Using soybean chaff lining to manage waterhemp (Amaranthus tuberculatus) in a soybean–corn rotation

Abstract

AbstractWaterhemp (Amaranthus tuberculatus[Moq.] Sauer) escapes are common in midwestern U.S. soybean [Glycine max(L.) Merr.] fields due to the continued rise in herbicide-resistant (HR) populations. In a conventional harvesting system, weed seeds are harvested with the crop grain and spread back on to the field. Harvest weed seed control methods such as chaff lining concentrate weed seed-bearing crop and weed chaff into a narrow row (chaff line). These chaff lines (30- to 50-cm wide) are undisturbed the following growing seasons, under the assumption that the chaff line creates an environment less favorable for weed seed germination and survival. Field experiments were conducted in a soybean–corn (Zea maysL.) rotation in 2020 and 2021 in Ames, IA, and Roland, IA, to quantify the effectiveness of chaff lining for managingA. tuberculatusseeds. About 70% of theA. tuberculatusseeds were retained on the mother plant at soybean harvest in 2020. The chaff lining system concentrated more than 99% of theA. tuberculatusseeds exiting the combine into the chaff line. AlthoughA. tuberculatuspopulation density in 2021 was 76% higher inside the chaff line than outside the chaff line,A. tuberculatusaboveground biomass was 63% lower inside the chaff line than outside the chaff line at 12 wk after corn planting. Similarly,A. tuberculatusinside the chaff line had delayed emergence compared withA. tuberculatusoutside the chaff line. Application of preemergence herbicides in corn inside the chaff line delayedA. tuberculatusemergence by more than 2 wk compared withA. tuberculatusoutside the chaff line. Additionally, a follow-up postemergence herbicide application in corn was needed only inside the chaff line to manageA. tuberculatus, suggesting the possibility of lower overall herbicide use. These results support implementing chaff lining in soybean-based crop systems of the U.S. Midwest to help manage HRA. tuberculatusseedbanks.