Weed Control and Crop Safety with Premixed <i>S</i>-Metolachlor and Sulfentrazone in Sunflower

Abstract

A preliminary study conducted in the central USA near Colby and Hays, Kansas (KS) in 2010 indicated a premix of S -metolachlor & sulfentrazone codenamed F7583 (Broadaxe ? ) had good potential for use in sunflower ( Helianthus annuus L.). Additional studies were conducted in 2011 at Colby, Hays, Manhattan, KS to refine rate and application timing of F7583 for weed control and crop safety. Four rates of F7583 (860, 1100, 1350 and 1840 g·ha-1) were compared to single rates of S -metolachlor and pendimethalin, and applied 21 days preplant versus preemergence (PRE). F7583 at ≥1100 g·ha -1 applied preplant or PRE controlled Palmer amaranth ( Amaranthus palmeri S. Wats.) and kochia [ Kochia scoparia (L.) Schrad.] ≥95% and 100%, respectively in neutral pH soils. In slightly acidic soils, PRE application of F7583 was more effective against Palmer amaranth and grass weeds compared to preplant application. No benefit was gained by increasing the rate of F7583 from 1100 to 1350 g·ha -1 at either application timing. Puncturevine ( Tribulus terrestris L.) control was not commercially satisfactory with F7583 at any rate or time of application. Both S -metolachlor at 1070 g·ha -1 and pendimethalin at 1600 g·ha -1 applied either preplant or PRE were considerably less effective on all three broadleaf weeds compared to F7583 treatments. Individually, S -metolachlor and pendimethalin were more effective when applied PRE compared to preplant application. F7583 did not reduce sunflower plant population or visibly injure sunflower anytime during the season.