Soybean Cultivars and Fungicide Responses to Frogeye Leaf Spot – Ten Years of Field Data.

Frogeye leaf spot (FLS) caused by Cercospora sojina Hara is a common foliar pathogen of soybean in the southern United States and regularly present in parts of the Midwestern United States. Infection due to this disease can lead to dramatic loses of photosynthetic area on green leaves, premature loss of leaves, and can lead to compromised stems, pods, and seeds.  Yield losses ranging from 20-40% are not uncommon in years where weather conditions are favorable for fungal growth and cultivars lack genetic resistance. Producers, in areas where FLS has historically caused yield losses, have attempted to combat the disease with cultivar selection and a foliar fungicide spray regime.  To screen cultivars for FLS resistance yearly cultivar trials were conducted in Milan, TN from 2003 – 2013 in a continuous no-till. Cultivars were arranged in a randomized split-plot design, with cultivars as the main plot and fungicide application at growth stage R3 as sub plots with 4 replications. Cultivars tested included maturity group (MG) III, MG IV, and MG V. The severity of FLS and yield on treated and nontreated plots were recorded to determine FLS effect on cultivar and the effect of fungicide application on FLS severity and yield of each cultivar. Results based on this research continue to support that some of the most useful techniques for producers to manage FLS and increase yield are to use cultivar selection coupled with an appropriate fungicide regime. Further classification of cultivars into low, moderate, and highly susceptible categories may better guide fungicide decisions based on the results of these trials.