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Causes & Identification

Purdue Extension > Managing Moldy Corn > Causes & Identification

Causes and Identification

Gibberella ear rot
Photo by Charles Woloshuk

Publications

Diseases of Corn: Aspergillus Ear Rot
Purdue Extension publication BP-83-W.

Alfatoxin Testing: Illinois, Indiana, Michigan, Ohio (Source: PDF 35 KB)
USDA-RMA publication provides information about aflatoxin testing laboratories.

Loss Adjustment Procedures for Aflatoxin (PDF: 25 KB)
USDA-RMA publication

Guidance for Industry: Action Levels for Poisonous or Deleterious Substances in Human Food and Animal Feed
Recommendations from the U.S. FDA.

Diseases of Corn: Gibberella Ear Rot
Purdue Extension publication BP-77-W.

Diseases of Corn: Diplodia Ear Rot
Purdue Extension publication BP-75-W.

Aflatoxins and Other Mycotoxins
Purdue Extension publication NCH-52-W.

Chat ‘n Chew Café: Information Resources for Challenging Crop Harvest Conditions
A compilation of resources from Purdue and other universities that address challenging crop harvest conditions.


Frequently Asked Questions

What is a mycotoxin?
Mycotoxins (myco = fungus, toxin = poison) are substances produced by fungi that are harmful to animal and human health. Mycotoxins can be produced in grain during storage or processing, but are most frequently associated with fungal infection that occurs before harvest.

 

Which mycotoxins are of most concern?
The most common mycotoxins that affect corn in Indiana include aflatoxin, fumonisins, zearalenone, and vomitoxin (also known as deoxynivalenol, or DON). Aflatoxins are associated with Aspergillus species of fungi that are more common during dry years. Fumonisins are produced by several Fusarium species and can occur under similar environmental conditions as aflatoxins. Zearalenone and vomitoxin are produced by Fusarium species and are often associated with cooler, wetter weather. Collectively, these fungi are commonly called corn ear molds or corn ear rot fungi.

 

How can I determine if corn has mycotoxins?
A chemical analysis is required to verify the presence and amount of mycotoxins in grain. A separate test must be performed for each suspected mycotoxin. Visual observation of the molds on diseased ears indicates only that mycotoxins could be present. There are cases when grain grain is contaminated with mycotoxins, but there is no visual indication of mold damage.

 

Where can I test corn for mycotoxins?
Numerous facilities handle grain tests for mycotoxins, but to be certified for crop insurance purposes, a lab must be able to perform quantitative tests, use industry-recognized equipment and procedures, and not have an interest in the outcome of the test. A partial list of approved testing facilities in Illinois, Indiana, Michigan, and Ohio (PDF: 34 KB) is available from the USDA-RMA. The Indiana Animal Disease Diagnostic Laboratory (ADDL) at Purdue can test for mycotoxins, including aflatoxin, vomitoxin (DON), zearalenone, fumonisin, and others less common in Indiana. Visit the ADDL website for details.You also can contact your Purdue Extension county educator or specialist to help you find a testing facility.

 

How can I identify what kind of mold is on my corn?
The Purdue Plant and Pest Diagnostic Laboratory (PPDL) is equipped to identify diseases (including fungi) on corn and other plants. They can also tell you if the fungus identified is capable of producing mycotoxins. However, the PPDL does not test grain for mycotoxins. The PPDL website provides details, including sample handling fees and how to submit a sample. You can also call the PPDL at (765) 494-7071.

 

Is it possible to visually identify mycotoxins in corn?
It is not possible to visually detect the presence of any mycotoxin in grain. However, there is a visual test that is used on corn to help determine if aflatoxins are present. When the aflatoxin-producing fungus (Aspergillus flavus) grows on corn kernels, it often produces a substance called kojic acid. We know that the kernel produces oxidative enzymes that convert the kojic acid to a form that fluoresces a greenish yellow when examined under ultraviolet light ("black light," 365 nm).

To see the fluorescence, corn kernels need be split to expose the insides. If a yellow-green fluorescence is visible, the risk of aflatoxin contamination is high, and a chemical test should be performed. It is important to say that the fluorescence test is not without error. If the kernel enzymes are not functional, fluorescence will not develop. Research also has shown variation among strains of Aspergillus flavus — some strains produce very little fluorescence. As a result, there will be cases when the black light test will detect fluorescence but there will be no aflatoxin present. And there will be some cases when the corn has high aflatoxin levels, but the black light test does not show any detectable yellow-green fluorescence. Thus, solely relying on the black light test to screen for aflatoxin is highly discouraged. A chemical test must be performed to determine whether aflatoxins are present and how much.

 

What caused the disease problems this season?
This season the mycotoxin problem is aflatoxin contamination. The high temperatures and drought conditions increased corn stress and made the plants susceptible to Aspergillus infection. Fields with light or sandy soils will experience drought stress most severely. The 2012 growing season was especially hot and dry over much of the corn growing area of the Midwest, which led to a high incidence of Aspergillus ear rot in some locations.

 

Are there corn varieties resistant to ear diseases?
Corn hybrids vary in their resistance to the various types of ear molds. Check with your seed company or local seed dealer to find out more about resistant varieties.

 

Why were ear molds only in certain areas of a field and not the whole field?
Aspergillus ear rot and aflatoxins will be the greatest in areas of fields that experienced the most stress. Hillsides will experience more drought stress than lower areas in a field. The same is true for areas in a field where the soil is lighter, as they tend to dry out more readily. Areas of a field with ear infesting insects may have higher incidence of ear rot and mycotoxin contamination because they create wounds in the kernel that allow easy entry for the fungus.

 

Will ear molds be a problem next season?
Ear mold development is highly dependent on environmental conditions, especially temperature and moisture. We don't know what the weather will be like in 2013, but that will be the primary determining factor.

 

If a field had a high percentage of ear mold damage this season, what does that mean for next year?
Fields that had ear mold problems this season are at higher risk of having ear mold if planted back to corn the following season. Factors that increase the risk of ear molds in a previously infected field include planting corn following corn or planting corn following wheat. In addition, some hybrids are more susceptible to ear molds than others. Finally, planting corn in a previously infected field using no-till or reduced-tillage, where there is significant surface residue present, could also increase the risk of ear mold next growing season.

 

How can I reduce the risk of ear molds next season?
Ultimately, weather will be a major factor of determining whether ear rotswill be a problem again, but growers can take steps to prevent the potential impact. If possible, rotate corn fields with another crop, such as soybeans. Choose a corn hybrid that is less susceptible to drought stress and ear rot diseases — visit with your seed company or dealer to discuss options. Tillage can promote the breakdown of corn residue where much of the disease inoculum resides and overwinters.

 

Will tillage clean up fields for the next year's crop or will these diseases carry over to next season?
Tillage can reduce the amount of the pathogen that lives in crop residue, but it will not eliminate its presence.

 

Are fields in continuous corn more at risk for ear mold problems than fields in a corn-soybean rotation?
Yes. The fungal pathogens in corn that cause ear rot diseases can survive in the crop residue. If environmental conditions are favorable next year, the pathogen will more easily move from the crop residue to the next crop of corn. Planting soybeans will allow time for the crop residue to degrade.

 

For More Information

Bob Nielsen, Extension Agronomist, Corn
(765) 494-4802, Email: rnielsen@purdue.edu

Charles Woloshuk, Extension Mycotoxin Pathologist
(765) 494-3450, Email: woloshuk@purdue.edu

Kiersten Wise, Extension Field Crops Disease Specialist
(765) 496-2170, Email: kawise@purdue.edu