Frequency of Drive (Quinclorac) Treatments on Common Bermudagrass Tolerance and on Large Crabgrass Control

Abstract

Abstract When a postemergence (POST) herbicide is used to control large crabgrass [Digitaria sanguinalis (L.) Scop.] in common bermudagrass [Cynodon dactylon (L.) Pers.], the herbicide should maintain optimum weed control for 8 to 10 weeks without causing undesirable injury to the turfgrass. A field experiment was conducted during 1993 and 1994 to determine the lowest rate of Drive (quinclorac) needed to control large crabgrass without causing undesirable injury to bermudagrass turf. Drive (quinclorac) applied at 0.28 kg ai/ha (0.25 lb ai/A) initially in early May and repeated at the same rate at a 2-week interval, controlled 85% large crabgrass for 16 weeks in 1993 and 70% for 10 weeks in 1994. The control in 1994 was 96% for 17 weeks when the herbicide was applied at 0.28 kg ai/ha (0.25 lb ai/A) in each of three applications on May 2, May 29, and June 13. The maximum bermudagrass injury in 1993 from Drive (quinclorac) applied at 0.28 kg ai/ha (0.25 lb ai/A) in each of two applications at 2- to 4-week interval was ≤ 27% compared to ≥ 33% when ≥ 0.56 kg ai/ha (≥ 0.5 lb ai/A) was applied as a single application. Bermudagrass treated initially with Drive (quinclorac) at 0.28 kg ai/ha (0.25 lb ai/A) was injured higher in 1994 (≤ 35%) than in 1993 (≤ 14%). Bermudagrass injury was ≥ 40% when the second application was delayed until mid- to late June either year or when the herbicide was applied in three applications during May and June 1994.