Turfgrass response to flazasulfuron and trifloxysulfuron sodium deposited by runoff water

Flazasulfuron is a selective herbicide registered for use in warm‐season turfgrass. Concerns have been raised over its mobility in surface water runoff. Studies were conducted in Blacksburg, VA and Charlottesville, VA to evaluate injury to Lolium perenne L. (perennial ryegrass) downslope of plots treated with transition‐assisting herbicides, including flazasulfuron, pronamide, and trifloxysulfuron sodium. Flazasulfuron (52 g a.i. ha–1) and pronamide (1120 g a.i. ha–1) consistently injured L. perenne greater than trifloxysulfuron sodium (17 g a.i. ha–1) or lower rates of flazasulfuron (9 and 26 g a.i. ha–1). At Charlottesville, soil was more saturated, and a natural rainfall increased the rate of runoff and severity of L. perenne injury below treated plots. At this site, flazasulfuron (52 g a.i. ha–1) and pronamide (1120 g a.i. ha–1) caused visible injury to L. perenne 10 to 16 m below treated plots. Based on L. perenne injury, flazasulfuron mobility at the rates tested can be considered equivalent or greater than trifloxysulfuron sodium, and equivalent or less than pronamide when subjected to excessive irrigation or rainfall soon after application to saturated soils. Precautions should be taken to avoid application of these herbicides to saturated soils and apply when rainfall is not expected for sufficient time to rinse turfgrass foliage and incorporate nonabsorbed herbicide into soil via light irrigation.