Sept. 10, 2010

In spite of the very different weather conditions that Nebraska experienced this growing season compared to 2009, ear rots may still be a concern in some fields and producers and crop consultants should continue to scout as they prepare for harvest.

The UNL Plant and Pest Diagnostic Clinic this year has tested samples positive for ear rot diseases. Although ear rots do not appear to be as widespread this year as they were in 2009, producers will still want to be aware of them and make preparations for harvest or even reconsider storage of affected grain.

Ear Rot Diseases and Grain Molds

Ear and grain molds are important because they can reduce the quality of grain and, under the right conditions, may lead to the accumulation of mycotoxins. Development of ear rots and grain molds can be minimized by

• reducing plant stress during the season,
• reducing damage from insects and handling,
• planting tolerant hybrids in high-risk areas, and especially by
• maintaining proper storage conditions after harvest.

Drying grain prior to storage will slow the growth of fungi in the bin. These fungi can seriously reduce grain quality and accumulate mycotoxins. Even under the best storage conditions, grain molds will usually continue to grow and, in some cases, may take over the entire bin.
In recent years losses of up to 30% have been reported in south central Nebraska when grain was removed from storage, especially after mild winter conditions. Even during cold winters, remember that conditions inside the bin may be very different from surrounding conditions. Temperatures inside the bin may take several weeks to stabilize and condensation may develop, adding unwanted moisture that promotes fungal growth.

Minimize Grain Molds

Take the following steps to minimize losses due to grain molds:

• Avoid further damage to kernels during harvest and handling.
• When possible, avoid storage of grain harvested from fields with a high incidence of ear rot diseases.
• If storage is necessary, store for a minimum amount of time.
• Dry grain to less than 15% moisture within 48 hours of harvest to slow further growth of fungi.
• Remove old grain from empty bins because it harbors fungi that can infect new grain.
• Stir and aerate grain bins during storage to prevent the development of hot spots.

Identifying Ear Rots

Several fungi common to production fields can cause ear rot diseases. Some of the most common in samples submitted to the UNL Plant & Pest Diagnostic Clinic this year are diplodia ear rot and fusarium ear rot.

Diplodia Ear Rot.  So far this year, the most common problem appears to be Diplodia (also called Stenocarpella) ear rot. Diplodia ear rot (Figure 1) is a common disease in the Corn Belt. The fungus that causes this disease is not known to produce a mycotoxin in the United States, but can significantly reduce grain quality.

Extensive and rapid fungal growth usually begins at the base of the ear and can overtake the entire ear creating a lightweight mummified ear. In addition to these symptoms, this disease can be recognized by the production of small raised, black fungal reproductive structures on infected kernels, stalks, and/or husks (Figure 2) giving them a rough feeling when touched, similar to sandpaper.

Fusarium Ear Rot. Fusarium ear rot also has occurred this year. Fusarium may infect any part of the ear and take advantage of wounds created by insects or hail. The species that causes this disease also can secrete mycotoxins called fumonisins into the grain. This mycotoxin is carcinogenic, but is not regulated at concentrations as low as that of aflatoxins (up to 50 ppm). It is particularly toxic to swine and horses and can cause the blind staggers.

Fusarium ear rot is favored by a wide range of environmental conditions and can be recognized by its scattered tufts of white to pink mold on the ears. It may be accompanied by starburst patterns on the kernels.

Diagnostic Assistance

If you are in doubt about the identity of a disease or cause of another plant problem, submit a sample to the UNL Plant and Pest Diagnostic Clinic (P&PDC) for diagnosis. For more information about these and other plant diseases or for submission instructions and forms, visit the Plant Disease Central website.

Tamra Jackson
Extension Plant Pathologist
Amy (Ziems) Timmerman
UNL Plant and Pest Diagnostic Clinic Coordinator