Wheat freeze damage depends on growth stage, conditions
Delayed spring planting isn't the only issue cropping up with recent freezing temperatures in the central U.S. and Corn Belt. This year's winter wheat crop -- much of which is developing ahead of the typical pace -- could fall victim to early April freezing temperatures.
"Normally, a hard freeze in early April is not a problem for wheat," says Kansas State University agronomist Jim Shroyer of the typical Kansas wheat crop. "This year, however, the crop is about two weeks ahead of normal development in all but northwest Kansas."
Location and level of progress in the growing season are key factors in gauging freeze damage in wheat, says a Purdue University crop specialist.
"Depending upon where you are...your wheat is anywhere from tillering stage to starting to joint (pre-joint) to jointing," says Purdue University Extension soybean specialist Shawn Conley of wheat growers in his state of Indiana. "If your wheat is in the tillering stage, that crop can withstand temperatures down to -12 degrees Fahrenheit. If the wheat is standing upright and just prior to joint, then the temperature that injury occurs is -20 degrees. If you are able to detect a node (joint), then the temperature where injury occurs is 24 degrees.
"Cold injury at jointing can cause moderate to significant yield loss."
How can you tell if your wheat has been damaged by sub-freezing spring temperatures? Much depends on the crop's level of development, according to Shroyer. "Cold temperatures after spring freezes delay development of injury symptoms, but injury to vital plant parts usually can be detected by careful examination," he says. "It is important to know the plant parts that are most vulnerable at each growth stage."
During the spring tillering stage, Shroyer says freeze damage can be seen in the "twisted and light green to yellow" leaves that are "necrotic (burned) at the tip within one or two days after freezing.
"A strong odor of dehydrating vegetation may be present after several days," Shroyer adds. "Injury at this stage slows growth and may reduce tiller numbers, but growth of new leaves and tillers usually resumes with warmer temperatures."
Further along, in the jointing stage, Shroyer says damage is most evident when examining the plant's growing point. If the growing point is yellowish-green in color, the plant has likely not incurred significant freeze damage. If that same location on the plant is more off-white or brown in color, however, the sensitive growing point may have incurred enough damage to cut yield potential.
"Partial injury at this stage may cause a mixture of normal tillers and late tillers and result in uneven maturity and some decrease in grain yield. with severe freeze damage," according to Shroyer. "The growing point does not appear damaged immediately after a freeze. It will become dry and off-white to brown if the stem is damaged. Also, the growing point will not move upward. The loss of these early tillers releases the later tillers that would not normally develop because of too much competition."