Aflatoxin in Drought Stressed Corn
August 21, 2012 by Andrew Westhoven, CCA
The 2012 corn crop is quickly coming to an end across much of Indiana and a topic on many producers’ minds other than low yields is the potential for Aflatoxin. A historic drought and record high temperatures during silk and grain fill stages are certainly key criteria needed for the development of Aflatoxin.
What are Aflatoxins? Aflatoxins are naturally occurring by-products produced by two types of molds: Aspergillus flavus and Aspergillus parasiticus. Aspergillus flavus is the most common and often found when corn is grown under stressful conditions such as drought. Aflatoxins are harmful and can cause several problems in livestock, most commonly a reduction in feed efficiency and reproductivity, suppression of immune system, and in rare instances, death. The most abundant aflatoxin, aflatoxin B1, is a carcinogen. This raises human health concerns because aflatoxin can appear in the milk of dairy cows fed contaminated corn.
The Food and Drug Administration (FDA) has established levels for Aflatoxins present in food or feed. The following levels for corn are set by the FDA to maintain an adequate margin to protect both animal and human health.
Identifying Aspergillus Ear and Kernel Mold Aspergillus flavus can be identified as an olive green or yellowish green powdery fungus on drought stressed corn ears. The fungi survive on plant residue and produces abundant spores. These spores are then carried by wind to infect silks and damaged kernels. Short husks that expose ear tips are more susceptible to kernel damage from insects and weather, therefore more prone to infection by Aspergillus.
Managing Aflatoxins in Corn:
• Scout fields prior to harvest for presence of Aspergillus ear mold.
• Set combines and grain handling equipment to minimize kernel damage and remove cracks, fines, and lightweight diseased kernels.
• Aspergillus does not compete well with other fungi when corn is above 20 percent moisture. Harvesting corn when moisture content is above 20 percent followed by rapid drying to at least 14 percent within 24 to 48 hours of harvest keeps further Aspergillus growth and toxin production at a minimum. Corn that will be held long term should be dried to 13 percent.
• Do not store grain in trucks, combines, bins, or any non-aerated site for more than 4 to 6 hours. These conditions quickly escalate aflatoxin levels and deteriorate grain quality because fungal growth and grain respiration will rise quickly in high-moisture grain.
• The amount of Aflatoxin produced in storage is determined by storage conditions. The most important factors are grain moisture content and temperature. Optimum storage temperature for Aspergillus to grow is 80–90°F; optimum grain moisture content is 18-22 percent. Cool grain once dried to 35-40°F for the duration of winter.
Testing for Aflatoxin
To reduce financial loss through the Federal Crop Insurance Program, it is recommended to contact your insurance provider if there is a possibility of grain contaminated with Aflatoxin. An insurance adjuster must collect grain samples believed to be infected prior to harvest and storage and send to a GIPSA (Grain Inspection, Packers and Stockyards Administration) approved laboratory for testing. Most generally the sample size should be no less than ten pounds of harvested grain and consist of subsamples as Aflatoxin is usually not distributed uniformly.
References:
Munkvold, G. et. al. 2009. Aflatoxins in Corn. Iowa State University, University Extension. PM1800. http://www.extension.iastate.edu/Publications/PM1800.pdf
