LAUSR

BACKGROUND The transgenic event DAS44406-6 - E3 - makes soybeans that are herbicide (glyphosate, 2,4-D and glufosinate) and caterpillar resistant. The E3 soybean was commercially released for the 2021/2022 harvest in Brazil. We conducted this study to test if glyphosate (Gly) and 2,4-D applied alone and in a commercial mixture affect Asian soybean rust (ASR). Assays were conducted through detached leaf, and in vivo, in a controlled environment, using the herbicides Gly, 2,4-D, and Gly+2,4-D, and pathogen inoculation. Disease severity, and spore production were evaluated. RESULTS Only the herbicides Gly and Gly+2,4-D caused inhibitory ASR in detached leaves and in vivo. When applied preventatively and curatively in vivo, these herbicides reduced the severity of disease and spore production of the fungus. In vivo, the inhibition of disease severity reached 87% for Gly+2,4-D and 42% for Gly. A synergistic effect of commercial Gly+2,4-D mixture was observed. The application of 2,4-D alone in the in vivo assays did not reduce or increase severity. Gly and Gly+2,4-D act residually in inhibiting the disease. Growing E3 soybeans may combine weed and caterpillar management benefits and ASR inhibition. CONCLUSION The application of Gly and Gly+2,4-D herbicides in resistant E3 soybean presents inhibitory activity for ASR.