Efficacy of Seed-Applied Fungicides Against Damping-Off Caused by Pythium and Globisporangium spp. in Soybean ( Glycine max ) in North America

Damping-off of soybean caused by soilborne oomycetes of the genera Globisporangium and Pythium pose a significant threat to soybean production, reducing emergence and yield in North America. Metalaxyl and metalaxyl-M are widely used against oomycetes in soybeans and corn; however, the repeated use of these active ingredients might lead to reduced sensitivity of some populations, increasing the interest in potential alternative active ingredients. Few field studies have assessed the effect of commercially available fungicide seed treatments on damping-off caused by these pathogens. This study evaluated the efficacy of fungicide seed treatments against Globisporangium and Pythium species across North America. In 2024, eight field trials were conducted in Indiana, Iowa, Ohio, Ontario, Michigan, North Dakota, Tennessee, and Wisconsin. Trials in Ohio, Ontario, and Tennessee relied on natural inoculum, whereas others were infested at planting with different pathogen species. Five commercial fungicide seed treatments were tested at label rates: (i) imidacloprid, mefenoxam, fluoxastrobin, and prothioconazole; (ii) clothianidin, ethaboxam, ipconazole, and metalaxyl; (iii) inpyrfluxam; (iv) thiamethoxam, mefenoxam, fludioxonil, and sedaxane; and (v) thiamethoxam, picarbutrazox, mefenoxam, fludioxonil, and sedaxane. A nontreated control was included. Fungicide seed treatment significantly improved seed emergence at the growth stages VC ( P = 0.0178) and V2 ( P = 0.0056). All treatments showed a positive yield effect compared with the nontreated control, although the differences were not statistically significant ( P > 0.7081). These findings suggest that seed treatments provide protection against damping-off, but further research is needed to clarify their utility in soybean production, particularly under low seeding rates.