Storing Mycotoxin-Affected Corn Grain

***Updated in 2025, this version replaces the previous 2016 Storing Mycotoxin-Affected Grain publication.***

The fungi that cause several corn ear rot diseases can produce mycotoxins, which are chemical substances that can be dangerous to humans and livestock. Corn affected by ear rots requires important management steps to limit yield losses and reduce mycotoxin concentrations.

This publication outlines how to manage stored corn grain affected by mycotoxins.

Harvest Diseased Grain First

Once corn reaches maturity, farmers may leave the crop to dry down in the field to save on drying costs. However, the presence of ear rot diseases should be a key consideration when determining harvest timing. The fungi that cause ear rot diseases can continue to grow, spread, and produce mycotoxins both after corn reaches maturity and during storage if grain is not dry.

The most common mycotoxins associated with ear rots are aflatoxin (associated with Aspergillus ear rot), fumonisins (associated with Fusarium ear rot), and deoxynivalenol (associated with Gibberella ear rot) (Figure 1). If Aspergillus ear rot, Fusarium ear rot, or Gibberella ear rot are detected during pre-harvest scouting, or if significant insect or bird damage is observed, prioritize harvesting affected fields first. Immediately dry the grain to moisture levels that prevent fungal growth and mycotoxin production.

Set the combine to harvest clean, whole kernels, as aflatoxins and fumonisins are often concentrated in light, damaged kernels. To minimize kernel damage, use the lowest possible cylinder speed necessary to shell the grain effectively while maintaining acceptable loss levels (less than 1%). Excessive cylinder speed is the leading cause of kernel damage, so adjust concave clearance to avoid breaking cobs excessively before increasing the cylinder speed. Ensure sufficient airflow to remove chaff and small, light kernels.

For additional details on identifying ear rot diseases in the field, refer to An Overview of Ear Rots (CPN-2001).

Dry Affected Grain Quickly

Drying corn (and other grains) helps prevent fungi from infecting or further degrading and producing mycotoxins in previously infected grain. Wet grain can deteriorate quickly in a harvest truck or grain bin, especially under warm post-harvest conditions, leading to increased mycotoxin levels (Figure 2). Proper storage at low moisture levels can significantly reduce the risk of mycotoxin development.

High-temperature drying effectively stops fungal growth and mycotoxin production. However, it will not reduce existing mycotoxins levels already present in the grain. Quick drying at high temperatures is preferable to slow drying with low temperatures. Exercise caution when using low-temperature, in-bin dryers for moldy corn, and ensure proper airflow and ventilation when storing dry corn to maintain grain quality. 

A good post-harvest drying target for storing grain is 15.0 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.

For long-term storage, especially through the hottest summer months, dry grain to less than 13 percent moisture. At this moisture level, mycotoxin-producing fungi are typically unable to grow.

Remove Damaged Grain

Damaged corn kernels can disrupt airflow during storage and increase the risk of fungal growth. Several factors can contribute to kernel  damage.

Ear rot diseases often damage kernels, causing them to break and weigh less at harvest. If the ear rot fungi present are mycotoxin-producing species, there is a high risk of mycotoxin contamination in the grain (Figure 3). Mechanical damage during the shelling process can damage healthy kernels. In addition, postharvest handling, such as dropping grain through dryers, elevator spouts or other equipment can damage grain (Figure 4).

Broken kernels and fine material (called “fines”) can accumulate in the center of the storage bin during filling unless a spreading device is used. This central core of fines hinders uniform air movement through the grain mass, increasing the risk of grain spoilage. To mitigate this, withdraw some grain from the bin after it is filled, or “core” the bin to remove the bulk of the broken kernels and fine material that accumulate in the center.

If mycotoxins are present in the harvested grain, the majority of the mycotoxins can be detected in the broken kernels and fines. Although costly, cleaning the grain before selling may reduce the level of mycotoxin contamination. Cleaning usually involves passing the grain over a series of screens to remove broken kernels and fines. 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.

Manage Your Grain Bins

Before filling any grain bin, remove any existing 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 with mycotoxins and mycotoxin-producing fungi.

Regularly monitor storage bins for potential issues. Inspect for structural leaks and condensation in the headspace, as water dripping onto the grain surface can initiate fungal growth and lead to surface crusting. Pay attention to sour, musty, earthy, or putrid odors, which often indicate fungal problems caused by high grain moisture from improper drying, leaks, or insect activity. Be sure to wear proper personal protection equipment, if necessary, for examining grain bins.

If the grain becomes wet, use fans to increase airflow and reduce grain moisture levels, preventing fungal growth. If mycotoxin-producing fungi begin to grow in high-moisture corn, the mycotoxin level in the stored grain can increase. During warmer months, if odors are detected, fungus-feeding insects, such as foreign beetles and hairy fungus beetles may be present. In such cases, treating the grain with an insecticide labeled for stored grain may be necessary.

Acknowledgments

Authors

Travis Faske, University of Arkansas; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Tom Isakeit, Texas A&M University; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; Damon Smith, University of Wisconsin-Madison; Albert Tenuta, OMAFA; and Kiersten Wise, University of Kentucky.

Reviewers

Daisy Ahumada, North Carolina State University; Alyssa Betts, University of Delaware; Mandy Bish, University of Missouri; Alyssa Collins, Penn State University; Maira Duffeck, Oklahoma State University; Dean Malvick, University of Minnesota; Boyd Padgett, LSU AgCenter; Madalyn Shires, South Dakota State University; Adam Sisson, Iowa State University; and Darcy Telenko, Purdue University.

Sponsors

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 thank the Grain Farmers of Ontario for their support.