Golf Course Management

JUL 2013

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

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research for annual bluegrass control in turfgrass (7,10). Annual bluegrass is highly susceptible to herbicide resistance development, and thus, methiozolin should be used judiciously to delay the onset of resistance issues. Results from this study suggest two years of applications of methiozolin signifcantly reduces annual bluegrass populations. Thus, once these populations are reduced to acceptable levels, an aggressive paclobutrazol regime could be maintained until further applications of methiozolin would be needed. Xonerate Xonerate is a newly developed herbicide for annual bluegrass control in warm- and cool-season grasses, but creeping bentgrass greens are not listed on the product label. Four spring applications of Xonerate at 1 ounce/acre (70 grams/hectare) failed to provide adequate (>70%) annual bluegrass control at either location. Spring turf quality was unacceptable (5.5) at Walker GC, but was 7.0 at Cross Creek Plantation, suggesting some variability in the safety of Xonerate at these rates on creeping bentgrass greens in the Southeast as previous research has reported (3,16). This could be attributed to environmental conditions at the time of application as Xonerate effcacy is highly temperature-dependent (13), or reduced photosynthetic effciency as Xonerate is a photosystem II-inhibiting herbicide (14). Because Xonerate is potentially phytotoxic to creeping bentgrass (14,16) and because paclobutrazol does not control annual bluegrass at the reduced rate for greens, reduced rates of Xonerate were evaluated in combination with Trimmit and Velocity. Annual bluegrass control was signifcantly increased at Cross Creek Plantation compared to Trimmit alone (50%) when four spring applications of Xonerate at 0.5 ounce/acre (35 grams/hectare) were added to the Trimmit program (79%). However, similar control (~65%) was observed at Walker GC with these programs. Therefore, low rates of Xonerate may increase annual bluegrass control compared to Trimmit alone, but this was not consistently shown in this study. Xonerate + Velocity combinations did not provide comparable annual bluegrass control or seedhead suppression to other treatments. Low rates of these products were used to achieve creeping bentgrass safety, but these results suggest higher rates are probably needed to control annual bluegrass. Methiozolin was applied three times at higher rates (64 ounces/acre) for annual bluegrass control to this plot at Walker GC. One year of this aggressive treatment removed annual bluegrass too quickly, leaving voids in creeping bentgrass greens, which reduced turf and putting quality and time to heal (top). Two years of treatment with methiozolin applied six times in the fall and spring (32 ounces/acre) at Cross Creek Plantation provided more than 80% annual bluegrass control (bottom). Summary Results from this study confrm multiple paclobutrazol (Trimmit, TGR, Turf Enhancer) applications remain the most effective option curJuly 2013 GCM 91

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