Scout for corn molds and ear rots this harvest season

The Iowa State University Veterinary Diagnostic Laboratory (VDL) has received several questions from southwest Iowa producers about corn mold this harvest season. Based on producer descriptions of black mold or black dust that becomes airborne when the plants are disturbed, common corn smut is the most likely culprit in many of these cases.

Corn smut is caused by the fungus Ustilago maydis or Ustilago zeae and at harvest can typically be identified as black masses of spores that create a dark dust when the corn plants are disturbed. This spore material often is described as powdery or sooty in consistency and can be found on various parts of the corn plant including ears, tassels, stalks, and leaves.

Iowa State Extension and Outreach beef program specialist Chris Clark said corn smut can impact grain quality and yield but generally is not associated with mycotoxin production.

"If a mold in question is truly corn smut, the grain can probably be fed to livestock without any great concern about toxicity," he said.

Corn smut can, however, be confused with other corn molds and fungal ear rot organisms that can produce dangerous mycotoxins. Corn plants are susceptible to numerous fungal organisms, some of which are commonly associated with mycotoxin production.

Iowa State veterinary toxicologist Steve Ensley said Aspergillus, Fusarium, Gibberella, and Penicillium organisms are most commonly associated with production of mycotoxins that can be negatively impact animal health and performance.

There also is evidence that smut-infected ears are more susceptible to infection by Fusarium and Aspergillus. The smut fungus may not directly produce mycotoxins but can potentially cause greater susceptibility to secondary infections with organisms that are associated with mycotoxin production. That's why it's important to scout fields and identify corn molds affecting the crop.

The Iowa State VDL offers mycotoxin screening of grain and feed samples. Producers can find sampling guidelines, submission forms, prices and other information on the VDL website. The site also includes a great deal of information about mycotoxins including species affected and health effects.

Both Clark and Ensley are available to address questions and concerns about corn molds and mycotoxins. Contact Clark by phone at 712-250-0070 or email at Call Ensley at 515-294-2783 or email him at


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