By Scout Nelson
Tar spot, a fungal disease in corn, was confirmed in V6-V9 corn in several Nebraska counties during the week of June 15, 2025. While it seems early, such timing has become common in areas where the fungus is now established.
“Fungicide applications are not recommended at this time for tar spot management,” researchers emphasized. The most effective treatment timing remains between R2 and R3 stages, even if the disease appears earlier.
Caused by Phyllachora maydis, tar spot is recognized by black fungal spots on corn leaves and husks. It spreads easily and can severely reduce yields if conditions are favorable, especially during grain filling.
Favorable conditions include moderate temperatures (60–70°F), high humidity over 75%, extended leaf wetness, and heavy rainfall or fog. These factors are often worsened by center pivot irrigation systems, especially during August and September.
Research by the University of Nebraska–Lincoln (UNL) from 2023–2024 shows that center pivot irrigation cools air temperatures by up to 16.5°F and increases relative humidity by as much as 46%. It also extends leaf wetness by over eight hours compared to rainfed areas, particularly in inner pivot spans.
In 25 corn fields studied, disease severity was highest in the second span of pivot irrigation systems, where tar spot reached 3.5% and southern rust 5.4%. Rainfed corners recorded much lower levels—only 1.6% and 1.9%, respectively.
UNL researchers are exploring new irrigation strategies and fungicide chemigation. Until then, growers are advised to scout early and focus on inner pivot zones where conditions are most favorable for disease.
This research highlights the importance of understanding how irrigation practices can unintentionally increase disease risks, and the need for careful monitoring throughout the growing season.
Photo Credit:gettyimages-oticki
Categories: Nebraska, Crops, Corn