Bermudagrass Encroachment into Creeping Bentgrass as Affected by Herbicides and Plant Growth Regulators

Bermudagrass (Cynodon spp.) encroachment into creeping bentgrass (Agrostis stolonifera var. palustris Huds.) golf greens is a severe problem where both grasses are grown. Research was initiated to determine the effects of dates and frequency of herbicide-plant growth regulator (PGR) treatments on tolerance of creeping bentgrass and encroachment of three bermudagrass cultivars under golf green conditions. Treatments were arranged in a split-plot design with frequency of herbicide-PGR application as main plots and bermudagrass cultivars as subplots. Soil type was an artificial rootzone mix. Creeping bentgrass was injured more when treated with various herbicide-PGR combinations in September than in April. However, creeping bentgrass injury was unacceptable (>30%) with mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)-sulfonyl] amino]phenyl]acetamide} applied in sequence with siduron [N-(2-methyl-cyclohexyl]-N-phenylurea] or ethofumesate [(±)2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] at either date. In general, herbicide-PGR treatments applied in April suppressed foliage and stolon growth of bermudagrass equal to or better than treatments applied in September and April. Bermudagrass growth was effectively suppressed until late May or early June when treated with siduron, siduron with flurprimidol {α-(1-methylethyl)-α-[4-(trifluoromethoxy)-phenyl]-5-pyrimidine-methanol}, or ethofumesate with flurprimidol. There generally was no difference in foliar growth suppression from treatments applied to ‘Tifway’, ‘Tifgreen’, both C. transvaalensis Burtt-Davy ✕ C. dactylon (L.) Pers., and common bermudagrass, C. dactylon (L.) Pers. When chemicals were applied only in April, the length and number of bermudagrass stolons were effectively suppressed for several weeks but stolon growth recovered and increased rapidly from mid-May until June. The suppression of stolon growth of all bermudagrass cultivars in June was as good or better when treated with ethofumesate plus flurprimidol than with other treatments. Contribution from the Georgia Agric. Exp. Stn. supported by Grant-in-aid from Georgia Golf Course Superintendents Association and by Hatch and State funds.