According to the Purdue University publication “Managing the 2009 Harvest...” fields with significant ear rot symptoms should be harvested early as possible, handled separately and dried to 15 percent moisture (or lower) immediately after harvest.
Diplodia
Diplodia is characterized by bleached husks with tiny black specks. Removal of the husk of an infected ear will reveal white fuzzy growth of the pathogen between the kernels, which often starts at the base of the ear, and the cob can also appear rotted. In the U.S., mycotoxins have not been associated with diplodia; however, feeding value and storability of the grain is reduced. Drying to 15 percent moisture and cooling grain below 50 degrees will prevent further growth of the fungus.
Gibberella
Gibberella rot is easily identified in the field on intact ears, but it is much more difficult to identify once the grain has been shelled. Peel back husks and look for a pink to reddish mold that begins at the tip and develops toward the base. This disease usually involves only part of the ear but certain hybrids are more vulnerable than others. Infection occurs during silking, enhanced by cool, wet weather; hence this year’s favorable growing conditions. Pathologists report that gibberella will be most severe in fields where corn follows corn or wheat, due to fusarium head scab in wheat is caused by the same pathogen.
Mycotoxins
Mycotoxins are a toxic compound produced by fungi. The pathogen that causes gibberella ear rot can produce two toxins deoxynivalenol (a.k.a. DON or vomitoxin) and zearalenone. Vomitoxins can be deadly to monogastric livestock (one stomach animals like swine and poultry). Pork and poultry producers that are feeding grain that has not been tested could be at risk this year. Pig feed intake will decrease with feed DON levels that are more than 2 parts per million and pigs will probably refuse feed completely when DON levels are at 10 parts per million or greater. Poultry are not as sensitive as hogs are to the toxins produced by gibberella mold.
Vomitoxin is known to suppress the immune system in swine and poultry, making them more susceptible to sickness. Levels of DON known to have these effects begin to occur at about 7.5 parts per million, or less.
For more detailed information and pictures of these ear rots, see the following websites:
“Managing the 2009 Harvest: for Drying, Storing, Grain Quality, Crop Insurance and Marketing” (http://extension.entm.purdue.edu/grainlab/content/pdf/2009_Harvest_10_30_09.pdf)
“Get Grain Tested for Mycotoxins before making a Decision” by OSU Cereal Grains Pathologists Pierce Paul and Dennis Mills in C.O.R.N. newsletter 2009-37 (Oct. 27-Nov. 10, 2009), article B. (http://corn.osu.edu/)
Jonah T. Johnson is the extension educator, agriculture and natural resources, Ohio State University Extension
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Clark County
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