September 25, 2002
Drying Grain Quickly Will Limit Mycotoxins
LINCOLN, Neb. — Corn growers need to keep a close eye on their corn's moisture content and dry down their grain as soon as possible to reduce fungus-related corn diseases this fall, a University of Nebraska plant pathologist said.
Drought stress during the growing season coupled with recent rains across parts of Nebraska created ideal growing conditions for mycotoxins, including aflatoxin and possibly fumonisin contamination, said Jim Stack, plant pathologist in NU's Institute of Agriculture and Natural Resources.
"This could be the worst contamination year in a decade for Nebraska," Stack said. "However, this is a manageable problem and we can deal with this."
In Nebraska, grain molds occur every year to varying degrees in field corn, seed corn, white corn and other specialty corn hybrids, Stack said. Most grain mold pathogens become associated with the kernel in the field, however, this year the temperature, relative humidity and grain moisture may allow the molds to grow within the colonized kernel and spread to adjacent kernels during transport and storage.
Aflatoxin has been confirmed in southeast and northeast Nebraska. In 2001, fumonisin contamination was a problem in the state and may be more widespread this year, Stack said.
Corn growers need to be especially watchful in areas where mold and mycotoxin contaminations have been common, Stack said. Mycotoxins reduce grain quality and can be toxic to farm animals, wildlife and humans. No fungicides are labeled in Nebraska for managing molds or mycotoxins in corn post-harvest.
Since the molds can develop in the grain bin, it's also important to keep the grain aerated.
"Delaying harvest to let the grain dry in the field increases the risk of stalk rots and grain molds," Stack said. "In some cases, it may be better to harvest at higher grain moisture and dry the grain rapidly."
Key management steps to help minimize grain mold and mycotoxin contamination are:
– Ensure proper storage conditions, including grain moisture, temperature and relative humidity.
– Minimize mechanical damage during harvest and post-harvest shipping and handling.
– Minimize insect damage in pre-harvest and post-harvest storage.
– Plant some of the tolerant hybrids available.
– Keep storage facilities sanitized.
– Assay moldy grain for mycotoxins at a toxicology lab or at UNL's Veterinary Diagnostic Center.
– Segregate, blend or destroy contaminated grain according to state and federal agencies and Food and Drug Administration regulations.
Levels of contamination in Nebraska have ranged up to 400 parts per billion, but the impact depends on the intended use of the grain, Stack said.
"Grain with mold symptoms should be assessed for the presence of mycotoxins prior to use as food or feed," Stack said. "The presence of mold does not indicate contamination of the grain with mycotoxins."
The FDA tolerances for aflatoxin are: 0.5 parts per billion for milk; 20 parts per billion for humans, immature animals and dairy cattle; 100 parts per billion for mature breeding cattle, swine and poultry; 200 parts per billion for finishing swine and 300 parts per billion for finishing beef. The FDA tolerances for fumonisins are: 5 parts per million for horses, 10 parts per million for swine and 50 parts per million for cattle.
Some grain elevators use a black light test as a preliminary indication of potential contamination, but the test is very unreliable. Only laboratory analysis can establish the occurrence and concentration of mycotoxins, Stack said.
Mycotoxins are stable molecules and can withstand drying processes as well as many industrial processes. Grain with limits above those recommended by the FDA for food grade grain usually are sent to feedlots or elevators which only buy grain for feeding cattle.
If the corn contains more than 300 parts per billion, it can be fed to mature cattle if it is blended with other grain to reduce the total level of mycotoxins.
Stack said all grain handlers should use caution and wear dust masks. Exposure to mycotoxins in humans can lead to acute allergic responses or chronic allergic response. Some can cause serious disease in people with lowered immune systems.
Symptoms in humans include: suppression of the immune system, reproductive dysfunction, cancer and death. Animals symptoms include: feed refusal, short-term illness, reproductive dysfunction and death.
For more information on grain molds, including how to identify the different types and their effects, consult NU Cooperative Extension NebGuides G00-1408-A, Grain Molds and Mycotoxins in Corn, or G87-850-A, Understanding Mold Toxins, both available at local Cooperative Extension offices and on the Web.
09/25/02-SA
Jim Stack
Plant Pathology
Extension Plant Pathologist
(402) 762-4435
Sandi Alswager Karstens IANR News and Photography (402) 472-3030
Department: Plant Pathology
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