Corn Harvest Headache

Reports of Aflatoxin in Corn Begin in Droughty States

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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The tell-tale army-green mold of Aspergillus fungus is a dreaded sight for corn farmers, because some strains produce a dangerous mycotoxin called aflatoxin. (Photo courtesy of Alison Robertson, Iowa State University)

ROCKVILLE, Md. (DTN) -- One week in, and the corn harvest in northeastern Oklahoma has already brought bad news.

"Aflatoxin has showed its dirty face," said Zack Rendel, who farms near Miami, Oklahoma. "We thought we were doing really good -- decent looking corn that isn't showing much drought stress. But everybody is starting to have issues around here."

Growers in droughty parts of Kansas, Oklahoma and Missouri will be at risk for the dangerous mycotoxin this year, which is produced by many strains of the drought-loving fungus, Aspergillus, said Kansas State University Plant Pathologist Doug Jardine.

"The potential is certainly there because it's not hard to find Aspergillus in fields in southeast Kansas and a few in east-central Kansas," he said. "Later-planted cornfields seem to be a common denominator."


Aspergillus ear mold usually appears as army-green-colored mold, most often at the tip of an ear of corn, although some strains can be more yellowish, said Jardine.

He recommends checking 20 ears in five different spots in the field, so the total number of infected ears you find can translate simply to the percentage of that field's infestation.

Keep in mind that the level of Aspergillus in a field does not directly correlate to the level of aflatoxin in your corn, Jardine cautioned. So a 10% Aspergillus infection rate does not automatically mean 10% of your corn will have the toxin.

"I use the scouting to measure for potential," Jardine explained. "So if a field is 50% colonized, that will have more potential for aflatoxin than one that is 5%."


Rendel has two elevators nearby, each with different dockage triggers for aflatoxin. The determining factor is where the corn ends up -- one elevator directs most of its grain to chicken feed, the other to cattle feed, Rendel explained.

Not only do different types of livestock -- poultry, cattle, horses and pigs -- have different tolerances to aflatoxin, but the age of the livestock matters, as does its purpose. For example, breeding cattle are limited to 100 parts per billion (ppb) whereas cattle destined for finishing can tolerate 300 ppb.

Since they cannot surpass 0.5 ppb in their milk, dairy cattle have the lowest tolerance -- 20 ppb -- the same amount permitted for human food.

See a complete listing of tolerances from the FDA here:…

To add to the complexity, the procedure for testing loads of corn for aflatoxin can be extremely unreliable, in part because of the spotty nature of toxin production in a cornfield.

Elevator employees pull samples with a probe from multiple places within a truck, but can easily hit or miss concentrated hot spots. Rendel has seen the wild fluctuations first hand: "One field, the first several loads were testing almost 300 ppb. The next load we hauled was zero -- from the same field."

Jardine suggests growers who get a bad reading the first time on the scale should consider getting back in line or heading to another elevator down the road for another sampling.

"If you get rejected twice with a different sample, you probably have a problem," he said.


If you have fields at risk for aflatoxin production, watch the weather carefully, Jardine said. A slow drydown in the cornfield can actually create higher levels of the toxin.

"Some research shows that when corn is at 20% to 25% moisture, that is when the fungus does a good job at pumping out toxins," he said. "When it's hot and dry and windy, we can blow from 25% to 15% in a really short period. But if it's cool and damp, you get a really slow dry-down, and that can be bad." In that case, consider harvesting early and turning your attention to proper grain storage, he said.

Remember that once your harvested corn has a certain level of aflatoxin, it cannot go down.

"It won't go away in the bin, but you can stop it from getting worse," Jardine said. The fungus can continue to grow at moisture levels above 13%, along with warm weather. But if you can dry it down quickly to 12% and keep the grain cool and aerated, you can stop that fungal growth and toxin production.

Getting the grain dry should be your first priority, Jardine said. For growers without bin dryers, that might mean running fans during the day, rather than at night when humidity levels rise. Once the grain is dry enough, consider switching to nighttime aeration to lower temperatures in the bin, he said.

For more tips on harvest, grain handling and storage of corn with aflatoxin, see this University of Georgia publication:…

Emily Unglesbee can be reached at

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Emily Unglesbee