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Corn+Soybean Digest

Watch For Frost Damage In Corn Crops

This week's freezing temperatures in much of Minnesota have ended the growing season for most of the state’s landscape, according to Mark Seeley, University of Minnesota Extension climatologist. While the outlook does not seem to be critical for the crops that have reached maturity, some corn may be affected.

"The majority of the corn in Minnesota is at or beyond the half-milk stage, and most of it in southern Minnesota is at or very close to maturity," says Jeff Coulter, a corn specialist in Extension. "A hard killing frost at the half-milk stage could reduce final grain yield by 8-12%; however, the impact of frost on corn yield decreases as the crop gets closer to maturity. Corn is mature when there is no visible milk line and a black layer is present just under the tip of the kernel. For corn that is nearly mature, a killing frost will have little impact on grain yield."

Coulter and Seeley agree that corn prematurely killed by a frost will dry in the field at a rate that is similar to corn that reaches maturity before a frost. Seeley adds, "The cold may even spur faster field drydown rates so farmers won't have to spend so much money on drying." On average, we can expect a drying rate of 0.5-0.25%/day between Oct. 6 and Oct. 15, and 0-0.33%/day between Oct. 16 and Oct. 31 in Minnesota.

The grain moisture of corn naturally drops as the crop matures, but corn grain that is prematurely frozen and at a high moisture level will need sufficient sun and wind to facilitate in-field drying. This is particularly important, as there is a lot of moisture in the cobs of frost-damaged corn, and sometimes the husks on these plants do not loosen as well as normal.

In cases of early frost damage on less-mature corn, different management of the crop may need to happen. University of Minnesota Extension has created a Web site for corn and soybean producers who are dealing with frost. It can be found at

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