Tar Spot Spreads Into Southwest Nebraska

Confirmations in Perkins, Chase and Dundy counties bring Nebraska's statewide total above 70 counties.

Updated on Nov. 2, 2026 in Botany

Close view of green corn leaves in a flat Plains field, several leaves dotted with dark tar-black lesions under open overcast sky. — Tar spot, a corn fungus, was confirmed in Perkins, Chase and Dundy counties, pushing Nebraska's statewide total past 70 of its 93 counties. AI Illustration. Upload story photo >

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Tar spot was confirmed in Perkins, Chase and Dundy counties in southwest Nebraska, pushing the statewide total past 70 of the state's 93 counties. Increased easterly winds accelerated the fungus's westward movement into the region.

Why it matters

Tar spot can cause rapid loss of healthy corn leaf area and accelerate plant drydown, threatening yields across the state's corn-growing regions. Cool, wet conditions favor the disease, so its spread through Nebraska's fields is a concern for growers.

Confirmed county counts show tar spot now covers more than 70 of Nebraska's 93 counties, compared with yield losses of 50-60 bushels per acre in susceptible hybrids during the 2018 and 2021 outbreaks. Disease thresholds include temperatures between 60°F and 73°F, relative humidity above 75% and seven or more hours of leaf wetness, while the 2026 impact on yields has not been determined.

The players

Phyllachora maydis

The fungus that causes tar spot in corn, which overwinters in fields and spreads through wind and splashing water.

The details

Tar spot, caused by the fungus Phyllachora maydis, spreads through wind and splashing water and overwinters in fields, redeveloping when conditions become favorable. Disease became more severe in many central and southern Nebraska fields during August and September, and fields with a history of severe tar spot may face greater risk in later years.

2015: Tar spot first reported in the United States in northern Indiana and Illinois.
2018 and 2021: Severe outbreaks caused yield losses of up to 50-60 bushels per acre in susceptible hybrids.
August and September 2026: Disease became more severe in central and southern Nebraska fields.
2026: Tar spot confirmed in southwest Nebraska, bringing the statewide total above 70 counties.

Seasonal Patterns

The 2026 spread follows the severe 2018 and 2021 outbreaks, which caused yield losses of 50-60 bushels per acre in susceptible hybrids after tar spot was first reported in the United States in 2015. The present infestation extends that multi-year pattern westward into southwest Nebraska.

Growers in Nebraska should monitor susceptible corn fields for tar spot, particularly where conditions are cool and wet. Fields with a history of severe disease may warrant closer scouting, and fungicide decisions can reference the approximately 6% ear leaf severity threshold.

The takeaway

Scouting susceptible corn fields during cool, wet weather can help growers detect tar spot early. Monitoring confirmed county reports can also indicate where disease pressure is building.