WEST LAFAYETTE, Ind. — Corn producers should be scouting
fields to get a head start on managing any grain problems that could result from
conditions favorable to several ear rots this year, a Purdue Extension plant
Different fungi cause different ear rots, and environmental
conditions at the silking stage or just after it influence which rot may be a
problem. Ear rots can cause significant economic loss, especially if the fungi
produce mycotoxins, which pose problems for both livestock and humans.
“As harvest begins, it’s important to identify fields that
may have rots to ensure timely harvest and proper storage of moldy grain,”
Kiersten Wise said. “And proper identification of ear rots is key to managing
Wise said farmers should be examining corn for Aspergillus,
Fusarium, Diplodia and Gibberella ear rots this year.
Aspergillus ear rot is caused by the Aspergillus flavus
fungus and is characterized by an olive green, dusty mold at the tip of the ear
or scattered on kernels. Symptoms usually appear first in fields with dry soils,
nutrient deficiencies or insect damage. It’s also one of the most concerning ear
rots because of its associated mycotoxin, aflatoxin.
“Aflatoxin is a potent carcinogen and is regulated in feed
and silage,” Wise said. “It’s particularly of concern to dairy producers because
Food and Drug Administration regulations require aflatoxin residues in milk to
be less than 0.5 parts per billion.”
To prevent carryover into milk, silage and other feed
components shouldn’t contain more than 20 parts per billion of aflatoxin.
Fusarium ear rot, primarily caused by Fusarium
verticilliodes fungus, often overlaps with Aspergillus since warmer temperatures
favor infection. The mycotoxin fumonisin is associated with this ear rot.
Infected ears might have white fungal growth on the cob or discolored kernels
“Fungal growth isn’t always visible, but a white starburst
pattern in kernels can sometimes be observed on infected ears,” Wise
A common Corn Belt disease is Diplodia ear rot, caused by
the Stenocarpella maydis fungus. It survives in corn residue and infects plants
about two weeks after pollination. Humidity and rain before and after
pollination also help the disease develop.
With Diplodia ear rot, white fungal growth on the cob often
forms a mat of fungus across the ear. Other symptoms include brown or gray
kernels and small black fungal structures called pycnidia that may form on the
kernels or cob.
The fungus is reported to produce the mycotoxin
diplodiatoxin in South America and South Africa, but no toxic effects on
livestock or humans have been reported in the U.S.
Gibberella ear rot, caused by the Gibberella zeae fungus,
infects plants during early silking and pollination. It favors cooler
temperatures than the other ear rots, and produces a pink or reddish mold that
can form a fungal mat similar to Diplodia.
Gibeberella zeae produces the mycotoxin deoxynivalenol, also
called vomitoxin. Wise said this mycotoxin can be extremely harmful to swine and
is carefully regulated by the FDA.
“If ear rots are observed in a field, affected areas should
be harvested early and grain segregated to avoid contaminating non-infected
grain with mycotoxins,” she said.
Mycotoxins are byproducts of the fungal infections, not
living organisms. They cannot be killed or removed from the grain. But producers
can remove small particles such as foreign material containing mycotoxins by
screening or cleaning the grain or coring grain bins to help reduce the
The U.S. Department of Agriculture’s Grain Inspection
Handbook, available at www.gipsa.usda.gov/Publications/pub_fgis.html, has
additional information on mycotoxins and handling of infected grain.