Using sound crop rotation, harvesting corn early and then drying it, southern growers can likely reduce the threat of dreaded aflatoxin.
As corn acres have increased in the South, so have the chances of growers seeing the mycotoxininvade their fields and feasibly ruin good profit potential.
Even if a grower's yields are bin busters, aflatoxin can bite deeply into profit, says Dennis Gardisser, University of Arkansas Extension agricultural engineer.
“If you plant corn on corn, a lot of disease problems can occur, including aflatoxin,” adds Pierce Paul, Ohio State University plant pathologist.
Aspergillus flavus and aspergillus parasiticus fungi produce the aflatoxin mold. They are cancer-causing agents.
Alfatoxin levels in food corn is restricted to no more than 20 ppb; even smaller readings have forced grain shipments to be rejected by buyers, especially for export. The allowable contamination rate increases to 200 ppb for some feed corn uses and 300 for others. Aflatoxin-stricken corn can also be turned down for biofuel production since dried distillers grain with solubles (DDGS) for livestock feed is a major byproduct of ethanol.
Aflatoxin is attracted to corn that faces stress. If daytime temperatures reach 90 F or higher, relative humidity is 80% or higher and corn is in some type of stress situation, look out. Affected ears will have greenish-yellow areas from spore production on or between the kernels. “It's different from any other ear rot fungi,” says Paul.
He says ear injury or stress caused by insects, birds or hail, as well as drought stress, can expose the crop to fungus colonization.
“Rainfall at the end of the growing season that postpones harvest and prevents dry-down and storage conditions with corn moisture above 13% increases the risk of aflatoxin contamination,” Paul adds.
Continuous corn can allow the fungus to overwinter, especially in the South where temperatures aren't as cold. But even in Southern areas, where aflatoxin is also no stranger to cotton, rotation may not always work.
Gardisser says keeping corn healthy is often the best way to prevent aflatoxin. “We don't want to sensationalize aflatoxin,” he says, “but we certainly want growers to do all they can for the crop. We've learned through past years how to manage for the highest-quality, pathogen-free commodity. The keys are healthy corn harvested at the right moisture content and managed properly during drying and storage.”
Harvesting corn early can help prevent it from suffering late summer drought stress. For growers with on-farm storage, Gardisser recommends using a pass dryer to push high volumes of hot air through the corn for quick drying.
“That can take the initial moisture level down 3 to 4 percentage points,” he says. “Air quality is often good enough that you won't need artificial heat for in-bin drying. As corn is dried and then cooled, the chance for fungalactivity diminishes.”
Testing for aflatoxin ppb is no exact science. Testing equipment can differ in readings. A load of corn may test clean at the local elevator and with a higher ppb level at the terminal. More than one railcar of thought-to-be-clean corn has been denied at the export terminal.
Paul says the most effective method of testing is to take 10-15 sample probes in different parts of a load or bin, combine them,mix them well then sample for aflatoxin or other diseases.
Growers should also consider planting more drought-tolerant corn hybrids, some of which may ward off aflatoxin invasions. The National Corn Growers Association Mycotoxin Task Force is monitoring USDA and university aflatoxin research on better hybrids and production methods.
The Ohio State plant pathology department has additional information on corn and other plant diseases. For more information, go to www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm .