Prevalence of Stenocarpella maydis and Stenocarpella macrospora Causing Diplodia Ear Rot in Kentucky

Kentucky corn (Zea mays L.) fields were surveyed in 2019 and 2020 for the presence of Diplodia ear rot (DER) to document the prevalence and distribution of the disease and determine the frequency of DER causal agents Stenocarpella maydis (Berk.) Sutton and Stenocarpella macrospora (Earle) Sutton. In 2019, 92 fields were surveyed, and 125 of 4,600 inspected ears were confirmed to be infected by either causal agent. In 2020, 87 fields were surveyed, and 45 of 4,350 ears examined were confirmed to be infected by either causal agent. Fungi were isolated from corn ears with suspected signs and symptoms of DER, and the causal species was identified based on conidia morphology. S. macrospora was identified in 33.8% of inspected ears in 2019 and 36.9% in 2020, and S. maydis was confirmed in 66.2% of inspected ears in 2019 and 63.1% in 2020. In 2019, ears infected with S. macrospora had greater disease severity than those infected with S. maydis (P = 0.0245). The incidence of DER was greater in fields with a previous crop rotation of double crop wheat/soybean (P = 0.0113); however, DER severity was not affected by previous crop rotation (P = 0.3454). The results from this study emphasize the importance of including both Stenocarpella species in future research and discussions on DER.