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Frost a concern for corn and soybeans

Late last week, farmers in the northern part of the state had good reason to be concerned about the threat of frost. In Wayne County, Louie Rehm had a hard, killing frost that left ice on the leaves of his young corn plants in the low areas on his farm. The just-emerging soybeans on Rehm’s farm are also a concern.

Rehm was not alone in his concern about the crops and the frost on May 25.

“Many counties in Ohio experienced a couple of hours of near-freezing temperatures Friday night,” said Brad Miller, from Monsanto. “For the most part, air temperatures at ground level did not drop below 30 degrees F. In my observations Saturday afternoon, corn in the V1-stage of growth appears to have pulled through without injury. Soybeans in the unifoliate stage demonstrated some wilting on 25% of the leaf surface area, with some stem drooping. Forecasted rainfall and warmer temperatures this week should result in rapid recovery as corn and soybean seedlings continue growth and development.”

In cases where temperatures remained above 28 degrees, corn plants may show signs of damage, but should recover. Temperatures below 28 degrees are more likely to kill the growing point of the plant, even if it is just below the soil surface.

Ohio State University Extension corn specialist Peter Thomison provided an overview of frost concerns in the CORN Newsletter.

“Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (six leaf collars visible), and thereby relatively safe from freezing air temperatures. Moreover, the cell contents of corn plants can sometimes act as an ‘antifreeze’ to allow temperatures to drop below 32 degrees F before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees F or lower for even a few minutes,” Thomison said. “To assess the impact of these freezing temperatures on emerged corn, check plants about 5 days after the freezing injury occurred (and preferably when growing conditions conducive for regrowth have occurred). New leaf tissue should be emerging from the whorl. You can also observe the condition of the growing point (usually located half to three-quarters of an inch in below the soil surface) by splitting seedlings lengthwise. If the growing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good.”

If the plants have darkened or soft growing points, they will likely die, according to Monsanto.

Soybeans are more susceptible to frost injury, but they can recover depending upon the severity. Soybean fields can also tolerate the potential stand reduction better than corn.

“Soybean plants are more vulnerable than corn to damage by frost or cold temperatures because their growing points are above ground as soon as the crop emerges. Auxiliary buds develop at each leaf axial of a plant, including the cotyledons. Following freeze or frost damage, recovery is possible if any of these buds remain viable. However, soybean seedlings will be killed if freeze damage extends below the cotyledons,” Thomison said.

After a few days, soybean stands should be evaluated for frost damage. If the plants are fairly evenly distributed and the stand is higher than 100,000 plants per acre, replanting probably not needed, according to Monsanto.

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