September 28, 2005

Summer's hot, dry weather leads to ear rot concerns in corn

WEST LAFAYETTE, Ind. – Lower yields aren't the only thing corn producers can expect from the hot, dry weather this summer. A Purdue University plant pathologist said farmers should also be on the lookout for an ear rot that may cause a potent carcinogen.

Aspergillus ear rot is caused by a type of mold, Aspergillus flavus. It can cause aflatoxin contamination in corn.

"We have that problem when it's hot, the plants are stressed, the overnight temperatures have been very high in the 70s and 80s and we haven't had a lot of rain, " said Charles Woloshuk. "That doesn't mean that ear rot will be there, but we tend to get worried about it."

"Aflatoxin is one of the most potent natural carcinogens," Woloshuk said. For that reason the Food and Drug Administration has set aflatoxin thresholds of 20 parts per billion in grain products and 0.5 parts per billion in milk. Lactating animals that ingest feed containing aflatoxins can pass the toxins through to the milk.

"Right now is a good time to scout your fields for ear rot," Woloshuk said. "Once the grain is combined, it's more difficult to assess aflatoxin contamination."

Producers should look for aspergillus ear rot on hills and in areas where the soil is light or other areas where the corn is stressed or stunted, he said. Another approach would be to cut a swath across the field with a combine and then examine ears along the swath for ear rot.

In either case, Woloshuk said, "You have to randomly take ears and pull the husks back and look for an olive green mold. It's not blue-green, it's not green-green, and you might find those."

Other colored molds may indicate other problems and a high number of moldy ears can mean the corn has other toxins or won't store well.

Aspergillus ear rot may be at the base or the tip of the ear, but it can always be identified by its powdery texture and olive green color. Photos of aspergillus are available on the web.

"My advice to someone who finds an ear with Aspergillus is to harvest ears around the area and see if there's a lot or just one ear. Most of the time you'll just see one, but one ear could have a lot of toxin in it, so if it's harvested and mixed into the corn, it still could have an impact on the overall toxin level."

For farmers who do find evidence of aspergillus ear rot in their fields, Woloshuk suggests harvesting as soon as possible.

"If a storm dumps rain on a field and it rewets the ears, then we could see toxin levels that eventually grow quite high," he said. "Until we see the weather cool down, I think producers need to think about getting the corn out of the field and drying it down to at least 14 or 14.5 percent."

Corn that does have aflatoxin contamination can be used in animal feed, so long as it remains under the FDA's limits. Woloshuk said poultry and young animals are especially susceptible to aflatoxins, which affect the liver. Long-term effects can include low weight gain, weakened immune systems and cancer.

More information about scouting for Aspergillus ear rot is available on the Web in the Sept. 9, 2005 issue of the Pest and Crop Newsletter from Purdue University. The newsletter is available on the web.

Writer: Kay Hagen, (765) 494-6682, kjh@purdue.edu

Source: Charles Woloshuk, (765) 494-3450, woloshuk@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, forbes@purdue.edu
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