On Sept. 12, 2025, high levels of fungal disease are lurking in corn fields across the U.S. Midwest, threatening to reduce yields of a record-large crop and cause headaches for farmers during the autumn harvest, growers and crop experts said.

The outbreaks are a blow to farmers in the world’s biggest corn-producing country as they struggle to make money due to low grain prices and rising costs for fertilizer, seed and other inputs. Farmers had hoped to produce the biggest possible yields to offset low prices, and crop diseases put that plan at risk.

The U.S. Department of Agriculture projected in August that farmers would produce a record-breaking yield of 188.8 bushels per acre. However, most analysts in a Reuters survey expect the government to lower its estimate in a monthly report on Friday, due partly to disease. Their estimate for a yield of 186.2 bushels per acre would still set a record and produce ample supplies.

The main culprit is southern rust, which blows northward from tropical regions and can reduce yields by up to 45%, according to the Crop Protection Network, a consortium of university experts.

Another disease, tar spot, was also widely detected. Both fungal diseases attack corn leaves and interfere with photosynthesis. In corn plants, the process converts sunlight and water into sugars needed to produce grain. Infected corn plants often produce smaller kernels, reducing yields.