Evaluation Of Peanut Tolerance To Mid-Season Applications Of Ppo-Inhibitor Herbicides Mixed With Different Surfactants

Protoporphyrinogen oxidase (PPO) inhibitor herbicides are being increasingly used to control acetolactate synthases (ALS) inhibitor-resistant weeds in peanuts (Arachis hypogaea L.). However, PPO-inhibitor herbicides can injure the crop under certain application conditions, especially under abiotic stress and surfactants may exacerbate this injury. The objectives of this study were to 1) investigate the effect of PPO-inhibitor based treatments on dryland peanut growth and yield when applied at three timings in mid-season, 2) evaluate the interactions of surfactants, chloroacetamide herbicides, and PPO-inhibitors, and 3) assess the level of correlation of normalized difference vegetation index (NDVI) readings to traditional visible injury rating. Field studies were conducted in Henry and Escambia counties in Alabama, U.S. during 2018, and 2019. Up to 55% of visible peanut injury was observed with acifluorfen, lactofen, and carfentrazone-ethyl treatments. In general, the NDVI readings correlated significantly with traditional visible injury ratings. A tank mixture of chloroacetamide herbicides (pyroxasulfone, S-metolachlor, dimethenamid-P) with lactofen did not lead to more injury or yield loss than lactofen applied alone. Yield losses up 27% were observed with carfentrazone-ethyl plus a high surfactant oil concentrate (HSOC) at 75 and 90 days after planting (DAP) as compared to the non-treated check (NTC). Overall, treatments with HSOC and/or carfentrazone-ethyl were more likely to cause significant injury and yield loss than treatments with acifluorfen or lactofen plus nonionic surfactant (NIS). Peanuts are more sensitive to PPOinhibitor herbicides at 75 DAP. NDVI did provide additional plant health information to subjective injury ratings, however, neither of these measurements are reliable predictors of peanut yield loss.