Paul Vincelli, Plant Pathology, University of Kentucky
Last month, I wrote an article about Diplodia ear rot, our most common corn ear rot in Kentucky. Diplodia has no known associations with mycotoxins in corn. Gibberella ear rot is associated with mycotoxins and in some cases may look very similar to Diplodia. Normally, Gibberella ear rot is not a widespread problem in Kentucky, but this is not a normal year.
Gibberella ear rot is caused by Fusarium graminearum, the very same fungus that causes head scab of wheat. Normally Gibberella ear rot can be a problem in northern state, but in Kentucky, we generally see very little of this disease. I am hearing of reports of epidemics of Gibberella ear rot in central and even southern areas of neighboring states to our north. Again, that doesn’t seem surprising, given the cool, wet weather generally experienced post-silking in many fields.
What concerns me, though, are reports that the appearance of this disease is not always fitting the typical pattern. Commonly, Gibberella ear rot attacks from the ear tip downward, whereas Diplodia ear rot usually progresses from the base of the ear upward. That helps distinguish these ear rots in the field. Plus, while both diseases produce a moldy growth, the moldy growth of Gibberella is normally a pinkish to whitish-pink color, whereas there is no pink color in the moldy growth of Diplodia. However, some of the cases of Gibberella from the northern states are reportedly looking like Diplodia—moldy growth from the bottom of the ear, with very little to no pink color.
The Diplodia fungus isn’t known to produce mycotoxins in the U.S., so normally it is safe to feed to animals. However, the Gibberella fungus produces at least two mycotoxins in corn: deoxynivalenol (=DON, =vomitoxin) and zearalenone. You can see that mistaking Gibberella ear rot for Diplodia ear rot could be hazardous to livestock producers. I have heard of a recent case where the corn was mistakenly fed to swine because the producer thought it was Diplodia ear rot, resulting in poisoning from Gibberella mycotoxins.
Therefore, growers whose corn is exhibiting ear and kernel rots should have it tested for mycotoxins. Laboratories where such tests can be obtained can be found at http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-1.pdf.
A good article on Gibberella ear rot, with pictures, is available at http://www.agry.purdue.edu/ext/corn/news/others/2009/Ear_Rots-1019.pdf.
Information on the biology and utilization of Gibberella-affected corn can be found in the UK Extension publication, Fumonisin, Vomitoxin, and Other Mycotoxins in Corn Produced by Fusarium Fungi, available at http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf.