Safety of carfentrazone-ethyl following application of bensulide to creeping bentgrass putting greens

Golf course superintendents may use bensulide to control annual grassy weeds and carfentrazone-ethyl (CE) to control silvery-thread moss (Bryum argenteum Hedw.) in creeping bentgrass putting greens. Creeping bentgrass injury has been reported if CE is applied soon after treatment with bensulide and the safe application interval varies as much as 68 days. Our goal was to improve the precision of recommendations for safe application of CE following bensulide, considering both CE rate and timing. We used a factorial treatment structure that included (1) bensulide or no bensulide, (2) three rates of CE, and (3) nine CE application timings in 2018 and 2019 at locations in Nebraska and Ohio. Because of limited effects in 2018, different CE rates and application timings were used in 2019. Significant creeping bentgrass injury was only observed at 6.7 or 13.4 fl oz acre⁻¹ rates of CE that were applied within 3 days of applying bensulide. Even the 13.4 fl oz acre⁻¹ rate (a 2× rate) of CE did not injure creeping bentgrass when applied at least 7 days after applying bensulide. The 2.0 fl oz acre⁻¹ rate of CE never injured creeping bentgrass, even when applied the same day as bensulide. Cultivar, management, and environmental differences may influence whether subsequent application of bensulide and CE injures creeping bentgrass. Based on the environmental/cultural conditions and cultivars used in this research, golf course superintendents should expect little to no injury when CE is applied at least 1 week after applying bensulide.