Storing Mycotoxin-Affected Grain
The fungi that cause several corn ear rot diseases produce mycotoxins, chemical substances that can be dangerous to humans and livestock. If you have corn affected by ear rots, there are important management steps to take to limit your losses.
This publication outlines how to manage stored grain affected by mycotoxins.
Harvest Diseased Grain First
After corn reaches maturity, farmers often allow the crop to dry down in the field to save on drying costs. However, the presence of ear rot diseases should influence harvest timing. The fungi that cause ear rot diseases can continue to grow, spread, and produce mycotoxins even after corn reaches maturity.
The most common mycotoxins associated with ear rots are deoxynivalenol (associated with Gibberella ear rot), fumonisins (associated with Fusarium ear rot), and aflatoxin (associated with Aspergillus ear rot) (Figure 1). If you find Aspergillus ear rot, Fusarium ear rot, or Gibberella ear rot during pre-harvest scouting, harvest the affected fields first and immediately dry the grain to levels that stop the fungus from growing and producing mycotoxins.
More information about identifying ears rots in the field is available in Corn Disease Management: Ear Rots (CPN-2001).
Figure 1. Corn with Aspergillus ear rot.
Dry Affected Grain Quickly
Drying corn (and other grains) helps prevent fungi from infecting or further degrading previously infected grain. Wet grain degrades quickly in a harvest truck or grain bin and mycotoxin levels can increase (Figure 2). This is especially true when temperatures are warm after harvest. However, if grain is stored at appropriately low moisture, evidence shows that mycotoxin levels will not increase.
High-temperature drying stops mold growth and mycotoxin production. However, it will not reduce mycotoxins already present in the grain. Using high temperatures to quickly dry grain is preferable to using low heat to slowly dry grain. Be wary of using low-temperature, in-bin dryers for moldy corn, and be sure to meet proper ventilation requirements for storing dry corn.
A good post-harvest drying target for storing grain is 15 to 15.5 percent moisture. This moisture level is sufficient for short-term storage over the winter. Additionally, cooling the grain to below 55°F (13°C) will slow the growth of fungi and inhibit insect activity.
If you plan to store corn into the hottest months of summer, dry grain to less than 13 percent moisture. At this moisture level, mycotoxin-producing fungi are typically unable to grow.
Figure 2. Be sure to dry grain before storing or moving. When grain is wet, mycotoxins can continue to accumulate.
Remove Damaged Grain
Damaged corn kernels can cause airflow problems during storage. There are a variety of factors that can damage the kernels.
Ear rot diseases often damage kernels, causing them to break and be lightweight at harvest. If the ear rot fungi in your corn are species that produce mycotoxins, the risk of mycotoxin contamination in your grain will be high (Figure 3). During the shelling process, machinery can damage healthy kernels. Additionally, impact forces can damage grain — such as when grain is dropped during postharvest handling through dryers, from elevator spouts, and so on (Figure 4).
Broken kernels and fine material (called “fines”) will accumu-late in the center of the storage bin during filling unless the bin is equipped with a spreading device. This central core of fine material will hinder uniform air movement through the grain mass, which increases the risk that the grain will spoil. Withdraw grain from the bin after you fill it, or “core” the bin to remove most of the broken kernels and fine material that accumulate there.
If there are mycotoxins in the harvested grain, the majority of the mycotoxins can be detected in the broken kernels and fine material. Although costly, cleaning the grain before you store or sell it can greatly reduce the level of mycotoxin contamination. Cleaning usually involves passing the grain over a series of screens to remove broken kernels and fine material. Gravity separators can also remove the lightweight infected kernels. Although cleaning grain will reduce mycotoxin concentrations, the cleaned grain often still contains significant mycotoxin concentrations.
Figure 3. These broken kernels are infected with Aspergillus flavus, the fungus that causes Aspergillus ear rot and produces aflatoxin.
Figure 4. Kernels can become damaged during transport.
Manage Your Grain Bins
Before filling any grain bin, clean it by removing all grain from the floor and walls (Figure 5). Thorough cleaning will help remove any grain carryover from the previous crop, including grain that may be contaminated by mycotoxins.
Regularly monitor storage bins. Check for leaks in the structure, and be on the lookout for condensation in the headspace. If condensed water drips on the grain surface, fungi may resume growing and this may lead to surface crusting. Inspect bins for sour, musty, earthy, or putrid odors. These odors indicate a fungal problem — most likely due to high grain moisture from improper drying, leaks, or insect activity.
If the grain gets wet, use a fan to increase airflow and reduce grain moisture — this can halt fungal growth. If mycotoxin-producing fungi begin to grow in high-moisture corn, the level of mycotoxins in your stored grain can increase. If you detect odors during warmer months, it is likely that fungus-feeding insects (foreign beetles and hairy fungus beetles) are in the grain. In such cases, you may need to treat the grain with insecticides.
Figure 5. Interior of a grain bin.
Travis Faske, University of Arkansas; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Anna Freije, Purdue University; Tom Isakeit, Texas A&M University; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; Damon Smith, University of Wisconsin; Albert Tenuta, OMAFRA; Kiersten Wise, Purdue University; and Charles Woloshuk, Purdue University.
Gary Bergstrom, Cornell University; Alyssa Collins, Pennsylvania State University; Andrew Friskop, North Dakota State University; Doug Jardine, Kansas State University; Hillary Mehl, Virginia Tech University; Alison Robertson, Iowa State University; and Adam Sisson, Iowa State University.
All photos were provided by and are the property of the authors and reviewers, except Figure 1, which was provided by Burt Bluhm, University of Arkansas.
Funding for this project was provided by the United States Department of Agriculture National Institute for Food and Agriculture (USDA-NIFA) project Integrated Management Strategies for Aspergillus and Fusarium Ear Rots of Corn. NIFA Award Number: 2013-68004-20359. The authors also hank the Grain Farmers of Ontario for their support.
This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel.
This information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.
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