Cover crops and fall residual herbicides for managing Italian ryegrass

Abstract

North Carolina growers have long struggled to control Italian ryegrass, and recent research has confirmed Italian ryegrass biotypes resistant to nicosulfuron, glyphosate, clethodim, and paraquat. Integrating alternative management strategies is crucial to effectively control such biotypes. The objectives of this study were to evaluate Italian ryegrass control with cover crops and fall-applied residual herbicides and investigate cover crop injury from residual herbicides. This study was conducted during the fall/winter of 2021-22 in Salisbury and fall/winter of 2021-22 and 2022-23 at Clayton, NC. The study was designed as a 3x5 split-plot, where the main plot consisted of three cover crop treatments (no-cover, cereal rye at 80 kg ha^-1, and crimson clover at 18 kg ha^-1), and the subplots consisted of five residual herbicide treatments (S-metolachlor, flumioxazin, metribuzin, pyroxasulfone, and nontreated). In the 2021-22 season at Clayton, metribuzin injured cereal rye and crimson clover 65% and 55%, respectively. However, metribuzin injured both cover crops ≤6% in 2022-23. Flumioxazin resulted in unacceptable crimson clover injury with 50% and 38% in 2021-22 and 2022-23 in Clayton and 40% at Salisbury, respectively. Without preemergence herbicides, cereal rye controlled Italian ryegrass 85% and 61% at 24 WAP in 2021-22 and 2022-23 at Clayton and 82% in Salisbury, respectively. In 2021-22, Italian ryegrass seed production was lowest in cereal rye treatments at both locations, except when cover crop was treated with metribuzin. For example, in Salisbury, cereal rye plus metribuzin resulted in 39324 seeds m^–2, compared to ≤4386 seeds m^–2 from all other cereal rye treatments. In 2022-23, Italian ryegrass seed production in cereal rye was lower when either metribuzin or pyroxasulfone were used PRE (2670 and 1299 seeds m^–2, respectively) when compared to cereal rye without herbicides (5600 seeds m^–2).