What we've learned about tar spot of corn epidemiology in Maryland's climate
Agronomy & Pest Management
Andrew Kness
Agriculture Agent
University of Maryland Extension
Street
Abstract
Tar spot is a disease of corn caused by the fugus Phyllachora maydis and was first detected in the United States in 2015. The disease has spread rapidly throughout the US corn belt and significant yield reductions have been associated with tar spot epidemics. Tar spot was first confirmed in the Mid-Atlantic region of the US in Lancaster County, PA in 2020, followed by Maryland in 2022, and Delaware and New Jersey in 2023. Since the confirmation of tar spot in Harford County, MD in 2022, we have studied the distribution and management of this new disease in Maryland. In all three production years (2022-2024), tar spot was first confirmed in late August through September at relatively low levels, with most field infections ranging between 2-5% severity. To date, tar spot has been confirmed in 10 Maryland counties; however, no significant yield reductions have been associated with tar spot infections in Maryland, which is contrasting to data from the Midwest. Recently published research on tar spot epidemiology suggests that temperature is a major driver of infections; local weather data suggest that these parameters are not met in much of Maryland’s climate until mid-to-late August, which is several weeks past the critically susceptible growth stages and consistent with our observations of first reports of tar spot infections from 2022-2024. In 2023 we also conducted an on-farm fungicide trail to evaluate two fungicide timings for managing tar spot. A one-pass program at tasseling and a two-pass program (tassel and R2) suppressed tar spot infections early, but did not contribute to significantly greater yields compared to the non-treated control. This initial research on tar spot suggests that the impact and management of this disease may differ in Maryland and other warmer climates compared to the corn belt.
Authors: Andrew Kness
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Andrew Kness Agriculture Agent, University of Maryland Extension, Maryland, 21154