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Robertson urges farmers to scout for Aspergillus ear rot

By Jean Caspers-Simmet

Date Modified: 10/10/2012 3:46 PM

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KANAWHA, Iowa — Iowa State University Extension plant pathologist Alison Robertson told farmers at last week's ISU Northern Research Farm field day at Kanawha she would put their fields at low to medium risk for aflatoxin.

"You are definitely not out of the woods," Robertson said.

Reports of aflatoxin in corn have come in from southern and central Iowa with levels ranging from 8 parts per billion to almost 200 ppb. The FDA action level for aflatoxin in grain is 20 ppb.

Aflatoxin is a chemical substance that is produced by the Aspergillus flavus fungus, which infects the corn ears causing Aspergillus ear rot. Powdery olive-green mold is a characteristic sign of Aspergillus ear rot.

Aflatoxin is harmful or fatal to livestock and considered carcinogenic to animals and humans. The Iowa Department of Agriculture and Land Stewardship started mandatory aflatoxin screening and testing of milk received in Iowa beginning Aug. 31.

"We're worried about Aspergillus ear rot this year because hot, dry conditions at pollination are favorable for the fungus," Robertson said. "At black layer, the fungus invades inside the kernels. If we have hot conditions, the fungus can produce aflatoxin."

Robertson said the state had hot, dry conditions at pollination. High temperatures were in the 90s and lows were in the 65 to 70 range day after day.

"Aflatoxin is more of a problem when night time temperatures are the 70s," Robertson said.

She encouraged farmers to scout their fields looking first in areas that are down due to storms or are stressed because of drought. They should also look in good parts of the field.

Scout at 10 locations in fields. At each location peel back husks on 10 ears and look for the mold. Robertson passed around ears infected with Aspergillus ear rot that were found in southern Iowa.

If farmers find it, they should first call their insurance agent because corn will only be adjusted in the field, Robertson said. Once the grain is in the bin, it is no longer covered.

The corn should be harvested as soon as possible, Robertson said. The goal is to cool (below 50 F) and dry (to less than 15 percent moisture) the grain as quickly as possible to prevent the fungus from growing and producing aflatoxin.

Elevators don't accept corn with 20 ppb or more of aflatoxin unless they have a known use for the particular level of aflatoxin.

The most sensitive corn users will be dairy, pet food, direct human consumption and processors that either export or sell some products to sensitive uses.

Corn containing aflatoxin at 100 ppb or less can be used in breeding cattle and swine and mature poultry. Corn with 200 ppb or less can be used with finishing swine greater than 100 pounds in weight and corn with 300 ppb or less can be used in finishing beef cattle.

In August, the state ag department submitted a request to FDA to allow corn containing more than 20 ppb of aflatoxin to be blended with non-aflatoxin containing corn for animal feed. The FDA has granted a similar request in previous years when aflatoxin has been present in Iowa.