Corn Mycotoxin FAQs

***Updated in 2025, this version replaces the previous 2016 Mycotoxin FAQ publication.***

1. What are mycotoxins?

Mycotoxins are natural chemicals produced by certain fungi. Some of these mycotoxin-producing fungi can cause ear rots in corn, subsequently leading to mycotoxin contamination in corn grain. Mycotoxins can harm humans, pets, livestock, and other animals if they consume contaminated food or feed.

2. What mycotoxins occur in corn?

There are five major mycotoxins associated with ear rot diseases of corn.

Aflatoxins are found in corn with Aspergillus ear rot (Fig. 1).

Deoxynivalenol (DON, sometimes called vomitoxin) and zearalenone are associated with Gibberella ear rot (Fig. 2).

Fumonisins are found in corn with Fusarium ear rot.

Ochratoxin is found in corn infected with Penicillium verrucosum, although some species of Aspergillus also produce this mycotoxin.

3. What are the effects of mycotoxins?

The toxic effects of mycotoxins vary by type, concentration, period of exposure (acute vs. repeated exposure), and the animal species consuming toxin-contaminated grain.

Aflatoxins damage the liver (hepatotoxicity), cause liver cancer, and suppress the immune system of animals and humans.

Fumonisins also damage the liver (hepatotoxicity) and cause esophageal cancer, pulmonary edema (fluid in the lungs), and leukoencephalomalacia (irreversible, fatal brain damage) in horses and rabbits.

DON affects the gastrointestinal tract, often causing vomiting, feed refusal, and reduced weight gain. DON also suppresses the immune system, and can inflame the central nervous system.

Zearalenone causes hyperestrogenism (estrogen overload), a condition that is particularly harmful to female breeding animals.

Ochratoxin can cause cancer after repeated exposure, while brief exposure can cause kidney toxicity.

4. What levels of mycotoxins are safe in food and feed?

The United States Food and Drug Administration (FDA) has developed action levels (legally allowed concentrations) for aflatoxin and advisory levels (cautionary concentrations) for fumonisins and DON. In Canada, Health Canada and the Canadian Food Inspection Agency (CFIA) regulate the maximum allowable levels of mycotoxins in human food and livestock feed. The action, advisory, and maximum allowable concentrations vary by mycotoxin and the intended use of the final corn products.

Up-to-date information on action levels and advisory levels for aflatoxin, DON, and other mycotoxins, can be found by clicking on the FDA information page on mycotoxins or Health Canada/CFIA guidelines page.

If grain or grain end products contain mycotoxin concentrations exceeding legal action levels/advisory levels, the grain may be required by law to be destroyed, but at minimum the load can be docked for price or rejected. Acceptable mycotoxin concentrations are typically determined at the point of sale and outlined in contract specifications. Exported corn must also meet the limits set by the importing country, which may be  stricter than those in the United States or Canada. While certain compounds can be added to animal feed to reduce the effects of mycotoxins, the mitigation they provide is modest and adds to production costs.

5. When should I test for mycotoxins?

If the field has any kernel or ear rot problems (more than 10% of the ears in the field are moldy), test the grain for mycotoxins. Additionally, feed refusal in swine should trigger testing of the feed. Testing for aflatoxin is recommended for corn that is severely drought-stressed (Fig. 3).

More information about grain sampling and mycotoxin testing is available in Corn Grain and Silage Sampling and Mycotoxin Testing (CPN-2003).

6. How do I scout for potential problems?

Scout Fields Before Harvest

Scout fields for ear rot at kernel maturity (black layer; R6 growth stage) and just before harvest.

Pay close attention to areas where the crop may have been drought-stressed, damaged, or exposed to extreme environmental conditions. These areas include hillsides where drought stress may be more severe (for Fusarium and Aspergillus ear rots) and low areas where moisture from fog or high-dew conditions prevail (for Gibberella ear rot).

When scouting, randomly select plants and pull back the husks to examine the ears (Fig. 4). A quick method is to select 100 plants across the field (20 ears each from five different areas spaced more than 25 feet apart). If a diseased ear is found, examine an additional 10 ears from adjacent plants.

During your examination, ask three questions:

1. Which ear rot is present?

2. What percent of the ear is affected by ear rot (what is the severity of the disease)?

3. What proportion (%) of the field is affected (10% or high indicates a significant concern for mycotoxin contamination)?

After answering these questions, determine the next steps (see below). More information about identifying ear rots is available in An Overview of Ear Rots (CPN-2001).

Know When to Test for Mycotoxins

The risk of mycotoxins in harvested grain increases with the number of infected kernels on an ear. Assume diseased kernels contain mycotoxins, but note that surrounding, apparently healthy kernels may also contain mycotoxins. Mycotoxin concentrations may vary among diseased ears. Additionally, ears that appear to have low levels of ear rot may still have high mycotoxin concentrations. Due to these issues in variability and potential for high concentrations of mycotoxins in visibly healthy kernels, it is advised to test all grain used for feeding livestock to be sure you know what the concentrations are so that you may manage these issues before animals are affected.

7. What are the mycotoxin testing options?

Mycotoxins are complex chemical compounds, which makes them difficult to quantify. However, several technologies can assess mycotoxin concentrations in corn grain.

For this reason, never rely solely on visual methods to confirm the presence of mycotoxins. A common visual test—the black light test—can indicate the presence of the fungus Aspergillus flavus, but it does not detect aflatoxin in the corn kernels (Fig. 5).

For an accurate assessment, send grain samples to a professional laboratory for analysis. Local laboratories and grain inspection services may test individual corn samples for mycotoxins; however, sample testing can be expensive. Check with your local extension personnel for a more complete list of grain testing facilities in your area. The cost and submission procedures will vary by provider.

See Corn Grain and Silage Sampling and Mycotoxin Testing (CPN-2003) for more information.

8. Will drying, heating, freezing, or applying chemicals reduce mycotoxins in grain?

No. Mycotoxins are extremely stable, and heating, freezing, roasting, or treating them with chemicals cannot reliably reduce the mycotoxin concentrations present within kernels. In some cases, the overall mycotoxin concentration in the grain sample may be reduced by removing broken grain (fines), grain dust, foreign materials, and lightweight moldy kernels. In grain with extremely high concentrations of mycotoxins, cleaning and removing fines might not reduce the applied discounts at the point of sale.

Additional accumulation of mycotoxins in harvested grain in storage may be greatly reduced by properly drying corn to less than 15% moisture. For long term storage, dry grain to 13%.

When grain moisture concentrations are greater than 16%, the risk of aflatoxin and ochratoxin accumulation increases. Moisture greater than 18% elevates the risk of DON, zearalenone, and fumonisins. Warm conditions can further accelerate the rates of spoilage and mycotoxin accumulation. No evidence exists that mycotoxin concentrations will increase in grain stored at an appropriately low moisture (e.g., 13%).

It is important to point out that while high-temperature drying will stop mold growth and mycotoxin production, it will not reduce the concentration of mycotoxins already present. Rapid drying is preferred over low-heat drying. Be wary of low-temperature, in-bin dryers for moldy corn, and be sure to meet proper ventilation requirements for dry corn storage.

More information about proper grain storage is available in Storing Mycotoxin-affected Grain (CPN-2004).

Acknowledgments

Authors

Damon Smith, University of Wisconsin-Madison; Tom Allen, Mississippi State University; Martin Chilvers, Michigan State University; Travis Faske, University of Arkansas; Tom Isakeit, Texas A&M University; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; 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; Paul Esker, Penn State University; Dean Malvick, University of Minnesota; Boyd Padgett, LSU AgCenter; Alison Robertson, Iowa State University; and Darcy Telenko, Purdue University.

Sponsors

Funding for this project was provided by the United States Department of Agriculture - National Institute of Food and Agriculture (USDA-NIFA) project Integrated Management Strategies for Aspergillus and Fusarium Ear Rots of Corn. NIFA Award Number: 2013-68004- 20359. We also thank the Grain Farmers of Ontario for their support.