Peanut cultivar tolerance and weed control with fluridone applied preemergence in Georgia

Increasing challenges associated with herbicide resistance in weeds necessitates the exploration of herbicides with underutilized modes of action. Currently, fluridone is labeled in cotton for preemergence (PRE) control of small-seeded broadleaf weeds and annual grasses. But, no information is available evaluating current peanut cultivar response to fluridone and its utility in a peanut weed control system. Thus, three unique field experiments were conducted and replicated in time from 2019 through 2022 to determine the response of seven peanut cultivars to PRE applications of fluridone and to determine the efficacy of fluridone at multiple rates and tank-mixtures (acetochlor, diclosulam, dimethenamid-P, pendimethalin, S-metolachlor, and trifludimoxazin) for weed management. At rates ≥ 168 g ai/ha, fluridone caused significant peanut injury in the form of leaf bleaching and necrosis under extreme moisture and temperature conditions. In this scenario, fluridone at 336 and 673 g ai/ha caused 18% and 54% yield losses. Under ideal environmental conditions only 673 g ai/ha of fluridone resulted in significant peanut yield loss (6%). Fluridone rates ≤ 252 g ai/ha did not reduce peanut yield in any experiment. Although peanut cultivar differences were not common across experiments, GA-16HO exhibited increased leaf bleaching and necrosis when compared to GA-18RU. In the weed control experiment, PRE fluridone tank-mixtures were less injurious to peanut when compared to the current standard flumioxazin system at 2 weeks after application (WAA). Palmer amaranth control with fluridone based systems was ≥ 86%, wild radish control was ≥ 92%, and annual grass control was ≥ 94%, which was similar to the standard flumioxazin based systems. Collectively these data support the use of fluridone at a maximum rate of 168 g ai/ha in a total peanut weed control system. In 2023, fluridone received a federal label for use in peanut at rates ranging from 126 to 168 g ai/ha.