WOOSTER, Ohio – With several types of ear rot diseases appearing on Ohio's corn crop, properly identifying them is important for producers to make decisions about feeding grain to livestock.
"It is important to identify ear rot problems before harvest because some ear rot fungi produce mycotoxins that are harmful to livestock," said Pierce Paul, an Ohio State University Extension plant pathologist with the Ohio Agricultural Research and Development Center. "After harvest is becomes much more difficult to tell what's causing the problem."
Current weather conditions are favorable for ear rot development: wet weather late in the season, frost occurring before maturity, corn standing in the field for an extended period, and delayed maturity. Other indicators of potential ear rot problems include bird and insect damage, hybrid susceptibility and ears drying down in an upright position.
Three of the most common ear fungal diseases in Ohio are Gibberella, Diplodia, and Fusarium ear rots.
"Gibberella ear rot is the most prevalent of the ear rots this year. However, we also have received reports of Diplodia ear rot in some fields," said Paul. "It is fairly easy to tell ear rots apart in the field based on the color of the fungal growth on the ear, how the mold develops, and how the moldy kernels are distributed on the ear."
With Gibberella ear rot, the fungus enters the ear tips and leaves a pinkish mold on the kernels that progresses down from the tip toward the base of the ear. Gibberella ear rot develops best when cool temperatures and frequent rainfall occur during the 3-week period after silk emergence.
Like Gibberella ear rot, Fusarium ear rot also causes a pink discoloration on the kernels, but the disease develops best when warm, wet weather occurs during the 2 to 3-week period after silking. In addition, the pink moldy kernels are usually scattered all over the ear and as the disease develops, the infected kernels may become tan or brown or have white streaks.
Diplodia ear rot is the most different of the three diseases. It causes a thick white mold on the ear, usually starting from the base and progressing toward the tip. Infection can begin before tasseling up to silking, and disease development is favored by wet weather and mild temperatures during early ear development. As the disease develops, the husk becomes bleached.
Paul emphasizes that symptoms of ear rot don't always appear on the outside of the husk.
"This is particularly true with late infections," said Paul. "To determine if you have an ear rot problem, walk fields, strip back the husks of about 50 plants and look for telltale symptoms."
The Gibberella ear rot fungus produces mycotoxins that are harmful to animals. These include deoxynivalenol (Vomitoxin), zearalenone and T-2 toxin.
"Suspect grain should be tested for these mycotoxins by chemical analysis before being fed to animals," said Paul. "As a general rule do not feed any grain with 5 percent or more Gibberella moldy kernels.
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.
For more information, log on to the OSU Extension Agronomic Crops Team Web site at http://agcrops.osu.edu.