HERBICIDE EFFICACY ON 4 AMARANTHUS SPECIES IN SOYBEAN (GLYCINE-MAX)

Field and greenhouse studies were conducted in 1995 and 1996 in Kansas to determine the efficacy of 21 herbicide treatments for control of t umble pigweed, Palmer amaranth, redroot pigweed, and two biotypes of c ommon waterhemp in soybean. In field studies, nine of eleven preemerge nce treatments controlled all four species 90% or more. However, pendi methalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than the other preplant incorporated and preem ergence treatments. With the exception of flumiclorac and NAF-75, post emergence treatments controlled 75 to 90% of all four species. A bioty pe of common waterhemp collected in Iowa was not controlled by acetola ctate synthase-inhibiting herbicides. Greenhouse results were similar to field experiments. Results suggest at least 90% control of these Am aranthus species is possible with proper herbicide selection.