WOOSTER, Ohio – Ohio corn growers may have relished record corn yields in 2009 – with a state average of 174 bushels per acre – but grain quality is turning out to be a different story.
Abnormally cool, wet weather late in the production season and during harvest has resulted in widespread levels of vomitoxin contamination of harvested grain – a mycotoxin harmful to humans and animals caused by the fungal pathogen Gibberella zeae. The fungus causes Gibberella corn ear rot, resulting in moldy grain when environmental conditions are favorable.
Pierce Paul, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center, said that producers don't normally have to deal with vomitoxin in corn. They see it more frequently in wheat when this same fungus causes the more familiar head scab.
As a result, said Paul, many producers are struggling with properly sampling and testing their grain for vomitoxin levels and how to properly handle potentially moldy corn in the grain bins.
"Many producers are simply asking why this is occurring this year. Some of them have been planting the same hybrids year after year under the same cropping system and have avoided plant diseases," said Paul. "Based on the extent of the problem in 2009, most hybrids seem to be susceptible to these fungal pathogens, and if weather conditions are favorable for fungal growth and ear rot development like they were in 2009, you are most likely going to run into mycotoxin issues."
Paul said that the best way to reduce fungal growth and subsequent mycotoxin levels is to dry the corn down in the field below 15 percent. However, for many growers this year, field dry-down was simply not possible due to the weather conditions.
The next best step, said Paul, is to periodically sample the corn kernels in the grain bin for mold and vomitoxins, and check temperature and moisture levels. An increase in mold development is a sure sign that storage temperatures and moisture are inadequate and could lead to vomitoxin increase in storage.
"I like to tell growers to take as many samples as are practically possible. You can sample one part of the field or bin and read negative, but then sample another part of the same load and read positive," said Paul. "Specialists recommend five to 10 samples from multiple locations based on the size of the field and the shape of the storage bin or loading truck."
Producers can learn more about procedures for sampling grain lots for vomitoxin and where to test for mycotoxins in the OSU Extension Agronomic Crops Team Crop Observation and Recommendation Network (C.O.R.N.) newsletter at http://corn.osu.edu/story.php?setissueID=335&storyID=1963.
Properly storing and handling moldy grain is just as important as testing whether or not the grain contains vomitoxin.
Paul recommends that growers store dried grain at cool temperatures (36 degrees to 44 degrees Fahrenheit) in clean, dry bins.
"Be sure to carefully clean each empty bin before refilling it with fresh grain from the field," said Paul. "The grain is still alive and as such is still respiring. Two of the end products of respiration are water and heat, exactly what the fungus needs to grow and produce toxin."
He added that kernels close to the walls of the grain bin tend to be at a lower temperature than kernels towards the center, and the exchange of warm air from the center with cool air from the top or sides of the bin may lead to further moisture buildup.
Paul also recommends that growers periodically check grain for mold, insects and temperature. When doing so, safety is top priority, said Paul.
"Wear gloves and dust masks before handling grain in the bins," said Paul. "Moldy grain and vomitoxin are just as harmful to humans as they are to animals. You can hurt yourself simply by inhaling the dust from ground moldy grain."
Producers can learn more about properly handling and storing corn in the OSU Extension C.O.R.N. newsletter at http://corn.osu.edu/index.php#B.
The Gibberella ear rot fungus produces such mycotoxins as vomitoxin, T-2 toxin and zearalenone, all of which can cause health problems in both humans and animals.
As a general rule, do not feed any grain with 5 percent or more vomitoxin-infected kernels to livestock, particularly hogs, which are highly susceptible to mycotoxins. For humans, vomitoxin levels for bran, flour and germ are set at 1 part per million per the Food and Drug Administration.
Some grain elevators will reject grain with vomitoxin levels above 3 parts per million. Some elevators accepting grain for ethanol production will reject grain with vomitoxin at 7 parts per million.
Mycotoxin development in corn can be disastrous for growers if they are not aware of the problem at harvest or do not follow proper storage conditions.
"The corn will come out of the bin in very bad, perhaps unmarketable conditions, surprising the grower and affecting the bottom line significantly," said Paul.
For the latest information on mycotoxins in grain, log on to http://agcrops.osu.edu.