Assessing Wheat Freeze in Kentucky
Carrie Knott and Chad Lee, University of Kentucky Grain Crops Specialists
It has been about eight days since the May8/9 freeze occurred. This is about the minimal time needed to begin seeing initial freeze damage. At this point, a fairly accurate assessment of damage should be able to be made, but as days progress the damage will become much more evident. From the April 15/16 freeze, damage was most evident about two and a half weeks to three weeks after the freeze. Unfortunately, this is likely the case for this freeze as well, given that weather conditions are expected to be cloudy and cool for much of the state this week.
For wheat fields that were flowering (Feekes 10.5.1 to 10.5.3) or in early stages of kernel development (Feekes 10.5.4) the damage will most likely occur to the kernels themselves.
In the western part of the state, minimal damage is expected. However, in the Central and Bluegrass regions, considerable damage may have occurred. Dr. Chad Lee was scouting fields in Central KY and found that damage was variable.
Damage to kernels are due to the fact that the kernels have basically stopped growing and have begun to shrivel due to loss of high moisture content when those kernels were alive and developing. This is depicted in images from Dr. Lee.
In Figure 1, the kernels near the top half of the wheat head appear to be developing normally and will likely result in mature kernels. These kernels are likely about three to five days ‘older’ than the kernels at the bottom of the head. The kernels near the bottom of the head appear to be much smaller (Figure 1) and once dissected out of the head, they are shriveled and wrinkled (Figure 2). Sometimes, these damaged kernels are associated with visible damage to the awns and spikelets themselves (Figure 3), but not always. Therefore, it is important to dissect out kernels from damaged heads and also heads that do not appear to be damaged to determine if the freeze aborted the developing wheat kernels.
Assessing the extent of freeze damage will be very important to understanding potential yield impacts and also for those producers determining whether a fungicide application to help control infection of fusarium head blight is needed.
Resources
A Comprehensive Guide to Wheat Management in Kentucky. http://www2.ca.uky.edu/agcomm/pubs/id/id125/id125.pdf
Identifying Wheat Growth Stages. http://www2.ca.uky.edu/agcomm/pubs/agr/agr224/agr224.pdf
Figure 1. Developing wheat kernels that appear healthy and sound near the top of the wheat head and damaged kernels near the bottom of the head. Photo Chad Lee.
Figure 2. Damaged wheat kernels that are shriveled and wrinkled from a freeze event about eight days ago. Photo Chad Lee.
Figure 3. Wheat heads showing typical freeze symptoms to the spikelets. Photo Chad Lee.