Late Spring Frost Injury to Winter Small Grains Unlikely

Freezing temperatures and frost in April are always a concern for grain producers. Will this affect the yield? Can this kill and damage crops? Whether or not a frost injury occurs during such an event depends on multiple factors, starting with temperature, duration of exposure, and crop growth stage at the time of exposure.

Risk Factors

Small grains are cold hardy during tillering and become increasingly susceptible to frost injury as they develop through jointing into boot and flowering, when they are most at risk, and when injury results in severe yield effects. For example, according to The University of Kentucky, for wheat at Feekes stage 5 or the end of tillering (leaf sheaths strongly erect and the growing point is below the soil surface), temperatures need to reach a frigid 12 degrees Fahrenheit for two or more hours for injury to occur. In wheat at Feekes stage 6 (first node detectable and growing point is above the soil surface), temperatures must reach 24 degrees Fahrenheit for two or more hours for injury. At Feekes stage 10, or boot (head fully developed, swollen flag leaf sheath), temperatures must reach 28 degrees for two or more hours for wheat injury to occur. At Feekes stage 10.5, or flowering (anthers visible), temperatures need only reach 30 degrees for 2 hours for injury to occur. For the complete University of Kentucky, read Freeze Damage Experience and Results.

Another factor that plays a significant role is general crop cold hardiness. Crop species have an inborn tolerance level to cold; this is why northern parts of the state plant spring barley instead of winter barley—because it is too cold for winter barley to overwinter. Though there is significant variability among varieties of a single species, we can generalize that the average cereal rye is cold hardier than all other small grains. Next in cold hardiness is triticale, followed by wheat, then barley, which is most susceptible.

Environmental and crop health considerations can impact frost injury, too. A blanket of snow provides insulation for crops, protecting them from below-freezing temperatures. Moist soil changes temperature more slowly than dry soil to function as a buffer to short-lived cold snaps. Nutrient-deficient, diseased, insect-damaged, or otherwise stressed stands are more susceptible to frost damage than healthy, robust stands.

Can Damage Occur?

If there is a crop at risk, it would be an early-planted, nutrient-deficient, low-lying, windward, or north-facing sloped barley field that did not have snow cover. Temperatures might have dipped below 32 degrees, and barley is more susceptible to cold and further developed than other crops. If, by chance, the barley had its growing point near the flag leaf, an injury may have occurred.

Even though injury is unlikely, it is still a good exercise to scout fields to check for injury. We occasionally see yield-reducing frost injury in this area, and it is good to know what to look for. Symptoms can take a week to become visible, so if you scouted the morning after a cold night on April 8th, for example, you may have missed something.

Step into the small grain field and look for discoloration and deformation of leaves and stems. At tillering (growth before Feekes 5), the main symptoms to look for are yellowing and burning of leaf tips, silage odor, and a blue cast to fields. If injury is found, it should have only a slight to moderate effect on yield. Between Feekes 6 and 8, freeze-damaged plants become twisted and turn light green or yellow, with die-back of the leaf tips. At Feekes 8, the emerging flag leaf appears yellow or dead instead of healthy green, indicating that the growing point is damaged or killed. At any point after Feekes 6, the growing point can be directly inspected for frost damage several days after a freeze. To inspect, split open the stem to reveal the growing point, where the early developing seed head is visible. A healthy growing point will appear white to light green and turgid, while a frost-damaged growing point will appear watery and darker green to brown. Secondary, unaffected tillers will develop and produce grain, but tillers with damaged growing points will stop growing and will not produce a head. This can have a moderate to severe impact on yield. Additionally, lodging or the topping over of plant stems is a genuine concern if stems are frost-injured.

^a Numbers in parentheses refer to the Feekes scale.

Overall, it is unlikely that your small grain fields will suffer frost damage during late spring freeze events. However, it is worthwhile to check susceptible fields for damage; severely damaged fields may warrant use for forage instead of grain in some situations.