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Aflatoxin can be produced by two fungi, Aspergillus flavus and Aspergillus parasiticus and can infect corn kernels in the field and during storage. The fungi can be recognized by yellow-green (A. flavus) or green-gray (A. parasiticus) mold on the corn kernels (Figure 1).1 The fungi overwinter on plant residues from which they can produce abundant spores if conditions are favorable. One requirement for sporulation is moisture. Through wind dispersal, the spores land on silks and kernels and under favorable conditions, begin growing. Wounds from insect feeding create ideal growth sites.
Hot, dry days and warm nights coupled with moisture content levels of 17 to 30%, are favorable for Aspergillus development. Under stress, the fungi can initiate aflatoxin production on infected kernels of susceptible products. The most common stresses leading to aflatoxin production in the field include excessive heat and drought conditions. In the South, higher insect populations and temperatures make Aspergillus infection and aflatoxin production a regular concern. Drought conditions coupled with high humidity or high nighttime temperatures can also lead to sporadic outbreaks. Post-harvest Aspergillus infection and aflatoxin production on infected kernels can be caused when there is poor grain conditioning and storage conditions, insufficient drying and storage.
Aflatoxin does not occur uniformly in bulk corn, so be sure to sample in several areas of a load or bin. Contact your grain testing laboratory for specific sampling and handling instructions. A chemical test can be performed at a certified laboratory to detect and quantify potential aflatoxin accumulation in a sample. Table 1 lists the Food and Drug Administration’s (FDA) guidelines for acceptable aflatoxin levels based on intended use of grain.2 A black light test can be used only to detect the presence of Aspergillus, not aflatoxin itself.2 Since not all Aspergillus strains produce aflatoxins, black light test results should not be accepted as grounds for rejection of corn.
Corn product selection is an important step in managing aflatoxin production. Products with larger, tighter fitting husks, insect resistance traits, and drought tolerance can help reduce the potential production of aflatoxin. Other factors that may have an effect on aflatoxin production are: maturity, flowering time, and days to maturity.
Farmers with contaminated grain has some options; however, contaminated grain cannot cross state lines and discounted prices are likely. As an alternative, grain that is contaminated with aflatoxin at levels below 300 ppb (parts per billion) can be fed to local beef cattle.4 Another alternative for contaminated grain may be ethanol production. Aflatoxin does not accumulate in the ethanol, but can be concentrated in the byproduct dried distiller’s grains (DDGs). Therefore, some ethanol plants may not want contaminated grain because they would not be able to sell the DDGs as animal feed.
If cleaning the grain sounds more appealing than an alternate use, it can be done with a screen or gravity table. Finally, feed additives, such as beta-glucans, may reduce the toxicity of mycotoxins, such as aflatoxin, by reducing absorption in the animal. Reduced intestinal absorption results in less exposure to the animal and less transfer to milk in ruminants.