Figure 1. Symptoms of slight freeze damage may occur only on the awns as the spike is emerging from the boot or after heading. Awns become twisted and bleached or white instead of their normal green color.

June 8, 2007

A late spring freeze the morning of Friday, June 8 has many wheat farmers assessing the potential for damage at the current growth stage. Reports from western Banner County indicate that the ground was white with frost and a report from Cheyenne County mentioned a layer of ice on the dog's water bowl this morning. Unfortunately, there is a good deal of winter wheat in the Nebraska Panhandle that is still in the flowering stage and this is wheat's most freeze-sensitive stage. Small differences in temperature, duration of exposure, or other conditions can cause large differences in the amount of injury.

Potential Effects of Freeze

Flowering Stage. Exposure to freezing temperatures at the flowering stage kills the male flower parts and causes sterility. After freezing, the anthers are white and dessicated or shriveled instead of their normal yellow color. Freeze injury at this stage causes either complete or partial sterility and void or partially filled heads.

Flowering proceeds from the florets near the center of the wheat heads to florets at the top and bottom of the heads over a two- to four-day period. This small difference in flowering can result in the center, or one or both ends of the heads, being void of grain because the male flowers in those florets were at a sensitive stage when they froze. Grains may develop in other parts of the heads, however, because flowering hadn't started or was already completed in those florets at the time of the freeze.

Milk Stage. Wheat that is past flowering and in the milk stage of kernel development is less likely to be seriously injured by freezing temperatures. Injured kernels may be white or gray and have a rough , shriveled appearance rather than their normal light green, plump appearance. The kernel may fail to develop after the freeze, which is a major indicator of injury.

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Figure 2. Freeze damage at heading causes glumes to become yellow and have a water-soaked appearance instead of being green and turgid	Figure 3. A whitish frost ring encircles the stem at the juncture of the stem and flag leaf at the time of the freeze.

Heading Stage. Some late planted winter wheat is just now heading. This wheat is slightly less sensitive to freezing temperatures than wheat that is flowering, but injury can still be significant. The major symptoms at this stage are sterility, leaf dessication or drying and lesions on the lower stem. The most apparent symptom may be chlorosis or bleaching of the awns or beards so that they are white instead of the normal green color. Freezing temperatures that injure the awns may also kill the male flower parts with the resulting injury described above.

Assessing Damage

Figure 4. As healthy kernels continue to develop, they will contain a clear liquid.

Growers should wait five to seven days and then check their wheat crop for kernel development. Remember that freeze damage is often not uniform across a field and tends to be worse in low areas. If serious yield loss is expected, wheat can be cut for hay or ensilage. The feed quality of hay or ensilage is good through the soft dough stage. The nitrate content of wheat for hay or ensilage after freezing should be checked to avoid toxicity to livestock.

More Information

For more information on how to assess freeze injury in winter wheat, see Freeze Injury to Nebraska Wheat (UNL Extension publication EC132) or visit UNL's Wheat Production Systems Web site.

Drew Lyon
Extension Dryland Cropping Systems Specialist
Panhandle REC, Scottsbluff
Bob Klein
Extension Cropping Systems Specialist
West Central REC, North Platte