Presence of Mold and Mycotoxins in Corn
November 09, 2009
Starting off the year with a cool spring, cooler than normal summer, and now a wet harvest, we have one more obstacle to deal with: ear molds appearing in the field. High rainfall amounts, immature crops plus cooler weather have increased the risk for mold development in corn. Along with the mold development, comes questions about how best to control the problem and what can we expect later in the season.
There are a number of common ear molds that can be found in the fields this year. These are the most common that I have seen:
Gibberella Ear Rot can be easily identified in the field on intact ears. Look for a pink to reddish mold that begins at the tip of the ear and develops towards the base. The husks may adhere tightly to the ear and the pink mold may grow into the husks. The corn ears are generally susceptible only when they are very young, and cool, wet weather within 3 weeks of silking favors disease development. If Gibberella ear rot is present, it should also be assumed that mycotoxins are also present. Gibberella can produce vomitoxin and zearalenone. A test is needed to determine the level of contamination and should be done by someone properly trained in collecting the samples.
Penicillium Ear Rot appears to be most common this year. Penicillium rot produces a light blue-green mold that grows between the kernels, on the cob, and in the husk. Infected kernels could become bleached or streaked. Penicillium can be a serious problem if corn is stored at high moisture levels (greater 18%).
It is important to remember that not all ear molds produce mycotoxins. Just as important, if an ear mold is present, there is no guarantee that there will be high levels of toxins present. The amount and type of toxin produced is dependent on the host,
pathogen, the strain of the fungus, and weather conditions. Ear molds are an indication of potential toxin problems and with proper handling and storage of grain, the level of toxins can be minimized.
Management
When ear rot is a problem, the corn should be harvested and dried to 15% or below as soon as possible. However, if the problem is severe, check with your crop insurance provider regarding adjustments for the damage to the crop. Generally these assessments must be made on standing corn before it is harvested. When harvesting, increase your air speed to remove moldy kernels, particles, and chaff. Incorporate a screen cleaner into your handling system to remove fine materials not removed by the combine before the corn is placed in the bin. The screen cleaner may also remove some of the smaller shriveled kernels that have been infected by ear rots. Screenings are usually the moldiest and have the highest levels of toxins.
Once corn is below 20% moisture, there should be no significant growth of Diplodia and Gibberrella in the stored corn. Storage molds including Penicillium, Aspergillus, and Eurotium should not grow when moisture is below 15%, providing the grain is kept below 50°F. Drying to a slightly lower moisture of 14% w ill be more expensive but will also provide additional protection from mold growth. Do not mix corn with high levels of mold damage with good corn. The dried corn should be cooled below 50°F immediately after drying and eventually cooled to 32 to 35°F if it wi ll be held into the winter. The corn should be marketed or fed to animals as soon as possible and should not be held until spring. Ethanol plants may reject corn with high levels of mold damage because it will reduce their yields and, if there are toxins present, those toxins can be concentrated by a factor of 3 in the co-products such as DDGS and WDG. These co-products are usually marketed as an animal feed ingredient. While the corn is in storage, keep it well aerated. Inspect the bins regularly so that problems can be detected early.
This is not the year to place corn in the bin at 19% and air dry it. Higher moisture grain is more susceptible to mold development and the possibility of storage problems increase greatly.
Testing for mycotoxins can be done before or after putting the grain in storage. The best sampling method is to take a composite sample of at least 10 pounds from a moving grain stream, or to take multiple probes for a composite 10-pound sample. If toxins are present, it is possible that it can be fed to a less sensitive livestock species, such as beef cattle (depending on the specific toxin and its concentration). A veterinarian or extension specialist can help with these decisions. If the grain is sold, there may be a reduced price due to mold damage.
Sources:
http://www.ipm.iastate.edu/ipm/icm/node/1558/print
http://extension.entm.purdue.edu/pestcrop/2009/issue26/index.html Harvesting, Handling, and Drying Corn with Ear Rots in 2009 – (Richard Stroshine, Professor, Agricultural and Biological Engineering Department)
http://www.omafra.gov.on.ca/english/crops/field/news/croppest/2006/17cpo06a1.htm
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