Dean Malvick, Department of Plant Pathology, University of Minnesota
Recently there have been numerous reports of "moldy corn" across Minnesota. The late harvest, high moisture corn, and continuing wet conditions have contributed to this problem. At least two main questions should be considered. Are the problems at this point significant ear and kernel rots that are damaging the kernels, or is the problem primarily superficial growth of fungi on the grain surfaces? Both types of fungal growth on corn can cause greater problems with grain quality if the corn is not harvested and dried properly. The current problems with "moldy corn" are still not completely clear, but we can make some general comments on what we have seen and heard so far.
Although there may be ear and kernel rots or superficial surface growth of fungi occurring, the detailed reports coming in to date suggest the primary problem now is superficial growth on the surface of kernels. Surface growth of fungi may be an opportunistic situation where various fungi simply are taking advantage of a wet, nutrient-rich environment to grow. Once the corn is harvested and dried, they may stop growing. Or if corn is not dried sufficiently and is damaged, they may continue to grow and reduce grain quality. Depending on the type of fungus and the storage environment, these fungi may or may not produce mycotoxins. The more severe ear and kernel rots may damage a few kernels or large parts of a corn ear, and may be associated with the presence of mycotoxins.
Several types of ear and kernel rots and fungal growth and can occur on corn in MN, especially Fusarium ear rot, Gibberella ear rot, and Aspergillis ear rot. Aspergillis ear rot is generally of greatest concern on corn due to potential production of aflatoxin, but the cool summer this year did not favor it in most parts of Minnesota. Diplodia ear rot appears to be very uncommon in Minnesota. Other types of common fungi that may grow on corn include Penicillium and Trichoderma, and these may often have a superficial growth habit. More information on ear and kernel rot fungi and mycotoxins can be found at these web sites.(http://www.extension.umn.edu/cropenews/2007/07MNCN42.html, http://agcrops.osu.edu/specialists/corn/specialist-announcements/AbnormalCornEarsPoster_000.pdf/view?searchterm=earabnormalities, http://www.uwex.edu/ces/crops/MoldsMycotoxins.pdf)yeDiagnosis and harvest can help clarify the problem with "moldy corn" and reduce or solve it. For diagnosis and identification of the types of fungal growth and kernel infection on corn, samples can be sent to the Plant Disease Clinic at the University of Minnesota (http://pdc.umn.edu/). Harvest and drying may be the solution. The problems that we have been seeing most often may be stopped or slowed by harvesting and drying the corn. Information on harvesting and drying can be found in this article (http://www.extension.umn.edu/cropenews/2004/04MNCN22.htm ) and this Minnesota late harvest web site (http://www.extension.umn.edu/lateharvest/).