P-312 - Successfully managing Cercospora beticola in sugar beet using host resistance and timely fungicide applications

Cercospora beticola causes Cercospora leaf spot (CLS), the most economically damaging foliar disease of sugar beet. In 2016, USA growers lost over $200 million due to fungicide resistance and a CLS epidemic. In 2021, CR+ cultivars, which contain the C. beticola BvCR4 resistant gene, became available. Field trials were conducted in Foxhome, MN from 2021 through 2024 to determine the best time for fungicide applications to manage CLS in moderately tolerant cultivars (non-CR+) and improved CR+ cultivars that were artificially inoculated. Fungicide applications were applied on both a calendar basis and as-needed, depending on the presence of symptoms and favorable environmental conditions. Field trials showed that fungicides were essential to protect non-CR cultivars, but were generally unnecessary for CR+ cultivars during dry and warm summers. During wet and warm summers, fungicides were required for both non-CR and CR+ cultivars. Non-CR cultivars needed more fungicide applications and at shorter application intervals. Our research demonstrated that fungicide applications, starting either at row closure or when symptoms first appeared, followed by additional treatments based on symptom presence and favorable environmental conditions, resulted in effective disease management, high recoverable sucrose, and favorable economic returns. The availability and use of newer CR+ cultivars will enhance the economic viability of the sugar beet industry and help reduce the inoculum load, potentially making it feasible to grow non-CR+ cultivars in areas where CLS pressure is less severe.