University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

Figure 1. Wheat leaf beginning to turn slightly yellow. Note the purple/reddish stems because the sugars have no place to go. The head is dead without tiller damage. (Photos courtesy of Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader at Kansas State University.)
Figure 2. Note the dead leaf in the plant whorl and the purplish-reddish stem, indicating advanced damage from that shown in Figure 1.
Figure 3. There is stem damage on the primary tiller, but two new tillers have begun to grow.

April 27, 2007

Freeze-Damaged Wheat Responding to Warmer Temperatures

Much of the winter wheat crop in Nebraska escaped significant injury from the freezes that occurred from April 3 to April 9. The lowest temperature — 7° F — occurred at North Platte the morning of April 7. At Beatrice the low on April 7 was 16° F and on April 8 it was 13° F. As we mentioned in an earlier CropWatch, winter wheat development was up to two weeks ahead of normal at the time of the freeze. The major reason for the advanced development was the warm March. At UNL's West Central REC rainfed farm near North Platte this was the warmest March since records were started in 1907. This year March was 9.6 degrees warmer than average.

Where wheat plants were injured, regrowth has begun in most situations. This is from both uninjured secondary tillers and from basal tillers. It is still too early to determine the amount of injury to winter wheat unless it was killed. We have often been surprised by winter wheat’s ability to recover from injury.

It is difficult to estimate the yield potential when the primary tillers are killed and replaced by secondary and even basal tillers. Where the secondary tillers are healthy and number three to five per plant, do not expect more than 50-75% of the yield potential of the crop before the freeze.

If the winter wheat has to start over from the basal tillers, yields will likely be comparable to spring wheat. Since the crop will be much later, it also will fill much later and likely be exposed to high temperatures, which will shorten the filling period and reduce yield.

A few years ago, in a test plot at Grant, the well fertilized plots had more and larger heads with more kernels but the plants were later. Hot weather hit and the unfertilized plot, which was further along in filling when the heat hit, had the highest yield.

In conclusion, if the regrowth is coming from basal tillers, do not expect a higher yield than you would with spring wheat. In general, in Nebraska, spring wheat yields of more than 25 to 30 bushels are uncommon.

In the Gage County area in southeast Nebraska about 10% of fields appear to be a total loss with yields of less than 30 bu/ac. In some fields, where growing points appear dehydrated and the stem below the growing point is badly damaged, plants are just starting to collapse.

In western Nebraska, where most of the state’s wheat is grown, the crop was not significantly injured by the freezing temperatures in early April. As this wheat continues to develop, however, it will be more susceptible to future freezing temperatures.

Robert Klein, Extension Crops Specialist
West Central REC, North Platte
Paul Hay
Extension Educator, Gage County
Drew Lyon, Extension Dryland Cropping Systems Specialist
Panhandle REC, Scottsbluff

© 2007 by the University of Nebraska Board of Regents. All rights reserved.
Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture.
The University of Nebraska-Lincoln does not discriminate on the basis of gender, age, disability, race, color, religion, marital status, veteran's status, national or ethnic origin, or sexual orientation.