Evaluation of Organic Fungicides for Control of Hemp Powdery Mildew, Geneva, NY, 2025

Powdery mildew, caused by the fungus Golovinomyces ambrosiae, is a common disease of greenhouse-grown hemp ( Cannabis sativa L.). Symptoms include white, powdery patches on the adaxial leaf surface that spread to other plant tissues including stems and inflorescences, impacting the plant's photosynthetic capacity and marketability. The purpose of this study was to evaluate the efficacy of organic fungicides commonly used to manage hemp powdery mildew in New York. The field trial was conducted in 2025 in Geneva, NY, on ‘White CBG’, a hemp cultivar with known susceptibility to G. ambrosiae. This report provides useful information for hemp growers who aim to reduce losses from powdery mildew infections and to develop disease management programs.