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We've Had a Frost -- Now What?

Sep 16, 2011

Question: We got frost early.  Do you have any advice on what to do now with our corn?

Answer: When temperatures reach around 30 F, the corn growing season halts, reports Joe Lauer, University of Wisconsin Extension corn agronomist, in his recent article "Handling Immature Corn After an Early Frost."
"Corn is killed when temperatures are near 32 F for a few hours, and when temperatures are near 28 F for a few minutes. A damaging frost can occur when temperatures are slightly above 32 F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, such as clear skies, low humidity, no wind."
Lauer says symptoms of frost damage will start to show up about one to two days after a frost, and frost symptoms are water-soaked leaves that eventually turn brown. He says that because it is difficult to distinguish living from dead tissue immediately after a frost, the assessment should be delayed 5 to 7 days.
The severity of the damage depends on the length of time and the extent of the below-freezing temperatures, according to Iowa State University's National Corn Handbook. Substantial damage would occur if the temperature remained below freezing for four to five hours. Leaves are most susceptible to frost because of their whorl arrangement and thin composition, making it difficult to retain heat. 
The best and only thing a farmer can really do for corn that has been hit with a frost is to simply hold off and let it dry down, says Jeff Coulter, University of Minnesota extension corn specialist.
 Farmers should check the field the morning after a frost once the sun has risen and started thawing the plant, according to the National Corn Handbook.
Coulter's advice for future years is to avoid pushing the maturity because it only takes one bad year to cause problems. Farmers should choose plant corn varieties that are reasonable for their areas. Corn hybrids should be chosen based on when they reach physiological maturity, according to the National Corn Handbook. The plants should reach maturity before the average date there is a freeze risk greater than 50%. 
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