HPPD inhibitor-susceptible soybean growth, yield, and economic return following isoxaflutole and mesotrione applied postemergence

Abstract

The use of different herbicide-resistant soybean technologies in proximity could lead to injury and yield loss due to an application error. Research was initiated to evaluate the effect of 6.25, 12.5, and 100% doses of isoxaflutole and mesotrione field use doses applied postemergence to 4-hyroxyphenylpyruvate (HPPD)-susceptible soybean, representing physical drift or misapplication doses. Visible injury manifested as chlorosis with slight necrosis, progressing to necrosis and height reduction, with visible height reduction as the only symptom. Isoxaflutole at 6.25 and 12.5% injured V2 soybean greater than V1 or V4 soybean at all evaluation dates. This is supported by soybean height data 14, 28, and 42 d after treatment (DAT). Following the 100% dose, maximum injury occurred 28 DAT with V1, V2, and V4 soybean injured 90, 85, and 72%, but injury declined over time. All isoxaflutole treatments reduced yield at least 310 kg ha-1, with no differences among application timings or between the two lowest doses for a revenue loss of 147 to 623 US$ ha-1. Visible injury following mesotrione manifested as chlorosis and necrosis advancing to visible height reduction. Following mesotrione at 6.25 and 12.5%, injury ranged 20 to 36% among application timings and did not differ 3 to 21 DAT. Soybean heights 28 and 42 DAT do not support injury observations; therefore, the greater injury was due to chlorosis and necrosis. Following mesotrione at 100%, sensitivity decreased when applied to later growth stages 3 to 14 DAT with no differences 42 DAT. Yields did not differ among application timings, but yield losses were at least 240 kg ha-1, with revenue losses of 60 and 373 US$ ha-1. Producers are cautioned to prevent off-target movement or errant application of isoxaflutole or mesotrione to HPPD susceptible soybean.