Cool-season Weed Response to Flumioxazin

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Bill J. Williams and Donnie K. Miller, Northeast Research Station, Louisiana State University Agricultural Center, Saint Joseph 71366

Abstract

Cool-season weed response to flumioxazin applied in February of 2002 and 2003 was evaluated in Louisiana. Plots naturally infested with cool-season weeds were treated with 840 g ai/ha glyphosate, 530 g ai/ha paraquat, 35 g ai/ha flumioxazin, 70 g/ha flumioxazin, 140 g/ha flumioxazin, 840 g/ha glyphosate plus 35 or 70 g/ha flumioxazin, or 530 g/ha paraquat plus 35 or 70 g/ha flumioxazin. Glyphosate controlled the broadest spectrum of weeds. Flumioxazin at 140 g/ha did, however, result in better control of cutleaf eveningprimrose than glyphosate or paraquat. Henbit control from 70 or 140 g/ha flumioxazin was also higher than glyphosate and equal to paraquat. When applied alone, cool-season weed control was most consistent from flumioxazin applied at 70 g/ha or more. The best (90% or more) curly dock and swinecress control was observed when 70 g/ha flumioxazin was mixed with glyphosate. While cutleaf eveningprimrose control from paraquat combinations with flumioxazin was similar to glyphosate combinations with flumioxazin, curly dock and swinecress control was lower. This research indicates mixing 35 to 70 g/ha flumioxazin with glyphosate or paraquat improves the control of several cool-season weeds compared to flumioxazin, glyphosate, or paraquat applied alone.

Introduction

The optimal time to plant cotton, April 15 to May 15 (A. M. Stewart, personal communication), and corn, March 1 to March 20 (D. Y. Lanclos, personal communication), in Louisiana is relatively short. Delays in planting are common, when spring tillage operations are delayed by wet periods during late winter or early spring. Planting can also be delayed by the lack of moisture when fields are tilled in early- to mid-spring.

Timely planting is one of the main benefits of the stale seedbed system that led to its popularity in Louisiana (5,6). Stale seedbeds are typically prepared in the fall following harvest using tillage practices that range from extensive to no tillage (4,5). Before planting in the spring herbicides are used to kill cool-season and early spring weeds, commonly known as preplant burndown.

Herbicide selection and application timing must be carefully considered when developing a "burndown" program for removing winter vegetation prior to planting (11). Glyphosate or paraquat forms the backbone of most burndown programs (11). Both herbicides fail to control several cool-season weeds, such as cutleaf eveningprimrose, curly dock, swinecress, Carolina geranium (Geranium carolinianum L.), Italian ryegrass (Lolium multiflorum Lam.), and Pennsylvania smartweed (Polygonum pensylvanicum L.) (7,8,11). As a result, glyphosate and paraquat are commonly applied with 2,4-D, dicamba, a commercial mix of thifensulfuron plus tribenuron, or oxyfluorfen for broad spectrum weed control (11). Glyphosate or paraquat combinations with cyanazine were popular before cyanazine’s removal from the US market (3).

It’s commonly recommended that weeds be removed at least 3 weeks before planting (1). In Louisiana, weeds often germinate and/or regrow before planting during this 3 week period (10). Thus, without residual control, multiple herbicide applications maybe needed to ensure a clean seedbed at planting. With the loss of cyanazine, oxyfluorfen is the only residual herbicide recommended for pre-plant applications in most Louisiana row crops (10). Oxyfluorfen provides residual control of several winter annuals, but is weak on cutleaf eveningprimrose and curly dock (11). Herbicides that provide residual control of cool-season weeds including Carolina geranium, curly dock, cutleaf eveningprimrose, smartweed species, and swinecress are needed.

Flumioxazin has demonstrated excellent control of several warm-season broadleaf weeds (2,9,12), and is reported to have good residual activity (9). Flumioxazin can be applied 30 days or more before planting most Louisiana row crops and may be a good candidate for burndown programs requiring residual control [Valor herbicide supplemental label (EPA Reg. No. 59639-99), Valent U.S.A. Corporation, Walnut Creek, CA]. However, very little information is available on cool-season broadleaf weed response to flumioxazin (10). The objectives of this research were to determine the efficacy flumioxazin on cool-season weeds and to determine if cool-season weed control from glyphosate or paraquat is improved when mixed with flumioxazin.

Site Description and Experimental Design

Field experiments were conducted in 2001 and 2002 at the Northeast Research Station near Saint Joseph, LA to evaluate flumioxazin in cool-season weed management programs. The soil type was a Bruin silt loam (Oxyaquic Eutrudept) with pH 5.9 and 1.6% organic matter. Seedbeds were prepared in October of 2000 and 2001 by mowing existing vegetation and disking twice, after which beds were rebuilt and rolled. Corn (Zea mays L.) was previous crop both years.

The experiments were conducted in randomized complete block designs with four replications. Flumioaxazin was applied at 35, 70, and 140 g/ha to determine its potential as a burndown herbicide (flumioxazin alone treatments were applied with 1% v/v Agridex, 83% paraffin base petroleum oil, and 17% surfactant blend; Helena Chemical Company, Memphis, TN). The 140-g/ha rate of flumioxazin is a standard rate, while 35 and 70 g/ha are reduced rates that are more economical when mixed with either glyphosate or paraquat. To evaluate flumioxazin as a component of standard burndown programs it was mixed at the rate of 35 or 70 g/ha with 840 g/ha glyphosate or 530 g/ha paraquat. [Treatments containing paraquat were applied with 0.25 % v/v Induce, nonionic low foam wetter-spreader adjuvant containing 90% nonionic surfactant (alkyarylopolyoxyalkane ether and isopropanol), free fatty acids; Helena Chemical Company, Memphis, TN]. A glyphosate alone, paraquat alone, and a nontreated were added as controls. Herbicide treatments were applied on February 21st both years to plots measuring 2 by 8 m using a CO₂ backpack sprayer calibrated to deliver 140 liter/ha with TDXL 11002 nozzles (TDXL 11002, Medium Pressure TurboDrop XL Venturi Nozzles. Greenleaf Technologies, Covington, LA).

Data Collection and Analysis

Common chickweed (Stellaria media (L.) Vill), curly dock (Rumex crispus L.), cutleaf eveningprimrose (Oenothera laciniata Hill), henbit (Lamium amplexicaule L.), shepherd's-purse (Capsella bursa-pastoris (L.) Medicus), and swinecress (Coronopus didymus (L.) Sm.) heights at time of application are recorded in Table 1. Weed control was estimated 1, 2, 4, 6, and 8 weeks after treatment (WAT) using a 0 to 100% scale, where 0% equals no injury/control and 100% equals complete control. Data were tested for normality and homogenous variances. In many cases, year by treatment interactions prevented combining data across years. As a result for simplicity and to highlight differences in weed control between years data were not combined across years. Transformations were not necessary and data were subjected to ANOVA and means separated using Fishers’ Protected LSD at P = 0.05. Weed control trends at 1, 6, and 8 weeks after treatment (WAT) were similar to the trends observed at 2 and 4 WAT and are not discussed.

Table 1. Average weed heights at the time of herbicide application.

Weed species		2001	2002
Weed species		Avg. height (cm)
common chickweed	Stellaria media (L.) Vill	5	10
curly dock	Rumex crispus L.	5	10
cutleaf eveningprimrose	Oenothera laciniata Hill	10	10
henbit	Lamium amplexicaule L.	12	12
shepherd's-purse	Capsella bursa-pastoris (L.) Medicus	12	12
swinecress	Coronopus didymus (L.) Sm.	5	5

Common Chickweed Control

Common chickweed control in 2001 was generally good to excellent with all treatments (Table 2). There was no difference in common chickweed control (88 to 90%) between glyphosate and paraquat 2 WAT. Though differences between flumioxazin rates were not detected, only 70 and 140 g ai/ha resulted in common chickweed control equal to glyphosate and paraquat. Control of common chickweed with glyphosate or paraquat was not affected by the addition of flumioxazin. Though slightly higher in most cases, the level and trends of common chickweed control were essentially the same at 4 WAT as 2 WAT.

Table 2. Common chickweed, curly dock, and cutleaf eveningprimrose control 2 and 4 weeks after treatment with glyphosate, paraquat, flumioxazin, and selected combinations applied February 21 in 2001 and 2002.

Herbicide^x	Rate (g a.i./ ha)	Common chickweed				Curly dock				Cutleaf eveningprimrose
		2001		2002		2001		2002		2001		2002
		Weeks after treatment
		2	4	2	4	2	4	2	4	2	4	2	4
		Control (%)
glyphosate	840	90	95	76	94	61	93	78	79	58	81	63	73
paraquat	530	88	90	84	74	60	0	79	58	58	60	60	53
flumioxazin	35	76	68	83	70	55	63	68	0	75	71	76	66
flumioxazin	70	84	84	84	76	60	80	76	50	78	75	84	70
flumioxazin	140	86	80	91	91	60	80	79	56	85	85	90	79
glyphosate+ flumioxazin	840+ 35	90	94	81	90	85	91	83	90	89	94	80	91
glyphosate+ flumioxazin	840+ 70	91	95	93	94	91	90	91	93	88	90	90	95
paraquat+ flumioxazin	530+ 35	84	85	89	85	68	58	89	84	56	50	90	76
paraquat+ flumioxazin	530+ 70	90	88	95	85	80	58	89	87	85	84	95	91
LSD (0.05)		12	9	9	16	7	8	10	12	8	7	7	10

^x All treatments containing glyphosate were applied without additional adjuvants, all treatments containing paraquat were applied with 0.25% v/v nonionic surfactant and 1% v/v crop oil concentrate was added to flumioxazin alone treatments.

Several interesting trends in common chickweed control were observed in 2002. Glyphosate, paraquat, 35 g/ha flumioxazin, and 70 g/ha flumioxazin resulted in similar levels of common chickweed control (76 to 84%) 2 WAT. Though only statistically different from glyphosate (76%), 140 g/ha flumioxazin was the only herbicide applied alone resulting in at least 90% common chickweed control 2 WAT. Common chickweed control from glyphosate alone was only 76% 2 WAT, but when mixed with 70 g/ha flumioxazin control improved to 93%. Tank mixes of glyphosate with 35 g/ha flumioxazin resulted in common chickweed control similar to glyphosate alone. Similarly, common chickweed control from paraquat alone was increased from 84 to 95% when tank mixed with 70 g/ha flumioxazin. As with glyphosate, tank mixing paraquat with 35 g/ha flumioxazin resulted in common chickweed control similar to paraquat alone. By 4 WAT, only glyphosate alone or tank mixed with flumioxazin and 140 g/ha flumioxazin controlled common chickweed at least 90%. Paraquat and flumioxazin at less than 140 g/ha resulted in less than 80% common chickweed control. Though not statistically significant, there was a trend for increased (from 74% to 85%) common chickweed control 4 WAT when paraquat was applied with 35 or 70 g/ha flumioxazin.

Curly Dock Control

Curly dock control at 2 WAT was poor (less than 70%) when glyphosate, paraquat, or flumioxazin was applied alone (Table 2). Curly dock control was increased from 61% when glyphosate was applied alone to 85 or 91% when glyphosate was applied with 35 or 70 g/ha flumioxazin, respectively. Tank mixing flumioxazin with paraquat also resulted in improved curly dock control compared to paraquat alone. However, only the 70-g/ha rate of flumioxazin resulted in greater than 80% curly dock control when tank mixed with paraquat. At 4 WAT, all glyphosate treatments controlled curly dock 90 to 93%. Paraquat did not control curly dock at 4 WAT when applied alone. Flumioxazin at 35 g/ha resulted in 63% curly dock control, while both the 70- and 140-g/ha rates resulted in 80% control.

In 2002, curly dock control 2 WAT with glyphosate, paraquat, and flumioxazin alone was higher than that observed in 2001. Still, curly dock control was less than 80% from each herbicide when applied alone. Curly dock control with glyphosate was improved (from 78 to 91%) when applied with 70 g/ha flumioxazin. Tank mixing paraquat with either 35 or 70 g/ha flumioxazin increased curly dock control from 79% when paraquat was applied alone to 89%. At 4 WAT, glyphosate alone controlled curly dock 79%, while all other herbicides applied alone resulted in less than 60% control. Curly dock control from glyphosate alone was increased to 93% when tank mixed with 70 g/ha flumioxazin. There was no difference in curly dock control between glyphosate tank mixed with 35 or 70 g/ha flumioxazin. Similarly, curly dock control from paraquat alone was increased from 58 to 84 and 87% when applied with 35 and 70 g/ha flumioxazin, respectively.

Cutleaf Eveningprimrose Control

Cutleaf eveningprimose control was best when glyphosate or paraquat was applied with 70 g/ha flumioxazin (Table 2). In 2001, 140 g/ha flumioxazin controlled cutleaf eveningprimose 85% 2 WAT and was the only treatment resulting in at least 80% cutleaf eveningprimose control when applied alone. Glyphosate and paraquat both controlled cutleaf eveningprimose 58% 2 WAT, while 35 and 70 g/ha flumioxazin controlled cutleaf eveningprimose 75 and 78%, respectively. Cutleaf eveningprimose control by glyphosate was increased to 85 or 91% when applied with 35 or 70 g/ha flumioxazin, respectively. Unlike glyphosate, 70 g/ha flumioxazin was required in tank mixes with paraquat to increase cutleaf eveningprimose control (85%). By 4 WAT, there was little change in cutleaf eveningprimose control from flumioxazin, paraquat, or paraquat plus flumioxazin combinations. The best cutleaf eveningprimose control (90 to 94%) was observed with glyphosate combinations with flumioxazin, which was better than glyphosate alone (81%).

In 2002, cutleaf eveningprimose control 2 WAT with flumioxazin increased when the rate increased from 35 (76%) to 70 (84%) or 140 (90%) g/ha. As in 2001, cutleaf eveningprimose control from glyphosate or paraquat applied alone was poor (60 to 63%). Compared to glyphosate alone, cutleaf eveningprimose control was improved to 80 or 90% when glyphosate was tank mixed with 35 or 70 g/ha flumioxazin, respectively. Tank mixing paraquat with 35 or 70 g/ha flumioxazin increased cutleaf eveningprimose control to 90 or 95%, respectively. At 4 WAT, glyphosate plus 35 or 70 g/ha flumioxazin and paraquat plus 70 g/ha flumioxazin were the only treatments resulting in 90% or better cutleaf eveningprimose control. All other treatments resulted in less than 80% control.

Henbit Control

Henbit control was generally good to excellent from all treatments except glyphosate alone in 2001 (Table 3). Henbit control by glyphosate increased from 78% at 2 WAT and 89% at 4 WAT to 90% or more when glyphosate was mixed with flumioxazin. In 2002, henbit control from glyphosate was similar to that observed in 2001 except that, when tank mixed, 70 g/ha flumioxazin was required to increase control to at least 80% 2 WAT and 96% 4 WAT. Flumioxazin rate had little affect on henbit control 2 WAT (84 to 89%) or 4 WAT (90 to 95%). Henbit control from paraquat was similar to that observed with flumioxazin.

Table 3. Henbit, shepherd’s-purse and swinecress control 2 and 4 weeks after treatment with glyphosate, paraquat, flumioxazin, and selected combinations applied February 21 in 2001 and 2002.

Herbicide^x	Rate (g ai/ha)	Henbit				Shepherd's purse				Swinecress
		2001		2002		2001		2002		2001		2002
		Weeks after treatment
		2	4	2	4	2	4	2	4	2	4	2	4
		Control (%)
glyphosate	840	78	89	73	89	90	95	71	96	70	83	85	86
paraquat	530	94	97	83	88	94	83	84	94	70	60	86	79
flumioxazin	35	86	97	84	90	93	85	84	71	63	60	83	81
flumioxazin	70	89	97	85	93	93	85	83	71	61	60	83	85
flumioxazin	140	90	99	89	95	93	95	84	94	66	73	86	89
glyphosate+ flumioxazin	840+ 35	93	99	78	83	94	99	80	95	88	88	79	94
glyphosate+ flumioxazin	840+ 70	90	97	80	96	95	97	86	96	86	92	91	96
paraquat + flumioxazin	530+ 35	91	97	94	93	95	97	95	96	55	60	83	90
paraquat + flumioxazin	530+ 70	95	97	95	95	95	97	94	96	66	60	88	96
LSD (0.05)		7	5	6	4	3	9	11	3	9	4	12	10

Shepherd’s-purse Control

Shepherd’s-purse control was excellent (90 to 95%) at 2 WAT in 2001 with all treatments (Table 3). However at 4 WAT, only glyphosate, 140 g/ha flumioxazin and glyphosate or paraquat tank mixed with flumioxazin (35 or 70 g/ha) controlled shepherd’s-purse at least 95%. Paraquat and 35 or 70 g/ha flumioxazin resulted in 83 to 85% control. In 2002, shepherd’s-purse control 2 WAT was generally lower than that observed in 2001 except for paraquat plus 35 or 70 g/ha flumioxazin. However, shepherd’s-purse control was at least 95% following glyphosate, paraquat, 140 g/ha flumioxazin, and glyphosate or paraquat plus 35 or 70 g/ha flumioxazin. Flumioxazin at 35 or 70 g/ha resulted in less than 80% shepherd’s-purse control.

Swinecress Control

Swinecress control 2 WAT in 2001 was 70% or less following all herbicides when applied alone (Table 3). Tank mixing glyphosate with 35 or 70 g/ha flumioxazin increased swinecress control from 70% to at least 86%. Tank mixing paraquat with flumioxazin did not improve swinecress control compared to paraquat alone. At 4 WAT swinecress control from glyphosate alone had improved to 83%. Tank mixing glyphosate with 35 or 70 g/ha flumioxazin increased swinecress control to 88 or 92%, respectively. Paraquat alone, flumioxazin (all rates) alone, and paraquat plus flumioxazin (all rates) resulted in less than 73% control.

Generally, swinecress control was better in 2002 than in 2001. At 2 WAT, swinecress control ranged between 83 and 86% when herbicides were applied alone. Tank mixing flumioxazin with either glyphosate or paraquat did not increase swinecress control over that observed with the herbicides applied alone. Still, glyphosate plus 70 g/ha flumioxazin resulted in the best (91%) swinecress control and was substantially better than glyphosate plus 35 g/ha flumioxazin (79%). Swinecress control at 4WAT was 86, 79, 81, 85, and 89% with glyphosate, paraquat, 35 g/ha flumioxazin, 70 g/ha flumioxazin, and 140 g/ha flumioxazin, respectively. Swinecress control was increased from 86% with glyphosate alone to 96% when glyphosate was mixed with 70 g/ha flumioxazin. There was no difference in swinecress control when glyphosate was tank mixed with either 35 or 70 g/ha flumioxazin. Tank mixing paraquat with 35 and 70 g/ha flumioxazin increased swinecress control from 79 to 90 and 96%, respectively.

Implications for Burndown Weed Management

Cool-season weed control did differ between years, but overall trends were the same. It is suspected that weed size and density influenced the level of control. Additional research is needed to determine the effect of weed size on flumioxazin efficacy and to refine rates. Overall, glyphosate resulted in better and broader spectrum weed control when applied alone than did paraquat or flumioxazin. When applied alone, weed control was most consistent when flumioxazin was applied at 140 g/ha. Weed control was often better at 2 WAT when glyphosate was applied with 70 g/ha flumioxazin than with 35 g/ha flumioxazin. Apparently, this difference was primarily due to speed in activity because at 4 WAT there were few differences between glyphosate applied with 35 or 70 g/ha flumioxazin. Unlike glyphosate, control of several weeds at both 2 and 4 WAT was generally better when paraquat was applied with 70 g/ha flumioxazin compared to 35 g/ha.

As reported by Williams et al in 2002 (11) glyphosate and paraquat failed to adequately control curly dock, cutleaf eveningprimrose, henbit, and swinecress. Flumioxazin at 140 g/ha did show promise as a burndown herbicide on henbit, chickweed, and shepherd’s-purse but was not as broad spectrum as glyphosate or paraquat, especially on grasses (data not shown). Combining glyphosate and paraquat with flumioxazin did improve curly dock, cutleaf eveningprimrose, henbit, and swinecress control. These data suggest that flumioxazin at 35 to 70 g/ha, with 70 g/ha being more consistent, applied with glyphosate improves cool-season weed control compared to glyphosate alone. In burndown programs based on paraquat, at least 70 g/ha flumioxazin is needed to improve the control of cool-season weeds.

Acknowledgments

This research was partially supported from funds provided by the Louisiana Soybean and Feedgrain Research and Promotion board. Drs. Sandy Stewart and David Lanclos, assistant specialists with the LSU Agricultural Center, provided information regarding planting dates. Dr. James Geaghan, Professor of Experimental Statistics with the LSU Agriculture Center, assisted with data analysis.

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