Field experiments were conducted in 2002 and 2003 to evaluate weed control and dry bean response to fomesafen and fomesafen tank mixtures. In the first experiment, six market classes of dry bean were treated at the first trifoliate growth stage with fomesafen nonionic surfactant (NIS) urea ammonium nitrate solution (UAN) at rates ranging from 210 to 840 g/ha. In the second experiment, fomesafen NIS UAN at 280 g/ha was applied alone or combined with imazamox at 36 g/ha, bentazon at 560 g/ha, or clethodim at 140 g/ha, and each treatment was applied postemergence at either the unifoliate, first trifoliate, or third trifoliate growth stage to six dry bean cultivars. Crop injury from fomesafen in the form of stunting and leaf crinkling was apparent 7 d after treatment (DAT), but crop injury was temporary and plants recovered. Common lambsquarters and hairy nightshade control increased from 61 to 71% and 74 to 92%, respectively, as fomesafen rate increased from 210 to 280 g/ha. Redroot pigweed, kochia, and common purslane were controlled at the ≥90% level by fomesafen at 210 g/ha. Applying fomesafen and fomesafen tank mixtures at the unifoliate growth stage caused less dry bean injury and improved redroot pigweed, common lambsquarters, and hairy nightshade control compared with treatments made at the first or third trifoliate growth stage. Decreased weed control caused by delaying herbicide application to the third trifoliate growth stage resulted in a 17% decrease in crop yield, compared with treatments where herbicides were applied at the unifoliate growth stage. Combining fomesafen with other herbicides increased crop injury 4%, 14 DAT. A tank mixture of fomesafen plus imazamox caused more crop injury than fomesafen plus bentazon. Combining fomesafen with imazamox or bentazon improved hairy nightshade control to 92 and 87%, respectively; however, common lambsquarters control was improved only with tank mixtures of fomesafen with bentazon.
Nomenclature: Bentazon; clethodim; fomesafen; imazamox; common lambsquarters, Chenopodium album L. #3 CHEAL; common purslane, Portulaca oleracea L. # POROL; hairy nightshade, Solanum sarrachoides Sendt. # SOLSA; kochia, Kochia scoparia (L.) SCHRAD. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; dry bean, Phaseolus vulgaris L. black, Great Northern, light red kidney, navy, pink, pinto, ‘Shadow’, ‘Marquis’, ‘Chinook’, ‘Schooner’, ‘Viva’, ‘Poncho’.
Additional index words: Field beans, interference, seed yield.
Abbreviations: DAT, days after treatment; NIS, nonionic surfactant; POST, postemergence; UAN, urea ammonium nitrate solution.