Warm, wet conditions as grain dried down in September favored the development of ear rots. In the eastern Corn Belt, university plant pathologists report that diplodia ear rot (see accompanying photo) is prevalent this fall (visit the C.O.R.N. Newsletter; The Bulletin; and the Pest and Crop Newsletter). In Illinois, there are reports of grain being turned away from elevators because of poor quality due to Diplodia ear rot. 

DIPLODIA EAR ROT: This fungus is usually recognized by dense, white mycelium that starts at the base of the ear and grows between the kernels. If you see ear mold in your field, contact your crop insurance agent immediately.

Corn coming in to the Iowa State University Grain Quality Lab from field trials in central, northeast, and southeast Iowa has been affected by a variety of ear rot fungi, and many individual ears display symptoms of multiple fungi, says Alison Robertson, ISU Extension plant pathologist. Some of these ear rot diseases are capable of producing mycotoxins, which can result in marketing restrictions for affected grain.

Unfortunately, the risk at this point is not generalizable—fumonisins, deoxynivalenol (vomitoxin), aflatoxin, and zearalenone are all potential suspects in locations throughout the state, she says. Corn earworm injury has been noted in central Iowa samples; these samples were also heavily impacted by ear rot fungi.

If ear rots are a problem in a field, harvest that corn now

It is important to scout fields to determine if ear rots are a problem, says Robertson. If greater than 10% of the ears are moldy, fields should be scheduled for an early harvest to prevent further deterioration of grain. ISU grain quality expert Charlie Hurburgh offers some tips for grain handling and storage.

Some farmers in Iowa are seeing symptoms of diplodia ear mold at harvest this fall; it may be the most common fungus. The good news is that diplodia ear rot is not associated with mycotoxin production. However, this fungus can continue to grow in storage unless the harvested grain is dried thoroughly, says Hurburgh. Other ear molds such as aspergillus, fusarium and gibberella can develop mycotoxins, he notes.

Publications and training modules are available if you would like to learn more. The Crop Protection Network recently posted publications on corn ear rots and mycotoxins that are available for download. Moreover, the Iowa Grain Quality Initiative has a training module describing mycotoxin development.

Handling, storing, feeding or selling mold-infested grain

Due to the fungus-infected grain, regardless of the specific ear rot, the grain will have lower test weight and poor grain quality, says AgriGold Seed Company agronomist Mike Kavanaugh. Test weight is reduced due to the rots infecting the kernels before they have reached physiological maturity. The ear rots interrupt the flow of starch being packed tightly into the kernels prior to the plants natural senescence. Because of this, handling, storing, feeding or selling the grain can be very challenging.

Handling and storing rotten corn. Due to the lower test weight, depending on combine settings, the combine may discard infected kernels leaving a grower with less yield, says Kavanaugh. Combine settings can be adjusted to keep the damaged grain, but if the percentage of damaged kernels is too high, elevators may dock and/or reject the sample/load. Special care needs to be taken not to damage healthy, intact kernels as mold will spread and grow on physically damaged kernels.

Moldy corn produces more fines and broken kernels so growers need to monitor their dryers and keep them cleaned out. There have been dryer fires this fall from this, says Kavanaugh. He advises farmers to dry this corn down to 14% and cool it to 50 degrees F as quickly as possible, as this will keep mold from spreading in the bin. Once the grain reaches 30 degrees close bin up and try to keep the grain temperature there. Damaged corn will have a shorter storage life even if it has been successfully dried down. This corn has been stressed and that will cause it to lose condition sooner. Growers should plan on delivering this grain before their better quality grain, he adds.

Poor grain quality reduces feed value for livestock. In general, ear rots lower feed value by making the corn unpalatable, says Kavanaugh. In addition, animals such as hogs can actually smell the molds in the grain causing feed refusal. This can cause reduced weight gain in animals. However, the largest concern are the toxins that are produced from these molds, specifically gibberella. Gibberella ear rot is a serious concern because the fungus produces several different mycotoxins.

Deoxynivalenol (DON or vomitoxin) and zearalenone are the two most common produced in infected kernels. These toxins can impact the health of many monogastric animals, but hogs are particularly sensitive. DON can cause feed refusal and/or regurgitation if grain concentrations are around 1 ppm. The FDA regulates that DON concentrations cannot exceed 5 ppm or 20% of the diet. Zearalenone is an estrogenic factor causing infertility and abortions in hogs and other animals. For hogs, 0.5 ppm concentrations of zearalenone should not be fed to swine.

Selling contaminated grain can be difficult. Grain contamination and grain rejection is handled differently by different elevators. Most grain buyers are analyzing samples for overall damage on a percent basis, says Kavanaugh. A 100 gram sample is inspected for damage and FM. The percent of each is simply the amount in grams divided by 100. This is used to determine the grade of corn. Each grain buyer may handle this differently so corn growers must check with their local buyer on how they will handle damaged corn. Having a good representative sample to show them may speed the process along. Discounts may vary by buyer, however, this discount schedule below seems to be common:

Less than 5% damaged kernels: no discount

5%-10% damage $.04 pet point discount

10%-20% damage $.05 per point discount

Greater than 20% damage $.06 per point discount

Greater than 30% damaged grain could be rejected depending on the buyer.