Broadleaf Weed Control in Sunflower (<i>Helianthus annuus</i>) with Preemergence-Applied Pyroxasulfone with and without Sulfentrazone

Abstract

A field study was conducted at two locations in Kansas, USA in 2011 and 2012 to test weed control efficacy and crop response to preemergence-applied pyroxasulfone alone and in combination with sulfentrazone in sunflower. Treatments included three rates of pyroxasulfone (100, 200 and 400 g · ha -1 ) applied alone and tank-mixed with sulfentrazone at 70, 140 and 280 g · ha -1 . Commercial standards sulfentrazone at 140 g · ha -1 + pendimethalin at 1390 g · ha -1 and sulfentrazone at 140 g · ha -1 + S-metolachlor at 1280 g · ha -1 were also included. Pyroxasulfone at 100 g · ha -1 controlled Palmer amaranth 87% at 3 weeks after application (WAA), but control decreased to 76% at 6 WAA. Increasing pyroxasulfone rate to ≥200 g · ha -1 or tank mixing with sulfentazone at 140 g · ha -1 provided ≥90% Palmer amaranth control for at least 6 WAA. Sulfentrazone alone at 70 g · ha -1 controlled Palmer amaranth 77% at 3 WAA, but control dropped to 69% at 6 WAA. Increasing sulfentrazone rate from 70 to 140 or 280 g · ha -1 increased control to >90% at 3 WAA, but did not maintain acceptable control at 6 WAA. Tank mixing sulfentrazone at 140 g · ha -1 with pendimethalin at 1390 g · ha -1 or S-metolachlor at 1280 g · ha -1 controlled Palmer amaranth ≥90 and 84% at 3 WAA and 6 WAA, respectively. The lowest rate of pyroxasulfone (100 g · ha -1 ) controlled kochia 98% and the control was complete with all other treatments. However, no treatment provided as much as 90% puncturevine control at 3 WAA and the control was commercially unacceptable (<75%) at 6 WAA. No treatment visibly injured sunflower anytime during the season or reduced sunflower plant population.