It is already the third week of October and most of the corn is still standing in the field. Some of the earlier-planted fields are being harvested, but at relatively high moisture levels. This is causing some concern among producers as to the potential for ear rot and mycotoxin problems. In fact, we have already received several samples of moldy ears from some fields, but so far the problem does not seem to be widespread, with only a few fields affected. Moreover, not every ear rot is associated with vomitoxin or other mycotoxin contamination of the grain. However, ear rots could potentially become more of a problem if it continues to rain and the corn remains in the field for an extended period.
One of the very first steps to determining whether you will have a problem with vomitoxin or other mycotoxins is to know which ear rot you have in your field. Generally, it is fairly easy to tell ear rots apart based on the color of the fungal growth on the ear, where the moldy kernels are located, and how they are distributed on the ear. Other good indicators are the prevailing weather conditions and susceptibility of the hybrids. For the two most common ear rots in Ohio, Gibberella and Diplodia, both of these diseases develop best when wet weather conditions occur during the first few weeks after silking, with Gibberella being favored by slightly cooler temperatures than Diplodia. For both diseases, spores of the fungus are splashed onto the silk where they penetrate and grow into the ear. However, infection may also occur at the base of the ear, especially if it rains late in the season and the ears remain in an upright position, collecting water at the base between the husks and the kernels.
Diplodia causes a thick grayish-white mass of mold to grow on the ear, usually beginning from the base and growing toward the tip. With Gibberella, a visible white to pink mold usually covering the tip or more of the ears is characteristic of this disease. The Gibberella ear rot fungus produces mycotoxins that are harmful to animals. These include deoxynivalenol (Vomitoxin) and zearalenone and T-2 toxin, all of which may cause health problems in livestock. Therefore, suspect grain should be tested for these mycotoxins by chemical analysis before being fed to animals. As a general rule, do not feed any grain with 5% or more Gibberella moldy kernels. Hogs and young animals are particularly sensitive to these mycotoxins. Diplodia ear rot is less of a concern from a mycotoxin standpoint, but animals do refuse to eat grain with high levels of Diplodia-damaged kernels. Additionally, severely affected grain has low nutritional value.
Certain hybrids are more susceptible to one or more ear rots than others. Examine ears to determine the presence of ear molds. Make a note of which ear rots are present and hybrids that are most affected. Make future hybrid choices based on this information. Growers are advised to follow certain harvest and storage guidelines to minimize problems associated with kernel rots and mycotoxin contamination:
1. Harvest at the correct moisture and adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in (machine or insect) damaged kernels.
2. Dry harvested grain to 15% moisture and below to prevent further mold development in storage.
3. Store dried grain at cool temperatures (36 - 44F) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.
4. Periodically check grain for mold, insects, and temperature.
5. If mold is found, send a grain sample for a mycotoxin analysis to determine if toxins are present and at what level. For more on moldy grain, mycotoxins, and mycotoxins sampling and analysis visit the following websites: ( http://ohioline.osu.edu/ac-fact/pdf/0052.pdf ).