Peanut Response to Postemergence Applications of Chlorimuron

There has been a renewed interest in the use of chlorimuron to control late-season Florida beggarweed in peanut. Postemergence (POST) applications of chlorimuron are one tool to help reduce economic losses from late-season Florida beggarweed populations. However, prior research has shown that peanut cultivar tolerance to chlorimuron varied among peanut cultivars and that applications of chlorimuron can increase the incidence of tomato spotted wilt virus (TSWV). Therefore, small-plot field trials were conducted from 2021-2024 near Ty Ty, Georgia to evaluate the response of seven peanut cultivars to POST applications of chlorimuron. Three separate experiments, each conducted three times, evaluated the response of AU-NPL17, FloRun 331, Georgia18RU, Georgia-20VHO, TifNV-High O/L Georgia-12Y and Georgia-16HO to chlorimuron applied POST. In each study, chlorimuron was applied at 9 g ai ha -1 with a non-ionic surfactant at 0.25% v/v to peanut at 65, 75, and 90 d after planting (DAP); a no chlorimuron treatment was included for comparison. Results indicated there was no interaction between chlorimuron timing and peanut cultivar. Application timing influence on peanut height and TSWV varied. When averaged over application timings, peanut height and TSWV incidence varied based on cultivar response ranging from 36 to 48 cm, and 9% to 38%, reduction compared with the non-treated, respectively. This is likely the result of natural variations in height and sensitivity to TSWV. Height reductions and increases in TSWV were observed depending on the experiment. However, regardless of height reductions and TSWV increases, peanut yield was reduced (8%) in experiment 2 (Georgia-12Y) when chlorimuron was applied 65 DAP and (13%) in experiment 3 (Georgia-16HO) when chlorimuron was applied at 75 DAP. These results suggest that these new cultivars express tolerance variability to POST applications of chlorimuron. Peanut growers should carefully consider cultivar selection for fields with problematic populations of Florida beggarweed if chlorimuron is to be used as a POST management strategy.