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How to check corn for freeze damage

Like farmers and crop advisors across the Corn Belt, Brandon Hulme is winding through backroads on May 15, looking at the young corn crop. Hulme, agronomist for Champion Seeds, is based near Ames, Iowa, where temperatures the evening of May 9 dipped to 27 degrees for a few hours – the temperature at which young corn can suffer freeze damage. 

“A lot of Iowa had 30 to 32 degrees and we were able to see brown, water-soaked tissue on some of our earlier-planted corn within a few days,” Hulme says.   

Since then, those fields have received a few rain showers and some heat, and look as if they’re growing out of the symptoms. 

That’s a positive sign, says Emerson Nafziger, Extension corn specialist at the University of Illinois.

“With different low temperatures across regions, and with damage ranging from minor leaf loss to death, the only way to know if seedlings that are still alive will survive is to see if they produce new, green tissue after a few days with warmer temperatures,” he explains. “By early next week, we’ll know.”

Nafziger and Ignacio Ciampitti, Extension crop specialist at Kansas State University, offer clues as to what farmers should look for in their corn fields. 

But first, here’s why frozen temperatures are harmful, and some factors that could influence crop response. 

Following germination, seedlings enter the emergence process, reducing plant metabolism and vigor, potentially causing stunting or death of the seminal roots, deformed elongation (“corkscrewing”) of the mesocotyl, and either delayed or complete failure of emergence, often leafing out underground. Chilled seedlings may also be more sensitive to herbicides and seedling blights, Ciampitti says.

Freeze damage and chilling injury to corn can vary with:

  • Soil type (as related to water holding capacity) and soil moisture. Less freeze injury is expected with wetter soils than dry soils. Dry soils are more sensitive to changes in temperature.
  • Residue: The effect of residue is not entirely straightforward. The more surface residue, the more the emerging seed and seedlings will be insulated and protected from temperature fluctuations. However, soils with less residue will warm up faster, resulting in less freeze injury when compared with no-till conditions where more residue is on surface.
  • Duration and intensity of cold weather: More than 2 to 4 hours of soil temperatures in the mid-to-low 40’s could result in some injury. Shorter periods of more intense cold or periods of more than 4 hours of soil temperatures in the mid-40’s could be equally damaging.
  • Field natural gradient: Low areas are most sensitive to freeze injury.
  • Growth stage: On newly planted corn, the emergence process could be affected. On newly emerged plants (before V4-V6), the first leaves could be burned but plants can recover as long as the growing point remains below the soil surface.

Ciampitti notes early planted corn has the risk of facing cold injury, reducing yield potential. “However, if the corn emerged uniformly and had good early-season growth then a longer growing season could be expected from these early planting dates – and possibly higher yield potential,” he adds.

Assuming the plant makes it through the initial cold and or freezing temperature problems, it is still not necessarily out of the woods for cold-related problems. 

“Over the years, we have observed another type of chilling injury that occurs in the crown. It is often referred to as cold weather crown stress or cold weather crown rot,” he says. “This condition often develops when young corn plants are exposed to an extended period of cold soils combined with soil moisture levels near saturation.”

Read More: Cool temperatures slow corn planting pace

It is not clear if there is an exact stage of growth when the corn is most susceptible to this problem. When this type of chilling injury occurs, plants are usually stunted and may display nutrient deficiency symptoms including nitrogen, phosphorus, or especially potassium. Root development is usually normal, but the crown will have a dark brown or black discoloration in the crown area, which can be seen by splitting the stem. 

Plants often survive, but will be slow to grow and often produce a smaller ear. 

“More importantly, if heat and drought stress occur during the later reproductive stages of development, these plants will be more likely to develop stalk rot and lodge,” Ciampitti says. 

Hybrids that have been developed from ‘southern’ germplasm appear to be more susceptible than those developed from “northern” germplasm, he adds. 

In the meantime

Nafziger says the big unknown is whether damaged plants will produce green leaf tissue, begin to regrow and turn into productive plants. 

“My suggestion is to take a realistically pessimistic approach to this, and to include in stand counts only those plants that look ready to make normal growth by May 17 or 18,” he says. “With what we hope will be warm, drier weather coming after that, replanted fields should get off to a fast start, which will help to restore yield potential.”

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