Effect of AC 263,222, Imazethapyr, and Nicosulfuron on Weed Control and Imidazolinone-Tolerant Corn (Zea mays) Yield

Imidazolinone herbicides injure currently available commercial field corn cultivars; however, cultivars resistant to these herbicides have been developed. Sicklepod, Texas panicum, and annual morningglory control using AC 263,222 (36 and 72 g ai/ha), imazethapyr (36 and 72 g ai/ha), or nicosulfuron (35 g ai/ha) applied POST at 2, 4, and 6 wk after planting were evaluated in imidazolinone-tolerant corn. Studies were conducted at Attapulgus and Plains, Georgia from 1992 through 1993. Nicosulfuron and AC 263,222 at 72 g/ha controlled Texas panicum at least 87% when applied 2 wk after planting. Imazethapyr did not consistently control Texas panicum or sicklepod, regardless of application rate. AC 263,222 at both rates and nicosulfuron controlled sicklepod at least 86% when applied 2 wk after planting; however, later application or application under dry conditions generally resulted in reduced control. All herbicides controlled the entireleaf and pitted morningglory complex at least 84% when applied 2 wk after planting. Imidazolinone-tolerant corn was tolerant to all herbicides, regardless of rate and timing, and generally yielded greater when weeds were controlled early in the season. Nomenclature : AC 263,222, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl- 3-pyridinecarboxylicacid ; imazethapyr, 2-[4,5 -dihydro-4-methyl-4-(1-methylethyl)-5-oxo-lH- imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)- amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; entireleaf morningglory, 1pomoea hederacea var. integriuscula Gray # 3 IPOHG; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; Texas panicum, Panicum texanum Buckl. # PANTE; corn, Zea mays L., 'Pioneer 33431R.'