiclorac, can

increase or decrease weed control.

Field Experiments

Corn. Adding ﬂuthiacet or ﬂumiclorac to atrazine, dicamba, 2,4—D, bromoxynil,
halosulfuron, or primisulfuron plus prosulfuron increased corn injury 7 DAT compared
with these herbicides alone (Table 4). Corn injury was greater from ﬂumiclorac tank
mixtures with atrazine, bromoxynil, halosulfuron, and 2,4-D compared with ﬂuthiacet
tank mixtures. These results support our greenhouse observations that suggested corn
injury increased more by the addition of ﬂumiclorac to these herbicides.

Fluthiacet or ﬂumiclorac tank mixtures with atrazine, dicamba, or 2,4-D increased
velvetleaf control 56 DAT compared with the control provided by atrazine, dicamba, or
2,4-D alone. However, Pennsylvania smartweed control was less than 50% 35 DAT
when 2,4-D was tank mixed with ﬂuthiacet or ﬂumiclorac. Broadleaf weed control in the
greenhouse and in the ﬁeld was not reduced when ﬂuthiacet or ﬂumiclorac was tank
mixed with atrazine, dicamba, or 2,4-D. However, corn yield did not increase with
increased weed control. Schmenk and Kells (1998) reported reduced velvetleaf
competition in corn following an atrazine application. Thus, applying atrazine, dicamba,
or 2,4—D may reduce velvetleaf competitiveness in corn to a level where increased

velvetleaf control from ﬂuthiacet or ﬂumiclorac tank mixtures would not increase com

91

yield.

In contrast to our greenhouse studies, velvetleaf, common lambsquarters, and redroot
pi gweed control with bromoxynil in the ﬁeld were not affected by the addition of
ﬂuthiacet or ﬂumiclorac. Fluthiacet or ﬂumiclorac tank mixtures with the fast-acting
contact herbicide lactofen displayed similar inconsistences.

Tank mixtures of ﬂuthiacet or ﬂumiclorac with halosulfuron increased early season
cormnon lambsquarters control (data not presented), but by 56 DAT, common
lambsquarters control was less than 75%. In contrast to our greenhouse studies, broadleaf
weed control did not decrease in the ﬁeld when ﬂuthiacet or ﬂumiclorac were tank mixed
with halosulfuron. F luthiacet or ﬂumiclorac tank mixtures with primisulfuron plus
prosulfuron increased common lambsquarters control 56 DAT compared with
primisulfuron plus prosulfuron alone.

Soybean. Fluthiacet or ﬂumiclorac added to bentazon, imazethapyr, lactofen, or
oxasulfuron increased soybean injury 7 DAT compared with these herbicides alone
(Table 5). In the greenhouse, soybean injury was similar from tank mixtures of ﬂuthiacet
or ﬂumiclorac with bentazon, imazethapyr, lactofen, and oxasulfuron. However, soybean
injury in the ﬁeld was greater from ﬂumiclorac tank mixtures with bentazon or
oxasulﬁrron compared with ﬂuthiacet plus bentazon or oxasulﬁiron.

Tank mixtures of ﬂuthiacet or ﬂumiclorac with bentazon increased velvetleaf, common
lambsquarters, and redroot pi gweed control in the greenhouse (Table 3). Similarly,
broadleaf weed control in the ﬁeld with bentazon plus ﬂuthiacet or ﬂumiclorac was
greater than 90% for all species 14 DAT (data not presented). However, late emerging

redroot pigweed, common ragweed, and eastern black nightshade reduced season-long

92

control to less than 80% with these tank mixtures (Table 5).

In the ﬁeld, common lambsquarters control with lactofen increased by adding ﬂuthiacet
or ﬂumiclorac compared with lactofen alone, but was less than 60% 56 DAT (Table 5).
The addition of ﬂuthiacet to lactofen reduced common ragweed control in the ﬁeld but
increased control in the greenhouse compared with lactofen alone. Fluthiacet or
ﬂumiclorac tank mixtures with lactofen did not provide season-long broadleaf weed
control in the ﬁeld. Data suggests ﬂuthiacet or ﬂumiclorac tank mixtures with fast—acting
contact herbicides, such as lactofen or bromoxynil, may provide fewer beneﬁts than tank
mixtures with other herbicides.

Despite reports of aciﬂuorfen or bentazon antagonism with imazethapyr (Cantwell et al.
1989), weed control in the greenhouse and in the ﬁeld was not reduced by ﬂuthiacet or
ﬂumiclorac tank mixtures with imazethapyr. Tank mixtures of imazethapyr with
ﬂuthiacet or flumiclorac increased common ragweed control and soybean yield in the
ﬁeld compared with imazethapyr alone. Common lambsquarters control with ﬂuthiacet
or ﬂumiclorac plus imazethapyr was 90 and 92% 56 DAT, respectively. Similarly,
common lambsquarters control with 2 or 3 g ha‘l thifensulfuron (3-[[[[(4—methoxy-6-
methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2- thiophenecarboxylic acid)
plus 70 g ha" imazethapyr was 85 and 93% 28 DAT, respectively (Simpson and Stoller
1995)

Tank mixtures of ﬂuthiacet or ﬂumiclorac with oxasulfuron increased redroot pigweed
and common ragweed control in the ﬁeld yet reduced common ragweed control in the
greenhouse compared with oxasulfuron alone. Fluthiacet or ﬂumiclorac tank mixtures

with oxasulfuron increased eastern black nightshade control compared with oxasulfuron

93

alone, yet control was less than 60% 35 DAT.

Fluthiacet and ﬂumiclorac display activity on various broadleaf weeds. A single
application of these herbicides provided exceptional velvetleaf control but insufﬁcient
broad-spectrum broadleaf weed control in the ﬁeld (Fausey and Renner 1998). Likewise,
no other postemergence herbicide applied alone provided season-long control of all
broadleaf species evaluated. However, tank mixtures of atrazine, dicamba, imazethapyr,
and primisulfuron plus prosulfuron with ﬂuthiacet or ﬂumiclorac provided season-long
broadleaf weed control of all the species evaluated. These results conﬁrm reports by
James et al. (1994) and Kurtz and Pawlak (1993) that adding ﬂuthiacet or ﬂumiclorac to
atrazine, bentazon, dicamba, imazethapyr, or 2,4-D improved broadleaf weed control.

Corn and soybean exhibited minor leaf necrosis from tank mixtures with ﬂuthiacet or
ﬂumiclorac but outgrew the injury by 21 DAT (data not presented). Kapusta et al. (1986)
and Wichert and Talbert (1993) reported that leaf necrosis does not affect soybean yield,
yet the effect Protox-inhibiting herbicides have on corn yield remains unclear. Corn yield
did not increase when weed control increased with ﬂuthiacet or ﬂumiclorac tank mixtures
plus atrazine or dicamba. However, soybean yield increased when ﬂuthiacet or
ﬂumiclorac was tank mixed with imazethapyr or oxasulfuron compared with imazethapyr
or oxasulfuron alone.

Tank mixtures including ﬂuthiacet or ﬂumiclorac have several advantages. Increased
weed control with ﬂuthiacet or ﬂumiclorac tank mixtures would decrease future weed
infestations by reducing weed seed return to the soil seed bank. Tank mixtures including
ﬂuthiacet or ﬂumiclorac also provide additional strategies for managing weed resistance.

Research investigating ﬂuthiacet or ﬂumiclorac tank mixtures in herbicide resistant com

94

and soybean would be beneﬁcial for weed control programs in these genetically modiﬁed

crops.

ACKNOWLEDGMENTS

The authors thank Jason Simon, Gary Powell, and Andy Chomas for their assistance in

this research. Appreciation is extended to Valent U.S.A. Corporation and Novartis Crop

Protection, Inc. for their ﬁnancial support.

95

10.

ll.

12.

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Seefeldt, S. S., J. E. Jensen, and E. P. Fuerst. 1995. Log-logistic analysis of
herbicide dose-response relationships. Weed Technol. 92218-227.

Simpson, D. M. and E. W. Stoller. 1995. Response of sulfonylurea-tolerant
soybean (Glycine max) and selected weed species to imazethapyr and

thifensulfuron combinations. Weed Technol. 92582-586.

Wesley, T. M. and D. R. Shaw. 1992. Interactions of diphenylether herbicides
with chlorimuron and imazaquin. Weed Technol. 61345-35 1.

Wichert, R. A. and R. E. Talbert. 1993. Soybean [Glycine max (L.)] response to
lactofen. Weed Sci. 41:23-27.

97

26. Young, B. G., S. E. Hart, and L. M. Wax. 1996. Interactions of sethoxydim and
corn (Zea mays) postemergence broadleaf herbicides on three annual grasses.
Weed Technol. 10:914-922.

98

Table 1. Weed species sensitivities to ﬂuthiacet and ﬂumiclorac in the greenhouse.a

 

 

 

 

 

 

 

Growth Dry weight basis Field ratec
Species stage Fluthiacet Flumiclorac Fluthiacet Flumiclorac
True leaves — g ha'l

Velvetleaf 2 0.1 a 0.7 b 3 b 2 a
4 0.3 a 2.5 b 6 a 8 b
6-7 0.2 a 1.5 b 4 a 5 b
Common lambsquarters 6-8 2.9 a 3.0 a 70 b 10 a
Redroot pigweed 4-6 0.9 a 2.4 b 22 b 8 a
Common ragweed 6-8 1.1 a 3.3 b 27 b 11 a
Common cocklebur 4-5 0.8 a 3.0 b 19 b 10 a
Eastern black nightshade 5-7 0.4 a 3.4 b 10 a 11 a
Wild mustard 5-6 1.2 a 74.1 b 30 a 245 b

 

aAll treatments included 0.25% (v/v) nonionic surfactant (NIS) and 1.0% (WV) 28% urea
ammonium nitrate (UAN). Signiﬁcance between herbicides is only to be compared across
rows. Values followed by a common letter are not signiﬁcantly different at the 5% level.
bDry weight reduction represents the g ha'I required to reduce plant growth by 50%,
whereas percent of the ﬁeld use rate represents the percent of either 4 g ha“l ﬂuthiacet or
30 g ha‘1 ﬂumiclorac required to reduce plant grth by 50%.

cCalculated based on a ﬁeld use rate of 4 g ha" ﬂuthiacet and 30 g ha‘l ﬂumiclorac.

99

Table 2. Corn injury 3 d after treatment (DAT) and broadleaf weed control 14 DAT in
the greenhouse with ﬂuthiacet or ﬂumiclorac tank mixtures.a

 

 

 

 

 

Herbicide Rate ZEAMA ABUTH C HEAL AMARE AMBEL
g ha" % injury % control
Atrazine 210 0 19 31 72 59
Atrazine + ﬂuthiacet 210 +1 5 59 45 78 63
Atrazine + ﬂumiclorac 210 +8 10 74 53 93 71
Dicamba 70 0 30 57 60 61
Dicamba + ﬂuthiacet 70 + 1 3 50 67 65 62
Dicamba + ﬂumiclorac 70 + 8 6 68 77 81 74
2, 4-D 140 5 39 77 32 53
2,4-D + ﬂuthiacet 140 +1 8 61 77 62 60
2,4-D + ﬂumiclorac 140 +8 11 60 78 85 74
Bromoxynil 70 l 43 32 15 67
Bromoxynil + ﬂuthiacet 70 + l 6 63 48 49 65
Bromoxynil + ﬂumiclorac 70 + 8 12 63 57 85 66
Halosulfuron 9 0 71 0 58 75
Halosulfuron + ﬂuthiacet 9 + 1 3 67 21 63 66
Halosulfuron + ﬂumiclorac 9 + 8 6 54 26 70 53
Prinrisulﬁrron + prosulfuron 10 0 72 51 64 76
Primisulfuron + prosulfuron 10 + 1 4 68 48 75 73
+ ﬂutlnacet
Primisulfuron + prosulfuron 10 + 8 7 67 52 81 75
+ ﬂumrclorac
Untreated control — 0 0 0 0 0
LSD (0.05) 2 6 5 8 6

 

aAll atrazine treatments included 1.0% crop oil concentrate (COC); bromoxynil, dicamba,
halosulfuron, primisulfuron plus prosulfuron, and 2, 4-D treatments included 0.25% (v/v)
nonionic surfactant (NIS).

100

Table 3. Soybean injury 3 d after treatment (DAT) and broadleaf weed control 14 DAT
in the greenhouse with ﬂuthiacet or ﬂumiclorac tank mixtures.a

 

 

 

 

 

Herbicide Rate GLYMA ABUTH CHEAL AMARE AMBEL
g ha‘1 % % control

Bentazon 210 1 65 33 35 46
Bentazon + ﬂuthiacet 210 + 1 1.2 96 40 58 49
Bentazon + ﬂumiclorac 210 + 8 12 95 47 80 53
Imazethapyr 1 8 10 66 28 78 46
Imazethapyr + ﬂuthiacet 18 + 1 12 68 36 80 53
Imazethapyr + 18 + 8 12 67 40 93 64
Lactofen 26 1 5 43 20 87 79
Lactofen + ﬂuthiacet 26 + 1 19 67 39 87 89
Lactofen + ﬂumiclorac 26 + 8 20 81 57 97 92
Oxasulfuron 16 7 85 5 1 66 5 5
Oxasulfuron + ﬂuthiacet 16 + l 10 87 44 60 46
Oxasulfuron + ﬂumiclorac 16 + 8 12 81 47 76 42
Untreated control — 0 O 0 0 0

LSD (0.05) 2 6 6 9 8

 

aAll bentazon treatments included 1.0% crop oil concentrate (COC); imazethapyr and
oxasulfuron treatments included 0.25% (v/v) nonionic surfactant (NIS) plus 1.0% (WV)
28% urea ammonium nitrate (U AN); and lactofen treatments included 0.5% (v/v) COC.

101

 

 

 

 

 

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104

CHAPTER 5

Incorporating Fluthiacet and Flumiclorac into Annual Weed Control
Programs for Corn (Zea mays) and Soybean (Glycine max)

ABSTRACT

Greenhouse and ﬁeld studies evaluated annual weed control programs for corn and
soybean that included ﬂuthiacet and ﬂumiclorac. Fluthiacet or ﬂumiclorac added to
imazethapyr, quizalofop, sethoxydim, or clethodim did not affect giant foxtail and
barnyardgrass control. Fluthiacet or ﬂumiclorac added to ﬂuazifop increased giant foxtail
control compared with ﬂuazifop alone. However, barnyardgrass control with ﬂuazifop
decreased in the greenhouse when ﬂumiclorac was added. Velvetleaf control with
ﬂuthiacet and ﬂumiclorac was greatest 7 DAT when applied to 5 cm tall plants in the
ﬁeld. However, season-long velvetleaf control with both herbicides was greatest when
applied to 45 or 60 cm tall plants. In ﬁeld studies, ﬂuthiacet or ﬂumiclorac applied POST
following metolachlor or metolachlor plus atrazine PRE increased velvetleaf control
compared to only a PRE application of metolachlor plus atrazine. Similarly, ﬂuthiacet or
ﬂumiclorac added to 2,4-D applied POST following metolachlor applied PRE increased
velvetleaf control compared to metolachlor followed by 2,4-D alone. Velvetleaf control

also increased when ﬂuthiacet or ﬂumiclorac were tank mixed with nicosulfuron plus

105

atrazine, or nicosulfuron plus dicamba applied POST. In soybean, metolachlor plus
metribuzin plus clomazone applied PRE, metolachlor applied PRE followed by ﬂuthiacet
or ﬂumiclorac applied POST, metolachlor plus metribuzin applied PRE followed by
ﬂuthiacet or flumiclorac applied POST, imazethapyr plus ﬂuthiacet or ﬂumiclorac
applied POST, glyphosate alone, and tank mixtures of glyphosate with ﬂuthiacet or
ﬂumiclorac applied LATE POST controlled giant foxtail, common lambsquarters, redroot
pigweed, and velvetleaf in 1997. However, only metolachlor plus metribuzin applied
PRE followed by ﬂuthiacet or ﬂumiclorac applied POST and imazethapyr plus ﬂuthiacet
or ﬂumiclorac applied POST controlled these weeds in 1998.

Nomenclature: Atrazine, 6-chloro-N-ethyl-N’-(1-rnethylethyl)-1,3,5-triazine-2,4-
diamine; bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; 2,4-D, (2,4-
dichlorophenoxy)acetic acid; clethodim, (E,E)-(:t)-2-[1-[[(3-chloro-2-
propenyl)oxy]imino]butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one;
clomazone, 2-[(2-chlorophenyl)methyl]4,4-dimethyl-3-isoxazolidinone; dicamba, 3,6-
dichloro-Z-methoxybenzoic acid; ﬂuazifop, (i)-2-[4-[[5-(triﬂuoromethyl)-2-
pyridinyl]oxy]phenoxy]propanoic acid; ﬂuthiacet, methyl[[2-chloro-4-ﬂuoro-5-
[(tetrahydro-3-oxo- 1H, 3H—[ 1 ,3 ,4]thiadiazolo[3,4-a]pyridazin-1-
ylidene)amino]phenyl]thio]acetate; ﬂumiclorac, pentyl[2-chloro-4-ﬂuoro-5-(1,3,4,5,6,7-
hexahydro-l,3-dioxo-2H-isoindol-2-yl)phenoxy]acetic acid; glyphosate (N-
(phosphonomethyl)glycine); imazethapyr, 2-[4,5~dihydro-4-methyl-4-(1-methylethyl)-5-
oxo-1H-imidazol-2-y1]-5-ethyl-3-pyridinecarboxylic acid; metolachlor, 2-chloro-N-(2-
ethyl-6-methy1phenyl)—N—(2-methoxy- l -methylethyl)acetamide; metribuzin, 4-amino-6-

(1 ,1-dimethylethyl)-3-(methylthio)-1 ,2,4-t1iazin-5(4H)-one; nicosulfuron (2-[[[[(4,6-

106

dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-B-
pyridinecarboxamide); oxasulfuron, 2-[[[[(4,6-dimethyl—2-pyrimidinyl)-
amino]carbonyl]amino]sulfonyl] benzoic acid, 3-oxetany1 ester; quizalofop (:t)-2-[4-[(6-
chloro-Z-quinoxalinyl)oxy]phenoxy]propanoic acid; sethoxydim, 2-[1-
(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; 2,4-D, (2,4-
dichlorophenoxy)acetic acid; common lambsquarters, Chenopodium album L. # CHEAL;
redroot pigweed, Amaranthus retroﬂexus L. # AMARE; barnyardgrass, Echinochloa
Crus-galli L. Beauv. ECHCG; giant foxtail, Setariafaberi Herrm. # SETFA; velvetleaf,
Abutilon theophrasti Medik. #' ABUTH; wild mustard, Brassica kaber (D.C.) L.C.
Wheeler # SINAR; corn, Zea mays L. # ZEAMA; soybean, Glycine max (L.) Merr. #
GLYMA.

Key Words: Antagonism, herbicide interaction, Protox, ABUTH, AMARE, CHEAL,
SETFA, GLYMA, ZEAMA.

Abbreviations: COC, crop oil concentrate; DAP, days after planting; DAT, days after
treatment; LATE POST, late postemergence; NIS, nonionic surfactant; POST,
postemergence; Protox, protoporphyrinogen oxidase; PRE, preemergence; UAN, 28%

urea ammonium nitrate.

 

'Letters following this symbol are a WSSA-approved computer code from Composite List

of Weeds, Revised 1989. Available from WSSA, 810 East 10th Street, Lawrence, KA
66044-8897.

107

INTRODUCTION

Fluthiacet and ﬂumiclorac are cyclic imide herbicides that effectively control
velvetleaf, one of the most troublesome broadleaf weeds in corn and soybean (Porpiglia
et a1. 1994; Kamoshita et a1. 1993). These selective herbicides control weeds by
inhibiting the protoporphyrinogen oxidase (Protox) enzyme in susceptible plants (Duke et
a1. 1990; Duke et al. 1991; Mito et al. 1991).

F luthiacet and ﬂumiclorac provided greater than 96% season-long velvetleaf control
(Brown et a]. 1991; Kapusta et al. 1995). However, season-long common cocklebur
control with ﬂuthiacet was 83% (Kapusta et al. 1995), and Pennsylvania smartweed
control with ﬂumiclorac was 60% (Brown et al. 1991).

Broad-spectrum weed control is commonly achieved by tank mixing herbicides. Tank
mixtures including ﬂuthiacet or ﬂumiclorac may enhance velvetleaf control and provide
more consistent broadleaf weed control compared with the tank mix partner alone (Dill et
a1. 1994; James et al. 1994; Kurtz and Pawlak 1992). Understanding herbicide
performance in tank mixtures is important when creating weed management programs
(Young et al. 1996). Giant foxtail control with sethoxydim (2-[1-(ethoxyimino)butyl]-S-
[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one) was not affected by the addition of
ﬂuthiacet or ﬂumiclorac (James et al. 1994; Young et al. 1996); however, shattercane
(Sorghum bicolor (L.) Moench) control was reduced (Young et al. 1996). Similarly,
large crabgrass (Digitaria sanguinalis (L.) Scop.) control with sethoxydim was not
affected by the addition of ﬂuthiacet, however, control was reduced by adding
ﬂumiclorac. F luthiacet or ﬂumiclorac tank mixtures with glyphosate (N-

(phosphonomethyl)glycine) increased velvetleaf and common ragweed control compared

108

with glyphosate alone (Lich et a1. 1997). However, adding ﬂuthiacet to oxasulfuron
reduced common ragweed control compared with oxasulfuron alone (Nelson and Renner
1998)

Potential beneﬁts of ﬂuthiacet and ﬂumiclorac include low use rates, short-half lives,
resistance management, and the ability to broaden the spectrum of other herbicides
(Anonymous 1995). Research investigating broad-spectrum weed control programs in
corn and soybean with ﬂuthiacet or ﬂumiclorac is limited. Field research has not
determined the most effective time to apply ﬂuthiacet or ﬂumiclorac in corn or soybean
or their performance with other postemergence herbicides. Therefore, the objective of
this research was to evaluate broad-spectrum weed control programs in corn and soybean

that include ﬂuthiacet and ﬂumiclorac.

MATERIALS AND METHODS

Greenhouse Experiments

Annual Grass Control with Fluthiacet and Flumiclorac Tank Mixtures. Giant foxtail
and barnyardgrass seed was obtained ﬁ'om a commercial seed supplier-z. Seeds were
planted in BACCTO3 potting soil in 946 m1 plastic pots. Environmental conditions were
maintained within a greenhouse at 27 :t 5 C. Plants were grown under a 16-h photoperiod

of natural and supplemental high pressure sodium lighting with a photosynthetic photon

 

2Seed, V & J Seed Farms, PO. Box 82, Woodstock, IL 60098.

3BACCTO professional planting mix, Michigan Peat Co., PO. Box 98129, Houston, TX
77098.

109

flux density of 1000 ,umol m‘2 5". Plants were thinned to 1 plant pot“, fertilized with 50
ml of a water-soluble fertilizer solution (400 ppm N, 400 ppm P205, and 400 ppm K20),
and watered as needed. Herbicides were applied with a continuous belt-linked sprayer
ﬁtted with an 8001E ﬂat-fan nozzle4 traveling at 1.53 km h" and delivering 234 L ha‘l at
193 kPa of pressure.

The experiment was a completely randomized design with four replications. Giant
foxtail and barnyardgrass were visually evaluated in each experiment 3, 7 and 14 d after
treatment (DAT). Visual ratings were based on a scale from O to 100%, with 0 indicating
no effect and 100 indicating plant death. Evaluations represented visual stunting,
chlorosis, and necrosis.

Experiments evaluated giant foxtail and barnyardgrass control with tank mixtures
including ﬂuthiacet and ﬂumiclorac. Treatments included an untreated control, 18 g ha‘l
imazethapyr, 12 g ha" quizalofop, 52 g ha'l sethoxydim, 35 g ha'1 clethodim, and 52 g
ha'l ﬂuazifop applied alone and in a tank mixture with 1 g ha" ﬂuthiacet or 8 g ha"
ﬂumiclorac. All treatments were applied with crop oil concentrate5 (COC) (1 .0% v/v).
Giant foxtail plants were 10 cm tall with three to four leaves, and barnyardgrass plants
were 10 cm tall with two to three leaves at application. Giant foxtail and barnyardgrass
were visually evaluated for phytotoxicity 7 and 14 DAT. Visual ratings were based on a
scale from 0 to 100%, with 0 indicating no effect and 100 signifying plant death.

Evaluations represented visual stunting, chlorosis, and necrosis.

 

4Teejet ﬂat-fan nozzles, Spraying Systems Co., North Avenue and Schmale Road,
Wheaton, IL 60532.

5Herbimax, 83% petroleum oil, 17% surfactant, Loveland Industries Inc., PO. Box 1289,
Greeley, CO 80632.

110

Field Experiments

Annual Grass Control with Fluthiacet and Flumiclorac Tank Mixtures. Research was
conducted at the Michigan State University Research Farm in East Lansing, MI in 1997.
The soil was a Capac sandy clay loam (ﬁne-loamy, mixed mesic Aerie Ochraqualfs) with
2.8% organic matter and a pH of 6.6. The site was fall moldboard plowed with secondary
tillage consisting of two ﬁeld cultivations at planting. ‘Conrad’ soybean was planted in
76-cm rows at 345,000 seed ha". Plots were 3 m wide by 10.6 min length.

The experiment was a randomized complete block with four replications. Treatments
included an untreated control, 140 g ha’l clethodim, and 210 g ha’l ﬂuazifop applied alone
and in a tank mixture with 5 g ha‘l ﬂuthiacet or 45 g ha‘l ﬂumiclorac. All treatments
included COC5 (1 .0% v/v).

Herbicides were applied on June 17, 1997, 35 d after planting (DAP), with a
compressed air tractor-mounted sprayer traveling at 6.3 km h‘1 and delivering 178 L ha"
at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-fan nozzles spaced 51 cm
apart and 48 cm above the weed canopy. At application, soybean plants were 8 to 10 cm
tall with one fully developed trifoliolate; and giant foxtail and barnyardgrass plants were
1 to 12 cm tall with one to ﬁve leaves.

Giant foxtail and barnyardgrass control was evaluated 7, 14, and 28 DAT. Visual
ratings were based on a scale from O to 100%, with 0 indicating no effect and 100
signifying plant death. Evaluations represented visual stunting, chlorosis, and necrosis.
Velvetleaf Control. Experiments were conducted at the Michigan State University
Research Farm in East Lansing, MI in 1996 and 1997. The soil was a Capac sandy loam

(ﬁne-loamy, mixed mesic Aeric Ochraqualfs) with 2.5 and 2.4% organic matter in 1996

111

and 1997, respectively. The soil pH was 6.5 in 1996 and 1997. Sites were spring chisel
plowed with secondary tillage consisting of two ﬁeld cultivations at planting. Dekalb6
‘404 SR’ corn was planted in 76-cm rows at 62,000 seed ha". Plots were 3 m wide by
9.1 m in length.

The experiment was a randomized complete block with four replications. Treatments
included 4 and 5 g ha“ ﬂuthiacet or 30 and 45 g ha'l ﬂumiclorac applied with COC5 0.5%
(v/v). Herbicides were applied on June 12, July 2, and July 9, 1996 and June 10, June 27,
and July 1, 1997 with a compressed air tractor-mounted sprayer traveling at 6.3 km h'1
and delivering 178 L ha'l at 207 kPa of pressure. Treatments were applied with 8003 ﬂat-
fan nozzles spaced 51 cm apart and 48 cm above the weed canopy. At application,
velvetleaf plants were 2 cm tall and from cotyledon to two-leaf stage; 45 cm tall with
eight to 10 leaves; and 60 cm tall with ten to 12 leaves.

Corn injury was visually evaluated 3, 7, and 14 DAT. Velvetleaf control was evaluated
7 and 14 DAT, and 21 d after the third application timing. Visual ratings were based on a
scale from 0 to 100%, with 0 indicating no effect and 100 signifying plant death. Corn
injury and velvetleaf control evaluations represented visual stunting, chlorosis, and
necrosis.

Annual Weed Control in Corn. Experiments were conducted at the Michigan State
University Research Farm at East Lansing, MI and at the Michigan State Horticultural
Research Station at Clarksville, MI in 1998. The East Lansing soil was a Capac sandy
clay loam (ﬁne-loamy, mixed mesic Aeric Ochraqualfs) with 2.5% organic matter and a

pH of 6.5. The Clarksville soil was a Lapeer sandy loam (coarse-loamy, mixed mesic

 

6Corn, DEKALB Genetics Corporation, 3100 Sycamore Road Dekalb, IL 60115.

112

Mollic Haplaquepts) with 1.9% organic matter and a pH of 6.8. Sites were spring
moldboard plowed with secondary tillage consisting of two ﬁeld cultivations at planting.
Dekalb6 ‘493 RR’ corn was planted in 76-cm rows at 62,000 seed ha". Plots were 3 m
wide by 10.6 m in length.

The experiment was a randomized complete block with four replications. Treatments
included a weed-free and an untreated control. All POST atrazine treatments included
COC5 (1.0% v/v). All 2,4—D, dicamba, and bromoxynil treatments included Activator 9O7
(NIS) (0.25% v/v). Fluthiacet, ﬂumiclorac, and glyphosate treatments included NIS7 plus
UAN (0.25 + 1.0% v/v).

PRE herbicide applications were applied on May 26, 1998 at East Lansing and May 19,
1998 at Clarksville. POST herbicide applications were applied at East Lansing and
Clarksville on June 26, 1998 and June 18, 1998, 31 and 30 DAP, respectively. LATE
POST applications were applied at East Lansing and Clarksville on June 29, 1998 and
June 23, 1998, respectively. All herbicide treatments were applied with a compressed air
tractor-mounted sprayer traveling at 6.3 km h'l and delivering 178 L ha‘l at 207 kPa of
pressure. Treatments were applied with 8003 ﬂat-fan nozzles spaced 51 cm apart and 48
cm above the weed canopy. At the time of POST applications corn plants were 25 to 30
cm tall with ﬁve collars; giant foxtail plants were 1 to 15 cm tall with one to four leaves;
common lambsquarters plants were 1 to 10 cm tall with two to 18 leaves; redroot
pigweed plants were 1 to 8 cm tall and from cotyledon to ten leaves; and velvetleaf plants

were 1 to 10 cm tall and from cotyledon to six leaves. At the time of LATE POST

 

7Activator 90, nonionic surfactant, a mixture of alkyl polyoxyethylene ether and fatty
acids, Loveland Industries, Inc., PO. Box 1289, Greeley, CO 80632.

113

application corn plants were 30 to 38 cm tall with six collars; giant foxtail plants were 1
to 22 cm tall with one to six leaves; common lambsquarters plants were 1 to 15 cm tall
with two to 30 leaves; redroot pigweed plants were 1 to 18 cm tall with two to 12 leaves;
and velvetleaf plants were 1 to 18 cm tall with two to eight leaves.

Corn injury was visually evaluated 7 and 14 DAT. Weed control was evaluated for
each species 14, 28, and 56 DAT. Visual ratings were based on a scale from O to 100%,
with 0 indicating no effect and 100 signifying plant death. Corn injury and weed control
evaluations represented visual stunting, chlorosis, and necrosis. The two middle rows
from each plot were harvested with a Massey 108 small-plot combine. Corn yield was
adjusted to 15.5% moisture.

Annual Weed Control in Soybean. Experiments were conducted at the Michigan State
University Research Farm at East Lansing, MI in 1997 and 1998. The soil was a Capac
sandy clay loam (ﬁne-loamy, mixed mesic Aeric Ochraqualfs) with 2.8 and 4.2% organic
matter in 1997 and 1998, respectively. The soil pH was 6.6 and 6.3 in 1997 and 1998,
respectively. Sites were fall chisel plowed with secondary tillage consisting of two ﬁeld
cultivations at planting. Asgrow9 ‘2701 RR’ soybean was planted in 76-cm rows at
345,000 seed ha". Plots were 3 m wide by 10.6 m in length.

The experiment was a randomized complete block with four replications. Treatments
included a weed-free and an untreated control. All ﬂuthiacet, ﬂumiclorac, imazethapyr,
oxasulfuron, and glyphosate treatments were applied with NIS7 plus UAN (0.25 + 1.0%

v/v). All clethodim treatments included COC5 (1 .0% v/v).

 

8Kincaid Equipment Manufacturing, PO. Box 400, Haven, KS 47543.
9Soybean, Asgrow Seed Company, PO. Box 7570, Des Moines, IA 50322.

114

PRE herbicide applications were applied on May 13, 1997 and 1998. POST herbicide
applications were applied on June 17, 1997 and June 8, 1998, 35 and 26 DAP, and LATE
POST applications were applied on June 22, 1997 and June 14, 1998. All herbicide
treatments were applied with a compressed air tractor-mounted sprayer traveling at 6.3
km h" and delivering 178 L ha" at 207 kPa of pressure. Treatments were applied with
8003 ﬂat-fan nozzles spaced 51 cm apart and 48 cm above the weed canopy. At the time
of POST applcations soybean plants were 10 to 14 cm tall with two fully developed
trifoliolates; giant foxtail plants were 1 to 15 cm tall and from one to four leaves;
common lambsquarters plants were 1 to 10 cm tall with two to 22 leaves; redroot
pi gweed plants were 1 to 8 cm tall and from cotyledon to ten leaves; and velvetleaf plants
were 1 to 10 cm tall and from cotyledon to ﬁve leaves. At the time of LATE POST
applications soybean plants were 15 to 20 cm tall with two to three trifoliolates; giant
foxtail plants were 1 to 20 cm tall and ﬁ'om one to six leaves; common lambsquarters
plants were 1 to 15 cm tall with four to 26 leaves; redroot pigweed plants were 1 to 10 cm
tall with two to 12 leaves; and velvetleaf plants were 1 to 13 cm tall and from cotyledon
to seven leaves.

Soybean injury was visually evaluated 7 and 14 DAT. Weed control was evaluated for
each species 14, 28, and 56 DAT. Visual ratings were based on a scale from O to 100%,
with 0 indicating no effect and 100 signifying plant death. Soybean injury and weed
control evaluations represented visual stunting, chlorosis, and necrosis. The two middle
rows from each plot were harvested with a Massey 108 small-plot combine. Soybean

yield was adjusted to 13% moisture.

115

Statistical Analyses

All experiments were repeated over time, and data were analyzed using analysis of
variance (ANOVA). When data for individual experiments revealed no treatment by time
interaction experiments were combined. Means were separated by Fisher’s protected

least signiﬁcant difference test (LSD) at the 5% level.
RESULTS AND DISCUSSION

Annual Grass Control with Fluthiacet and Flumiclorac Tank Mixtures. F luthiacet
tank mixed with imazethapyr, quizalofop, sethoxydim, clethodim, and ﬂuazifop did not
reduce giant foxtail or barnyardgrass control with these herbicides in the greenhouse
(Table 1). Similarly, when ﬂumiclorac was added to imazethapyr, quizalofop,
sethoxydim, or clethodim giant foxtail and barnyardgrass control was not reduced (Table
1). Giant foxtail control with ﬂumiclorac plus ﬂuazifop increased by 4%, yet
barnyardgrass control decreased by 32% in the greenhouse when compared with ﬂuazifop
alone. Similarly, Young et al. (1996) reported giant foxtail and large crabgrass control
with sethoxydim was not affected by the addition of ﬂuthiacet; however, large crabgrass
control with sethoxydim was reduced by the addition of flumiclorac. Adding ﬂuthiacet
or ﬂumiclorac to clethodim or ﬂuazifop did not reduce giant foxtail or barnyardgrass
control in the ﬁeld when compared with clethodim or ﬂuazifop alone (Table 2).
Differing results between the greenhouse and ﬁeld may be explained by ﬂumiclorac and
ﬂuazifop application rates; both were applied in the greenhouse at one-fourth the

application rate used in the ﬁeld. Thus, increased herbicide rates in the ﬁeld may have

116

overcome any antagonism between ﬂumiclorac and ﬂuazifop. Regardless, our results
suggest that ﬂuthiacet and ﬂumiclorac do not antagonize giant foxtail or barnyardgrass

control by imazethapyr, quizalofop, sethoxydim, or clethodim.

Weed Control Programs.

Velvetleaf Control. Velvetleaf control was equivalent between 4 and 5 g ha‘l ﬂuthiacet
and 30 and 45 g ha‘l ﬂumiclorac in the ﬁeld at all three application timings, thus the data
for each herbicide is combined over application rates. Fluthiacet and ﬂumiclorac
provided greater than 80% control of 60 cm-tall velvetleaf plants (Table 3). Velvetleaf
control with ﬂuthiacet and ﬂumiclorac was greatest 7 DAT when applied to 5-cm tall
plants in the ﬁeld. However, season-long velvetleaf control with both herbicides was
greatest when applied to 45 or 60 cm tall plants. Because ﬂuthiacet and ﬂumiclorac have
no soil activity, delaying herbicide application allowed more velvetleaf to emerge prior to
herbicide application. Similarly, Tharp and Kells (1997) reported that delaying
glyphosate or glufosinate (2-amino-4-(hydroxymethylphosphinyl)butanoic acid)
applications, which also have no soil activity, enhanced season-long weed control.
Annual Weed Control in Corn. Corn exhibited leaf necrosis from tank mixtures
including ﬂuthiacet or ﬂumiclorac (Table 4), but injury was no longer evident by 21 DAT
(data not presented). Giant foxtail, common lambsquarters, and redroot pigweed were
controlled by all of the herbicide programs evaluated. A POST application of ﬂuthiacet
or ﬂumiclorac following metolachlor or metolachlor plus atrazine applied PRE increased
velvetleaf control 56 DAT compared with metolachlor plus atrazine applied PRE (Table

4). Adding ﬂuthiacet or ﬂumiclorac to 2,4-D applied POST following metolachlor

117

applied PRE increased velvetleaf control compared with metolachlor followed by 2,4-D
alone. Velvetleaf control also increased when ﬂuthiacet or ﬂumiclorac were added to
nicosulfuron plus atrazine, or nicosulfuron plus dicamba applied POST.

Corn yield in the metolachlor applied PRE followed by ﬂuthiacet plus atrazine applied
POST treatment was greater than yield in the metolachlor plus atrazine applied PRE
followed by ﬂuthiacet applied POST. Corn yield with metolachlor applied PRE followed
by 2,4-D applied POST, nicosulfuron plus bromoxynil applied POST, and glyphosate
alone and tank mixtures of glyphosate with ﬂuthiacet or ﬂumiclorac applied LATE POST
had lower yields when compared with the weed-free control. The yield reduction in the
metolachlor applied PRE followed by 2,4-D applied POST and the nicosulfuron plus
bromoxynil applied POST treatments resulted from a lack of velvetleaf control.

However, corn yield did not increase with increased velvetleaf control from tank mixtures
of ﬂuthiacet or ﬂumiclorac with nicosulfuron plus atrazine or dicamba. Schmenk and
Kells (1998) reported reduced velvetleaf competitiveness in corn following an atrazine
application. Thus, applying atrazine or dicamba may reduce velvetleaf competitiveness
to a level where increased velvetleaf control from tank mixtures including ﬂuthiacet or
ﬂumiclorac would not increase corn yield. Because reduced corn yield cannot be
attributed to a lack of weed control in the glyphosate and glyphosate tank mixture
treatments, yield loss may be attributed to weed competition. All glyphosate treatments
were applied LATE POST, three to ﬁve days alter POST herbicide treatments. Our data
suggests weed competition during this time period reduced corn yield.

Annual Weed Control in Soybean. Soybean exhibited leaf necrosis from tank mixtures

with ﬂuthiacet or ﬂumiclorac, but injury was not evident by 21 DAT (data not presented).

118

Kapusta et al. (1986) and Wichert and Talbert (1993) reported that leaf necrosis from
Protox-inhibiting herbicides did not reduce soybean yield.

In 1997, metolachlor plus metribuzin plus clomazone applied PRE, metolachlor applied
PRE followed by ﬂuthiacet or ﬂumiclorac applied POST, metolachlor plus metribuzin
applied PRE followed by ﬂuthiacet or ﬂumiclorac applied POST, imazethapyr plus
ﬂuthiacet or ﬂumiclorac applied POST, or glyphosate, and glyphosate tank mixtures with
ﬂuthiacet or ﬂumiclorac applied LATE POST provided season-long, common
lambsquarters, redroot pigweed, and velvetleaf control (Table 5). However, only
metolachlor plus metribuzin applied PRE followed by ﬂuthiacet or ﬂumiclorac applied
POST, or imazethapyr plus ﬂuthiacet or ﬂumiclorac applied POST controlled these
weeds in 1998 (Table 6).

Precipitation affects herbicide performance (Wanamarta and Penner 1989). The ﬁrst
rainfall greater than 2.5 cm occurred 5 and 18 d after PRE application in 1997 and 1998,
respectively. The total PRE herbicide program of metolachlor plus metribuzin plus
clomazone provided adequate season-long weed control in 1997, but the lack of rainfall
for two weeks after herbicide application resulted in insufﬁcient weed control in 1998.
Alternatively, the total POST treatments of ﬂuthiacet or ﬂumiclorac plus imazethapyr
resulted in season-long weed control both years. Overall, PRE applications followed by
POST applications and total POST herbicide programs provided more consistent weed
control when compared with total PRE herbicide programs.

Previous research showed tank mixtures of ﬂuthiacet or ﬂumiclorac plus imazethapyr
or oxasulﬁrron increased broadleaf weed control compared with imazethapyr or

oxasulfuron alone (Fausey and Renner 1998). However, acceptable broad-spectrum weed

119

control was only achieved by ﬂuthiacet or ﬂumiclorac tank mixtures with imazethapyr.
F luthiacet or ﬂumiclorac tank mixtures with oxasulfuron and quizalofop provided less
than 80% giant foxtail control in 1997 and less than 60% redroot pigweed control in
1998, and soybean yield was reduced compared with the weed-free control in 1997 and
1998.

Glyphosate and glyphosate tank mixtures with ﬂuthiacet or ﬂumiclorac provided
season-long weed control with soybean yields equal to the weed-free control in 1997.
However, the addition of ﬂuthiacet to glyphosate reduced redroot pigweed control
compared with glyphosate alone. Weed control with glyphosate alone and in tank
mixtures including ﬂuthiacet or ﬂumiclorac provided excellent weed control 14 DAT in
1998 (data not presented). However, dry conditions followed by rainfall after herbicide
application resulted in late emerging weeds. These weeds reduced soybean yield in the
glyphosate treatments when compared with the weed-ﬁee control.

Field results suggest herbicide selection and time of application are critical to assure
maximum crop yield. Cantwell et al. (1989) and Wesley and Shaw (1992) reported that
tank mixtures with Protox-inhibiting herbicides may increase or decrease weed control.
Thus, careful consideration must be given when choosing a tank mix partner for ﬂuthiacet
or ﬂumiclorac. These herbicides control velvetleaf and have activity on common
lambsquarters and redroot pigweed. However, a single ﬂuthiacet or flumiclorac
application in the ﬁeld provided sufﬁcient broad-spectrum weed control when applied
following a PRE application of metolachlor plus atrazine in corn or a PRE application of
metolachlor plus metribuzin in soybean. Likewise, a PRE application of metolachlor

followed by atrazine or 2,4-D tank mixed with fluthiacet or ﬂumiclorac provided season-

120

long broadleaf weed control in corn. James et al. (1994) and Kurtz and Pawlak (1993)
reported that adding ﬂuthiacet or ﬂumiclorac to several postemergence herbicides
enhanced broadleaf weed control. Fluthiacet or ﬂumiclorac tank mixtures with
nicosulfuron plus atrazine or nicosulfuron plus dicamba in corn and imazethapyr in
soybean provided season-long broadleaf weed control.

Weed control programs that include ﬂuthiacet or ﬂumiclorac have several beneﬁts over
current commercial standards. These herbicides provide unprecedented postemergence
velvetleaf control and have the ﬂexibility to be used in corn and soybean. Tank mixtures
including these herbicides also provide an additional mode of action for managing weed
resistance. Further research should investigate crop tolerance and weed control programs

with ﬂuthiacet and ﬂumiclorac in herbicide resistant corn and soybean.

ACKNOWLEDGMENTS

The authors thank Gary Powell for his assistance in this research. Appreciation is

extended to Valent U.S.A. Corporation and Novartis Crop Protection, Inc. for their

ﬁnancial support.

121

10.

ll.

12.

LITERATURE CITED

Brown, W. B., M. S. DeFelice, and C. S. Holman. 1991. Weed control in corn and
soybeans with V-23031. Proc. N. Cent. Weed Sci. Soc. 46:40.

Cantwell, J. R., R. A. Liebl, and F. W. Slife. 1989. Imazethapyr for weed control
in soybean (Glycine max). Weed Technol. 7 2345-35 1.

Dill, T. R., J. R. James, L. Stahlberg, and E. R. Hill. 1994. Update on the
herbicidal activity of CGA-248757 in corn in the Midwest. Proc. N. Cent. Weed
Sci. Soc. 49:58.

Duke, S. O., J. M. Becerril, T. D. Sherman, J. Lydon, and H. Matsumoto. 1990.
The role of protoporphyrin IX in the mechanism of action of diphenyl ether
herbicides. Pestic. Sci. 30:367-378.

F ausey, J. C. and K. A. Renner. 1998. Broadleaf weed control in soybeans with
ﬂumiclorac and CGA-248757 alone and in tank mixtures. Abstr. Weed Sci. Soc.
Am. 38:9.

James, J. R., L. Stahlberg, T. R. Dill, and G. Hill. 1994. Update on the herbicidal
activity of CGA-248757 in soybeans in the Midwest. Proc. N. Cent. Weed Sci.
Soc. 49:129.

Kamoshita, K., E. Nagano, S. Hashimoto, R. Sato, R. Yoshida, and H. Oshio.
1993. V-23031-A new herbicide for postemergence weed control in soybeans and
ﬁeld corn. Abstr. Weed Sci. Soc. Am. 5323.

Kapusta, G., S. E. Curvey, and S. T. Autman. 1995. Soybean weed control with
CGA-248757 and CGA-277476 at three weed growth stages. Research Report N.
Cent. Weed Sci. Soc. 52:253-255.

King, C. A. and L. R. Oliver. 1992. Application rate and timing of aciﬂuorfen,
bentazon, chlorimuron, and imazaquin. Weed Technol. 6:526-534.

Kurtz, A. R. and J. A. Pawlak. 1992. Postemergence weed control in ﬁeld corn
with V-23031 herbicide. Proc. N. Cent. Weed Sci. Soc. 47:47.

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

Mito, N., R. Sato, M. Miyakado, H. Oshio, and S. Tanaka. 1991. In vitro mode of

action of N-Phenylimide photobleaching herbicides. Pestic. Biochem. Physiol.
40: 128-135.

122

13.

14.

15.

l6.

17.

18.

19.

Nelson, K. A. and K. A. Renner. 1998. Weed control in wide- and narrow-row
soybean (Glycine max) with imazamox, imazethapyr, and CGA-277476 plus
quizalofop. Weed Technol. 12:137—144.

Porpiglia, P. J ., E. R. Hill, and A. Tally. 1994. CGA-248757 for postemergence
broadleaf weed control in corn (Zea mays L.) and soybeans (Glycine max (L.)
Merr.). Abstr. Weed Sci. Soc. Am. 34:2.

Sander, K. W. and P. J. Porpiglia. 1996. GOA-248757 combinations for broadleaf
weed control in soybeans. Proc. N. Cent. Weed Sci. Soc. 51:132.

Schmenk, R. E. and J. J. Kells. 1998. Effect of soil applied atrazine and
pendimethalin on velvetleaf (Abutilon theophrasti) competitiveness in corn. Weed
Technol. 12:-47-52.

Tharp, B. E. and J. J. Kells. 1997. Weed management strategies in glufosinate
resistant and glyphosate resistant corn. Proc. N. Cent. Weed Sci. Soc. 52:64.

Wesley, T. M. and D. R. Shaw. 1992. Interactions of diphenylether herbicides
with chlorimuron and imazaquin. Weed Technol. 62345-351.

Young, B. G., S. E. Hart, and L. M. Wax. 1996. Interactions of sethoxydim and

corn (Zea mays) postemergence broadleaf herbicides on three annual grasses.
Weed Technol. 10:914-922.

123

Table 1. Giant foxtail and barnyardgrass control with ﬂuthiacet or ﬂumiclorac tank
mixtures in the greenhouse 14 d after treatment.3

 

 

 

 

 

Herbicide Rate Giant foxtail Bamyardgrass
g ha" % control
Imazethapyr 1 8 1 9 1 8
Imazethapyr + ﬂuthiacet 18 + 1 23 20
Imazethapyr + ﬂumiclorac 18 + 8 32 44
Quizalofop 12 98 98
Quizalofop + ﬂuthiacet 12 + 1 98 97
Quizalofop + ﬂumiclorac 12 + 8 97 98
Sethoxydim 52 8 1 89
Sethoxydim + ﬂuthiacet 52 + 1 84 93
Sethoxydim + ﬂumiclorac 52 + 8 86 94
Clethodim 35 86 98
Clethodim + ﬂuthiacet 35 + 1 86 98
Clethodim + ﬂumiclorac 35 + 8 86 97
F luazifop 52 8O 95
Fluazifop + ﬂuthiacet 52 + 1 83 95
Fluazifop + ﬂumiclorac 52 + 8 84 63
Untreated control —— O O
LSD (0.05) 2

 

a All treatments received 1.0% (v/v) crop oil concentrate (COC).

124

Table 2. Giant foxtail and barnyardgrass control with ﬂuthiacet or ﬂumiclorac tank
mixtures in the ﬁeld 28 d after treatment.3

 

 

 

 

 

Herbicide Rate Giant foxtail Bamyardgrass
g ha'l % control

Clethodim 140 100 100
Clethodim + ﬂuthiacet 140 + 5 100 98
Clethodim + ﬂumiclorac 140 + 45 100 100
Fluazifop 210 100 99
Fluazifop + ﬂuthiacet 210 + 5 99 100
Fluazifop + ﬂumiclorac 210 + 45 99 99
Untreated control — O O

LSD (0.05) 2 3

 

a All treatments included 1.0% (v/v) crop oil concentrate (COC).

125

Table 3. Corn injury and velvetleaf control with ﬂuthiacet and ﬂumiclorac in the ﬁeld“

 

 

 

 

 

Herbicide Plant height Cornb Velvetleaft Velvetleaf“
Fluthiacete cm % injury % control
5 4 96 64
Flumicloracf 45 8 97 95
60 1 0 92 94
5 9 96 65
45 l 5 89 84
6O 14 83 82
LSD (0.05) 3 3 10

 

8All treatments included 0.5 % (v/v) crop oil concentrate (COC).
b Corn injury 7 d after treatment (DAT).

° Velvetleaf control 7 DAT.

b Velvetleaf control 21 d after application timing three.

’3 Fluthiacet data averaged over 4 and 5 g ha“.

d Flumiclorac data averaged over 30 and 45 g ha".

126

 

 

 

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