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© 2006 Plant Management Network.
Accepted for publication 18 March 2006. Published 2 May 2006.

Triclopyr Safens the Use of Fluazifop and Fenoxaprop on Zoysiagrass While Maintaining Bermudagrass Suppression

J. Scott McElroy, Assistant Professor, and Greg K. Breeden, Research Associate, Department of Plant Sciences, University of Tennessee, Knoxville, TN 37996

Corresponding author: J. Scott McElroy. mcelroy@utk.edu

McElroy, J. S., and Breeden, G. K. 2006. Triclopyr safens the use of fluazifop and fenoxaprop on zoysiagrass while maintaining bermudagrass suppression. Online. Applied Turfgrass Science doi:10.1094/ATS-2006-0502-01-RS.

Abstract

Three sequential applications of fenoxaprop (1.0 lb/acre), fluazifop (0.09 lb/acre), fluroxypyr (0.23 lb/acre), and triclopyr (0.12 lb/acre) applied on 28-day intervals were evaluated alone and in various combinations for bermudagrass suppression in zoysiagrass turf. Triclopyr safened the use of fenoxaprop and fluazifop on zoysiagrass turf without decreasing bermudagrass suppression compared to fenoxaprop or fluazifop alone. The addition of triclopyr improved fenoxaprop suppression of bermudagrass over fenoxaprop alone. While similar in chemistry to triclopyr, fluroxypyr was less phytotoxic to bermudagrass and did not provide beneficial safening of fenoxaprop or fluazifop. Based on this research, triclopyr should be utilized in combination with fluazifop or fenoxaprop to decrease injury from these herbicides and increase bermudagrass suppression when using fenoxaprop.

Introduction

Bermudagrass (Cynodon spp.) is one of the most difficult species to control in turfgrass systems. Its extensive rhizome and stolon system, tolerance to environmental and management stresses, and aggressive nature are reasons why it is an excellent desirable turfgrass, as well as why it is difficult to eradicate. It is problematic in warm-season grasses, such as zoysiagrass (Zoysia spp.), centipedegrass (Eremochloa ophiuroides), and St. Augustinegrass (Stenotaphrum secumdatum), in addition to cool-season grasses, tall fescue (Festuca arudinacea), Kentucky bluegrass (Poa pratensis), and bentgrass (Agrostis spp.). Bermudagrass is especially problematic in zoysiagrass turf because they are both C-4 warm-season grasses with similar herbicide tolerances.

Fenoxaprop and fluazifop have been the primary herbicides evaluated for bermudagrass control in zoysiagrass turf. Four sequential monthly applications of fenoxaprop suppressed bermudagrass 97 to 99%, but yellowing of Korean zoysiagrass (Zoysia japonica Steud.) occurred (4). Others have reported that five sequential applications of fenoxaprop at 0.56 lb/acre suppressed bermudagrass up to 80% (6). Fluazifop applications have been reported to injure and reduce stand quality of ‘Emerald’ zoysiagrass (Zoysia japonica Steud. × Zoysia tenuifolia Willd ex. Thiele); however, the turf eventually recovered (5).

Triclopyr has been reported to significantly injure both common bermudagrass and ‘hybrid’ bermudagrass [Cynodon dacylon (L.) Pers. × C. transvaalensis Burtt-Davy] when applied at twice the labeled rate (4.3 lb/acre) (1). Multiple applications of triclopyr (0.45 lb/acre) or triclopyr + clopyralid (0.45 + 0.56 lb/acre) have been reported to injure bermudagrass up to 30%, and with >40% injury occurring to seashore paspalum (Paspalum vaginatum Swarz.) (7). Injury is so significant that attempts have been made to utilize triclopyr as a selective bermudagrass control herbicide. Sequential applications of fenoxaprop (0.47 lb/acre) or fenoxaprop + triclopyr (0.47 +1.25 lb/acre) have been reported to decrease bermudagrass ground coverage similarly (2). Limited information is available regarding triclopyr tank mixtures with fluazifop or fenoxaprop on zoysiagrass. Research was conducted to investigate the use of triclopyr as a selective bermudagrass suppression agent when utilized with fenoxaprop and fluazifop in zoysiagrass turf. Fluroxypyr was also evaluated in this research because of its similar chemistry to triclopyr and its recent registration for turfgrass use.

Evaluating Effects of Triclopyr on Herbicide Injury and Bermudagrass Suppression

Research was conducted in 2004 and 2005 at the Little Course at Conner Lane (henceforth referred to as Little Course), Franklin, TN, and in 2005 at the West Tennessee Research and Education Center (WTREC), Jackson, TN. In total, three zoysiagrass-tolerance experiments and two bermudagrass suppression experiments were conducted. Zoysiagrass tolerance studies at the Little Course were conducted on a ‘Meyer’ (Zoysia japonica Steud) and ‘Cavalier’ [Zoysia matrella (L.) Merr.] zoysiagrass fairways in 2004 and 2005, respectively. Fairways were mowed at a 0.5-inch mowing height and managed with 1.5 to 2.0 lb N per 1000 ft² per year. Golf course fairway area soils at the Little Course were a Maury silt loam fine, mixed, semiactive, mesic Typic Paleudalfs with pH 6.3 and 0.9% organic matter. Golf course rough area soils at the Little Course were pH 5.8 and 0.8% organic matter. The zoysiagrass tolerance study at WTREC was conducted on ‘Meyer’ zoysiagrass mowed at a ~2-inch height and the turf had not been fertilized or irrigated for the three years prior to research initiation. Soils at WTREC were a Loring silt loam fine-silty, mixed, active, thermic Oxyaquic Fragiudalfs with pH 6.4 and 1.1% organic matter. Common bermudagrass suppression was evaluated in 2004 and 2005, at the Little Course and WTREC, respectively. At both locations, common bermudagrass was mowed at a 3-inch mowing height, with no fertility or irrigation for the three years prior to research initiation.

Herbicides evaluated were fenoxaprop, fluazifop, fluroxypyr, and triclopyr applied alone and in combination treatments at the rates listed in Table 1. Combination treatments included fenoxaprop + fluroxypyr, fenoxaprop + triclopyr, fluazifop + fluroxypyr, and fluazifop + triclopyr. Treatments were initiated on 14 June 2004 and 6 June 2005 at the Little Course, and on 22 May 2005 at WTREC. Three applications were made of each herbicide treatment on 28-day intervals. Herbicide applications were made with a CO₂-pressurized spray system calibrated to deliver 30 gal/acre. The spray boom utilized four flat fan nozzles (Model 8002XR, Spraying Systems Co., Wheaton, IL) with 10-inch spacing. Plots were not mowed the day before or the day after application. Experiments were arranged in a randomized complete block design with four replicates. Experimental units were 50 ft² in size.

Table 1. Active ingredient and product names, along with equivalent active ingredient and product rates utilized in the studies.

 ^x Due to differences in herbicide chemistry, fluroxypyr and triclopyr active ingredient rates are presented in acid equivalents per acre, while fenoxaprop and fluazifop are presented as active ingredient per acre. Abbreviations: ae = acid equivalents; ai = active ingredient.

Visual ratings of zoysiagrass injury and bermudagrass suppression were made two weeks after the third herbicide application. Zoysiagrass injury was visually rated for both experiments using a 0-to-100 scale. For zoysiagrass injury, 0% equals no visual injury and 100% equals complete plant death. To facilitate discussion, > 20% injury was deemed as unacceptable visual injury. Mild phytotoxic bronzing of the leaf tissue is representative of a 20% injury rating. Bermudagrass suppression was rated on a similar scale of 0 to 100, where 0% equals no visual phytotoxicity and 100% equals complete plant browning of the above-ground vegetation. Note that suppression is different from control ratings that would evaluate regrowth of below-ground structures over time. Data were subjected to analysis of variance (P = 0.05). Non-significant treatment by experiment interaction allowed for pooling of data over experiments. Means were separated using Fisher’s Protected LSD (P = 0.05).

Significant herbicide treatment by experiment interactions prevented the pooling of zoysiagrass injury data over experimental run; therefore the data are presented separately for all three experiments (Table 2). While injury differences were observed between locations, some similar data trends were observed. Fluazifop + triclopyr injured zoysiagrass less in each experiment than fluazifop alone or fluazifop + fluroxypyr (Fig. 1). Fluazifop injured zoysiagrass 9 to 38% in each experiment; however no injury from fluazifop + triclopyr was observed in any experiment. Fluazifop + fluroxypyr injury to zoysiagrass was similar to fluazifop alone in each experiment.

Table 2. Response of 'Meyer' and 'Cavalier' zoysiagrass cultivars two weeks after three consecutive herbicide treatments.

 ^x Means within columns followed by the same letter are statistically equivalent according to least significant difference means separation (P = 0.05).

Fenoxaprop tank-mixtures with triclopyr or fluroxypyr yielded results similar to fluazifop treatments (Table 2; Fig. 1). Fenoxaprop and fenoxaprop + fluroxypyr injured zoysiagrass greater than fenoxaprop + triclopyr at the Little Course in 2004 and WTREC in 2005. While fenoxaprop and fenoxaprop + fluroxypyr injured zoysiagrass 18 and 16%, respectively, 5% injury from fenoxaprop + triclopyr was statistically equivalent at the Little Course in 2005. While these data indicate triclopyr safens the use of fenoxaprop on zoysiagrass, others have reported triclopyr + fenoxaprop applied at similar rates injured tall fescue and perennial ryegrass more than either herbicide applied alone (2). Across experiments, triclopyr and fluroxypyr alone injured zoysiagrass <10%.

While triclopyr reduced fluazifop-induced zoysiagrass injury, fluazifop, fluazifop + fluroxypyr, and fluazifop + triclopyr suppressed bermudagrass to similar extents, 74, 76, and 69%, respectively (Table 3). Fenoxaprop + triclopyr suppressed bermudagrass (67%) more than fenoxaprop or fenoxaprop + fluroxypyr (39 and 35%, respectively). Triclopyr alone suppressed bermudagrass (47%) greater than fluroxypyr alone. Multiple applications of triclopyr have also been utilized to control kikuyugrass in perennial ryegrass and Kentucky bluegrass (3).

Table 3. Common bermudagrass suppression two weeks after three consecutive herbicide treatments.

 ^x Means within columns followed by the same letter are statistically equivalent according to least significant difference means separation (P = 0.05).

Conclusions

While triclopyr is a pyridinyloxyacetic acid herbicide primarily active on broadleaf (dicotyledenous) weeds species, it is a beneficial herbicide for suppression of bermudagrass in zoysiagrass turf for two primary reasons. First, triclopyr safens the use of both fenoxaprop and fluazifop on zoysiagrass turf. Injury or quality reduction of zoysiagrass turf from multiple fenoxaprop or fluazifop applications has been previously reported (4,5), decreasing the potential use of these herbicides due to intolerance of turfgrass managers to potential phytotoxicity. However, with the addition of triclopyr, injury from fenoxaprop or fluazifop disappeared or decreased to tolerable levels. Second, multiple applications of triclopyr are phytotoxic to bermudagrass turf, thus improving suppression with fenoxaprop tank-mixtures and fluazifop tank-mixtures maintaining similar levels of suppression to fluazifop alone.

Acknowlegments

Special thanks to Jerry Craven and Joe Kennedy of the Vanderbilt Legends Club, Franklin, TN and Dr. Bob Hayes of the West Tennessee Research and Education Center, Jackson, TN for their assistance with this research.

Literature Cited

1. Bell, G. E., Martin, D. L., Kuzmic, R. M., Stone, M. L., and Solie, J. B. 2004. Herbicide tolerance of two cold-resistant bermudagrass (Cynodon spp.) cultivars determined by visual assessment and vehicle-mounted optical sensing. Weed Technol. 14:635-641.

2. Cudney, D. W., Elmore, C. L., Gibealut, V. A., and Reints, J. S. 1997. Common bermudagrass (Cynodon dactylon) management in cool-season turfgrass. Weed Technol. 11:478-483.

3. Cudney, D. W., Downer, J. A., Gibeault, V. A., Henry, J. M., and Reints, S. 1992. A new, non-disruptive alternative for kikuyugrass management in cool-season turf. Calif. Turf. Culture 42:1-4.

4. Dernoeden, P. H. 1989. Bermudagrass suppression and zoysiagrass tolerance to fenoxaprop. Pages 285-290 in: Proc. of the 6th Intl. Turf. Res. Conf., Tokyo, Japan

5. Johnson, B. J. 1992. Common bermudagrass (Cynodon dactylon) suppression in Zoysia spp. with herbicides. Weed Technol. 6:813-819.

6. Johnson, B. J., and Carrow, R. N. 1995. Influence of fenoxaprop and ethofumesate treatments on suppression of common bermudagrass (Cynodon dactylon) in tall fescue (Festuca arundinacea) turf. Weed Technol. 9:789-793.

7. Johnson, B. J., and Duncan, R. R. 2001. Effects of herbicide treatments on suppression of seashore paspalum (Paspalum vaginatum) in bermudagrass (Cynodon spp.). Weed Technol. 15:163-169.