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 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 causal species was identified based on conidia morphology. In 2019, S. macrospora was identified in 33.8% of inspected ears, and 36.9% of ears in 2020, while S. maydis was confirmed in 66.2% of inspected ears in 2019 and 63.1% in 2020. Incidence of DER was higher 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). Results from this study emphasize the importance of including both Stenocarpella spp. in future research and discussion on DER.