Aspergillus ear mold is favored by hot and dry conditions. While many areas of Kansas received above-average rainfall this growing season, select regions missed much of that precipitation. These localized drought-stressed fields are at greater risk for Aspergillus ear mold development. Aspergillus can produce aflatoxin, a known carcinogen that is highly regulated by the Food and Drug Administration (FDA).
Identifying Aspergillus ear mold
On the ear, colonies of Aspergillus flavus are a greenish-yellow, dime- to quarter-sized mold that grows between the kernels. In severe cases, the mold may cover much larger portions of the ear (Figure 1). Often, there is little correlation between the percentage of moldy ears in a field and the actual level of aflatoxin. Corn that dries down rapidly may accumulate less toxin, and some field strains are poor producers of aflatoxin. On the other hand, strains that produce copious amounts of aflatoxin may need to be present on a relatively low percentage of ears to cause problems at the elevator.
Figure 1. Aspergillus ear rot colony. Photo by Doug Jardine, K-State Research and Extension.
Figure 2. Severe case of Aspergillus ear rot. Photo by Doug Jardine, K-State Research and Extension.
Testing and grain acceptance
Most elevators now use one of several commercial quantitative tests that can be performed in a very short time period right at the point of delivery, rather than using the outdated black light method. Samples testing at less than 100 parts per billion (ppb) are usually accepted without penalty. Levels exceeding 100 ppb may be docked a percentage or not accepted at all.
The FDA has established 20 ppb or higher as the level deemed unsafe for human consumption. However, buyers of corn for human or pet consumption typically have much more stringent standards and may require levels to be 10 ppb or lower. Ethanol plants may also refuse aflatoxin-contaminated grain since the toxin is heat-stable and can concentrate as much as three- to four-fold in the distiller’s grains. Aflatoxin-contaminated corn at any level should not be fed to lactating dairy cows because it can be passed through to the milk.
Feeding guidelines by aflatoxin level
- 20-100 ppb: suitable for breeding cattle, swine, and mature poultry
- 100-200 ppb: limited to finishing swine over 100 lbs and beef cattle
- 200-300 ppb: finished beef cattle only
- >300 ppb: Cannot be used as feed unless cleaned or blended to safe levels
Blended corn can only be used for direct feeding on the farm where it is blended. It cannot be sold unless a specific blending exemption from the FDA is granted, such as occurred during the 2012 outbreak.
Silage concerns and testing information
Drought-stressed corn harvested for silage may also contain aflatoxin. Producers wishing to have silage tested for aflatoxin can do so through the Kansas State Veterinary Diagnostic Laboratory.
The Toxicology submission form is available at: https://www.ksvdl.org/docs/submission-forms/Toxicology-Submission-Form.pdf . Information on sample submission and pricing is available at https://vetview2.vet.k-state.edu/LabPortal/catalog/show/4231490 for information on pricing and sample submission.
Post-harvest management and storage
Once the fungus is detected in grain, the affected corn should be separated from “sound” corn, and extra care should be used in cleaning bins that held contaminated corn.
Producers can reduce the incidence of aflatoxin and other mycotoxins after harvest by taking the following precautions:
- Harvest when moisture content allows minimum kernel damage (24 to 26 percent).
- Adjust equipment for minimum kernel damage and maximum cleaning.
- Dry shelled grain to at least 15 percent moisture, 24 to 48 hours after harvest.
- Dry grain to below 13 percent moisture for long-term storage.
- Cool the grain as quickly as possible after drying to 35 to 40 degrees F, realizing that with current weather conditions, this is not feasible.
- Aerate and test for "hot spots" at one- to four-week intervals during the storage period.
Rodrigo Onofre, Extension Plant Pathologist
onofre@ksu.edu
Tags: corn disease aflatoxin ear mold aspergillus