Sensitivity of nonresistant winter wheat to quizalofop-P-ethyl in central Oklahoma and Kansas

Abstract

AbstractThe CoAXium® Production System includes a new herbicide-resistant wheat (AXigen®) that allows for fall and/or spring postemergence (POST) applications of quizalofop-P-ethyl (QPE) for control of winter annual grass weeds. As area planted with AXigen® wheat increases, so will the use of QPE herbicide, and with this comes an increased chance for physical drift, tank contamination, or misapplication to nearby sensitive plants. A total of eight field studies were conducted at four locations during the 2018–2019 and 2019–2020 growing seasons to understand the response of nonresistant wheat when exposed to various rates of QPE herbicide. Five rates of QPE were evaluated: 1× (92 g ai ha−1), 1/10×, 1/50×, 1/100×, and 1/200×. Treatments of QPE were applied in the fall (2- to 3-leaf wheat) or in the spring (3- to 4-tiller wheat). Results indicated an interaction between application timing and QPE rate on grain yield for half of the site-years. The 1× rate resulted in complete or near complete grain yield loss regardless of application timing. However, QPE at the 1/10× rate resulted in yield loss ranging from 0% to 41% when fall-applied, whereas spring application resulted in 80% to 100% yield loss. For site-years when only the main effect of QPE rate was significant, 86% to 100% yield loss was observed following exposure to QPE at the 1/10× and 1× rates. For all site-years, it was infrequent that significant yield reductions were observed following the three lowest rates of QPE. If the two highest QPE rates were considered to represent tank contamination or misapplication and the three lowest rates physical drift, we can assume that physical drift of QPE to non-AXigen® wheat is not of major concern if proper application guidelines are followed. Conversely, tank contamination and misapplication should be carefully considered by growers who have planted both AXigen® and non-AXigen® wheat varieties.