Corn Disease Expands Into Southwest Nebraska
The fungus Phyllachora maydis now affects most of the state, threatening yields in three newly impacted counties.
Updated on Oct. 27, 2026 in Botany
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The corn disease tar spot, caused by the fungus Phyllachora maydis, has expanded into three additional counties in southwest Nebraska. The pathogen is now present in more than 70 of the state's 93 counties following a season of favorable weather conditions.
Why it matters
Tar spot poses a significant economic threat to corn production, as severe outbreaks have historically resulted in yield losses of up to 50 to 60 bushels per acre. The fungus persists in fields with a prior history, creating a long-term management challenge for growers.
The fungus Phyllachora maydis thrives at temperatures between 60°F and 73°F when relative humidity exceeds 75% for at least seven hours. Past severe outbreaks saw yield losses of 50-60 bushels per acre compared to healthy baseline yields.
The players
Phyllachora maydis
A fungal pathogen responsible for tar spot disease in corn crops that thrives in cool, humid conditions.
The details
The disease spreads primarily through spores carried by wind and splashing water. Recent easterly winds facilitated the westward movement of the pathogen into Perkins, Chase, and Dundy counties. The fungus causes black, raised spots on corn leaves, which can reduce photosynthetic capacity once severity thresholds are met.
Timeline
2015: Tar spot is first reported in the United States.
2018 and 2021: Severe outbreaks cause documented yield losses.
August and September 2026: Disease severity increases across Nebraska fields.
Late summer and fall 2026: Favorable weather drives the fungus into new areas.
The Tech Race
The current expansion follows the trajectory set by the 2018 and 2021 outbreaks that first drew widespread agricultural concern in the U.S. Researchers are currently tracking whether this pathogen will continue its westward migration or stabilize based on regional climate variations.
Corn producers in southwest Nebraska should monitor fields for symptoms, especially in areas with a history of the disease. While no new chemical treatment is announced, growers can reference historical yield data to assess their long-term risk profile.
The takeaway
Tar spot is now a widespread concern for Nebraska corn growers, necessitating long-term field management strategies. Producers should monitor the Tar Spot Distribution Map to track the pathogen's movement next season.
Further reading
For more on plant pathology and regional crop health, visit Botany.
More information
View the most recent data on pathogen prevalence via the Tar Spot Distribution Map.
Source note: This article includes information reported by Unl.
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