By Scout Nelson
Tar spot, a corn disease caused by the fungal pathogen Phyllachora maydis, continued spreading across Nebraska during the 2026 growing season. New cases confirmed in Perkins, Chase, and Dundy counties increased the number of affected counties to more than 70, highlighting the need for continued disease monitoring and management.
The findings come from specialists at the University of Nebraska-Lincoln (UNL) Extension, including Tamra Jackson-Ziems, Talon Mues, Kyle Broderick, Samantha Daniel, and Ruby Collins, who have been tracking the disease and providing management recommendations for growers.
First identified in the United States in Indiana and Illinois in 2015, tar spot has since spread throughout much of the Corn Belt. Severe outbreaks in previous years showed the disease can cause significant yield losses in susceptible corn hybrids when conditions favor infection.
Tar spot is identified by small black fungal structures called stromata that develop on corn leaves. These spots cannot be rubbed off and may become larger over time, sometimes appearing with tan-colored fisheye lesions.
The disease spreads through spores carried by wind and splashing water. The fungus can also survive winter in infected crop residue, increasing the risk of recurring infections in affected fields.
Weather conditions play a major role in disease development. Cool temperatures, extended leaf wetness, high humidity, and irrigation can create favorable conditions for tar spot, making irrigated fields particularly vulnerable.
During August and September 2026, Nebraska Extension specialists reported increased disease activity across central and southern Nebraska. Increased moisture and stronger easterly winds likely contributed to the disease's continued movement into southwestern parts of the state.
Although tar spot is becoming more widespread, its presence does not always result in yield losses. Disease severity, timing of infection, weather conditions, and hybrid susceptibility all influence its impact on crop performance.
Severe infections can reduce healthy leaf area, weaken stalks, increase lodging risk, and accelerate crop drydown. These effects may influence both grain yields and harvest timing for corn producers.
Management efforts should focus on planting resistant hybrids and monitoring fields regularly for symptoms. Fungicides can also be effective when disease pressure is high, particularly when applied during key reproductive growth stages.
Growers are encouraged to use disease forecasting tools and seek diagnostic assistance if tar spot symptoms are suspected. Early detection and timely management remain essential for reducing disease-related risks and protecting corn yields.
Photo Credit: getty-images-alinamd
Categories: Nebraska, Crops, Corn