Vertical mobility, soil adsorption, and cotton tolerance to three Protoporphyrinogen oxidase (PPO) inhibiting herbicides in three West Texas soils
Asher, Brady Scott
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Soil-residual herbicides are very important in global crop production and are the foundation of an effective cotton (Gossypium hirsutum L.) weed management program. Soil-residual herbicides may reduce the number of postemergence (POST) herbicide applications that are needed and may prevent or delay weed shifts or the development of glyphosate- or glufosinate-resistant weeds. Increasing infestations of glyphosate- and ALS-resistant Palmer amaranth (Amaranthus palmeri S. Wats) in cotton has forced producers to utilize herbicides with alternative modes of action in their management systems, including glufosinate and protoporphyrinogen oxidase inhibiting (PPO) herbicides. Trifludimoxazin [1,5-dimethyl-6-sulfanylidene-3-(2,2,7-trifluoro-3-oxo-4-prop-2-ynyl-1,4-benzoxazin-6-yl)-1,3,5-triazinane-2,4-dione] is a new PPO herbicide under development by BASF Corporation that is being evaluated for possible use as a soil-residual treatment in cotton for the control of annual small-seeded broadleaf weeds, including Palmer amaranth. Laboratory and greenhouse studies were conducted to compare vertical mobility, soil adsorption, and cotton tolerance of trifludimoxazin in three West Texas soils [Acuff (Cotton Center, TX) - loam, 1.5% organic matter (OM), 8.3 pH, 22.1 cation exchange capacity (CEC); Amarillo (Seagraves, TX) - loamy sand, 0.3% OM, 8.2 pH, 8.7 CEC; Olton (Halfway, TX) - loam, 1.0% OM, 7.6 pH, 23.1 CEC] to flumioxazin and saflufenacil, which are two currently registered PPO herbicides for use in cotton. Vertical soil mobility of trifludimoxazin was similar to flumioxazin in the Acuff and Olton soils, but was more mobile in the Amarillo soil. The depth of movement, resulting from the 2.54 cm irrigation event, of trifludimoxazin in all soils ranged from 2.5 to 5.0 cm, which would not allow for crop selectivity based on placement, as ideal cotton planting is from a depth of 0.6 to 2.54 cm deep. Soil adsorption studies estimated that trifludimoxazin was ~70% adsorbed in the Acuff soil, ~ 60% in the Olton soil, and ~50-60% in the Amarillo soil. Additional adsorption studies with four additional soils indicated that percent OM was the only soil parameter that was important for adsorption of trifludimoxazin. Greenhouse studies indicated that preemergence treatments were more injurious than the 14 d preplant (PP) treatment when summarized across soils for the three herbicides (43% and 14% injury, respectively). No differences in visual cotton response or dry-weight was observed following PP trifludimoxazin treatments as compared to the nontreated control within each of the three West Texas soils and was similar to the flumioxazin PP treatments across soils. Based on the results of these studies, a use pattern for trifludimoxazin in cotton may be established with the utilization of a > 14 d PP application requirement prior to cotton planting.