Corn Ear Rots & Grain Molds
Figure 1. Diplodia ear rot usually begins at the base of the ear and can grow very quickly to take over the entire ear.
October 23, 2009
Cooler conditions in Nebraska and the rest of the Corn Belt have delayed harvest and slowed grain drying, leading to increased ear rot diseases and grain molds. Some producers and consultants also are observing rotted cobs, which can be related to several ear rot diseases.
Scouting is recommended to determine the extent of ear rot damage prior to harvest so action can be taken to minimize its impact on grain quality.
Ear and grain molds can reduce the quality of grain and, under the right conditions, may lead to the accumulation of mycotoxins. To minimize the development of ear rots and grain molds:
- reduce plant stress during the season,
- reduce damage caused by both insects and handling,
- plant tolerant hybrids in high-risk areas, and especially,
- maintain proper storage conditions after harvest.
Drying grain prior to storage will slow the growth of fungi in the bin that can seriously reduce grain quality and accumulate mycotoxins.
Ear rot pathogens may continue to grow during storage and lead to grain mold that can seriously reduce grain quality and lead to major deductions at the elevator. Even under the best growing conditions, grain molds will usually continue to grow and, in some cases, may take over the entire bin.
Figure 2. The fungus that causes Diplodia ear rot may also produce small black reproductive structures called pycnidia.
|Figure 3. The Diplodia reproductive structures, called pycnidia, are small and black and give the surface of the kernels and ears a rough texture.|
In southcentral Nebraska losses of up to to 30% have been reported when grain was removed from storage, especially after a mild winter. Even during cold winters, conditions inside the bin may be very different from their surroundings. Temperatures inside the bin may take several weeks to stabilize and condensation may develop, adding unwanted moisture that promotes fungal growth.
To minimize losses due to grain molds:
- Avoid further damage to kernels during harvest and handling.
- When possible, avoid storing grain 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.
Figure 5. The fungus causing Fusarium ear rot may develop anywhere on the ear, taking advantage of wounds created by insects or hail (pictured).
Figure 7. The fungus that causes Penicillium ear rot may infect at wound sites and exposed ear tips and produces masses of blue-green spores. The same fungus also causes a symptom on the grain known as “blue eye.”
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 does not produce a mycotoxin but can significantly reduce grain quality. Extensive 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 (Figures 2 and 3) and stalks, giving it a rough feeling when touched, similar to sandpaper.
Fusarium Ear Rot
Fusarium ear rot (Figure 4) also has been common this year. Fusarium may infect any part of the ear and takes advantage of wounds created by insects or hail (Figure 5). The species that cause 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 horses and can cause the blind staggers. Fusarium ear rot is favored by a wide range of environmental conditions and can be identified on the ear by scattered tufts of mold that may be white to pink in color and accompanied by starburst patterns on the kernels.
Gibberella Ear Rot
Giberella ear mold (Figure 6) is commonly recognized by the red or pink discoloration of the kernels and the red or pink mycelium growing around the kernels. Typically, infections begin at the tip of the ear. Mycotoxins called vomitoxin and zearalenone are produced by this fungus. Both of these mycotoxins are not regulated. Vomitoxin is associated with feed refusal or decreased feed consumptions. Thresholds for decreased feed intake are 1 ppm to swine and 10 to 20 ppm in ruminants. Zearalenone typically is not at high enough levels to adversely affect animals. Gibberella ear rot infections are favored by cool, wet weather after silking and through the late summer.
Penicillium Ear Rot
Another grain mold, penicillium (Figure 7), can cause a discoloration of the embryo known as “blue eye” and may be accompanied by the production of penicillic acid, which is not usually a toxigenic concern. This disease is particularly a storage problem and is favored by high moisture levels in grain bins. It has recently been reported again in Nebraska. This disease can be managed by reducing ear wounds caused by insects in the field and by maintaining low moisture while the grain is in storage.
Aspergillus Ear Rot
Aflatoxin is the best known mycotoxin in Nebraska and is produced by the fungus that causes Aspergillus ear rot. There have NOT been any reports of alfatoxin in corn in Nebraska this year. Hot, dry weather during the latter half of the growing season after pollination especially favors aflatoxin production. Drought-stressed corn, such as that in non-irrigated fields and the corners of fields that are out of range of center pivots, are especially vulnerable to the accumulation of aflatoxin.
Aflatoxin is toxic and carcinogenic to humans and livestock and therefore, its levels are strictly regulated in grain by the FDA. Aflatoxin is regulated at very low levels ranging from 0.5-300 parts per billion (ppb), depending upon its end use.
Identification of the ear rots and grain molds can be made by the UNL Plant and Pest Diagnostic Clinic and sample submission forms and more information can be found on the Plant Disease Central Web site.
Extension Plant Pathologist
Director of the Plant, Pest and Diagnostic Clinic