Effect of seed treatment on early season brown spot caused by Septoria glycines of soybean

Early season brown spot caused by Septoria glycines was compared in Illinois, Indiana, Iowa, Michigan, and Ontario, Canada, soybean fields planted with differing commercial seed treatments. Seed treatments that included fluopyram significantly reduced brown spot (P < 0.001). A greenhouse mist chamber experiment revealed that fluopyram seed treatment reduced the Area Under Disease Progress Curve of brown spot over a 6-week period (P < 0.001). Brown spot severity was unaffected by plant age at inoculation for the control treatment without fluopyram (P = 0.911); however, severity increased with plant age at inoculation for the fluopyram treatment (P = 0.009). The sensitivity of two S. glycines isolates to fluopyram was assessed by determining the effective concentration required to reduce its colony diameter growth in culture by 50% (EC₅₀). Both isolates had an EC₅₀ of 0.41 μg/ml of fluopyram. These results demonstrate that fluopyram seed treatment is effecttive at controlling early season brown spot in soybean.