Preemergence Flumioxazin and Pendimethalin and Postemergence Herbicide Systems for Soybean (Glycine max)

Field studies were conducted in 1998 and 1999 at two Illinois locations to compare flumioxazin and pendimethalin for preemergence (PRE) weed control and determine the benefit of these herbicides when followed by (fb) postemergence (POST) herbicides, glyphosate, imazethapyr, and imazamox. In early weed control ratings taken before POST applications, flumioxazin alone at 105 g ai/ha or pendimethalin alone at 1,120 g ai/ha resulted in less than 80% control of giant foxtail, but controlled common lambsquarters at least 85% in all experiments. Control of large-seeded broadleaf weeds with flumioxazin or pendimethalin varied greatly between experiments. At Urbana in 1998, where moisture was adequate before and after PRE applications, flumioxazin controlled velvetleaf, common cocklebur, and ivyleaf morningglory at least 90%. With the latter two species, control decreased in the subsequent year, probably because of the reduced precipitation after the PRE applications. Sequential applications including a PRE herbicide provided control up to 25% greater than did POST only treatments. At Dekalb in both years and Urbana in 1998, soybean yields were greater with most treatments containing a PRE fb POST application than with the treatments containing only POST applications.