Golf Course Management

JUL 2013

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research tation) provided seedhead suppression similar to methiozolin treatments at both sites. Only Cutless (furprimidol, SePRO) provided greater seedhead suppression (44%) than the untreated control at Walker GC, while suppression with Xonerate (52%), Velocity (bispyribac-sodium, Valent) + Xonerate (32%), and Cutless (22%) was greater than the untreated control at Cross Creek Plantation. Other treatments did not provide seedhead suppression different from the untreated control at either location. Turf quality Spring turf quality ratings (1 to 9, 9 = best) were most consistent between sites for Trimmit alone and Trimmit + Xonerate (7.9 to 8.1) (Table 2). Turf quality of methiozolin treatments at the low rate was 8.4 for Walker GC and 6.9 for Cross Creek Plantation; for the high rate, turf quality was 8.5 for Walker GC and 7.3 for Cross Creek Plantation. All other treatments evaluated in this study provided turf quality similar to the untreated control (7.1) with the exception of Xonerate alone at Walker GC (5.5). Discussion Turfgrass managers have used plant growth regulators for annual bluegrass control for many years (4). Currently, the standard for annual bluegrass control in creeping bentgrass is multiple At both research sites (Cross Creek Plantation is shown here), Trimmit (paclobutrazol) applied four times in the fall and four times in the spring (8-16 ounces/acre) provided excellent seedhead suppression. For effective suppression, paclobutrazol must be applied consistently throughout the fall and spring. 90 GCM July 2013 applications of paclobutrazol. (We used Trimmit in this study, but other plant growth regulators such as TGR and Turf Enhancer also have the active ingredient paclobutrazol.) Results from this study confrm paclobutrazol as the best plant growth regulator and currently labeled option for annual bluegrass control. Paclobutrazol does not remove (control) annual bluegrass at rates used on creeping bentgrass greens (8-16 ounces/acre [0.6-1.2 liters/ hectare]), but provides a gradual transition from annual bluegrass to creeping bentgrass by providing a competitive advantage to creeping bentgrass (9). Thus, to be effective, applications of paclobutrazol must remain constant as ceasing applications allows annual bluegrass to rebound from regulation and aggressively reinvade creeping bentgrass stands (8). For adequate annual bluegrass suppression, applications of paclobutrazol should cease only during periods of summer stress and when creeping bentgrass is not actively growing during winter. Paclobutrazol provides good suppression of annual bluegrass populations if applications remain consistent, but selective herbicides that effectively remove annual bluegrass from creeping bentgrass greens would be more benefcial long-term. Methiozolin Results from this and other research (1,2,3,6,12) suggest multiple methiozolin applications are effective at selectively reducing annual bluegrass populations in creeping bentgrass putting greens. Although both low- and high-rate methiozolin programs provided similar control in this study, we observed reductions in turf quality and creeping bentgrass coverage at both sites in the frst year of applications with high rates of methiozolin when heavy annual bluegrass populations were removed too quickly (data not shown). Therefore, multiple applications (6+) at lower rates (≤32 ounces/acre, 2.3 liters/hectare) over longer periods of time (14-17 days) may be safer and more effective. Although not different from the untreated control, turf quality of methiozolin treatments was lower at Cross Creek Plantation compared to Walker GC. This suggests some differences may exist in the susceptibility of creeping bentgrass cultivars to methiozolin. Research suggests methiozolin can reduce creeping bentgrass root length (15). Therefore, methiozolin should not be applied immediately following summer heat stress when creeping bentgrass roots are weakest. Two modes of action of methiozolin have been proposed and provide a new mode of action

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