# Quizalofop-p-ethyl Mixed with Synthetic Auxin and ACCase-Inhibiting Herbicides for Weed Management in Rice Production

Authors: Eric P. Webster; Samer Y. Rustom; Benjamin M. McKnight; David C. Blouin; Gustavo M. Teló
Journal: International Journal of Agronomy
 (2019)

---

## Abstract

A study was conducted near Crowley, Louisiana, to evaluate the efficacy of quizalofop-p-ethyl mixed with different synthetic auxin and ACCase-inhibiting herbicides for barnyardgrass and weedy rice control in rice production systems. Quizalofop was applied at 0 or 120 g ai·ha−1 mixed with 2,4-D at 1336 g ai·ha−1, triclopyr at 282 g ai·ha−1, quinclorac at 420 g ai·ha−1, cyhalofop-butyl at 314 g ai·ha−1, or fenoxaprop-p-ethyl at 122 g ai·ha−1. Cyhalofop, fenoxaprop, 2,4-D, quinclorac, and triclopyr antagonized quizalofop for barnyardgrass control at 14 days after treatment (DAT). At 28 DAT, an antagonistic response persisted for barnyardgrass control, except when cyhalofop was mixed with quizalofop, which indicated a neutral response. Red rice, CLXL-745, and CL-111 control decreased due to antagonism of quizalofop when mixed with 2,4-D. However, quinclorac, triclopyr, cyhalofop, or fenoxaprop mixed with quizalofop resulted in a neutral response for red rice, CLXL-745, and CL-111 control at 28 DAT.


---

## Body

## 1. Introduction

Weeds present a constant problem in rice (Oryza sativa L.) production and can reduce rice yield with early season competition [1, 2]. The lack of weed control can reduce rice yield over 90%; therefore, effective weed management programs are essential for maximizing rice production [2, 3]. Red rice and barnyardgrass are among the most common and troublesome weeds of rice production worldwide [4, 5]. Red rice (Oryza sativa L.) can become the dominant weed in cultivated rice due to its high competitive ability [6, 7]. Found in nearly every rice field, barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.) is another troublesome weed that can significantly reduce rice yields [3].In 2002, imidazolinone-resistant (IR) rice was introduced for commercial use [8, 9]. Imazethapyr was the first herbicide labeled for use in IR rice in the U.S., and for the first time, red rice control was possible with a postemergence herbicide application in a conventional rice crop. Imazethapyr provide control of barnyardgrass. However, within a few years of introduction, red rice and barnyardgrass populations were found resistant to imazethapyr [10, 11].BASF developed a new herbicide-resistant rice to be sold under the trade name Provisia®. The herbicide labeled for use is quizalofop, also sold under the trade name Provisia® [12]. Quizalofop inhibits acetyl coenzyme A carboxylase (ACCase), with postemergence activity on annual and perennial grass species [13, 14]. Producers can use ACCase-resistant rice (ACCase-R) to manage weedy rice and other grass species during cultivated rice production [15].Rotation of herbicides and herbicide mixtures with differing sites of action is important for sustainable rice production. These practices can help manage or slow the development of weed resistance. In order to increase weed control, herbicide mixtures have proven to be beneficial by increasing weed control spectrum, increasing the yield and economic returns [16–20]. Herbicide mixtures may exhibit three responses: synergistic, antagonistic, or neutral [15, 21–28]. A neutral response occurs when the observed control is equivalent to the expected control calculated using Colby’s response [15, 21, 23, 24, 27, 28]. A synergistic response occurs when the observed control is higher than the predicted value, and antagonism occurs when the observed control is less than the predicted control.Mixing quizalofop with synthetic auxin herbicides can increase the weed control spectrum, because the auxin herbicides have broad-spectrum activity on dicot and/or grass weeds [29, 30]. The auxin mechanism of action affects protein synthesis, cell division, and growth and stimulates ethylene evolution in plants [31]. Previous research has indicated ACCase-inhibiting herbicide activity can be antagonized when mixed with another herbicide [15, 32]. Antagonism interactions were reported when diclofop-methyl was mixed with 2,4-D, resulting in a decrease in foliar absorption of diclofop [30]. Consequently, synthetic auxin herbicides mixed with ACCase-inhibiting herbicides can reduce herbicide translocation from treated leaves to shoot and root meristems [33].The mixture of two ACCase-inhibiting herbicides is another option. These mixtures can broaden the spectrum of control for annual and perennial grass weeds; however, the potential for antagonism exists [34, 35]. A prepackage mixture of fluazifop and fenoxaprop is commercially available for use in cotton (Gossypium hirsutum L.) and soybean (Glycine max L.) [36]. Previous research reported synergism with a mixture of two ACCase herbicides, fluazifop plus sethoxydim, for control of annual grass weeds [37], and the ACCase-inhibiting herbicides have shown activity on lipid biosynthesis and auxin-induced growth [38]. Therefore, understanding mixture interactions of quizalofop with auxin activity herbicides or with other ACCase-inhibiting herbicides is important for developing an approach for weed management utilizing the new ACCase-R rice technology. The objective of this research was to evaluate the interactions of quizalofop-p-ethyl when mixed with synthetic auxin or other ACCase-inhibiting herbicides for weed management in ACCase-R rice production.


## 2. Materials and Methods

### 2.1. Field Research Site and Herbicide Application

A field study was conducted at the LSU AgCenter H. Rouse Caffey Rice Research Station (RRS) near Crowley, Louisiana (30.177147°N, −92.347743°W), in 2015 and 2016. The soil type at the RRS is a Crowley silt loam with a pH of 6.4 and 1.4% organic matter. Soil preparation consisted of a fall and spring disking followed by two operations in opposite directions with a two-way bed conditioner consisting of rolling baskets and S-tine harrows set at 6 cm depth.Plot size was 5.1 by 1.5 m, with eight-19.5 cm drill-seeded rows planted as follows: 4 center rows of ACCase-R “PVL01” long grain rice, 2 rows of inbred IR “CL-111” long grain rice, and 2 outside rows of IR “CLXL-745” hybrid long grain rice. PVL01, CL-111, and CLXL-745 were each planted at a rate of 70 kg·ha−1. Awnless straw-hull red rice was broadcast at 50 kg·ha−1 across the research area prior to drill seeding rice. The hybrid, inbred, and red rice represent a weedy rice population. The research area was naturally infested with barnyardgrass. The area was surface irrigated to a depth of 5 cm for 24 h after planting, and irrigation water was held for 24 h to allow for soil saturation.A permanent 10 cm flood was established when ACCase-R rice reached the four- to five-leaf stage and was maintained until three weeks prior to harvest. Herbicides were applied 24 h after permanent flood with a CO2-pressurized backpack sprayer calibrated at 145 kPa to deliver 140 L·ha−1 with five flat-fan 110015 nozzles spaced at 35 cm. Red rice, CLXL-745, and CL-111 were at the four-leaf to one-tiller growth stage, and barnyardgrass was in the three-leaf to one-tiller growth stage. Barnyardgrass and red rice populations were 100 to 125 plants m2 at herbicide application.


### 2.2. Plot Design Herbicide Rates and Application Timing

The study was a randomized complete block with a factorial arrangement of treatments with four replications. Factor A consisted of quizalofop applied at 120 g ai·ha−1 or no quizalofop. Factor B consisted of 2,4-D at 1336 g ai·ha−1, triclopyr at 282 g ai·ha−1, quinclorac at 420 g ai·ha−1, cyhalofop-butyl at 314 g ai·ha−1, fenoxaprop-p-ethyl at 122 g ai·ha−1, or no mixture herbicide. Source of materials is listed in Table 1. A second application of quizalofop was applied across the entire research area at a rate of 120 g·ha−1 at 28 days after the initial quizalofop treatment in an effort to salvage rice yield. A crop oil concentrate was added to each herbicide application at a rate of 1% v/v.Table 1
Source of materials.
Herbicide common name
Herbicide trade name
Concentration (g ai L−1)
Formulation
Manufacturer
2,4-D
Opti-amine
454
L
Helena Chemical Company, Collierville, TN
Cyhalofop-butyl
Clincher SF
285
EC
Dow AgroSciences LLC, Indianapolis, IN
Fenoxaprop-p-ethyl
Ricestar HT
70
EC
Bayer Crop Protection LLC, Greensboro, NC
Quinclorac
Facet L
180
EC
BASF Corporation, Research Triangle Park, NC
Quizalofop
Provisia
105
EC
BASF Corporation, Research Triangle Park, NC
Triclopyr
Grandstand
360
L
Dow AgroSciences LLC, Indianapolis, IN


### 2.3. Rice Injury and Weed Control Evaluation

Visual evaluations for this study included crop injury of PVL01 and control of barnyardgrass, red rice, CLXL-745, and CL-111. Control and crop injury were recorded as percentages, with 0% = no control or no crop injury and 100% = complete plant death at 14 and 28 days after treatment (DAT). ACCase-R rice plant height was recorded from four plants in each plot measured from the ground to the tip of the extended rice panicle, at harvest maturity.


### 2.4. Data Analysis

Data were analyzed using the Blouin et al. [21] augmented mixed model to determine synergistic, antagonistic, or neutral responses for herbicide mixtures by comparing an expected control which is calculated based on activity of each herbicide applied alone to an observed control [15, 23, 24, 27, 28]. The fixed effects for all models were the herbicide treatments and evaluation timing. The random effects were year, replication within year, and plot. Considering year or combination of years as a random effect accounts for different environmental conditions each year having an effect on herbicide treatments for that year [39, 40]. Normality of effects over all DAT was checked using the UNIVARIATE [41]. Significant normality problems were not observed.


## 2.1. Field Research Site and Herbicide Application

A field study was conducted at the LSU AgCenter H. Rouse Caffey Rice Research Station (RRS) near Crowley, Louisiana (30.177147°N, −92.347743°W), in 2015 and 2016. The soil type at the RRS is a Crowley silt loam with a pH of 6.4 and 1.4% organic matter. Soil preparation consisted of a fall and spring disking followed by two operations in opposite directions with a two-way bed conditioner consisting of rolling baskets and S-tine harrows set at 6 cm depth.Plot size was 5.1 by 1.5 m, with eight-19.5 cm drill-seeded rows planted as follows: 4 center rows of ACCase-R “PVL01” long grain rice, 2 rows of inbred IR “CL-111” long grain rice, and 2 outside rows of IR “CLXL-745” hybrid long grain rice. PVL01, CL-111, and CLXL-745 were each planted at a rate of 70 kg·ha−1. Awnless straw-hull red rice was broadcast at 50 kg·ha−1 across the research area prior to drill seeding rice. The hybrid, inbred, and red rice represent a weedy rice population. The research area was naturally infested with barnyardgrass. The area was surface irrigated to a depth of 5 cm for 24 h after planting, and irrigation water was held for 24 h to allow for soil saturation.A permanent 10 cm flood was established when ACCase-R rice reached the four- to five-leaf stage and was maintained until three weeks prior to harvest. Herbicides were applied 24 h after permanent flood with a CO2-pressurized backpack sprayer calibrated at 145 kPa to deliver 140 L·ha−1 with five flat-fan 110015 nozzles spaced at 35 cm. Red rice, CLXL-745, and CL-111 were at the four-leaf to one-tiller growth stage, and barnyardgrass was in the three-leaf to one-tiller growth stage. Barnyardgrass and red rice populations were 100 to 125 plants m2 at herbicide application.


## 2.2. Plot Design Herbicide Rates and Application Timing

The study was a randomized complete block with a factorial arrangement of treatments with four replications. Factor A consisted of quizalofop applied at 120 g ai·ha−1 or no quizalofop. Factor B consisted of 2,4-D at 1336 g ai·ha−1, triclopyr at 282 g ai·ha−1, quinclorac at 420 g ai·ha−1, cyhalofop-butyl at 314 g ai·ha−1, fenoxaprop-p-ethyl at 122 g ai·ha−1, or no mixture herbicide. Source of materials is listed in Table 1. A second application of quizalofop was applied across the entire research area at a rate of 120 g·ha−1 at 28 days after the initial quizalofop treatment in an effort to salvage rice yield. A crop oil concentrate was added to each herbicide application at a rate of 1% v/v.Table 1
Source of materials.
Herbicide common name
Herbicide trade name
Concentration (g ai L−1)
Formulation
Manufacturer
2,4-D
Opti-amine
454
L
Helena Chemical Company, Collierville, TN
Cyhalofop-butyl
Clincher SF
285
EC
Dow AgroSciences LLC, Indianapolis, IN
Fenoxaprop-p-ethyl
Ricestar HT
70
EC
Bayer Crop Protection LLC, Greensboro, NC
Quinclorac
Facet L
180
EC
BASF Corporation, Research Triangle Park, NC
Quizalofop
Provisia
105
EC
BASF Corporation, Research Triangle Park, NC
Triclopyr
Grandstand
360
L
Dow AgroSciences LLC, Indianapolis, IN


## 2.3. Rice Injury and Weed Control Evaluation

Visual evaluations for this study included crop injury of PVL01 and control of barnyardgrass, red rice, CLXL-745, and CL-111. Control and crop injury were recorded as percentages, with 0% = no control or no crop injury and 100% = complete plant death at 14 and 28 days after treatment (DAT). ACCase-R rice plant height was recorded from four plants in each plot measured from the ground to the tip of the extended rice panicle, at harvest maturity.


## 2.4. Data Analysis

Data were analyzed using the Blouin et al. [21] augmented mixed model to determine synergistic, antagonistic, or neutral responses for herbicide mixtures by comparing an expected control which is calculated based on activity of each herbicide applied alone to an observed control [15, 23, 24, 27, 28]. The fixed effects for all models were the herbicide treatments and evaluation timing. The random effects were year, replication within year, and plot. Considering year or combination of years as a random effect accounts for different environmental conditions each year having an effect on herbicide treatments for that year [39, 40]. Normality of effects over all DAT was checked using the UNIVARIATE [41]. Significant normality problems were not observed.


## 3. Results and Discussion

### 3.1. Herbicide Interactions Observed for Weed Control

#### 3.1.1. Herbicide Interactions Observed for Barnyardgrass Control

An antagonistic response was observed for barnyardgrass treated with 2,4-D, quinclorac, triclopyr, cyhalofop, or fenoxaprop mixed with quizalofop at 14 DAT (Table2). The addition of 2,4-D in a quizalofop mixture reduced barnyardgrass control to 24% compared with control of 77 to 86% for barnyardgrass treated with all other mixtures evaluated. At 28 DAT, cyhalofop mixed with quizalofop resulted in a neutral response with 97% control of barnyardgrass. However, all other mixtures evaluated resulted in antagonism of quizalofop for barnyardgrass control. Like quizalofop, cyhalofop is an ACCase-inhibiting (Group 1) herbicide with activity on barnyardgrass, and when mixed with quizalofop, the potential for antagonism may be reduced. However, fenoxaprop is also an ACCase inhibitor (Group 1) and antagonism was observed when mixed with quizalofop with 90% observed control compared with an expected control of 99%.Table 2
Barnyardgrass control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
24−
0.0001
Quinclorac
420
42
95
77−
0.0001
Triclopyr
282
0
91
79−
0.0001
Cyhalofop-butyl
314
75
98
86−
0.0001
Fenoxaprop-p-ethyl
122
72
98
85−
0.0001
28 DAT
None
—
0
—
98
—
2,4-D
1336
36
98
5−
0.0001
Quinclorac
420
59
99
86−
0.0001
Triclopyr
282
39
98
91−
0.0046
Cyhalofop-butyl
314
85
99
97
0.1126
Fenoxaprop-p-ethyl
122
75
99
90−
0.0001
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Barnyardgrass treated with 2,4-D mixed with quizalofop resulted in an antagonistic response and did not exceed 5% control at 28 DAT, compared with an expected control of 98% (Table2). Previous research indicates a similar response of 2,4-D amine antagonism of quizalofop for control of volunteer wheat (Triticum aestivum L.) [42] and is similar to research evaluating ACCase-inhibiting herbicides mixed with dicot herbicides [15, 32].


#### 3.1.2. Herbicide Interactions Observed for Red Rice, CLXL-745, and CL-111 Control

Red rice treated with quizalofop plus 2,4-D resulted in an antagonistic response at 14 and 28 DAT (Table3). The observed control of red rice with 2,4-D mixed with quizalofop was 51% at 14 DAT compared with an expected control of 94% and 37% control at 28 DAT compared with an expected control of 99%. A neutral response was observed with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop for red rice control across all evaluation dates. The neutral responses observed resulted in red rice control of 93 to 98% at 28 DAT, compared with the expected control of 99%.Table 3
Red rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
94
—
2,4-D
1336
0
94
51−
0.0001
Quinclorac
420
0
94
85
0.0799
Triclopyr
282
0
94
85
0.1079
Cyhalofop-butyl
314
0
94
88
0.2710
Fenoxaprop-p-ethyl
122
0
94
86
0.1188
28 DAT
None
—
0
—
99
—
2,4-D
1336
0
99
37−
0.0001
Quinclorac
420
0
99
96
0.6405
Triclopyr
282
0
99
93
0.3031
Cyhalofop-butyl
314
0
99
98
0.8440
Fenoxaprop-p-ethyl
122
0
99
94
0.3770
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Similar results were observed for CLXL-745 hybrid rice control compared with red rice (Table4). A neutral response was observed for CLXL-745 when treated with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop at both evaluation dates. As with red rice, an antagonistic response was observed with 2,4-D mixed with quizalofop resulting in an observed control of 41%, compared with an expected control of 91% at 14 DAT. At 28 DAT, CLXL-745 treated with quizalofop plus 2,4-D was controlled 37% compared with an expected control of 98%, resulting in severe antagonism of quizalofop.Table 4
Hybrid rice CLXL-745 IR control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
41−
0.0001
Quinclorac
420
0
91
84
0.2454
Triclopyr
282
0
91
85
0.2735
Cyhalofop-butyl
314
0
91
87
0.5016
Fenoxaprop-p-ethyl
122
0
91
84
0.2454
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
37−
0.0001
Quinclorac
420
0
98
95
0.6690
Triclopyr
282
0
98
93
0.3810
Cyhalofop-butyl
314
0
98
97
0.9282
Fenoxaprop-p-ethyl
122
0
98
96
0.7527
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Control of CL-111 was similar to red rice and CLXL-745. Quizalofop was only antagonized when mixed with 2,4-D at 14 and 28 DAT, and these results are similar to those reported by others for cultivated oat (Avena sativa L.) and wild oat (Avena fatua L.) control [30, 33]. A neutral response was observed for CL-111 control with all other herbicides mixed with quizalofop at both evaluation dates (Table 5). An application of 2,4-D mixed with quizalofop resulted in an observed control of 42 and 38% at 14 and 28 DAT, respectively, compared with an expected control of 95 to 98%.Table 5
CL-111 IR rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% control
14 DAT
None
—
0
—
95
—
2,4-D
1336
0
94
42−
0.0001
Quinclorac
420
0
94
84
0.0640
Triclopyr
282
0
94
84
0.0607
Cyhalofop-butyl
314
0
94
87
0.1974
Fenoxaprop-p-ethyl
122
0
94
84
0.0640
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
38−
0.0000
Quinclorac
420
0
98
94
0.3881
Triclopyr
282
0
98
94
0.4014
Cyhalofop-butyl
314
0
98
97
0.9044
Fenoxaprop-p-ethyl
122
0
98
96
0.6831
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.


### 3.2. PVL01 ACCase-Resistant Rice Response to Herbicide Treatment

No injury was observed on PVL01 across both evaluation dates (data not shown). PVL01 rice plant height was not influenced by any herbicide combination evaluated (data not shown).The initial herbicide applications were applied following establishment of the permanent flood when PVL01 rice was in the later tillering stage, because 2,4-D should be applied at this timing to avoid rice crop injury. As previously discussed, a second quizalofop application was made in an effort to salvage rice yield; however, early season weed competition from planting through permanent flood establishment resulted in little to no PVL01 rice grain available for harvest (data not shown).


## 3.1. Herbicide Interactions Observed for Weed Control

### 3.1.1. Herbicide Interactions Observed for Barnyardgrass Control

An antagonistic response was observed for barnyardgrass treated with 2,4-D, quinclorac, triclopyr, cyhalofop, or fenoxaprop mixed with quizalofop at 14 DAT (Table2). The addition of 2,4-D in a quizalofop mixture reduced barnyardgrass control to 24% compared with control of 77 to 86% for barnyardgrass treated with all other mixtures evaluated. At 28 DAT, cyhalofop mixed with quizalofop resulted in a neutral response with 97% control of barnyardgrass. However, all other mixtures evaluated resulted in antagonism of quizalofop for barnyardgrass control. Like quizalofop, cyhalofop is an ACCase-inhibiting (Group 1) herbicide with activity on barnyardgrass, and when mixed with quizalofop, the potential for antagonism may be reduced. However, fenoxaprop is also an ACCase inhibitor (Group 1) and antagonism was observed when mixed with quizalofop with 90% observed control compared with an expected control of 99%.Table 2
Barnyardgrass control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
24−
0.0001
Quinclorac
420
42
95
77−
0.0001
Triclopyr
282
0
91
79−
0.0001
Cyhalofop-butyl
314
75
98
86−
0.0001
Fenoxaprop-p-ethyl
122
72
98
85−
0.0001
28 DAT
None
—
0
—
98
—
2,4-D
1336
36
98
5−
0.0001
Quinclorac
420
59
99
86−
0.0001
Triclopyr
282
39
98
91−
0.0046
Cyhalofop-butyl
314
85
99
97
0.1126
Fenoxaprop-p-ethyl
122
75
99
90−
0.0001
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Barnyardgrass treated with 2,4-D mixed with quizalofop resulted in an antagonistic response and did not exceed 5% control at 28 DAT, compared with an expected control of 98% (Table2). Previous research indicates a similar response of 2,4-D amine antagonism of quizalofop for control of volunteer wheat (Triticum aestivum L.) [42] and is similar to research evaluating ACCase-inhibiting herbicides mixed with dicot herbicides [15, 32].


### 3.1.2. Herbicide Interactions Observed for Red Rice, CLXL-745, and CL-111 Control

Red rice treated with quizalofop plus 2,4-D resulted in an antagonistic response at 14 and 28 DAT (Table3). The observed control of red rice with 2,4-D mixed with quizalofop was 51% at 14 DAT compared with an expected control of 94% and 37% control at 28 DAT compared with an expected control of 99%. A neutral response was observed with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop for red rice control across all evaluation dates. The neutral responses observed resulted in red rice control of 93 to 98% at 28 DAT, compared with the expected control of 99%.Table 3
Red rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
94
—
2,4-D
1336
0
94
51−
0.0001
Quinclorac
420
0
94
85
0.0799
Triclopyr
282
0
94
85
0.1079
Cyhalofop-butyl
314
0
94
88
0.2710
Fenoxaprop-p-ethyl
122
0
94
86
0.1188
28 DAT
None
—
0
—
99
—
2,4-D
1336
0
99
37−
0.0001
Quinclorac
420
0
99
96
0.6405
Triclopyr
282
0
99
93
0.3031
Cyhalofop-butyl
314
0
99
98
0.8440
Fenoxaprop-p-ethyl
122
0
99
94
0.3770
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Similar results were observed for CLXL-745 hybrid rice control compared with red rice (Table4). A neutral response was observed for CLXL-745 when treated with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop at both evaluation dates. As with red rice, an antagonistic response was observed with 2,4-D mixed with quizalofop resulting in an observed control of 41%, compared with an expected control of 91% at 14 DAT. At 28 DAT, CLXL-745 treated with quizalofop plus 2,4-D was controlled 37% compared with an expected control of 98%, resulting in severe antagonism of quizalofop.Table 4
Hybrid rice CLXL-745 IR control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
41−
0.0001
Quinclorac
420
0
91
84
0.2454
Triclopyr
282
0
91
85
0.2735
Cyhalofop-butyl
314
0
91
87
0.5016
Fenoxaprop-p-ethyl
122
0
91
84
0.2454
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
37−
0.0001
Quinclorac
420
0
98
95
0.6690
Triclopyr
282
0
98
93
0.3810
Cyhalofop-butyl
314
0
98
97
0.9282
Fenoxaprop-p-ethyl
122
0
98
96
0.7527
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Control of CL-111 was similar to red rice and CLXL-745. Quizalofop was only antagonized when mixed with 2,4-D at 14 and 28 DAT, and these results are similar to those reported by others for cultivated oat (Avena sativa L.) and wild oat (Avena fatua L.) control [30, 33]. A neutral response was observed for CL-111 control with all other herbicides mixed with quizalofop at both evaluation dates (Table 5). An application of 2,4-D mixed with quizalofop resulted in an observed control of 42 and 38% at 14 and 28 DAT, respectively, compared with an expected control of 95 to 98%.Table 5
CL-111 IR rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% control
14 DAT
None
—
0
—
95
—
2,4-D
1336
0
94
42−
0.0001
Quinclorac
420
0
94
84
0.0640
Triclopyr
282
0
94
84
0.0607
Cyhalofop-butyl
314
0
94
87
0.1974
Fenoxaprop-p-ethyl
122
0
94
84
0.0640
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
38−
0.0000
Quinclorac
420
0
98
94
0.3881
Triclopyr
282
0
98
94
0.4014
Cyhalofop-butyl
314
0
98
97
0.9044
Fenoxaprop-p-ethyl
122
0
98
96
0.6831
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.


## 3.1.1. Herbicide Interactions Observed for Barnyardgrass Control

An antagonistic response was observed for barnyardgrass treated with 2,4-D, quinclorac, triclopyr, cyhalofop, or fenoxaprop mixed with quizalofop at 14 DAT (Table2). The addition of 2,4-D in a quizalofop mixture reduced barnyardgrass control to 24% compared with control of 77 to 86% for barnyardgrass treated with all other mixtures evaluated. At 28 DAT, cyhalofop mixed with quizalofop resulted in a neutral response with 97% control of barnyardgrass. However, all other mixtures evaluated resulted in antagonism of quizalofop for barnyardgrass control. Like quizalofop, cyhalofop is an ACCase-inhibiting (Group 1) herbicide with activity on barnyardgrass, and when mixed with quizalofop, the potential for antagonism may be reduced. However, fenoxaprop is also an ACCase inhibitor (Group 1) and antagonism was observed when mixed with quizalofop with 90% observed control compared with an expected control of 99%.Table 2
Barnyardgrass control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
24−
0.0001
Quinclorac
420
42
95
77−
0.0001
Triclopyr
282
0
91
79−
0.0001
Cyhalofop-butyl
314
75
98
86−
0.0001
Fenoxaprop-p-ethyl
122
72
98
85−
0.0001
28 DAT
None
—
0
—
98
—
2,4-D
1336
36
98
5−
0.0001
Quinclorac
420
59
99
86−
0.0001
Triclopyr
282
39
98
91−
0.0046
Cyhalofop-butyl
314
85
99
97
0.1126
Fenoxaprop-p-ethyl
122
75
99
90−
0.0001
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Barnyardgrass treated with 2,4-D mixed with quizalofop resulted in an antagonistic response and did not exceed 5% control at 28 DAT, compared with an expected control of 98% (Table2). Previous research indicates a similar response of 2,4-D amine antagonism of quizalofop for control of volunteer wheat (Triticum aestivum L.) [42] and is similar to research evaluating ACCase-inhibiting herbicides mixed with dicot herbicides [15, 32].


## 3.1.2. Herbicide Interactions Observed for Red Rice, CLXL-745, and CL-111 Control

Red rice treated with quizalofop plus 2,4-D resulted in an antagonistic response at 14 and 28 DAT (Table3). The observed control of red rice with 2,4-D mixed with quizalofop was 51% at 14 DAT compared with an expected control of 94% and 37% control at 28 DAT compared with an expected control of 99%. A neutral response was observed with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop for red rice control across all evaluation dates. The neutral responses observed resulted in red rice control of 93 to 98% at 28 DAT, compared with the expected control of 99%.Table 3
Red rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
94
—
2,4-D
1336
0
94
51−
0.0001
Quinclorac
420
0
94
85
0.0799
Triclopyr
282
0
94
85
0.1079
Cyhalofop-butyl
314
0
94
88
0.2710
Fenoxaprop-p-ethyl
122
0
94
86
0.1188
28 DAT
None
—
0
—
99
—
2,4-D
1336
0
99
37−
0.0001
Quinclorac
420
0
99
96
0.6405
Triclopyr
282
0
99
93
0.3031
Cyhalofop-butyl
314
0
99
98
0.8440
Fenoxaprop-p-ethyl
122
0
99
94
0.3770
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Similar results were observed for CLXL-745 hybrid rice control compared with red rice (Table4). A neutral response was observed for CLXL-745 when treated with quizalofop plus quinclorac, triclopyr, cyhalofop, or fenoxaprop at both evaluation dates. As with red rice, an antagonistic response was observed with 2,4-D mixed with quizalofop resulting in an observed control of 41%, compared with an expected control of 91% at 14 DAT. At 28 DAT, CLXL-745 treated with quizalofop plus 2,4-D was controlled 37% compared with an expected control of 98%, resulting in severe antagonism of quizalofop.Table 4
Hybrid rice CLXL-745 IR control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% Control
14 DAT
None
—
0
—
91
—
2,4-D
1336
0
91
41−
0.0001
Quinclorac
420
0
91
84
0.2454
Triclopyr
282
0
91
85
0.2735
Cyhalofop-butyl
314
0
91
87
0.5016
Fenoxaprop-p-ethyl
122
0
91
84
0.2454
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
37−
0.0001
Quinclorac
420
0
98
95
0.6690
Triclopyr
282
0
98
93
0.3810
Cyhalofop-butyl
314
0
98
97
0.9282
Fenoxaprop-p-ethyl
122
0
98
96
0.7527
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.Control of CL-111 was similar to red rice and CLXL-745. Quizalofop was only antagonized when mixed with 2,4-D at 14 and 28 DAT, and these results are similar to those reported by others for cultivated oat (Avena sativa L.) and wild oat (Avena fatua L.) control [30, 33]. A neutral response was observed for CL-111 control with all other herbicides mixed with quizalofop at both evaluation dates (Table 5). An application of 2,4-D mixed with quizalofop resulted in an observed control of 42 and 38% at 14 and 28 DAT, respectively, compared with an expected control of 95 to 98%.Table 5
CL-111 IR rice control with quizalofop-p-ethyl mixed with different synthetic auxin or ACCase-inhibiting herbicides in 2015 and 2016 crop seasons.
Mixture herbicidea
Rate (g ai·ha−1)
Quizalofop (g ai·ha−1)
P valuec
0
120
Observed
Expected
Observedb
% control
14 DAT
None
—
0
—
95
—
2,4-D
1336
0
94
42−
0.0001
Quinclorac
420
0
94
84
0.0640
Triclopyr
282
0
94
84
0.0607
Cyhalofop-butyl
314
0
94
87
0.1974
Fenoxaprop-p-ethyl
122
0
94
84
0.0640
28 DAT
None
—
0
—
98
—
2,4-D
1336
0
98
38−
0.0000
Quinclorac
420
0
98
94
0.3881
Triclopyr
282
0
98
94
0.4014
Cyhalofop-butyl
314
0
98
97
0.9044
Fenoxaprop-p-ethyl
122
0
98
96
0.6831
aEvaluation date and respective herbicide mixture. DAT, days after treatment. bObserved means followed by a plus (+) or a minus (−) are significantly different from Blouin’s modified Colby’s expected responses at the 5% level indicating a synergistic or an antagonistic response. No (+) or (−) indicates a neutral response. cP<0.05 indicates antagonistic response; P>0.05 indicates an additive response.


## 3.2. PVL01 ACCase-Resistant Rice Response to Herbicide Treatment

No injury was observed on PVL01 across both evaluation dates (data not shown). PVL01 rice plant height was not influenced by any herbicide combination evaluated (data not shown).The initial herbicide applications were applied following establishment of the permanent flood when PVL01 rice was in the later tillering stage, because 2,4-D should be applied at this timing to avoid rice crop injury. As previously discussed, a second quizalofop application was made in an effort to salvage rice yield; however, early season weed competition from planting through permanent flood establishment resulted in little to no PVL01 rice grain available for harvest (data not shown).


## 4. Conclusion

The addition of 2,4-D, quinclorac, triclopyr, or fenoxaprop antagonized quizalofop activity for barnyardgrass control. Antagonism was observed at 14 DAT with the quizalofop plus cyhalofop mixture, however, by 28 DAT a neutral response occurred. This neutral response indicates the potential for this mixture in an ACCase-R rice production system, but a mixture with the same site of action may not be advisable in a resistant management program.Red rice, CLXL-745, and CL-111 control indicated antagonism of quizalofop when applied in a mixture with 2,4-D. However, quinclorac, triclopyr, cyhalofop, or fenoxaprop mixed with quizalofop resulted in a neutral response for red rice and CLXL-745 control across both evaluation dates. These data indicate potential herbicide mixtures that can be used in ACCase-R rice to help broaden the weed control spectrum. However, caution should be taken when mixing quizalofop with other ACCase-inhibiting herbicides, because this mixture does not meet the standards for a resistance management program. As with any resistance management program, multiple applications of herbicides with different sites of action may prevent or delay the development of herbicide-resistant weeds. In ACCase-R rice production, producers should overlay herbicides with residual activity early in the growing season followed by two postemergence applications of quizalofop in combination with herbicides that control dicot weeds [15, 43].



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*Source: 6137318-2019-06-10.xml*