Postemergence Herbicide Safety and Efficacy for Control of Common Bermudagrass in a Zoysiagrass Fairway

Abstract

Golf course superintendents in the Transition Zone of the United States struggle to limit common bermudagrass [Cynodon dactylon (L.) Pers.] infestations in zoysiagrass (Zoysia japonica Steud.) fairways. When tank-mixed with triclopyr, aryloxyphenoxypropionate (AOPP) herbicides such as fenoxaprop and fluazifop result in more injury to bermudagrass than zoysiagrass and up to 76% suppression of bermudagrass (3). An alternative tank-mix partner with AOPP herbicides for selective removal of bermudagrass is mesotrione. Willis et al. (4) reported that mesotrione reduced bermudagrass cover by 45 to 98% when applied alone or tank-mixed with AOPP herbicides. Although the label indicates potential phytotoxicity to zoysiagrass, Huckabay (2) reported that three sequential applications of mesotrione up to 0.12 lb/acre resulted only in a maximum of 15% injury to ‘Meyer’ zoysiagrass. To date, there are no studies evaluating tank mixtures of AOPP herbicides with mesotrione on golf course fairways to determine long-term control of bermudagrass in zoysiagrass turf. Field plots were established on the 9th fairway of The Falls Golf Club in O’Fallon, MO. The fairway was established with ‘Westwood’ bermudagrass (1) in 1994 and renovated to ‘Meyer’ zoysiagrass by sod in 2009, following three sequential applications of glyphosate at 4 lb/acre applied four weeks apart. Shortly after sodding, bermudagrass began invading fairways and becoming interwoven with zoysiagrass. The fairway soil was a Keswick silt loam with a pH of 6.7 and 4.5% organic matter. The fairway was maintained at a 0.56-inch mowing height and received a total of 3 lb N/1000 ft2 fertilizer annually. Field plots measuring 5 by 10 ft were established on two locations of the same fairway and arranged as a randomized complete block design with four replications for one location, and three replications at the second location due to space limitations. Locations were fairly uniform with the possible exception that one area was heavily trafficked with golf carts. In addition to an untreated control, treatments included fenoxaprop or fluazifop tank-mixed with triclopyr or mesotrione and applied to the same plots over two years (Table 1). The initial application was made on 9 June 2010, with sequential applications made 3, 6, 8, and 10 weeks after initial treatment (WAIT) in the first growing season, and 52, 56, and 60 WAIT during the second growing season. Treatments were tank mixed with a non-ionic surfactant at 0.25% v/v, and applied with a CO -pressurized backpack sprayer calibrated to apply 22 gal/acre at a spray pressure of 40 PSI using four TeeJet XR8002 flat fan nozzles (Spraying Systems Co., Wheaton, IL). Zoysiagrass injury was rated on a 0 to 100% scale with 0 = no injury and 100% = complete death. Bermudagrass coverage was rated on a 0 to 100% scale, with 0% = no bermudagrass and 100% = complete bermudagrass coverage. Results were analyzed by PROC MIXED of SAS 9.2 (SAS Institute Inc., Cary, NC) and mean separation was conducted based on Fisher’s Protected LSD (P = 0.05). Percent bermudagrass coverage data were arcsine transformed prior to analysis. For clarity, non-transformed means were presented as there were no differences in interpretations. 2