Interactions between cover crops, herbicides and weeds in soybean production systems
The use of cover crops in soybean production systems has increased in recent decades. There are many questions surrounding cover crops, specifically their benefits to crop production and how to best manage them. One management aspect to consider is how to effectively terminate cover crops in the spring before soybean planting. Few studies have been conducted to evaluate the effect of different herbicide treatments on the termination of a variety of different cover crop species in the spring. An identical field experiment was conducted in 2016 in Arkansas, Indiana, Missouri and Wisconsin and repeated in Arkansas, Indiana, Mississippi and Missouri in 2017 to evaluate the most effective herbicide treatments for spring termination of regionally-specific cover crops, including annual ryegrass Austrian winter pea, cereal rye, crimson clover, hairy vetch, purple top turnip, triticale and wheat. Cover crop species were planted from September 4 to September 24 in 2015 and from September 27 to November 2 in 2016. Glyphosate-, glufosinate-, and paraquat-based treatments were applied between April 15 and April 29 in 2016 and April 10 and April 20 in 2017. Visible control of cover crops was determined 28 days after application. Glyphosate-based herbicide treatments were more effective and provided from 71 to 97% control of grass cover crop species across all site years compared to paraquat- and glufosinate-based treatments, which provided 72 to 83% and 64 to 76% control, respectively. Across all site-years, 1.12 kg glyphosate ha-1 applied alone and with 0.56 kg 2,4-D ha-1, 0.025 kg saflufenacil ha-1 or 0.56 kg clethodim ha-1 were the only treatments to be most effective on all grass cover crop species. Annual ryegrass control ranged from 85 to 94% with glyphosate alone or in combination with 2,4-D, saflufenacil and clethodim; and paraquat plus metribuzin plus 2,4-D ha-1. Glyphosate-, paraquat- or glufosinate-based treatments were generally most effective on broadleaf cover crop species when applied with 2,4-D or dicamba. Results from this research indicate that proper herbicide selection is crucial to the successful termination of cover crops in the spring.