Ohio has confirmed its first cases of tar spot for the 2026 growing season, with infections now identified in seven counties as corn moves through pollination and early grain fill. According to the latest updates released on July 29, the disease has been detected in Clark, Darke, Ross, Fayette, Wyandot, Morrow and Pickaway counties. The findings are important because tar spot can rapidly reduce photosynthetic leaf area during grain fill, potentially affecting yield when environmental conditions favor disease development.

The first confirmed case was reported on July 10 in Clark County, followed by additional detections over the next two weeks as field scouting intensified across the state. Since tar spot was first identified in Ohio in 2018, 49 of the state's 88 counties have now reported the disease at least once, illustrating how widely the fungal pathogen has expanded across one of the country's major corn-producing regions. During 2026, positive cases have also been confirmed in Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Nebraska, New York, Virginia and Wisconsin, highlighting its continued spread across the U.S. Corn Belt.

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Agronomists Recommend Close Monitoring as Humidity Increases

Field agronomists report that Ohio's corn crop remains in generally good condition, despite localized drought in parts of southern Ohio. Cooler temperatures during pollination helped improve pollen viability and reduced heat stress across many fields, supporting favorable crop development. However, increasing humidity and longer periods of leaf wetness are beginning to create more favorable conditions for foliar diseases, including tar spot, gray leaf spot and northern corn leaf blight. Although disease pressure is still considered relatively low, specialists recommend that growers continue regular scouting while evaluating whether fungicide applications will be needed during the grain-filling period.

Crop development has advanced rapidly across the state. The latest USDA Crop Progress report indicates that 63% of Ohio's corn had reached the silking stage by the week ending July 26, matching the five-year average and improving significantly from 42% one week earlier. In addition, 13% of fields had entered the dough stage, compared with 4% the previous week, indicating that much of the crop remains within the growth stages where disease management decisions can directly influence yield potential.

Despite the appearance of the season's first tar spot cases, overall crop conditions remain encouraging. According to the USDA, 60% of Ohio's corn is currently rated Good to Excellent, while only 5% falls into the Poor or Very Poor categories. These ratings suggest that timely rainfall, moderate temperatures and successful pollination have largely supported crop performance, even as growers prepare for the possibility of higher disease pressure during August.

For producers, the priority over the coming weeks will be balancing fungicide decisions with field-specific disease risk. Agronomists emphasize that not every field will require treatment, making continued scouting and accurate disease identification essential before making management decisions. If weather conditions remain favorable for fungal development, additional tar spot detections are expected as the crop progresses toward physiological maturity.

Ohio Corn Condition Ratings (Week Ending July 26, 2026)

Source: USDA Crop Progress Report (Week Ending July 26, 2026).