Oxathiapiprolin Alone or Mixed with Metalaxyl Seed Treatment for Management of Soybean Seedling Diseases Caused by Species of Phytophthora , Phytopythium , and Pythium .

Species of Phytophthora , Phytopythium , and Pythium affect soybean seed and seedlings each year, primarily through reduced plant populations and yield. Oxathiapiprolin is effective at managing several foliar diseases caused by some oomycetes. The objectives of these studies were to evaluate oxathiapiprolin in a discriminatory dose assay in vitro; evaluate oxathiapiprolin as a soybean seed treatment on a moderately susceptible cultivar in 10 environments; compare the impact of seed treatment on plant populations and yields in environments with low and high precipitation; and compare a seed treatment mixture on cultivars with different levels of resistance in four environments. There was no reduction in growth in vitro among 13 species of Pythium at 0.1 µg ml -1 . Soybean seed treated with the base fungicide plus oxathiapiprolin (12 and 24 µg a.i. seed -1 ) alone, oxathiapiprolin (12 µg a.i. seed -1 ) plus mefenoxam (6 µg a.i. seed -1 ), or oxathiapiprolin (24 µg a.i. seed -1 ) plus ethaboxam (12.1 µg a.i. seed -1 ) had greater yields in environments that received ≥50 mm of precipitation within 14 days after planting compared with those that received less. Early plant population and yield were significantly higher for seed treated with oxathiapiprolin (24 µg a.i. seed -1 ) + metalaxyl (13.2 µg a.i. seed -1 ) compared with nontreated for six of seven cultivars in at least one of four environments. Oxathiapiprolin combined with another Oomycota fungicide applied to seed has the potential to be used to protect soybean plant establishment and yield in regions prone to poor drainage after high levels of precipitation.