Effect of Stenocarpella maydis and Stenocarpella macrospora Inoculation Timing on Diplodia Ear Rot of Corn

Stenocarpella maydis (Berk.) Sutton and S. macrospora (Earle) Sutton are both causal agents of Diplodia ear rot (DER) of corn in the United States; however, DER caused by S. macrospora has not been as well studied as S. maydis in trials examining disease development. Field experiments were established in Kentucky to examine the effect of inoculation timing at one of four growth stages (eight-leaf collar [V8], silking [R1], blister [R2], and milk [R3]) on DER severity, yield, and test weight. Experiments were conducted under dryland and irrigated conditions in 2019 and 2020 and under irrigated conditions in 2021. Treatments inoculated by either pathogen at silking (R1) resulted in higher DER than treatments where inoculation occurred at the milk stage (R3) in all years. Yield was reduced in treatments inoculated at R1 compared to the noninoculated treatment in all trials and years, except the irrigated trial in 2019. A negative relationship was found between DER severity and corn yield and test weight: as DER severity increased, subsequent yield and test weight of corn decreased. This research indicates that an R1 inoculation timing of both Stenocarpella pathogens can negatively impact yield and grain quality.