Funded by the Illinois Soybean Association checkoff program.
M.S. Level Student
University of Illinois at Urbana-Champaign
Advised by Dr. Aaron Hager
Weed Management In Early-Planted Soybean
Field experiments were conducted in 2021 and 2022 at four locations across Central Illinois to determine the most effective weed management program in early-planted soybean. By extending the growing season with an earlier planting date, the relationship between soybean growth and weed emergence timings will influence herbicide applications to ensure minimal weed seed production and to protect crop yield. Therefore, the objectives of this research were to examine various herbicide treatment programs applied at different timings and rates to assess their effect on weed control and soybean yield. Preemergence (PRE) treatments consisted of a metribuzin plus S-metolachlor premix at planting and just prior to soybean emergence at either 1x or 1/2x rates. Postemergence (POST) treatments were applied when weeds reached 10 cm tall, and consisted of glufosinate + glyphosate + ammonium sulfate, with or without pyroxasulfone at a 1x or 1/2x rate. Treatments comprised of both a full rate of PRE and POST provided the highest and most consistent level of weed control. The addition of pyroxasulfone to POST treatments did not consistently improve late-season weed control, although weed emergence following POST applications was often reduced. This could be attributed to an earlier soybean canopy closure date that helped to suppress weeds. The full rate PRE extended the timing of POST application 2-3 weeks for 85% of the treatments at all locations except Urbana both years. Full-rate PRE treatments also reduced the time between soybean canopy date and the foliar application. Overall, a full rate PRE reduced early-season weed interference and helped alleviate soybean yield loss.