Watch for damage, disease when harvesting corn

Nebraska

Wet conditions and damage to corn caused by high winds or hail damage likely will increase diseases in corn both before and after harvest, a University of Nebraska-Lincoln plant pathologist said.

When maturing plants are damaged, the stalk quality can become compromised because the plant resorts to the stalk to provide what it needs to finish filling the grain, said Tamra Jackson, UNL plant pathologist.

"These weakened stalks are then more likely to become infected by stalk rot fungi surviving in past year's crop residue," Jackson said. "Corn that has fallen down will be exposed to longer periods of high moisture or humidity and require more time to dry."

Contact with soil and crop residue exposes the ears and stalks to more pathogens than normal. This results in ear and stalk rot diseases in the damaged corn.

Ear rotting fungi also can cause problems after harvest during storage if good storage conditions are not maintained, Jackson said.

"Remember, grain quality does not improve during storage," she said. "Under the best conditions, grain will maintain its quality but is more likely to decline as fungi continue to grow in the bin."

The UNL Plant and Pest Diagnostic Clinic has seen corn with Fusarium stalk rot and anthracnose stalk rot. Fusarium stalk rot often can be recognized by the presence of cottony white, pink or peach colored fungal growth around the nodes of the plants or by the presence of pink or red discoloration inside the stalk.

Shiny, black lesions visible on the outside of stalks are characteristic of anthracnose stalk rot.

In addition, fungi that cause ear rot diseases, such as Stenocarpella, Aspergillus and Fusarium, can survive a long time in the field and take advantage of wounds or favorable weather conditions to colonize in ears.

"The same fungi that infect these ears can continue to grow very quickly in the humid conditions of a grain bin and substantially reduce grain quality," she said.

This corn also is at higher risk for mycotoxins. Mycotoxins are toxins produced by the fungi.

"To manage this, first dry grain to less than 15 percent moisture within 48 hours of harvest to slow the growth of grain molds," she said.

To further minimize mold and mycotoxin contamination, it's important to:

--Plant tolerant hybrids;

--Ensure proper storage conditions;

--Minimize mechanical damage;

--Minimize insect damage;

--Sanitize storage facilities;

--Test moldy grains for mycotoxins; and

--Segregate, blend or destroy contaminated grains according to FDA regulations.

For more information about mycotoxin contamination and the ear rot diseases that lead to grain molds and mycotoxins consult UNL Extension NebGuide G1408, Grain Molds and Mycotoxins in Corn, available at a local UNL Extension office or online at www.ianrpubs.unl.edu/sendIt/g1408.html.

More information about storm-damaged corn and planning for harvest also can be found in Crop Watch, UNL Extension's crop production newsletter, at http://cropwatch.unl.edu/.

9/24/07

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