Farmers, crop inspectors and grain elevators in Nebraska, Iowa and other corn-producing states are keeping an eye out for corn contaminated by a poison-producing fungus.

They’re watching for signs of aflatoxins which are produced by mold fungi and at high levels are poisonous to humans and animals. They tend to show up during hot, dry summers.

Mark Fulmer of the Lincoln Inspection Service said to a local that most corn samples his company has tested this summer show little or no contamination. But he says some of the corn has tested out at more than four times the federal threshold.

Iowa agriculture officials say they’re requiring dairy farmers to test milk as it leaves farms. Aflatoxins can appear in the milk of dairy cows fed contaminated corn.