This summer’s hot, dry weather may have favored the development of corn ear rots, warns Dean Malvick, University of Minnesota plant pathologist.

Several types occur in Minnesota, but Aspergillus and Fusarium ear rots are of greatest concern because they produce mycotoxins, says Malvick.

Aspergillus ear rot can produce aflatoxin, a potent mycotoxin toxic to animals and humans. It can become a problem under low soil-moisture conditions when temperatures climb above 89ºF. It’s caused by the fungus Aspergillus flavus, which appears as patches of green-to-yellow spores on or between kernels and can become dark olive green to brown as it ages. Most common at ear tips, it often only affects a few kernels or small areas of the ear.

Aspergillus species can also cause storage rot, invading kernels with moisture levels as low as 15%, especially if kernels have been damaged.

“The presence of the Aspergillus ear rot does not mean the corn has high levels of aflatoxin,” says Malvick. “The grain must be tested to determine how much aflatoxin is present. Different types of screening tests for aflatoxin are available, including a simple black-light test that indicates the potential for aflatoxin as well as commercial test kits and chemical methods that measure aflatoxin levels.”

Fusarium ear rot is also favored by hot, dry weather, especially at tasseling. Damaged ears are most susceptible. Infected kernels have whitish-to-pink fungal growth, often at the ear tip, but sometimes scattered on the ear. Infected kernels can also have a "starburst" pattern (white lines radiating out from a point on the kernel) and kernels can be infected internally with no visible symptoms. The symptoms can differ depending on the hybrid, environment or disease severity.

Fusarium ear rot can produce mycotoxins called fumonisins that are also harmful to animals and humans, says Malvick.

Grain samples can be tested for aflatoxin and other mycotoxins by the University of Minnesota Veterinary Diagnostic Laboratory or other university or private lab in the region, he says.

For more information, he recommends Mycotoxins in Crops: A Threat to Human and Domestic Animal Health and Aflatoxins in Corn. Also read “Droughty Corn May Harbor Aflatoxin.”