Topramezone Weed Control Efficacy and Safety in Warm- and Cool-Season Turfgrasses.

Small plot experiments were conducted in the low desert near Phoenix, AZ on a golf course in a rough area infested with goosegrass (Eleusine indica) adjacent to a fairway with Tifway 419 bermudagrass during the summers in 2013 and 2014. The goosegrass was mature and seedheads were prevalent at the initiation of the field trial on 13 August 2013. Sequential applications of topramezone at 0.0055, 0.011, and 0.016 lb a.i./A were made on 03 September. A single application of topramezone at 0.022 lb a.i./A gave 95% goosegrass control but bermudagrass injury was severe for over 2 weeks.  Two applications of topramezone at lower rates controlled goosegrass but injury following the second application was especially severe on bermudagrass.  Topramezone at 0.0055 lb a.i./A gave marginally acceptable goosegrass control with bermudagrass recovering to an acceptable level. Another experiment was initiated on 11 July 2014 when the oldest goosegrass was in the boot stage and first seedheads were appearing and sequential applications were made on 07 August.  All topramezone treatments gave near complete control of goosegrass. Bermudagrass injury was approaching acceptable for only the 0.0055 lb a.i./A rate of application of topramezone.  Topramezone at 0.022 lb a.i./A combined with metribuzin or triclopyr applied once was extremely injurious to the bermudagrass while giving acceptable goosegrass control.

A series of small plot experiments were conducted at various elevations (2,100 to 4,500 ft) around Arizona where Tifway 419 bermudagrass is a weed that encroaches upon creeping bentgrass golf greens and into perennial ryegrass and Kentucky bluegrass mix collars around greens.  Fall or spring applications of topramezone at 0.022 lb a.i./A, three applications, and 0.033 lb a.i./A, 2 applications, demonstrated severe phytotoxicity on bermudagrass following each application.  Creeping bentgrass, perennial ryegrass, and Kentucky bluegrass were tolerant and exhibited minimal injury.