Abstract: Field studies were conducted in 1998 and 1999 to evaluate the sensitivity of a common sunflower population to acetolactate synthase (ALS)-inhibiting herbicides and evaluate alternative control methods for ALS-resistant common sunflower in soybean. Imazaquin, imazethapyr, imazamox, flumetsulam, chlorimuron, cloransulam, and CGA277476 provided 35 to 73% control of common sunflower with labeled rates. Postemergence glyphosate and sequential applications of bentazon effectively controlled ALS-resistant common sunflower. Although pendimethalin imazaquin imazethapyr preemergence followed by glyphosate postemergence with and without cultivation provided 100% control of ALS-resistant common sunflower, sequential applications of glyphosate provided net incomes approximately $50 to $110/ha higher than the alternative control methods. Pendimethalin preemergence followed by acifluorfen bentazon postemergence followed by bentazon 10 d later provided the lowest overall weed control and net income. In treatments with a soil-applied herbicide followed by glyphosate postemergence, cultivation generally did not improve weed control. Soybean yields were the same comparing glyphosate with a soil-applied herbicide followed by glyphosate.
Nomenclature: Acifluorfen, bentazon, chlorimuron ethyl, cloransulam, flumetsulam, glyphosate, imazamox, imazaquin, imazethapyr, CGA277476, pendimethalin, common sunflower, Helianthus annuus L. #3 HELAN; soybean, Glycine max (L.) Merr. ‘Asgrow 3601 RR*STS’.
Additional index words: Cultivation, herbicide resistance, sulfentrazone, Amaranthus rudis Sauer, Ipomoea hederaceae (L.) Jacq., Setaria faberi Herrm., Xanthium strumarium L., AMATA, IPOHE, SETFA, XANST.
Abbreviations: ALS, acetolactate synthase; cec, cation exchange capacity; CV, coefficient of variation; MPOST, mid postemergence; OM, organic matter; PRE, preemergence; WAT, weeks after treatment.
