Issue No. 24, Article 6/November 6, 2009
Dealing with Moldy Corn and Mycotoxin Risks
We've already had two articles in the Bulletin this year about corn ear molds (see "Diplodia Ear Rot Causing Problems in Corn Across the State" in issue 23 and "Fungal Ear and Stalk Rots" in issue 22), but questions are continuing to come in. The biggest two problems appear to be Diplodia ear rot and Gibberella ear rot. However, with all of the rainfall we've had, a number of other "opportunistic" fungi can move in as well. All of the ear rots can cause problems at the elevator with discounts due to damaged kernels or presence of foreign material (especially when the cob is badly rotted and does not separate well from the grain). Some of the ear rot fungi can cause additional problems because of their ability to produce mycotoxins that can contaminate the grain. If fed to livestock, moldy corn with mycotoxins can cause serious problems and even death, especially in nonruminant and young animals. Below are brief descriptions of some of the ear rots showing up this year and their risk in producing mycotoxins.
Diplodia ear rot. Diplodia ear rot was covered extensively in issue 23 of the Bulletin. In the U.S., the Diplodia ear rot fungus is not known to produce any mycotoxins, but other fungi that do produce mycotoxins may colonize Diplodia-affected ears and kernels.
Gibberella ear rot. Gibberella ear rot has been reported this year in Indiana, Iowa, and Missouri (Adobe PDF), and reports from Illinois also indicate its presence. Gibberella ear rot is caused by the fungus Gibberella zeae, which is the sexual stage of the fungus Fusarium graminearum. The disease generally appears as a pink to red fungal growth on the kernels. This growth generally occurs at the tip of the ear and can be associated with insect, bird, or hail damage. The Gibberella ear rot fungus can produce mycotoxins such as deoxynivalenol (DON, aka vomitoxin) and zearalenone.
Corn ear and kernels affected by Gibberella ear rot. (Photos courtesy Don White, University of Illinois.)
Fusarium ear rot. Fusarium ear rot, caused by Fusarium verticillioides (formerly F. moniliforme) and F. proliferatum, generally is one of the more common ear rots observed in most years, but it may be less prevalent this year. Fusarium ear rot generally appears as individual or small groups of kernels with white-pink fungal growth. Affected kernels also may have a "starburst" symptom. The fungi that cause Fusarium ear rot may produce fumonisin mycotoxin.
Individual kernels affected by Fusarium ear rot (top) and "starburst" symptoms on kernels (bottom). (Photos courtesy Don White, University of Illinois.)
Penicillium ear rot. Penicillium ear rot, caused by Penicillium species, is found most often on ears that have been damaged (by insects, birds, hail, etc.). Kernels affected by Penicillium ear rot generally have a green to blue-green fungal growth on and between the kernels. The fungi also can infect the kernel embryo, which causes a blue discoloration known as "blue eye." Fungi that cause Penicillium ear rot can produce ochratoxin mycotoxins.
Penicillium ear rot (top) and affected kernels with "blue eye" symptoms (bottom). (Photos courtesy Don White, University of Illinois.)
Opportunistic fungi. A number of opportunistic fungi are present in corn fields, and when wet weather prevails and harvest is delayed, some of these fungi will begin to grow on corn ears and kernels. In some cases, corn that has been killed prematurely by frost or stressed by other factors may be more susceptible to invasion. Some observations of kernels affected by Cladosporium ear rot (caused by Cladosporium herbarum) have been reported in Illinois and Iowa.
Implications for crop insurance, harvest, and storage. If you have crop insurance and have fields that are affected by ear rots, be sure to contact your agent as soon as possible, as particular documentation may be needed for a claim to be filed. If possible, harvest affected fields first so the grain can be dried to reduce moisture levels as quickly as possible. Adjusting the combine for minimum kernel damage and maximum cleaning may help minimize the number of infected kernels making it to the elevator.
To reduce the spread of molds to unaffected kernels in storage, it is important to dry the grain to below 18% moisture (15% moisture for longer-term storage). In general, damaged grain will not store well beyond the winter months.
Mycotoxin testing and feeding risks. Moldy grain should always be tested before being fed to livestock. In Illinois, grain can be tested for mycotoxins at the Illinois Department of Agriculture's Centralia Animal Disease Laboratory. Some grain inspection services may also be able to test grain samples for specific mycotoxins.
Mycotoxin risk levels for dairy cattle are listed in Table 2 (expressed on a total ration dry matter basis). Dilution with clean feed can reduce mycotoxin levels, but contaminated feed can vary greatly in mycotoxin concentration (note that some toxins are listed as parts per billion and others as parts per million). Additional mycotoxin risk levels for additional livestock animals are available from the Food and Drug Administration's Center for Veterinary Medicine.
Adding a mycotoxin binder to feed can reduce the impact of toxins by reducing their impact in the digestive tract and/or not allowing them to be absorbed. Binders include yeast cell wall extracts or MOS products and clay binders.
It is also important to know that distillers grain from ethanol production can concentrate the level of toxins in the original corn used. It is thus important to know the sources of distillers grain before feeding. Corn silage made late in the season with mold damage could have toxins, but the low pH will stop additional toxin production. Adding propionic acid at the time of ensiling can reduce mold development.--Carl A. Bradley and Mike Hutjens