Fall weather has allowed late planted corn to mature this fall increasing grain yield expectations - the USDA October yield estimate is 172 bushels per acre in Iowa. USDA will update that estimate with the release of its November Crop Report on November 10. Although high grain yields are being reported this fall, reports of quality issues are surfacing.
The cool wet fall conditions also favor the development of fusarium fungi; the white or pink ear rots that are often found in ear corn stored too wet. Field moistures in the low 20s over a long period are favorable for these fungi, which in turn can produce several toxins harmful to people and livestock – vomitoxin, zearalenone, and fumonisin. Grain with field mold should be tested for mycotoxins before feeding, says Charles Hurburgh, director of the Iowa Grain Quality Initiative at Iowa State University.
Harvesting fields with disease problems
"High moisture conditions favor growth of many ear and stalk rot fungi," says Alison Robertson, ISU Extension plant pathologist. "Fields should be scouted as soon as possible to determine the extent of disease problems. To minimize losses due to ear rot and increased mycotoxin levels, we recommend that farmers harvest problem fields (greater than 10% to 15% incidence of ear rot) as soon as possible."
The longer the corn remains in the field, the greater the chance of toxin production. The toxins most likely to increase in the field at this time are those associated with fusarium ear rots - namely vomitoxin, zearalenone and fumonisin.
Gibberella Ear Rot is a consistently important mycotoxigenic fungus in the northern cornbelt - producing vomitoxin, zearalenone and other toxins.
Diplodia Ear Rot is characterized by the appearance of raised black bumps on the moldy husk or kernels.
Diplodia ear rot is more prevalent this season than in previous years, says Robertson. Although mycotoxins are not usually associated with Diplodia ear rot, grain quality will decrease substantially if the corn is allowed to remain in the field, thus early harvest is also recommended in these fields. Adjust harvest equipment to minimize damage to kernels since mold and mycotoxin levels tend to be at greater levels in damaged kernels. Dry (to less than 15% moisture) and cool (to less than 45 degrees F) grain as quickly as possible to reduce further mold growth and toxin production. Elevator operators, especially in eastern Iowa report cases of visible mold damage levels 5% and higher. In normal years, overall mold damage levels are generally less than 2% in freshly harvested corn. High damage levels in harvested grain create challenges for grain grading, particularly in the harvest rush. Damaged corn sharply reduces the future storage life of the grain.
Storage issues need to be considered
Storage and harvest management are very important, says Hurburgh. Field damaged grain, regardless of reason, shouldn't be mixed with good grain. You should harvest around water holes, downed grain and immature areas. Don't mix damaged grain with good grain in storage. Regardless of condition, all grain should be aerated immediately to reduce temperature and equalize moisture.
Field damaged grain will not store beyond the winter months, he emphasizes. You need to maintain 1 to 2 percentage points lower moisture than normal grain (for example, 13% corn instead of more typical 15%). Do not try to hold field damaged corn at higher moistures to avoid drying expense. If you suspect mycotoxin problems, check with crop insurance providers to see if adjustments may be needed, and how to represent the areas to be adjusted. Your veterinarian or the local USDA grain inspection service provider (see below) can assist with obtaining mycotoxin testing. Crop adjustments for quality problems, including mycotoxins, must be done on standing corn at or before harvest.
Accurate grading of field-damaged grain is always difficult in the rush of harvest. Expect end-users, such as ethanol plants, to increase their level of grading because mold and weather damage reduce processing yields/byproduct quality.
An official USDA grade is the standard against which buyer analysis should be compared. It is important that company graders be trained to match USDA graders. Alternatively, samples can be submitted to USDA grading agencies but this process is slower and more costly. In the event of a dispute, use an official grader. The variety of damage types will be very challenging to evaluate. You can locate the official agency in your area. Contact your county ISU Extension service office for the phone number.
Livestock (swine, cattle, horses, poultry) are susceptible to certain mycotoxins, says Robertson. Therefore any grain that is fed to livestock should be tested for mycotoxins. Dairy producers should be particularly sensitive to mycotoxins (see tables below).
The wide variety of molds on these samples has created a range of mycotoxin possibilities – primarily vomitoxin, zearalenone and fumonisin. Prolonged cloudy, humid weather encourages production of the fusarium-based toxins.
Veterinarians can submit samples to the Iowa State Veterinary Diagnostic Lab. Alternatively, official USDA grading agencies can do quick tests for these toxins. Toxins concentrate in the distillers grains three to four times the levels in the corn. Ethanol plants are doing quick screening tests on inbound grain, especially on low test weight corn (less than 50 pounds per bushel). Please refer to ISU Extension publications "Aflatoxins in Corn" (PM 1800), and "Corn Ear Rots, Storage Molds, Mycotoxins and Animal Health" (PM 1698), for guidelines on sampling and sample handling. The black light test will not respond to fusarium.