RESPONSE OF BROADLEAF WEEDS AND SOYBEANS TO THE DIPHENYL ETHER HERBICIDES

The response of crop and weed species to herbicides within the same family may vary considerably. The detrimental effect of late seeding of soybeans [Glycine max (L.) Merr.] is expressed as a reduction in individual plant yield components. Any temporary suppression in plant growth due to herbicides may cause additional yield reductions. Field studies were conducted to determine the response of 15 weed species and soybeans to acifluorfen, fomesafen, and lactofen, and the effect of these herbicides on foliar injury and seed yields of determinate soybeans when seeded at post-optimal dates. Herbicides were applied to weeds and soybeans at 3 wk after seeding and to soybeans in the V4 to V5 stage when grown under weed-free conditions. Weed control was similar with all three herbicides. Differences observed in weed control among herbicides appeared to be of little practical importance. Soybeans exhibited differential herbicide tolerance (fomesafen > acifluorfen > lactofen). Soybean injury increased as rates of acifluorfen and lactofen increased, but was not affected by increasing rates of fomesafen. Soybean seed yields were not reduced by herbicides. Determinate soybeans seeded at post-optimal dates appear to recover from foliar injury caused by these herbicides and seed yields are not affected.