Palmer Amaranth and Kochia Control with Tank Mixed Pyroxasulfone and Sulfentrazone in Sunflower.

A study was conducted in 2011 near Hays and Colby, KS to evaluate the weed control efficacy and crop safety of pyroxasulfone alone and in combination with sulfentrazone applied preemergence in oilseed sunflower. Palmer amaranth (Amaranthus palmeri S. Wats.) and kochia [Kochia scoparia (L.) Schrad.] were predominate weeds at Colby and Palmer amaranth was the only species present at Hays.  Averaged across locations, preemergence-applied pyroxasulfone at 100, 200 and 400 g ai ha^-1 controlled Palmer amaranth 93, 98 and 100%, respectively, at 49 days after planting (DAP).  In comparison, sulfentrazone at 70 and 140 g ha^-1 controlled Palmer amaranth 96% at 29 DAP, but control declined to 84 and 75%, respectively, at 49 DAP.   Sulfentrazone at 280 g ha^-1 controlled Palmer amaranth 98% at 29 DAP and 89% at 49 DAP.  Tank mixing sulfentrazone with pyroxasulfone did not enhance Palmer amaranth control compared to the any rate of pyroxasulfone alone, nor was a mixture of sulfentrazone at 140 g ha^-1 plus S-metolachlor at 1270 g ha^-1 as effective as pyroxasulfone at 200 g ha^-1.  However, sulfentrazone at 140 g ha^-1 in combination with pendimethalin at 1375 g ha^-1 controlled Palmer amaranth 98% at 29 DAP and 96% at 49 DAP.  This combination was similarly effective as any rate of pyroxasulfone alone. At Colby, preemergence-applied pyroxasulfone at 100 g ha^-1 controlled kochia 96% and 200 and 400 g ha^-1 rates provided 100% kochia control at 70 DAP.  Similarly, sulfentrazone at 70 g ha^-1 controlled kochia 98%; control was complete at higher rates. Combinations of sulfentrazone at 140 g ha^-1 plus S-metolachlor at 1270 g ha^-1 or pendimethalin at 1375 g ha^-1 also provided nearly complete control of kochia at 70 DAP.  No treatment visibly injured sunflower anytime during the season.