When temperatures dipped well below freezing the night of April 6-7, it may have caused moderate to significant damage to wheat in parts of Kansas, said Kansas State University agronomist Jim Shroyer.
"Wheat that has either one or two joints can be injured by several hours of temperatures in the low 20s or lower," said Shroyer, who is a crops specialist with K-State Research and Extension. "Even wheat that is not yet jointed will probably have some damage to the leaves, but this is just cosmetic injury that will not affect yields."
Producers should not make any quick decisions about the condition of their wheat crop, however, he said.
"It will take several days of warm weather following the freezes to evaluate the condition of the crop and its yield potential," Shroyer said. "Even if some of the main tillers are injured or killed, producers should wait to see if enough other tillers have survived to compensate for the lost yield potential."
If areas of a field lodge shortly after the freeze, that may indicate damage to the lower stems, he said.
"Producers should keep an eye on this wheat over the next week or so, and examine the lower stems," he said. "Damage may not be immediately evident. If there are darkened or watersoaked lesions near the base of the stems, or if the stems are split, those tillers are damaged and will die. It´s also possible that stems may simply have leaned over due to the combination of high winds and wet conditions. In that case, the stems may eventually become upright again."
Patience is the key at this point in the season, he added. There should be time left in April to destroy the crop if necessary and plant corn, and even more time to plant grain sorghum, soybeans, or sunflowers, if herbicide carryover restrictions allow and depending on crop insurance considerations.
The most important thing to right after a freeze is to carefully evaluate the effect of the freeze on the wheat, he said.
Freeze injury symptoms for wheat in jointing stage
Three factors are important in determining whether there was damage to the wheat crop from recent freezes: stage of wheat development, temperatures, and wind speed, said Jim Shroyer, K-State Research and Extension crop production specialist.
Whether actual freeze injury occurred would depend on how low the temperature reached, how long the temperatures stayed that cold, temperature gradients in the field, wind speed, canopy density, and other microclimate factors, he said. Soil moisture is another factor that is usually important in determining freeze injury.
Wheat in much of southern Kansas was in the jointing stage at the time of the most recent hard freeze, the agronomist said.
"In the jointing stage, if temperatures get into the low 20s or lower for several hours, there can be some injury to the lower stems, the leaves, or the developing head. If it is windy during the nighttime hours when temperatures reach their lows, this increases the chance of injury," Shroyer said. "The soil may help radiate heat into the canopy and help protect wheat from freeze injury unless conditions are windy. If the soil has a good cover of residue, it will not be able to radiate heat as well."
If temperatures warm up rapidly within a few days after the frigid weather, damage may be apparent soon after the freeze. If temperatures stay cool for another week or two, it will take longer to notice any freeze injury, he added.
Injury symptoms will vary. If the main tillers were injured, secondary tillers may begin growing normally and fill out the stand. The wheat may have a ragged appearance because the main tillers are absent, but there may still be enough surviving tillers to produce good yields if spring growing conditions are good, Shroyer said.
"If the leaves of tillers are yellowish when they emerge from the whorl, this indicates that those tillers have been damaged. Where tillers are damaged at early jointing, they may stop growing and the head will never emerge. Later in the jointing stage, some of the damaged tillers may still exsert the head but the head may be partially or entirely blank," he said.
It´s not just leaves in whorl that can be damaged by freeze injury at this time, he added. A hard freeze at jointing can also damage the existing leaves so severely that they turn bluish, then bleach out. This usually results in the field having a "silage smell," the agronomist said.
If the lower stems were damaged by freeze injury, the wheat plants will likely lodge at some point, he added.
"Lodging could also be caused by other factors, however, so it will be important for producers to examine the lower stems on lodged plants to determine the cause. Plant may have simply leaned over due to environmental factors, such as a hard rain or high winds, after a freeze and will eventually come back up if the lower stem isn´t damaged," he said.
More information is available by contacting Shroyer at 785-532-5776 or firstname.lastname@example.org. Information is also available in the Extension publication C646: "Spring Freeze Injury to Kansas Wheat," available on the Web at: http://www.oznet.ksu.edu/library/crpsl2/c646.pdf.