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 the grain is contaminated with toxins," say Pierce Paul, Ohio State Extension plant pathologist. "Even if the grain is contaminated, the only way to determine whether toxins are present at high levels is to test it."
According to the Ohio Agricultural Statistics Service, 58% of Ohio's corn has been harvested, down 29% from this time last year. The delays are due to cool, wet weather conditions, which have slowed drydown and kept growers out of the fields.
Paul says harvest delays are not impacting yields, with reports of 200-250-bu./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," Paul says. "Not every fungus produces mycotoxins, but the one particular problem we have this year is associated with mycotoxins, and that's Gibberella ear rot."
With Gibberella ear rot, the fungus enters the ear tips and leaves a pinkish mold on the kernels and 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. Gibberella ear rot fungus produces mycotoxins that are harmful to animals. These include deoxynivalenol (DON, also known as vomitoxin), zearalenone and T-2 toxin.
Paul emphasizes ear rot symptoms don't always appear on the outside of the husk.
"This is particularly true with late infections," he says. "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 easier to tell if you have an ear rot problem by looking at corn in the field, rather than trying to eyeball the grain."
Whether farmers are harvesting the corn for grain, silage or ethanol, it's important to test the grain for ear mold.
"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," Paul says. "Vomitoxin will also remain and even builds up in DDGs."
The amount of Gibberella ear rot being found throughout Ohio cornfields is an unusual situation, Paul says.
Paul recommends farmers not feed any grain with more than 5 parts per million vomitoxin to swine.
"Avoid feeding moldy grain to animals, period," says Paul. "But if such grain is used, it should not make up more than 20% of the diet fed to swine and 40% of the diet fed to other animals."
For a list of mycotoxin testing laboratories visit Ohio State University.