Corn grain and silage in the drought-stricken Corn Belt may contain aflatoxin, a toxic carcinogen for livestock, warn Kiersten Wise and Charles Woloshuk, Purdue Extension plant pathologists.

The hot, dry conditions are perfect for the development of Aspergillus ear rot, which is caused by the fungus that produces aflatoxin, they say. The disease normally shows up near the end of the growing season as the crop reaches the dent phase. Growers can identify it by peeling back husks and looking for stunted ears with an olive-green, dusty mold.

"This year presents a unique challenge for producers since corn may be cut for silage, and many fields have poorly pollinated plants and limited kernel set," says Wise.

The fungus that causes ear rot needs kernels on an ear to develop. If ears with kernels are present in a field, she says it's important to determine if aflatoxin is present. Corn silage and grain can be submitted for analysis by a professional lab, such as Purdue's Animal Disease Diagnostic Laboratory.

USDA has set thresholds for the amount of aflatoxin tolerated in grain, depending on the end use. According to Woloshuk, those restrictions are especially tight for the dairy industry. Food and Drug Administration regulations require aflatoxin residues in milk to be less than 0.5 part per billion.

"To prevent the carryover of aflatoxins into milk, silage and other feed components should not contain greater than 20 parts per billion," he says.

The bad news for grain and livestock producers is that, at this point in the season, there is little they can do to manage Aspergillus ear rot or aflatoxin. The best they can do now, says Wise, is scout prior to harvest and determine if there is a problem and, if so, its severity.

"If any Aspergillus ear rot is observed in a field, affected areas should be harvested early and grain segregated to avoid aflatoxin contamination of non-infected grain. Grain harvested with suspected Aspergillus ear rot should be dried to below 15% moisture," she says, because aflatoxin can continue to accumulate in grain or silage with kernels kept above 15% moisture.

"All grain contaminated by ear-rot fungus should be stored separately from good grain and stored below 13% moisture to prevent further growth of fungi," Wise adds.

More information is available in a free Purdue Extension publication, Diseases of Corn: Aspergillus Ear Rot.