Weed control and snap bean (phaseolus vulgaris) response to reduced rates of fomesafen

Field experiments were conducted in 1996, 1999, and 2000 to evaluate weed control and snap bean response to postemergence applications of fomesafen at registered and reduced rates. S- Metolachlor was applied preemergence to all plots to suppress annual grasses. Snap bean injury generally increased as fomesafen rate increased, but at rates up to 0.28 kg ai/ha, injury by fomesafen was similar to or less than that from bentazon. Fomesafen at rates as low as 0.07 kg/ha provided near-complete control of common ragweed, and rates of 0.14 kg/ha or more of fomesafen controlled ivyleaf and pitted morningglories and 5-cm or smaller common lambsquarters as effectively as did bentazon. Control of all weed species from fomesafen alone at 0.21 kg/ha did not improve with the addition of bentazon at 0.28 kg/ha. Although snap bean injury from fomesafen was as high as 43% 1 wk after treatment, snap bean yield and net returns were similar to those from S-metolachlor alone. In a rate and application timing study, fomesafen at 0.14 kg/ha applied to three-trifoliolate snap bean was the least injurious to the crop, whereas applications at 0.28 kg/ha to one- or two-trifoliolate snap bean provided the best weed control.