Tar Spot Reaches Southwest Nebraska Corn
Confirmed in three more counties, the fungus has now reached more than 70 of Nebraska's 93 counties.
Updated on Nov. 2, 2026 in Botany
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Tar spot, a corn disease, was confirmed in Perkins, Chase and Dundy counties in southwest Nebraska, bringing the statewide total to more than 70 of the state's 93 counties. The disease is a research-stage and field-observed situation, not a new product, and its spread was documented by state and regional reporting.
Why it matters
Increased easterly winds accelerated the westward movement of the fungus into southwest Nebraska, and the disease became more severe in many central and southern Nebraska fields during August and September. Cool, wet late-summer and fall conditions favored its development and spread, which is why confirmations are now reaching the state's western edge.
The disease is caused by the fungus Phyllachora maydis, which infects corn leaves and can cause rapid loss of healthy leaf area. Severe outbreaks have produced yield losses of 50-60 bushels per acre in susceptible hybrids, though the figures come from earlier seasons rather than this year's confirmations.
The players
Crop Protection Network
A multi-university and extension collaboration that maintains the tar spot distribution map tracking confirmed reports across the Corn Belt.
The details
Tar spot spreads between plants and fields through wind and splashing water, and the fungus overwinters in fields and can redevelop when conditions become favorable. Favorable conditions include temperatures between 60°F and 73°F, relative humidity in the corn canopy above 75%, and leaf wetness lasting seven or more hours. When severe, the disease can accelerate plant drydown and lead to stalk cannibalization, in which the plant pulls sugars from its stalk to feed developing kernels.
Timeline
2015: Tar spot first reported in the United States in northern Indiana and Illinois.
2018 and 2021: Severe outbreaks documented with yield losses up to 50-60 bushels per acre.
August and September 2026: Disease became more severe in many central and southern Nebraska fields.
November 2, 2026: Tar spot confirmed in southwest Nebraska, bringing the statewide total above 70 counties.
The Tech Race
Tar spot's spread from its 2015 first report in northern Indiana and Illinois to more than 70 Nebraska counties shows how far the fungus has moved across the Corn Belt in about a decade. The westward movement into southwest Nebraska follows the same regional pattern documented during the 2018 and 2021 outbreaks.
Growers in Nebraska's southwest counties now face confirmed tar spot in their region, and fields with a history of severe disease may be at greater risk in later seasons when conditions are favorable. Scouting for the disease and watching leaf wetness and temperature conditions are the practical steps the extraction describes, though it does not specify a timeline for this season's losses.
The takeaway
Tar spot's westward movement into southwest Nebraska is a signal to watch whether confirmations continue to spread across the state's remaining counties in the coming season. Growers can track the Crop Protection Network distribution map for updated confirmations and check their fields against the disease-favoring conditions the extraction lists.
Further reading
For more on how fungal pathogens like this one move through crops, see Botany coverage across Nebraska's agricultural regions.
More information
The Crop Protection Network tar spot distribution map tracks confirmed reports across the Corn Belt.
Source note: This article includes information reported by AgUpdate.
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