Sunday, August 1, 2021

Post-cold snap for beans and corn

• Angela McClure •

two-leaf corn
Photo courtesy University of Kentucky

A few days ago, I posted a planting advisory ahead of our forecasted cold snap. The concern was mainly around the potential of 30-plus degree temperatures and rain to cause chilling damage to newly planted corn and soybean seed that were in the early stages of germination.

Based on reports from agents in different areas of the state, nighttime low temperatures appear to have stayed right at or above freezing, and most areas received very little to no rain during the cold snap, meaning soils were cool but not wet. Both of these factors likely reduced the potential for damage to corn or soybean seed that were planted close to the cold front.

Next week’s warmer day and nighttime temps should hasten germination and emergence of seed currently in the ground, and we should be able to get a better feel for planting success.

Some areas did receive a light frost on day two, especially in low lying areas, but which should have limited impact on emerged corn or soybean. Emerged corn is currently ranging from spiking to about two-leaf stage. Exposed corn leaves are susceptible to freeze damage when temps drop below 32 degrees Fahrenheit (symptoms include wilting, bronzing, necrosis visible within a week after frost event).

However, the growing point of corn remains below ground until closer to V6 stage, protected from cold. It takes extremely cold temperatures (i.e. April freeze of 2007) to kill the growing point of corn when it is below ground. Light frost burn to corn leaves is superficial and only occasionally does frost damage to spiking corn interfere with the ability of new leaves to push through the coleoptile shoot.

We don’t have as much experience with soybeans and frost, as usually planting is delayed into May. The cotyledon leaves of beans are thick and quite freeze resistant once the bean emerges. Temperatures have to drop below 28 F for several hours to kill exposed soybean tissue.

If leaves are showing some browning or wilting, check the health of the growing points about four or five days after the frost event. Healthy growing points will be light green in color and will continue to produce new leaves, while damaged ones will turn brown.

Dr. Angela McClure is University of Tennessee Extension corn and soybean specialist. She may be reached at athomp15@utk.edu

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