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Monday, September 10, 2012
Pouring salt into a wound- Despite recent rains the drought continues to reduce the value of this year's corn crop. To some area farmers' dismay, elevators are rejecting truckloads of grain based on the detection of aflatoxin in the grain.
Aflatoxin is a toxic and carcinogenic compound produced by the Aspergillus fungus. This ear rot fungus occurs most often in hot dry years. It will infect kernels through tiny cracks and where there has been damage by insects and birds. You will often see this fuzzy olive-green fungus on the tip of the ear where this kernel damage is most prevalent.
The FDA limit of corn entering the general market channels is 20 parts per billion(ppb). You may see the olive green fungus on the ears but the aflatoxin is inside the grain and the only way to determine the actual toxin level is to grind a sample and test it. Lab testing used to be required but now elevators and processors can use strip tests similar to pregnancy tests that use antibodies that respond to the aflatoxin.
If grain exceeds the 20 ppb level but is below the 300 ppb it might still be used in livestock feed to, if a livestock producing buyer can be found. Some elevators may have such arrangements in place with large feeders and may take the grain and keep it segregated. The FDA action limits for animal feed vary depending on the type of livestock, dairy-20ppb, breeding livestock and poultry-100ppb, finishing swine over 100 lbs-200ppb, and finishing beef cattle-300ppb.
What should a concerned farmer do?
I would recommend opening up a field and harvesting a strip to make it easy to sample. Walk down the edge of the strip and check for ear rots. Fortunately, the different ear rots are somewhat color coded. Also, which ear rots show up is very weather dependent.
Gibberella: pinkish starting at tip, likely when cool wet weather during silking
Diplodia: Cob rot white fungus between kernels, black specks on cob, dry early/wet late
Fusarium: salmon colored individual kernels, heat and insect stress
Penicillium: Blue-green on and between kernels
Aspergillus: Olive green, high day and night temps
After scouting if you see indications of Aspergillus contact your crop insurance agent for instructions. They will probably need to collect an official sample or may indicate to leave a test strip. The USDA Risk Management Agency has a factsheet on aflatoxin testing available at http://www.rma.usda.gov/fields/il_rso/2012/aflatoxin.pdf. This factsheet includes a list of approved certified labs that do aflatoxin testing. You need to prove the Aspergillus/aflatoxin occurred in the field and not in the bin in order to have a legitimate crop insurance claim.
Best management practices to minimize aflatoxin issues.
Adjust combine to minimize kernel damage and remove fines and debris. Do not allow wet grain to sit in wagons and trucks overnight.
If storing on-farm, run grain through a cleaner or screen before putting in the bin or dryer, if you have access to cleaner. (Do not feed screenings to livestock) Immediately dry to 15% if you are planning long term storage dry to 13%. As weather permits cool the grain as quickly as possible. Aerate as needed to keep temperature and moisture in the grain mass equalized.
Black light tests of the grain will show kernels which contain kojic acid a precursor to aflatoxin, but that does not indicate if aflatoxin is actually present. Many locations may use this as an indicator for more detailed toxin specific sampling and testing. Immunoassay quick test strips are often then used to check for aflatoxin. The simplest of these will only determine if levels exceed the 20ppb limit, the more advanced and expensive strips used in conjunction with an electronic reader will provide actual levels. On-site positive results should be confirmed by an actual laboratory analysis.
Utilizing affected grain
If it is below FDA levels, it can be sold to local livestock producers, generally at a discounted price. Aflatoxin will not show up in ethanol from infected grain but will be in the by-products that producers normally sell for livestock or pet feed. Therefore, ethanol producers will probably not be interested unless the price is highly discounted. As last resort, nutrients in the grain can be recycled by land application of contaminated grain. However, this may cause weed issues in the coming year.
Illinois Extension Drought Resources: web.extension.illinois.edu/drought/
Iowa State Grain Quality Aflatoxin page: www.extension.iastate.edu/Grain/Topics/Aflatoxin.htm
Plant Management Network-Ear and Kernel Mold Biology and Management on-line presentation by Dr. Woloshuk, Purdue: http://bit.ly/RlmtmH