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.
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 mycotoxin levels.
The U.S. Department of Agriculture's Grain Inspection Handbook, available at http://www.gipsa.usda.gov/Publications/pub_fgis.html, has additional information on mycotoxins and handling of infected grain.