Before starting up the combine, you should think about the possibility of ear rot and kernel rot diseases in your corn. Detecting these diseases before harvest is a good way to avoid problems and make proper decisions before it is too late. Some of these fungi can produce mycotoxins that are harmful to livestock, so it can pay to be aware of their occurrence in your fields.
To check for ear rots, strip back the husks on at least 100 plants scattered throughout the field. Scout fields separately according to hybrid, tillage and rotation history, and planting date. It is important to be able to recognize the ear rot diseases because their potential impact is very dependent on the particular fungus involved.
Fortunately, conditions have not been especially favorable for ear rot diseases this year. Although it has been cool, most of the state did not experience very wet conditions during the second half of the season, so the occurrence of Gibberella and Diplodia ear rots probably will not be extensive. On the other hand, it has not been hot enough for Aspergillus to become a problem.
When evaluating an ear rot problem, remember, certain ear rots are a warning sign to suspect toxins, but ear rots do not always lead to toxin problems. Many fungi are not known to produce toxins. Even those that can produce toxins do not always do so. Proper handling reduces the risk of toxin development in infected kernels. On the other hand, significant toxin concentrations can sometimes occur in grain that was not visibly moldy.
When potentially toxigenic ear rots are noticed in the field, grain can be managed so as to minimize toxin development. There is no real threshold for these diseases because toxin levels cannot be estimated from mold levels. If more than about 10 percent of ears have a significant amount of mold
(25 percent of the ear or more), these fields should be harvested as soon as possible. The combine will remove some of the moldiest kernels.
The best option for moldy grain is to feed it or sell it instead of storing it. However, it should be tested for toxins before feeding. If toxins are present, it is possible that it can be fed to a less sensitive livestock species, such as cattle. This will depend on the specific toxin and its concentration.
A veterinarian or extension specialist can help with these decisions. If the grain is sold, there may be a reduced price due to mold damage.
Testing for mycotoxins can be done before putting the grain in storage. If toxins are already present, storage is not a good option. Corn that is moldy going into storage will definitely not store well. Toxins only can stay the same or increase. Cleaning the grain will remove fine particles that are usually the moldiest and most susceptible to further mold development. Good storage conditions (clean bins, proper temperature and moisture content, aeration, insect control, etc.) and regular inspection are essential in preventing mold and toxin development in any corn.
Common Ear Rot Symptoms
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This article originally appeared on page 171 of the IC-476(24) -- October 7, 1996 issue.