A Note on Below Label Rate Fungicide Use

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Research across the nation has shown that fungicides have the greatest potential to increase corn yields when applied to a susceptible hybrid under conditions that favor a disease epidemic. The rates provided have been shown through years of research to provide effective control of the pathogens listed on the label. In addition, rates are chosen that reduce the risk of fungicide resistance development; if a product is applied at below labeled rates it increases the likelihood for resistant individuals to survive and reproduce. There are many examples of fungal pathogens developing resistance to fungicides. For example, populations of the pathogen that causes frogeye leaf spot are now resistant to products that contain a group 11 (stobilurin) mode of action in several Southern and Midwestern states, greatly limiting the products growers can use to manage this disease. I encourage anyone applying fungicides to follow the label to ensure that these important disease tools remain effective for years to come and to ensure product effectiveness during the growing season.