How Delayed Harvest Might Affect Ear Rots and Mycotoxin Contamination
By Alison Robertson and Gary Munkvold, Department of Plant Pathology
The corn harvest is later than it has been any time in recent memory, and the prolonged moist conditions are conducive for molds to develop on grain in the field. Over the past few days we have received numerous reports of ear rots developing in the field and questions concerning mycotoxin production when conditions are cool but wet.
Cladosporium ear rot
Apart from Fusarium, Gibberella and Diplodia ear rots, we are starting to see and hear of more reports of Cladosporium ear rot. Cladosporium ear rot symptoms we have seen are dark, greenish-black, blotched or streaked kernels that are scattered over the ear (Figure 1). In some cases, the pericarp has split to reveal clumps or tufts of dark mold growth. In addition we have seen the ear rot develop as dark green, fuzzy growth that grows on and between the kernels (Figure 2 and 3). This fuzzy growth looks very similar to the fuzzy growth associated with Trichoderma ear rot, though Trichoderma is usually a more intense green (Figure 4). Microscopic examination is necessary to definitively distinguish between the two fungi. Cladosporium ear rot is often associated with insect, hail or frost damage.
There are no reports of economic losses due to either Cladosporium or Trichoderma ear rot. Furthermore, no associated mycotoxin issues have been reported. If the percentage of damaged kernels is 5 percent or less, the grain is still acceptable as No. 2 corn. However, since corn ears can be infected with more than one ear rot simultaneously, mycotoxin contamination of grain should not be ruled out. All grain coming from fields suspected of being moldy should be tested for mycotoxins.
How will cold, wet weather affect ear mold development and mycotoxin contamination?
Unfortunately there is a lot of high moisture corn still in the field and current weather conditions are contributing little to dry down. Kernel moistures above 18 percent favor the growth of all ear mold fungi. Temperature affects the rate of growth of ear mold fungi. Cool temperatures slow the growth of most fungi, but they are still active, and the potential for mycotoxin production still exists. Past experiences indicate that extended wet falls, and therefore delayed harvests often result in elevated levels of DON (vomitoxin).
Management decisions
Fields should be scouted to determine if ear rots are prevalent. Problem fields (greater than 10 percent of the ears have mold on 10-20 percent of the grain) should be harvested as soon as possible, and dried to 15 percent moisture or less to prevent further mold growth. For more details on drying and storage of grain see 2009 Corn Quality Issues – Field molds. When harvesting, ensure the combine is properly adjusted to avoid additional damage to the kernels. Cleaning the grain with a rotary cleaner can reduce mycotoxin levels by removing fines which tend to have higher mycotoxin levels than whole kernels. Grain from fields with obvious mold problems should be tested for mycotoxin contamination. See Risk of Mycotoxins Associated with Hail Damaged Corn for guidelines on testing for mycotoxins.
Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at alisonr@iastate.edu. Gary Munkvold is an associate professor of plant pathology and seed science endowed chair in the Iowa State University Seed Science Center with research and teaching responsibilities in seed pathology. He can be reached at (515) 294-7560 or by email at munkvold@iastate.edu.
This article was published originally on 10/30/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.
Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.
-30-
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) Many materials can be made available in alternative formats for ADA clients. To file a complaint of discrimination, write USDA, Office of Civil Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call 202-720-5964.
PM-1698 Corn Ear Rots, Storage Molds, Mycotoxins, and Animal Health - Ths is a $3 publication, but is very good with color pictures that farmers might use to educate themselves about the molds.
I May Have Moldy Corn. Now What?
Testing for Mycotoxins
The ISU Veterinarian Diagnostic Lab has recently simplified there sample submission and testing for molds and mycotoxins of corn grain. They have a new sample submission sheet at which is very easy to follow:
http://vetmed.iastate.edu/sites/default/files/vdl/forms/MycotoxinForm.pdf
For example: If I want to check for mold and mycotoxins of the 4 largest concerns (aflatoxin, fumonisin, vomotoxin, zearlenone) I would select Mycotoxin Screen #3. That would cost $70 for the mold ID. If any of the molds are identified, then on request the lab would run a quantitative test to determine the mycotoxin concentration. The quantitative test for each mycotoxin is in the ballpark of $35 each. You would likely want to request the quantitative testing if you plan on feeding this grain to your livestock to understand if any feeding limitations exist. Potential feeding limitations are provided in: http://vetmed.iastate.edu/sites/default/files/vdl/MycotoxinInfo.pdf
Simple Test for Mold ID
The more expensive testing and steps to collect a representative sample described above is necessary to properly test for mycotoxins. However, if you just want a simple ID of the mold, a few ears could be sent to the Plant Disease Clinic for a $10 fee. The recommended procedure is:
1) Collect a few ears with the mold on them that you want identified.
2) Put them in a box with the husks pulled back, but included in the sample.
3) Fill out the sample submission sheet: /Publications/PD31.pdf
4) Enclose a $10 check as mentioned in the sample submission form.
5) Mail to the address on the sample submission form. Best to mail on a Monday or Tuesday.
6) Extension offices have available pre-paid pre-addressed US Post Office labels for your package(s) if you wish to stop in at the Extension office to pick this label which would cover your postage cost.
Again, this is just for disease ID. This sample will not be tested for any presence of mycotoxins. If the mold or molds identified are ones of concern for potential mycotoxin development, you would need to follow the directions under “Testing for Mycotoxins” to determine the extent of the problem.