Ear rots concern corn producers and grain elevators

Ear molds have been a problem this year in some corn fields. Elevators will reduce the price a farmer receives for their grain depending on the percentage of kernels infected with disease. Some ear molds produce mycotoxins. If mycotoxins levels are too high in a load of grain, an elevator may reject and not purchase the grain. Ears become susceptible to molds during periods of stress or damage from birds and insects. Generally, heat stress causes more mold problems than excess moisture. The use of genetically modified corn with the Bt gene, which protects against corn earworm and European corn borer, has reduced the potential for insect damage and ear mold infection Besides the potential for a lower grain price, ear molds in a field may force a farmer to change their harvest and storage management. They will need to harvest these fields at a higher grain moisture (harvest earlier) to prevent further disease development. The extra grain drying will increase the storage cost. If not dried quickly to 14% moisture, the disease kernels may spread to other areas of the bin. Also, a farmer cannot store diseased kernels for an extended period compared to disease-free grain. A farmer will have to make combine adjustments to deal with rotted grain and cobs. The disease material will break into small pieces and increase the amount of fine particles in the grain. Fines will decrease air flow during grain drying, making it more difficult to dry grain and may allow further mold development in storage. Farmers will increase the combine's fan speed and other adjustment in an attempt to blow out the lighter fines and diseased kernels during the thrashing process. The need to change combine settings from field to field is time consuming and the whole process will slow down harvest. There are four types of ear rots that may occur in our area. Gibberella ear rot is the one of most concern since it can produce mycotoxins. The disease will have white to pink mold covering parts of the ear. The tip and upper half of the ear is the most common infection area but it can occur anywhere on the ear, including the base. Weather conditions three weeks after pollination or areas damaged by insects and birds allow the disease to initially infect ears. When severe, Gibberella ear rot is a major concern because the fungus produces several mycotoxins, including deoxynivalenol (vomitoxin), that are harmful to livestock. Once the ear is infected by the fungus, these mycotoxins may be present even if no visual symptoms of the disease are detected. Hogs are particularly sensitive to vomitoxin. Therefore, the FDA advisory level for vomitoxin in corn to be fed to hogs is 5 ppm and corn fed is not to exceed 20% of the diet. Vomitoxins have been detected in some loads of grain being delivered to local elevators. Elevators have increased grain testing this fall to identify loads that may need to be adjusted to lower the mycotoxin levels before placing in long term storage. Another ear rot that can produce toxins is Fusarium. For this disease a white mold develops on infected kernels, which may develop a brown discoloration with light colored streaks. Infection generally occurs from bird or insect damage to ears. Affected ears usually have infected kernels scattered over the ear among healthy-looking kernels. Several different Fusarium species may be involved with Fusarium ear rot. One common species produces a toxin called Fumonisin. Horses are particularly sensitive to Fumonisin, but it generally does not bother cattle and sheep. Two other ear rots that are often seen in fields are Diplodia and Trichoderma ear rots. These two diseases are not known to produce mycotoxins but heavy infestation will lower grain quality and yields. Diplodia ear rot produces a thick white mass of mold on the ear, usually initiating from the base of the ear and growing toward the tip. Eventually the white mold changes to a grayish brown; kernels infected appear to be glued to the husk. Corn is most susceptible for infection during the three-week period from late vegetative growth to silking. Wet conditions and moderate temperatures during this period favor infection and disease development, and the disease tends to be most severe in no-till or reduce-till fields of corn planted after corn. Trichoderma ear rot produces thick greenish mold growing on and between the kernels and often causes grain to sprout while on the ear before harvest. Although some species of Trichoderma may produce mycotoxins, these toxins are usually not found in Trichoderma-affected ears under our growing conditions. Even though Diplodia and Trichoderma ear rots generally do not produce mycotoxins, livestock will avoid eating the moldy kernels, affecting the feed value of the grain. Local elevators will be testing corn deliveries for disease and mycotoxin to make handling and storage decisions. Farmers will note hybrids that have had disease incidents and make sure to not select them next year. Also, a farmer may select hybrids in the future that have the Bt gene to protect against many ear feeding insects. Additional information and images of ear molds and rots may be found at https://agcrops.osu.edu/newsletter/corn-newsletter/2018-28/ear-rots-corn-telling-them-apart and https://agcrops.osu.edu/newsletter/corn-newsletter/2022-34/harvesting-and-handling-ear-rot-affected-corn