Corn ear rot potential in Ohio corn
It is already the first week of October and most of the corn is still not ready for harvest. 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. We have received reports of ear rots in some fields and, understandably, after the vomitoxin problems we had in 2009, producers are asking whether we are likely to see a similar problem again this year. So far the problem does not seem to be widespread, with only a few fields affected, and not every ear rot is associated with vomitoxin contamination of grain. In particular, most of the reports indicate that the affected fields have Diplodia ear rot, which does not result in vomitoxin contamination. 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. Unlike 2009 when conditions were cool and rainy during the weeks after silking, conditions were relatively warm and dry this year. 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. There have been no reports of Diplodia producing mycotoxins that are harmful to animals in Ohio, but animals do refuse to eat grain with high levels of Diplodia-damaged kernels. Additionally, severely affected grain has low nutritional value.