Wayne County Corn Growers Face Tar Spot Decision

Tar spot has been confirmed in corn fields in Wayne County, Ohio, prompting growers to carefully evaluate crop stage, weather, and economics before applying fungicides. The disease, caused by the fungus Phyllachora maydis, is characterized by small, raised, black spots called stromata that cannot be rubbed off the leaf surface.

Under favorable conditions, tar spot can spread rapidly through the canopy, causing premature leaf death, reduced grain fill, lower test weight, and potentially significant yield loss. Purdue University researchers have documented yield losses ranging from 20-60 bushels per acre during severe outbreaks when disease developed before grain fill was complete.

While the appearance of tar spot is not unexpected given its spread across Ohio and the Midwest over the last several weeks, its confirmation raises important management questions for growers. Disease development depends heavily on weather, crop growth stage, hybrid susceptibility, and field-specific disease pressure.