Season-long Grassy Weed Control with Various Preemergence Herbicides

Grady L. Miller and Jan S. Weinbrecht

Devrinol, a preemergence herbicide recently registered for use in ornamentals and turfgrass, was evaluated for summer annual grassy weed control in a stand of Tifway II bermudagrass maintained under fairway conditions. Other herbicides evaluated for standard comparison included Barricade, Dimension, Pendulum, Ronstar, and Surflan. Plots were seeded with goosegrass and southern crabgrass at 30 seed/ft2. At 90 days after initial application, good (³80%) goosegrass and southern crabgrass control were evident following all treatments. Despite irrigation efforts to maintain a healthy turf, there was concern regarding questionable germination response through the unusually dry spring. To address this concern, an additional seeding was made July 7th in anticipation of more typical summer rain events, and to further evaluate season-long efficacy. By fall, there was no evidence of emergence of any of the grassy-weeds. Evaluation continued through the fall and winter seasons, however, to evaluate annual bluegrass efficacy and perennial ryegrass overseeding establishment response, particularly to those with August 1 sequential application dates. Efficacy ratings through the latter part of summer provided additional data for spotted spurge, old world diamond-flower, and globe sedge seedlings control. Good to excellent (³ 80%) spotted spurge control was only evident following Pendulum. Excellent (³ 90%) season-long globe sedge seedling control was evident following three 4.0 lb ai/A Devrinol applications in March, May, and August. Temporarily good (" 80%) globe sedge seedling control was evident following the 12 lb ai/A rate of Devrinol, the split March and May Dimension applications, both Pendulum treatments, and the single 4.0 lb ai/A rate of Ronstar. Best (³ 75%) long-term (November) old world diamond-flower control was observed following the two split applications of Barricade, the three split Dimension applications, both Pendulum applications, and the split Ronstar application. Significant (³20%) perennial ryegrass stand density reductions were observed during December following Devrinol and Surflan. These reductions, however, may have been attributed to unseasonably warm temperatures which may have competed with perennial ryegrass establishment. By January 7th, following three days of freezing temperatures, there were no significant stand density reductions observed with any of the treatments. The only significant level of annual bluegrass control (72%) was evident following the single March application of Surflan.