Johnsongrass Control, Total Nonstructural Carbohydrates in Rhizomes, and Regrowth After Application of Herbicides Used in Herbicide-Resistant Corn (Zea mays)1

Greenhouse and field experiments were conducted to evaluate the efficacy of nicosulfuron, primisulfuron, glyphosate, glufosinate, imazethapyr plus imazapyr, and quizalofop on johnsongrass biomass reduction, rhizome total nonstructural carbohydrate (TNC) content, and subsequent regrowth from rhizomes. In the greenhouse, johnsongrass plants originating from rhizome segments were controlled 88 to 97% with quizalofop, glyphosate, imazethapyr plus imazapyr, nicosulfuron, and primisulfuron and 56% with glufosinate 3 wk after treatment (WAT). Johnsongrass treated with quizalofop, glyphosate, and nicosulfuron did not regrow 6 WAT, whereas plants treated with primisulfuron, imazethapyr plus imazapyr, and glufosinate regrew from the rhizome of the treated plant. Rhizome TNC levels 3 WAT were not reduced by glufosinate or nicosulfuron, but they were reduced 64% by quizalofop, 32% by primisulfuron, 61% by glyphosate, and 29% by imazethapyr plus imazapyr. When rhizome TNC was reduced by 60% or more compared with nontreated plants, johnsongrass did not regrow from the treated rhizomes. In field experiments, nicosulfuron and glyphosate controlled johnsongrass 94 and 99%, respectively, whereas imazethapyr plus imazapyr (79%) and glufosinate (85%) provided less control 6 WAT. Nomenclature: Glufosinate; glyphosate; imazapyr; imazethapyr; nicosulfuron; primisulfuron; quizalofop; johnsongrass, Sorghum halepense (L.) Pers. #3 SORHA. Additional index words: Biomass reduction, carbohydrate analysis, corn yield, fresh weight. Abbreviations: DAT, days after treatment; POST, postemergence; TNC, total nonstructural carbohydrate; WAT, weeks after treatment.