Tolerance of imidazolinone-resistant corn (zea mays) to diclosulam

Field experiments were conducted in 1996 and 1997 to evaluate the tolerance of imida- zolinone-resistant (IR) and non-IR corn cultivars to preemergence (PRE) and postemergence (POST) treatments of diclosulam. Crop injury was evaluated early- (5 to 6 wk after planting [WAP]), mid- (10 to 11 WAP), and late-season (13 to 15 WAP). Early-season injury of IR corn was no more than 12% in systems that included diclosulam PRE or POST at 18, 27, or 36 g ai/ha. Early-season injury of non-IR corn ranged from 85 to 89% in systems that included diclosulam PRE at any rate. At the mid-season evaluation, crop injury to IR corn was 1% or less. Non-IR corn was injured 73 to 94% in systems that included diclosulam PRE, while systems that included diclosulam POST caused 45 to 58% injury at mid-season. At the late-season evaluation, non-IR corn was injured 56, 88, and 96% with diclosulam PRE at 18, 27, and 36 g/ha, respectively, whereas systems that included diclo- sulam POST had 11 to 14% injury. Injury to IR corn from diclosulam PRE or POST was not apparent at the late-season evaluation. Weed-free yield of IR corn treated with diclosulam was 6,490 to 6,850 kg/ha and was equivalent to or better than yield from IR corn treated only with atrazine plus me- tolachlor PRE. Yield from non-IR corn treated with any diclosulam-containing system did not exceed 3,770 kg/ha.