By Laura Lindsey, Andy Michel, Horacio Lopez-Nicora-OSU Extension, Ag Crops Team and edited by Mark Badertscher-OSU Extension, Hardin County
HARDIN COUNTY–When should I spray a foliar fungicide? First, consider the disease triangle. For a disease to develop, there must be a susceptible host (Is your soybean variety resistant or susceptible?, a virulent pathogen (Is there a history of a certain disease in your field? Do you see any visual symptoms of disease?), and conducive environmental conditions. Most foliar diseases, such as brown leaf spot and frogeye leaf spot, are favored by wet conditions.