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Poster: Epidemiology: Risk Assessment


Effect of soybean canopy closure on Sclerotinia sclerotiorum apothecia production, ascospore release, and primary plant infection of soybean
M. FALL (1), M. Chilvers (1), A. Byrne (1), J. Wilbur (2), D. Smith (2) (1) Michigan States University, U.S.A.; (2) University of Wisconsin-Madison, U.S.A.

Identifying the best timing for fungicide applications to get the optimum white mold control poses a major challenge to soybean producers. This study investigated the impact of canopy closure on apothecia development and ascospore release, to optimize fungicide application timing. In 2015, 0.355 m and 0.762 m row spacing replicated soybean plots were established at the MSU Montcalm Research Farm. The foliar fungicide Endura (boscalid) was applied to treated plots at the beginning of flowering, R1. The number of apothecia, ascospores, and the disease severity were monitored two times/week. Apothecia were first observed in the 0.355 m plots at full flower, R2, 8 d before they were observed in the 0.762 m plots, at beginning of pod development, R3. The number of apothecia was 50 times higher in the 0.355 m plots than in the 0.762 m plots. Incubated plants were symptomatic up to 13 and 18 days prior to symptom development in the 0.355 m and 0.762 m plots, respectively. There were no significant differences between non-treated and Endura treated plots in terms of final disease intensity and yield. However, there was a significant delay in disease severity (P<0.000) between treated and non-treated fungicide plots for the first 5 and 10 d after fungicide application in the 0.355 m and 0.762 m plots, respectively. There was a quantitative relationship between the number of apothecia and the soil temperature and between the number of apothecia and canopy closure.