Research trials conducted at two locations in the spring of 2004 evaluated the effect of soil temperature as an indicator for application timings of certain sulfonylurea herbicides for perennial ryegrass control while maintaining acceptable turfgrass quality during bermudagrass spring transition. Herbicide application timings began when soil temperatures reached 17 C (April 14, 2004). Greater perennial ryegrass control 4 wk after initial treatment (WAIT) was achieved when sulfonylurea herbicides were applied at 26 C soil temperature compared to 17 or 21 C. Bermudagrass density 6 WAIT increased with treatments applied at 26 C soil temperature compared to cooler soil temperatures. There was a decrease in overall turfgrass quality 2 WAIT when treatments were applied at 17 C. However, by 4 WAIT all application timings provided overall turfgrass quality comparable to the untreated control. Acceptable turfgrass quality and maximurn perennial ryegrass control was achieved by delaying transition-aid herbicide applications until soil temperatures reached 26 C and growing conditions were more conducive to bermudagrass growth.
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