Tar Spot Corn Disease Spreads Across Nebraska
The fungus Phyllachora maydis has reached three additional southwest counties in Nebraska.
Updated on Oct. 27, 2026 in Botany
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The corn disease tar spot, caused by the fungus Phyllachora maydis, has expanded its reach into Perkins, Chase, and Dundy counties. This fungal pathogen is now confirmed in over 70 of Nebraska's 93 counties.
Why it matters
The disease thrives in cool, wet conditions, making Nebraska's corn crops vulnerable when humidity and leaf moisture levels are elevated. Fields with a previous history of the infection allow for significant fungal buildup over time.
The fungus thrives in temperatures between 60°F and 73°F when relative humidity exceeds 75%. Past severe outbreaks resulted in yield losses as high as 50-60 bushels per acre.
The players
Phyllachora maydis
This is the fungal pathogen responsible for causing the tar spot disease in corn crops.
The details
Spore spread is facilitated by wind and splashing water, with recent easterly winds pushing the pathogen into southwest Nebraska. The fungus requires seven or more hours of leaf wetness to effectively infect corn crops.
Timeline
2015: Tar spot was first reported in the United States.
2018 and 2021: Severe outbreaks occurred, resulting in documented yield losses.
August and September 2026: Disease severity increased throughout Nebraska fields.
Late summer and fall 2026: Weather conditions favored spore dispersal into new areas.
The Big Picture
This expansion follows the spread patterns documented by the Crop Protection Network's distribution tracking. The ongoing movement of this fungus confirms that agricultural pathogens continue to adapt and migrate into new geographic zones under favorable weather conditions.
Local farmers in the newly affected counties should monitor fields closely, as a history of the disease increases the risk of severe future outbreaks. Understanding the specific humidity and temperature thresholds can help in planning future mitigation and crop protection strategies.
The takeaway
Tar spot remains a significant threat to corn yields when environmental conditions remain damp and cool for extended periods. Producers should prioritize monitoring for the fungus in fields where it has established a history of buildup.
Further reading
Learn more about the latest developments in Nebraska Botany.
More information
View the most recent data on the Tar Spot Distribution Map.
Source note: This article includes information reported by Unl.
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