This project seeks to build on previous fungicide application timing, fungicide droplet size, and soybean seeding rate research funded by the ND Soybean Council to improve white mold management and address common stakeholder questions. When conditions favor white mold as soybeans enter bloom, previous research showed that fungicides should be applied at canopy closure or as soon as 100% of plants reach R2, whichever occurs first. That research was conducted with a single fungicide application made with fine droplets; this project seeks to evaluate optimal timing when 1 versus 2 applications are made and droplet size is calibrated relative to canopy characteristics. Previous research showed that soybean yields under white mold pressure can be increased by 50-100% by calibrating fungicide droplet size relative to canopy closure and nozzle manufacturer. That research was done with TeeJet and Wilger nozzles and soybeans seeded to narrow (15-inch) or intermediate (21-inch) rows. This project seeks to optimize droplet size in soybeans seeded at three seeding rates in 21-inch and 30-inch rows. Testing will be conducted with TeeJet extended-range vs. John Deere ‘3D’ flat-spray nozzles, advertised to reduce driftable fine droplets by 50-70%. Evaluating multiple seeding rates will permit assessment of the impact of canopy density on optimal fungicide droplet size and the impact of low seeding rates on white mold management. Research conducted on dry beans has shown that optimal white mold fungicide application timing differs when one versus two applications are made, and canopy density within rows can impact optimal fungicide droplet size.

(1) Under conditions that favor white mold as soybeans enter bloom, identify optimal fungicide application timing for one versus two fungicide applications and fungicide droplet size calibrated relative to canopy characteristics. (2) Optimize fungicide droplet size for white mold management relative to canopy characteristics in soybeans seeded at different seeding rates in 21 vs. 30-inch rows. (3) Evaluate the performance of John Deere’s ‘3D’ drift-reducing flat-spray nozzles versus TeeJet extended range flat-spray nozzles. (4) Evaluate the impact of seeding rate on white mold management and soybean agronomic performance under white mold pressure.

(1) Development of rigorous recommendations for fungicide application timing, fungicide droplet size and soybean seeding rate that optimize disease management and soybean yield under white mold pressure. (2) Dissemination of results to North Dakota soybean growers, crop advisors, and extension personnel.

This project will improve the profitability of soybean production in fields where Sclerotinia is a problem by identifying profit-maximizing strategies to improve soybean agronomic performance and profitability under white mold disease pressure.