Corn Ear Molds: What Color are Your Ears?

Aspergillus flavus growing on a corn ear tip.

This is the time of the year when I tend to get a ton of telephone calls regarding the presence of rotten (moldy) corn ears.  Over the past few weeks I’ve observed a range of symptoms on corn ears.  In extreme cases the entire ear was covered with fungal growth and corn kernels were beginning to sprout but in the less severe cases only the tip was covered with fungus.  Many fungi can inhabit a corn ear and in some cases the specific fungus present will depend on health of the corn plant, whether or not the ear has sustained any damage (insect or otherwise), how far the ear filled out, previous crop in the field, length of time in the field past physiological maturity, plant stress and duration of the stress during the season, and environmental conditions.  Corn smut is another issue altogether so I’m excluding that disease from the discussion.  More often than not the color of the fungus on the corn ear, or on the kernels themselves will go a long way towards determining the specific fungus present and whether or not a toxin will result from infection.  In addition, there are times when symptoms other than the fungus itself will aid in determining whether or not the fungus present is one to be concerned about.  However, keep in mind, some fungi produce similar colors and can oftentimes be classified within the groups of organisms that can produce a toxin upon infection of the developing corn ear.  In addition, there are some fungi that are not included in the table below to not cloud the issue.

Several ear rots can be detected in any given field to a low level regardless of the year.  However, not all of them are indicative of a toxin present in the harvested grain.  In fact, just because a fungus, let’s use Aspergillus flavus as an example, is growing on the outside of the ear (on the husk or shuck) or even within the husk on the corn ear itself does not mean that a toxin resulted from the fungus having grown on the corn grain.  Conversely, if no mold is present this does not mean that no toxin is present.  Both of the above statements are important issues to consider.  Remember, toxins can be produced in the field prior to harvest or in stored grain as a post-harvest issue. 

Diplodia ear rot, see white fungus growing profusely on bottom ear.

The attached table should not be used as a diagnostic guide but is being provided as a tool to aid in the initial observation of ear mold.  Samples of corn ears with fungi that could produce a toxin should be submitted for testing.  Moreover, grain from fields with toxin producing fungi present on the ears prior to harvest should not be stored because if a toxin is present this will not decrease over time since it is presumed the causal fungus is still present and would likely only lead to an increase in toxin during storage.  To briefly describe some of the information in the table there are generally several species of Aspergillus and Fusarium that can cause ear molds.  Specifically, three different species of Alternaria are the most common ear rotters.  However, only A. flavus and A. parasiticus can produce aflatoxins if the environment is conducive.  As stated, several difference species of Fusarium can cause ear rot and in addition to an ear rot can produce a “starburst” pattern on kernels that were infected with the fungus.  However, the starburst pattern appears on an annual basis to low levels in most corn fields and should not be considered the only source of diagnoses regarding the potential presence of a toxin.  The only way to determine if a toxin is present is to submit a grain sample or hand harvested ears to be analyzed chemically.  See the attached photos for additional guidance.

Starburst pattern on kernels indicative of infection by Fusarium.

Aspergillus niger (the black fungus) and likely Gibberella (the pink fungus) growing on an ear tip.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Penicillium ear rot.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trichoderma ear rot (ears infected with this fungus can feel lighter than normal).