Several corn ear rots possible this year
Corn producers should scout fields to manage any grain problems that could result from conditions favorable to several ear rots, a Purdue Extension plant pathologist says.
Different fungi cause different ear rots, and environmental conditions at the silking stage or just after it influence which rot might 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 affected grain."
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 fungual growth on the cob or discolored kernels scattered throughout.
"Fungal growth isn't always visible, but a white starburst pattern in kernels can sometimes be observed on infected ears," Wise said.
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.
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