Field and greenhouse studies were conducted to evaluate sulfentrazone and flumioxazin as preemergence (PRE) herbicides for broadleaf weed control in potato. Sulfentrazone and flumioxazin were applied alone and in combination with s-metolachlor to determine the crop response and the weed spectrum controlled. These treatments were compared with metribuzin or rimsulfuron plus s-metolachlor treatments. Potato variety response to sulfentrazone and flumioxazin was evaluated in a separate field study. Sangre, Chipeta, Russet Norkotah, and Russet Nugget were treated with sulfentrazone from 0.14 to 0.28 kg/ha or flumioxazin from 0.035 to 0.07 kg/ha. Sulfentrazone and flumioxazin provided excellent broadleaf weed control at all the rates tested, whereas grass control increased as rate increased. Grass control improved when combined with s-metolachlor. Sulfentrazone and flumioxazin treatments were comparable with metribuzin and rimsulfuron treatments in weed control and total yield. Flumioxazin was safe when applied PRE to four selected varieties, whereas sulfentrazone produced initial phytotoxicity to Sangre and Chipeta at high rates but did not affect yields. Sulfentrazone increased the yield of U.S. No.1 potatoes compared with other treatments in the variety response study. Dose–response curves were used to generate the sulfentrazone, flumioxazin, and metribuzin herbicide rates required to reduce biomass by 50% (I50) for eight common weed species. Herbicides were applied PRE at several rates, and plant response was recorded. Log-logistic analysis was performed on bioassay data generated to estimate species sensitivity to each herbicide. Sulfentrazone reduced the biomass of hairy nightshade, black nightshade, redroot pigweed, kochia, common lambsquarters, and redstem filaree by more than 90% at 0.0175 kg/ha (the lowest rate evaluated), whereas flumioxazin had a similar effect on all broadleaf species except on kochia at 0.004 kg/ha (the lowest rate evaluated). Therefore, it was not possible to calculate I50 or even I80 values for most broadleaf species. Metribuzin I50 values could be calculated for most of the species tested. The metribuzin I50 value for hairy nightshade was 0.28 kg/ha, which was 16 and 70 times higher than the sulfentrazone and flumioxazin rates, respectively, that reduced hairy nightshade biomass by more than 90%. Sulfentrazone and flumioxazin appeared to be sufficiently safe when applied on potato and controlled several weed species common to potato production in the western United States.
Nomenclature: Flumioxazin; sulfentrazone; black nightshade, Solanum nigrum L. #3 SOLNI; common lambsquarters, Chenopodium album L. # CHEAL; hairy nightshade, Solanum sarrachoides Sendtner # SOLSA; kochia, Kochia scoparia L. # KOCSC; redstem filaree, Erodium cicutarium L. # EROCI; redroot pigweed, Amaranthus retroflexus L. # AMARE; potato, Solanum tuberosum L. ‘Chipeta’, ‘Russet Norkotah’, ‘Russet Nugget’, ‘Sangre’.
Additional index words: Arachis hypogaea, barnyardgrass, crop safety, diquat, ECHCG, Echinochloa crus-galli L., log-logistic analysis, MALNE, Malva neglecta Wallr., Panicum miliaceum L., PANMI, paraquat, Phaseolus lunatus, phytotoxicity, potato weed management, protoporphyrinogen oxidase inhibitors, Setaria viridis L., SETVI, weed dose–response, wild proso millet.
