WOOSTER, Ohio -- Ohio's corn crop, subjected to moist, cool conditions as it awaits harvest, is at risk from the development of ear mold -- a disease that can reduce grain quality and cause the accumulation of toxins that are harmful to livestock.
Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that reports of some ear mold problems are beginning to show up from growers who have been unable to harvest their crop due to heavy rains that have swept through portions of the state the past several weeks. According to the Ohio Agricultural Statistics Service, corn harvest is behind schedule with only 18 percent of the crop taken off.
"Ear mold, or ear rot, tends to be more severe when cool, wet conditions occur during silking and early grain fill, but with the weather we've had lately, the corn is likely to face these problems later in the season," said Paul, who also holds a partial Ohio State University Extension appointment. "Factors that can contribute to ear rot at this stage include stalk rot problems, because some of the same fungi that cause stalk rots also cause ear rots; ears that hang low to the ground because of stalk lodging, increasing the chances of fungal spores splashing onto the ears; and corn ears that stay upright, either because of hybrid characteristics or improper grain fill, trapping water at the base of the ear and creating conditions suitable for fungal infection."
Ear mold in Ohio is generally caused by three types of fungi: Diplodia, Gibberella and Fusarium.
Diplodia ear rot is characterized by a thick, white mold that covers the entire ear, a shrunken and lightweight ear, and kernels that appear glued to the husks. A sign of Gibberella ear rot is a pinkish to reddish mold that starts at the tip of the ear and progresses to the base. Fusarium ear rot covers individual kernels with a white, cottony mold.
All three diseases reduce grain quality, but Gibberella ear rot and Fusarium ear rot also produce toxins that may be harmful to livestock.
Gibberella fungi produce vomitoxin, the same mycotoxin that is also produced in head scab in wheat. Hogs are particularly sensitive to vomitoxin, which can cause feed refusal at concentrations in grain at around 1 part per million. The FDA advisory level for vomitoxin in corn to be fed to hogs is 5 parts per million and this is not to exceed 20 percent of the diet.
Fusarium fungi produce a mycotoxin called fumonisin. Horses are particularly sensitive to fumonisin, and cattle and sheep are relatively insensitive.
Paul recommends that growers test their grain at grain elevators or send samples to toxicology laboratories if they feel grain is infected or if they believe infection levels may be high.
"It is important that growers harvest those fields suspect of any disease problems first and as soon as possible," said Paul.
Paul also recommends that growers keep diseased grain separate from healthy grain and dry grain down to 15 percent moisture, as high moisture levels tend to cause further disease development and toxin production in storage. In situations of long-term storage, grain should be dried down to 13 percent moisture.
Other recommendations include:
• Harvest fields with stalk rot problems first to minimize lodging, and consequently, ear rot development.
• Adjust harvest equipment to minimize damage to kernels. Mold and mycotoxins tend to be higher in machine or insect-damaged kernels.
• Store dried grain at cool temperatures (36-44 degrees Fahrenheit) in clean, dry bins. Moderate to high temperatures are favorable for fungal growth and toxin production.
• Periodically check grain for mold, insects, and temperature.
For more information on ear rot in corn, log on to http://www.oardc.ohio-state.edu/ohiofieldcropdisease/, or refer to Ohioline Bulletin 802 at http://ohioline.osu.edu/b802/.