Field studies were conducted to evaluate corn vigor reduction, weed control, corn yield, and economic returns in a no-till system with various herbicide strategies using full and reduced rates of acetochlor and atrazine with glyphosate, glufosinate, or imazethapyr imazapyr in their respective type of herbicide-resistant, no-tillage corn. Crop vigor reduction due to herbicide injury was 10% or less with all treatments. A burndown plus a full label rate of a residual herbicide applied early preplant (EPP) generally provided less than 80% control of giant foxtail, common waterhemp, and common cocklebur but usually greater than 85% control of common ragweed and common lambsquarters. Two-pass strategies generally provided greater than 85% control of all species evaluated. Early postemergence, mid-postemergence (MPOST), and late postemergence strategies generally provided inconsistent and poor overall weed control. EPP–MPOST strategies generally provided lower weed control than strategies using acetochlor or atrazine EPP followed by a postemergence application. Corn yield and net economic returns followed a similar trend as weed control, with strategies that provided greater than 80% weed control showing minimal crop vigor reduction and high grain yields. Two-pass strategies with residual herbicides generally provided the highest yields, economic returns, and low coefficients of variation (CV) of net income. Although EPP strategies provided similar economic returns as some of the two-pass strategies, they had higher CVs, implying greater risk to economic return.
Nomenclature: Acetochlor; atrazine; glufosinate; glyphosate; imazapyr; imazethapyr; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common waterhemp, Amaranthus rudis Sauer. # AMATA; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L. ‘Dekalb 626’, ‘Pioneer 3395’, ‘Pioneer 34T14’.
Additional index words: Application strategies, application timing, tank mixes.
Abbreviations: ac/at , acetochlor EPP followed by atrazine plus; ALS, acetolactate synthase; CEC, cation-exchange capacity; CV, coefficients of variation; EPOST, early postemergence; EPP, early preplant; MPOST, mid-postemergence; LPOST, late postemergence; OM, organic matter.
