The basis of selectivity for flumioxazin use in peanut and associated weeds

Flumioxazin is a Protox- inhibiting herbicide applied preemergence for the control of broadleaf weeds in peanut. The selectivity of the herbicide came into question the first year of commercial introduction when peanut injury was observed in grower fields. The relative tolerances of peanut and other species to pre- and post-emergence applications of flumioxazin were investigated, along with the effect of application timing on peanut injury, to provide informatio n on the basis for selectivity. Although peanut was more tolerant to flumioxazin than the weed species tested, peanut exhibited cell leakage and necrosis after contact with low concentrations, suggesting that differences in biochemical tolerances are not the basis for selective use. The timing of application influenced the effect of flumioxazin on peanut, providing further evidence that avoidance of contact of the herbicide to peanut is necessary to prevent injury. Peanut tolerated limited seedling injury, and produced healthy new growth. Results indicated that the selective use of flumioxazin in peanut is based on several factors, making applications to maximize avoidance of contact of the herbicide with the crop, differences in location of germinating seeds, and the ability of peanut to withstand injury.