Thursday, September 6, 2012

Fusarium Ear Rot and Fumonisons

Paul Vincelli, Extension Plant Pathologist, University of Kentucky

Figure 1. Typical symptoms of Fusarium ear and kernel rot.
Note whitish fungal growth.
 Usually damage from Fusarium ear rot affects
scattered kernels or groups of kernels, as shown here.

The content of this article previously occurred in the Kentucky Pest News, number 1315.

Pre-harvest contamination of corn with fumonisins is a possibility in some lots of this year’s Kentucky corn crop. Fumonisins are a family of mycotoxins produced by the fungus that causes Fusarium ear rot. These natural toxins have the potential to cause lethal diseases of horses and swine (the diseases are equine luekoencephalomalacia and porcine pulmonary edema, respectively). Pre-harvest contamination of corn by fumonisins is most often associated with drought stress at the silking stage, a stress that occurred widely in Kentucky and beyond.



Symptoms of Fusarium kernel rot usually occur scattered throughout the ear on individual kernels or groups of kernels. Kernels affected by Fusarium kernel rot often exhibit salmon-pink to reddish discoloration on uninjured kernel caps. The rot is often associated with kernel injury, although unwounded kernels can be affected.

Once symptoms develop, if there is moisture under the shuck, the fungus can continue to spread and form a heavy cottony fungal growth that can consume the entire ear. Maturing ears which point upright during a heavy rain, would be at risk of extensive rotting.

It is advisable to scout corn fields for evidence of Fusarium ear rot, by walking fields and peeling the shuck of a sample of ears. Fields with moderate to high levels of Fusarium ear rot should be considered for harvest at 25-27% moisture content and drying to below 15% within a day or two of harvest.

Unfortunately, it is difficult to say how much Fusarium ear rot is too much in a given field, since mycotoxin levels in grain often don’t correlate well to amounts of kernel rot. However, if 2-5% or more of the ears have symptoms like those figures provided in this article, that would probably justify a quick harvest/dry-down. A dry-down may be especially justified for lots destined for food use, just from the quality-control standpoint.

While scouting for Fusarium ear rot, also look for olive-green mold typical of Aspergillus ear rot, especially on knolls of hills or other droughty areas. Aspergillus ear rot can result in aflatoxin contamination (see article from last week). This ear rot is most likely when corn is subject to severe drought stress during grain fill.

Questionable lots of corn should be tested for mycotoxins before feeding, especially to sensitive animals.

Producers should be aware that fumonisins can often be found at higher concentrations in injured and broken kernels than in sound kernels. Producers who clean their corn are advised not to feed screenings to livestock, since these pose the greatest risk. Many of the cases of poisonings of horses and swine from fumonisins in the Midwest result from feeding of screenings to livestock.
Sources of Additional Information
More information on fumonisin is available in the UK Extension publication ID-121, Fumonisin, Vomitoxin, and Other Mycotoxins in Corn Produced by Fusarium Fungi, available at http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf.

More information on aflatoxins is available in the publication ID-59, Aflatoxins in Corn, at http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf.

Some of the laboratories where mycotoxin testing is performed include those listed in: http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-1.pdf.

Commercially available rapid test kits for mycotoxin testing are listed at: http://www.gipsa.usda.gov/fgis/tech-servsup/metheqp/testkits.pdf.



Figure 2. Fusarium kernel rot at ear tip. Note white fungal growth. Also note association with insect injury.


Figure 3. Fusarium ear and kernel rot.  This rot normally doesn't progress from the base of the ear, but it is possible, as shown here.



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