Golf Course Management

AUG 2014

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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08.14 GOLF COURSE MANAGEMENT 97 bentgrass grown on a sand root zone built to USGA recommendations and, in Tennessee, the site was L-93 creeping bentgrass grown on a silt loam soil frequently topdressed with a USGA-recommended sand. The locations were maintained as putting greens. Plots were treated with herbicide on Oct. 24, 2011, and an adjacent location on May 22, 2012, in Indi - ana and on Oct. 17, 2011, and an adjacent lo- cation on May 1, 2012, in Tennessee. At both locations, herbicides were applied in 2 gallons water/1,000 square feet at 30 psi (81.5 milli - liters/square meter at 207 kilopascals) with a CO 2 -pressurized boom sprayer equipped with an XR8002VS fat-fan nozzle. Herbicides included in this study (Table 3) were all labeled for use on creeping bent - grass putting greens and applied at the put- ting green label rate and at a rate twice (2×) this labeled rate. One exception to this was the October 2011 application timing in Tennessee where only the label rate of each herbicide was applied. An untreated check was included for comparison at each location. Injury to creep - ing bentgrass and turf quality data were col- lected. All data were analyzed using statisti- cal software. Fall applications. Minor and transient in - jury was observed from fall treatments on creeping bentgrass putting greens in Indi - ana, but injury levels were acceptable (≥ 7, on a scale of 9-1, where 9 = no injury) for all treatments including herbicides applied at a 2× rate (Table 3). Minor but acceptable in - jury occurred from applications of 4-Speed, 4-Speed XT, Banvel, Trimec Bentgrass, Trimec Classic, Trimec Encore and Trimec Southern. In Tennessee, injury was minimal (<4%, on a scale of 0% -100%, where 0% = no injury) and transient from labeled appli - cation rates following 4-Speed, 4-Speed XT, Trimec Classic, and Trimec Southern appli - cations. Differences in turf quality were not seen among treatments in Indiana or Tennes - see (data not shown). Spring applications. The experiments were repeated in May 2012 to determine if more in - jury might be expected from late spring and summer applications during warmer tem - peratures. At both locations, more injury was observed from May 2012 applications than October 2011 applications. Applications at label rates did not cause unacceptable injury when applied in Indiana in May, but 2× rates of 4-Speed XT, Banvel and Trimec Southern did cause unacceptable injury two weeks after application (Table 3). That injury was accept - able by three weeks after application (data not shown). Results were similar in Tennessee with 4-Speed XT, Banvel and Trimec South - ern applied at the 2× rate also causing the most injury (11%-19%) (Table 2), but with injury decreasing to <4% three weeks after applica - tion (data not shown). While a labeled appli- cation rate of Banvel caused 10% injury two weeks after application in Tennessee, other products such as Mecomec 2.5, QuickSilver T&O, Trimec Bentgrass, Trimec Classic and Trimec Encore had <2% injury when applied at the labeled rate in May, similar to responses observed in Indiana. These data are supported by reports on the safe use of carfentrazone on creeping bentgrass for silvery thread moss (Bryum argenteum) control (15) and the use of Trimec Bentgrass for lesser swinecress (Cro - ronopus didymus) control (14). Findings of this research were that broad - leaf herbicides labeled for putting green use can be safely applied at labeled rates in the spring and fall; injury is more likely to occur from May herbicide applications than from October applications; some herbicides are Mouse-ear chickweed is a common weed in close-mowed bentgrasses. Silvery-thread moss is a common putting green weed, especially in close-mowed putting greens that receive frequent irrigation and low fertility.

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