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D.W. Williams and P.B. Burrus

Perennial ryegrass (PR) (Lolium perenne L.) is often used as a low-mowed turf in the transition climatic zone. However, control of the fungal disease gray leaf spot (Pyricularia grisea (Cooke) Sacc.) has drastically increased the cost of PR management. Seeded bermudagrasses (SB) [Cynodon dactylon (L.) Pers.] are viable options for turfgrass management operations with limited pesticide budgets. Field trials in 2000 and 2001 tested the effects of two herbicides and several plant growth regulators (PGR) during renovation of mature PR to either of two cultivars of SB. The herbicides glyphosate and pronamide, and the PGR's trinexapac-ethyl, ethephon, paclobutrazol, and flurprimidol were applied at label rates to mature stands of PR. `Mirage' and `Yukon' SB were seeded separately either 1 or 7 days after applications (DAA) of chemicals. SB establishment, first-winter survival, and turfgrass quality (TQ) were rated and compared to an untreated control. Results indicated that only applications of glyphosate resulted in acceptable renovation of PR to SB, but also resulted in significantly lower (P< 0.05) TQ during the transition. Applications of pronamide resulted in significantly less (P < 0.05) SB transition than did applications of glyphosate, but pronamide plots maintained higher TQ. None of the PRG treatements had a significant effect (P < 0.05) on SB transition. There were no consistent significant effects (P < 0.05) due to DAA among any of the chemicals evaluated. First-winter survival was significantly higher (P < 0.05) with `Yukon' than with `Mirage' in both years. We conclude that among the chemicals tested, only applications of glyphosate resulted in acceptable transition of PR to SB, but a significant reduction of TQ should be expected during the transition. Chemical names used: [N-(phosphonomethyl) glycine] (glyphosate); [3.5-dichloro-N-(1,1-dimethyl-2-propynyl)-benzamide] (pronamide); [(2-chloroethyl) phosphonic acid] (ethephon); [4-(cyclopropyl-α-hydroxy-methylene)-3,5-dioxo-cyclohexane-cabroxylic acid ethyl ester] (trinexapac-ethyl); [(±)-(R*R*)β-[(4-chlorophenyl)-methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol] (paclobutrazol); [α-(1-methylethyl)-α-[4-(trifluromethoxy)phenyl]-5-pyrmidinemethanol] (flurprimidol).