CORN Newsletter: 2004-38, November 9, 2004

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C.O.R.N Newsletter 2004-38
November 9, 2004 - November 23, 2004

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Diplodia Damaged Corn Grain: Assessing Feed Value
by Bill Weiss, Peter Thomison, Patrick Lipps


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Reports of corn damaged by Diplodia ear rot are widespread this year in Ohio. Relatively cool and wet weather conditions during the later whorl through silking growth stages were favorable for Diplodia infection. The symptoms and impact of Diplodia ear rot have been described in a recent newsletter article http://corn.osu.edu/story.php?setissueID=56&storyID=295. Diplodia ear rot is recognized as a thick mat of gray mold generally covering the lower part or the entire ear. Infected kernels are usually dark brown and moldy in shelled corn samples. Diplodia ear rot causes damage by causing lightweight kernels that reduce yield and by reducing the nutritional value of affected grain. Unlike fungi that cause Gibberella ear rot and Fusarium kernel rot, the Diplodia fungus does not appear to produce mycotoxins in the grain under field conditions usually occurring in Ohio. Additional, information on Diplodia diseases of corn can be obtained on the Ohio Field Crop Disease web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/corn/diplodia.htm.

The high incidence of moldy grain caused by Diplodia has resulted in dockage at some elevators. Large discounts on Diplodia affected grain, as high as 50 cents per bushel, have led to questions about using moldy grain on farm as animal feed. While there is considerable information available on managing moldy corn containing mycotoxins, less is know about using varying levels of moldy, mycotoxin-free corn grain in animal feed.
Grain contaminated with mycotoxins is of less value, or of no value, than grain with a mold that just reduces nutritional value of the grain. Although it appears that Diplodia is the fungus primarily responsible for many of the moldy corn problems in Ohio this year, moldy corn should be evaluated for mycotoxins before it is used as animal feed. Relying on a visual assessment to determine the fungus causing moldy grain is not sufficient, and could be dangerous. A directory of labs that provide analysis of grain for mycotoxins is available online at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.htm

A past evaluation suggests that moldy corn (not defined but with greater than 1,000,000 cfu/g) had about 10% less nutrient value compared with clean corn (<10,000 cfu/g). This is based on crude protein, amino acids, starch, fat, and estimated energy. In an unpublished study from Wisconsin, cows fed moldy (no detectable mycotoxin) high moisture corn (1 to 5 million cfu/g) produced about 8% less milk than cows fed clean corn (<10,000 cfu/g). In that experiment corn made up about 25% of the diet.

Although the mold level in grain in this study was characterized by colony forming units per gram of grain (cfu/g) this is not a precise measure of the quality of grain or of the amount of fungus in the grain. Evaluating grain using cfu/g is only an indication of the number of viable fungal spores in a gram of grain and this value can vary greatly depending on the fungal species present. Moldy grain should be subjected to chemical tests for the presence of specific mycotoxins (e. g. deoxynivalenol, zearalenone, T-2 toxin) to determine their presence and level before using moldy grain for feed. The reason for this is that several different fungi are capable of causing moldy grain and they frequently occur in the same field. Also, distinguishing among the different ear and kernel rots is not easy. In addition to a mycotoxin test, appropriate analysis of the nutritional value of the grain should also be conducted. The proper mycotoxin analysis and nutritional value will provide the livestock producer with the appropriate information needed to utilize the grain as a feed.

The bottom line, if the moldy corn will be fed to beef cows or to other animals at less than 25% of diet, the economic loss in reduced performance would probably be less than the 50 cent/bu (25%) discount. If fed to finishing animals in which 60 to 80% of the diet will be the moldy corn, loss in animal performance will probably equal or exceed the 50 cent discount.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868


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