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Late, Wet Corn Harvest Favors Ear Mold

Field moisture above 18 percent to 20 percent for a long time and temperatures above 45 degrees generally favor ear mold development.

Cooler, wetter conditions across much of the Midwest have delayed corn maturity and grain harvesting. Some states are reporting the extensive development of corn ear mold, frequently seen under the husks that remain tight to the ear and trap moisture. Similar ear molds are being observed in North Dakota. Field moisture above 18 percent to 20 percent for a long time and temperatures above 45 degrees generally favor ear mold development.

“We certainly have had ear moistures at these levels for an extended time, and recent temperatures have been favorable for some fungal growth,” says Marcia McMullen, North Dakota State University Extension Service plant pathologist.

These ear molds may be of various colors, such as green, pink, white, red or black. Color is one distinguishing trait of various fungi that commonly cause corn ear mold. Some of the fungi are growing on dead tissue and are relatively harmless but unsightly. Other corn ear mold fungi, such as gibberella and fusarium ear rots (with white to pink to red color), have the potential to produce mycotoxins, such as vomitoxin, zearalenone and fumonisin.

“Because very little corn has been harvested in the region, it is difficult to know if mycotoxins are present,” McMullen says. “The determination can be made through laboratory tests on harvested corn. Because these toxins may be harmful to people and livestock, grain with field molds should be tested for mycotoxins before feeding.”

The NDSU Veterinary Toxicology Lab can do the testing. However, the fee for sample testing varies. A full mycotoxin screen for North Dakota residents is $90, but individual toxin tests, such as for vomitoxin, aflatoxin or fumonisin, are $30. A trichothecene screen for 17 mycotoxins costs $55. Samples submitted from outside the state are charged an additional 20 percent. The lab will test shelled corn or whole cobs with the kernels attached, depending on the feed use of the grain.

The NDSU Veterinary Toxicology Lab may be reached at (701) 231-8307 or on the Web at Samples can be sent to the Veterinary Diagnostic Lab, NDSU Van Es Hall, 1523 Centennial Blvd., Fargo, ND 58102. Private testing labs also may be able to test corn samples.

Alison Robertson, Iowa State University Extension specialist, has recommended to Iowa corn growers that if mycotoxin problems are suspected, growers may want to check with crop insurance providers to see if adjustments may be needed. Crop adjustments for quality problems, including mycotoxins, must be done on standing corn at or just before harvest. Robertson also says that for corn going to ethanol production, toxins may concentrate in the distillers grains at three to four times the levels in the corn, so ethanol plants may be doing quick screening tests on inbound grain, especially if the test weight of the corn is less than 50 pounds per bushel.

Livestock, such as swine, dairy cattle, horses and poultry, are susceptible to certain mycotoxins, according to Greg Lardy, head of NDSU’s Animal Sciences Department. The U.S. Food and Drug Administration has various advisory levels for each group of livestock and each major mycotoxin. Livestock producers should exercise caution when molds are present, especially with gestating and lactating animals. Visual observation cannot detect the presence of toxins, so testing is advised before feeding moldy feeds. Once the level of toxins are determined, appropriate feeding recommendations can be implemented.

Corn ear molds also will cause storage problems. The molds will cause further deterioration of the grain if the corn is not properly dried and cooled in storage. Mold damage increases greatly as moisture content and storage temperatures increase. Extensive harvest and postharvest tips for the 2009 corn crop have been provided by Ken Hellevang, NDSU Extension grain-drying expert. A complete list of Hellevang’s recommendations is on the Web at

NDSU Agriculture Communication

Source:Marcia McMullen, (701) 231-7627,
Source:Greg Lardy, (701) 231-7660,
Source:Ken Hellevang, (701) 231-7243,
Editor:Rich Mattern, (701) 231-6136,
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