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College of Food, Agricultural, and Environmental Sciences


Worried About Moldy Corn? Test Grain to be Certain of Mycotoxins

November 19, 2009

WOOSTER, Ohio – The longer corn stands in the field, the greater the chances for ear molds and subsequent mycotoxin issues, but the only way to determine if grain is contaminated is to have it tested.

"The presence of fungi is an indication of potential mycotoxin problems, but that doesn't mean that the grain is contaminated with toxins. Even if the grain is contaminated, the only way to determine whether or not the toxin is at high levels is to test it," said Pierce Paul, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center.

According to the Ohio Agricultural Statistics Service, 58 percent of Ohio's corn has been harvested, down 29 percent from this time last year. The delays are due to cool, wet weather conditions, which have slowed dry-down and kept growers out of their fields.

Paul said that the harvest delays are not impacting yields (reports are coming in of 200-250 bushel per acre averages), but the problem lies with grain quality.

"Corn standing in the field creates problems and one of those problems is ear mold and ear rots, which can lead to grain contamination with mycotoxins," said Paul. "Not every fungus produces mycotoxins, but the one particular problem we are having this year is definitely associated with mycotoxin, and that's Gibberella ear rot."

With Gibberella ear rot, the fungus enters the ear tips and leaves a pinkish mold on the kernels that progresses down from the tip toward the base of the ear. Gibberella ear rot develops best when moderate temperatures and frequent rainfall occur during the three-week period after silk emergence. The Gibberella ear rot fungus produces mycotoxins that are harmful to animals. These include deoxynivalenol (vomitoxin) zearalenone and T-2 toxin.

Paul emphasizes that symptoms of ear rot don't always appear on the outside of the husk.

"This is particularly true with late infections," said Paul. "To determine if you have an ear rot problem, walk fields in 50-100 locations, strip back the husks of about 50-100 plants and look for telltale symptoms. It's always easier to tell if you have an ear rot problem by looking at corn in the field than trying to eyeball the grain."

Whether farmers are harvesting the corn for grain, silage or ethanol, it's important to test the grain if ear mold is present.

"Silage won't reduce mycotoxin levels. Vomitoxin is heat stable and water soluble, so despite whatever process it goes through, it'll stay in the silage," said Paul. "Vomitoxin will also remain and even builds up in dried distillers grains, the byproduct of ethanol production that is fed to livestock."

The amount of Gibberella ear rot being found throughout Ohio cornfields is an unusual situation, said Paul.

"It's something you don't see every year," he said.

Paul recommends that farmers do not feed any grain with more than 5 parts per million vomitoxin to swine.

"Avoid feeding moldy grain to animals, period," said Paul. "But if such grain is used, it should not make up more that 20 percent of the diet fed to swine and 40 percent of the diet fed to other animals."

For a list of mycotoxin testing laboratories go to:

Candace Pollock
Pierce Paul