Fluroxypyr Compatibility with Fenoxaprop for Smooth Crabgrass and White Clover Control in Tall Fescue

Patrick E. McCullough, Deptember of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223-1797, James T. Brosnan and Gregory K. Breeden, University of Tennessee, Knoxville, TN 37996-4561

Corresponding author: Patrick E. McCullough. pmccull@uga.edu

Abstract

Fenoxaprop effectively controls crabgrass (Digitaria spp.) in tall fescue (Festuca arundinacea Schreb.) turf. Antagonism with growth-regulating herbicides reduces potential to apply fenaxoprop in combination with many products for broadleaf weed control. Fluroxypyr is a pyridinoxy acid, broadleaf herbicide which may have potential for use in mixtures with fenoxaprop. Field experiments investigated fenoxaprop efficacy for smooth crabgrass (Digitaria ischaemum) control when applied alone and in combination with either fluroxypyr or a pre-packaged mixture of 2,4-D, dicamba, and mecoprop (MCPP) in tall fescue. Smooth crabgrass control from mixtures of fenoxaprop and fluroxypyr was similar to fenoxaprop alone. Smooth crabgrass control with mixtures of fenoxaprop with 2,4-D, plus dicamba, plus MCPP was nearly 50% less than fenoxaprop alone. White clover was completely controlled from mixtures of fenoxaprop and fluroxypyr which was similar to fenoxaprop applied with 2,4-D plus dicamba plus MCPP. Tall fescue injury was not detected on any rating date. Results suggest tank mixtures of fenoxaprop and fluroxypyr could provide effective control of smooth crabgrass and white clover in tall fescue.

Introduction

Tall fescue (Festuca arundinacea Schreb.) is widely used for residential lawns, golf courses, sports fields, and non-residential turf in the United States transition and cool, humid regions. Smooth crabgrass (Digitaria ischaemum) is a problematic summer annual weed that reduces tall fescue functionality and aesthetics during the spring and summer months (18). Smooth crabgrass has a light green color, coarse leaf texture, and produces unsightly seedheads that reduce turfgrass quality (14,18). More importantly, smooth crabgrass is an aggressive plant that competes with tall fescue for light, water, and nutrients (14).

Few herbicides are registered for postemergence control of smooth crabgrass in tall fescue. These herbicides include quinclorac, fluazifop, and MSMA. The efficacy of these herbicides for control of mature, multi-tiller plants has been reported to vary considerably (7,8,11,14,15,26). Furthermore, single applications of these materials often result in erratic control.

Fenoxaprop-P-ethyl (delineated fenoxaprop) disrupts fatty acid synthesis in sensitive plants by inhibiting the acetyl-CoA carboxylase enzyme (21) and has been reported to be more efficacious than quinclorac and MSMA for controlling multi-tillered crabgrass (1,3,13,16). Dernoeden and Fry (9) noted fenoxaprop effectively controlled multi-tillered smooth crabgrass with less Kentucky bluegrass (Poa pratensis L.) injury than MSMA. Despite its efficacy against multi-tillered crabgrass, fenoxaprop cannot be tank-mixed with many broadleaf herbicides safe for use in tall fescue due to potential herbicide antagonism (1,3,10,17).

Antagonistic responses to aryloxyphenoxypropionic herbicides, such as fenoxaprop, when applied in mixtures with auxin-type broadleaf weed herbicides have been reported in various cropping systems. Matthiasen (17) noted that fenoxaprop rate had to be increased from 60 to 130% when applied in mixtures with mecoprop to achieve the level of wild oat (Avena fatua L.) control observed with fenoxaprop alone. Blackshaw et al. (6) noted 2,4-D amine was highly antagonistic to clethodim and quizalofop applications to volunteer wheat (Triticum aestivum L.). Antagonism has been noted when 2,4-D was tank-mixed with diclofop-methyl and flamprop-methyl for wild oat control (23,24,25). Olson and Nalewaja (19) also reported antagonism following applications of auxin-type broadleaf herbicides tank-mixed with diclofop. While similar responses have also been reported by Shimabukuro et al. (22) Fitzsimmons et al. (12), and Barnwell and Cobb (4,5) with other aryloxyphenoxypropionic and auxin-type herbicides, only a single study has reported this response in fine turf (10).

Antagonism limits potential for fenoxaprop to be applied as part of a tank mixture to control various broadleaf weeds and multi-tiller smooth crabgrass in a single application. Taylor et al. (23) noted a broadleaf herbicide, fluroxypyr (Spotlight), did not antagonize efficacy of aryloxyphenoxypropionic herbicides, such as fenoxaprop. Fluroxypyr is a pyridinoxy acid herbicide, recently registered for use in turf, with activity on annual and perennial broadleaf weeds (2,20,21).

Although most broadleaf weed herbicides have been shown to antagonize fenoxaprop efficacy, fluroxypyr could be compatible in tank mixtures for controlling broadleaf weeds and multi-tiller smooth crabgrass in a single application. To test this hypothesis, field experiments were conducted to investigate smooth crabgrass control, white clover control, and tall fescue tolerance to tank mixtures of fenaxoprop and fluroxypyr.

Field Experiments Investigating Fenoxaprop Efficacy

Experiments were conducted on mature stands of tall fescue from June to August 2009 at the University of Georgia in Griffin, GA, and the University of Tennessee in Knoxville, TN. Soil in Georgia was a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) with 4.6% organic matter and a pH of 5.6. Soil in Tennessee was Sequatchie loam soil (fine, loamy, siliceous, semiactive, thermic humic Hapludult), measuring 6.2 in soil pH and 2.1% in organic matter content. The tall fescue cultivar at each location was unknown. Irrigation at each location was applied to prevent wilt and both sites were mowed weekly at 6.4-cm height with clippings returned. Smooth crabgrass and white clover ground cover averaged 21% and 23%, respectively, on the day of initial treatments in Georgia, and 50% and 15%, respectively, in Tennessee.

Experimental design was a randomized complete block with four replications. Fenoxaprop (Acclaim Extra 0.57SC, Bayer Crop Science, Montvale, NJ) was applied at 25, 50, 100, 200, or 400 g ai/ha alone, in combination with fluroxypyr (Spotlight 1.5L, Dow AgroSciences, Indianapolis, IN) at 0.53 kg ai/ha, and in combination with a pre-packaged mixture of 2,4-D + dicamba + MCPP (hereafter delineated as three-way mixture). This three-way mixture was a pre-packaged formulated product (Trimec Classic 2.72 SL, PBI Gordon Corp., Kansas City, MO) containing 237, 64, and 25 g/liter of 2,4-D, dicamba, and MCPP, respectively; it was applied in combination with each rate of fenoxaprop at 4.7 liters/ha or 1.1, 0.29, and 0.12 kg ai/ha, respectively. An untreated control was included in each block.

Treatments were applied on 10 June 2009 in Georgia and 3 June 2009 in Tennessee. In Georgia, treatments were applied to 1 × 4.5-m plots by making two passes in opposite directions with a single nozzle CO₂-pressured sprayer calibrated to deliver a total 375 liters/ha. In Tennessee, treatments were applied to 1.5 × 3-m with a CO₂-pressured sprayer containing four flat-fan nozzles calibrated to deliver 280 liters/ha. Sprayers in Georgia and Tennessee had 9504E and 8002 flat-fan nozzles, respectively (Tee Jet, Spraying Systems Co., Roswell, GA).

Weed control and turf injury were assessed visually, as Yelverton et al. (27) reported that visual ratings of herbicide responses in turf were highly correlated with those measured using the line intersect method or digital image analysis. Tall fescue injury was visually evaluated 2, 4, and 8 weeks after treatment (WAT) on a percent scale where 0 equaled no injury and 100 equaled dead turf. Smooth crabgrass control was also assessed visually on a percent scale, where 0 equaled no control and 100 equaled complete control (relative to the untreated control), at 2, 4, and 8 WAT. Data were subjected to analysis of variance at the 0.05 probability level with fenoxaprop, broadleaf herbicide, and location as variables. Treatment by location interactions were not detected, and thus, results were pooled over locations. Fenoxaprop rates were subjected to regression analysis to quantify smooth crabgrass control in the presence of each broadleaf herbicide.

Smooth Crabgrass & White Clover Control, and Tall Fescue Tolerance to Tank Mixtures of Fenaxoprop & Fluroxypyr

Smooth crabgrass control. A fenoxaprop by broadleaf herbicide interaction was detected for smooth crabgrass control. By 2 WAT, smooth crabgrass control from fenoxaprop ranged 45 to 100%, 11 to 93%, and 65 to 100% when applied alone, with the three-way mixture, and fluroxypyr, respectively (Fig. 1). By 4 WAT, fenoxaprop controlled smooth crabgrass 27 to 98%, 0 to 86%, and 52 to 97% when applied alone, with the three-way mixture, and fluroxypyr, respectively. By 8 WAT, fenoxaprop controlled smooth crabgrass 10 to 95%, 0 to 70%, and 45 to 96%, when applied alone, with the three-way mixture, and fluroxypyr, respectively.

Fig. 1. Smooth crabgrass control following fenoxaprop treatments with or without broadleaf herbicides in field experiments, 2009, Griffin, GA, and Knoxville, TN.

By 2 WAT, approximately 85% more fenoxaprop was required to provide 80% smooth crabgrass control (LD₈₀) when applied with the three-way mixture compared to applications alone or in combination with fluroxypyr. LD₈₀ values measured 90, 167, and 81 g ai/ha for fenoxaprop applied alone, with the three-way mixture, and fluroxypyr, respectively (Table 1). By 4 WAT, twice the amount of fenoxaprop was required to provide 80% smooth crabgrass control when applied with the three-way mixture, as LD₈₀ values were 100, 208, and 100 g ai/ha for fenoxaprop alone, with the three-way mixture, and fluroxypyr, respectively. By 8WAT, four times the amount of fenoxaprop was required to control smooth crabgrass by 80% when applied with three-way mixture compared to treatments alone or in combination with fluroxypyr. LD₈₀ values were 114, > 400, and 126 g ai/ha for fenoxaprop applied alone, with the three-way mixture, and fluroxypyr, respectively.

Table 1. Fenoxaprop rate required to control smooth crabgrass by 80% when applied alone or with broadleaf herbicides in Griffin, GA, and Knoxville, TN.

Broadleaf herbicide tank-mixed with fenoxaprop^b	2 WAT^a	4 WAT	8 WAT
Broadleaf herbicide tank-mixed with fenoxaprop^b	Fenoxaprop Rate LD₈₀^c (g ai/ha)
None	90	100	114
2,4-D + dicamba + MCPP (Three-Way Mix)	167	208	>400
Fluroxypyr	81	100	126
	Equations^d
None	r² = 0.70, y = 43 + 0.5x − 0.001x²; SE = 13	r² = 0.70, y = 28 + 0.62x − 0.001x²; SE = 17	r² = 0.68, y = 13 + 0.7x − 0.001x²; SE = 20
2,4-D + dicamba + MCPP	r² = 0.90, y = −9 + 0.7x − 0.001x²; SE = 12	r² = 0.80, y = −16 + 0.67x − 0.001x²; SE = 18	r² = 0.57, y = −13 + 0.42x − 0.001x²; SE = 25
Fluroxypyr	r² = 0.37, y = 59 + 0.34x − 0.001x²; SE = 19	r² = 0.34, y = 50 + 0.4x − 0.001x²; SE = 23	r² = 0.36, y = 45 + 0.4x − .001x²; SE = 24

^a LD₈₀ is the fenoxaprop rate required to control smooth crabgrass by 80%.

^c Fluroxypyr (Spotlight 1.5L, Dow AgroSciences, Indianapolis, IN) was applied at 0.53 kg ai/ha, and 2,4-D + dicamba + MCPP. The three-way mixture was a pre-packaged formulated product (Trimec Classic 2.72 SL, PBI Gordon Corp., Kansas City, MO) containing 237, 64, and 25 g/liters of 2,4-D, dicamba, and MCPP, respectively, and was applied at 4.7 liters/ha or 1.1, 0.29, and 0.12 kg ai/ha, respectively.

^d Equations calculate required rate of fenoxaprop (x) to control smooth crabgrass (y) on a percent scale when applied alone or in mixtures with fluroxypyr or the three-way mixture.

Fenoxaprop applications alone exhibited substantial activity against smooth crabgrass which is similar to previous reports (9,11). Tank mixtures of fenoxaprop with 2,4-D, dicamba, and MCPP exhibited an atagonistic response similar to that reported by Dernoeden and Fidanza (10). Zhang et al. (28) also noted that carfentrezone and triclopyr antagonized the efficacy of fenoxaprop against barnyardgrass [Echinochloa crus-galli (L.) Beauv ].

White clover control. A fenoxaprop rate by broadleaf weed herbicide interaction was not detected in white clover control data, thus results were pooled over fenoxaprop rates. The three-way mixture and fluroxypyr each resulted in 80, 100, and 100% white clover control by 2, 4, and 8 WAT, respectively (Table 2). These results suggest that when applied as a tank mixture, fenoxaprop may not reduce the efficacy of fluroxypyr or the three-way mixture for white clover control.

Tall fescue injury. Tall fescue injury was not detected from treatments on any rating date (data not shown).

Table 2. White clover control with broadleaf herbicides, pooled over five fenoxaprop rates, in field experiments in Griffin, GA, and Knoxville, TN.

Broadleaf herbicide^y	WAT^x
	2	4	8
	White clover control (%)
None	0	0	0
2,4-D + dicamba + MCPP (Three-Way Mix)	79	100	100
fluroxypyr	81	100	100
LSD0.05	4	1	5

^x WAT = week after treatment. Application dates were 3 June and 10 June 2009 in Tennessee and Georgia, respectively.

^y Fluroxypyr (Spotlight 1.5L, Dow AgroSciences, Indianapolis, IN) was applied at 0.53 kg ai/ha. The three-way mixture was a pre-packaged formulated product (Trimec Classic 2.72 SL, PBI Gordon Corp., Kansas City, MO) containing 237, 64, and 25 g/liters of 2,4-D, dicamba, and MCPP, respectively, and was applied at 4.7 liters/ha or 1.1, 0.29, and 0.12 kg ai/ha, respectively. Results are pooled over five fenoxaprop (Acclaim Extra 0.57SC, Bayer Crop Science, Montvale, NJ) rates including 25, 50, 100, 200, or 400 g ai/ha.

Conclusion

Herbicides for controlling multi-tillered smooth crabgrass are limited in tall fescue. Additionally, tank mixtures designed to control smooth crabgrass and broadleaf weeds, such as white clover, in a single application often result in some degree of herbicide antagonism. Results illustrate that fluroxypyr does not antagonize the efficacy of fenoxaprop when the two active ingredients are combined as a tank mixture. Tank mixtures of fluroxypyr and fenoxaprop are a new, effective option for controlling multi-tillered smooth crabgrass and white clover in a single application in tall fescue. This herbicide combination may also be applicable for crabgrass and white clover control in zoysiagrass but further research is required to investigate turf tolerance following treatments.

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