By Jim Shroyer, Kansas State University Extension Agronomy State Leader


Recent freezing temperatures in parts of Kansas have damaged the flowers and heads in some wheat. Wheat is particularly vulnerable to damage from freezing weather from the late boot stage, as the head starts to emerge, through the flowering stage.


Freeze injury at the boot stage causes a number of symptoms when the heads are enclosed in the sheaths of the flag leaves. Freezing may trap the spikes inside the boots so that they cannot emerge normally. When this happens, the spikes will remain in the boots, split out the sides of the boots, or emerge base-first from the boots.


Sometimes heads emerge normally from the boots after freezing, but remain yellow or even white instead of their usual green color.

When this happens, all or part of the heads have been killed. Frequently, only the male parts (anthers) of the flowers die because they are more sensitive to low temperatures than the female parts. Since wheat is self-pollinated, sterility caused by freeze injury results in poor kernel set and low grain yield.


If you are unsure whether there has been freeze damage to the flowers, wait several days and determine whether kernels are developing normally. A week after flowering, kernels should be well-formed up and down the head.


If flowering has already occurred and kernels were forming at the time of the freeze, there still could be damage. Generally, it takes colder temperatures to cause damage to kernel development than to floral structures.


Healthy, developing kernels shortly after flowering are greenish-white and as they grow, they turn more greenish. But if they are damaged, they will turn grayish-white, shriveled and rough and will not continue to enlarge. Producers might need to check heads several times to determine the amount of damage.


Summary
If the primary tillers were in the early heading stage at the time of the hard freeze, then it is very likely that most of the heads were killed. However, some spikelets or entire heads may have survived. If a spikelet flowers and the kernels start to develop, then that spikelet is fine. About 5 days after flowering, a tiny developing kernel should become visible if the spikelet is alive and developing normally. By 10 days after flowering, the kernel length should be fully developed.


For more information about spring freeze damage to wheat, see K-State publication C-646, "Spring Freeze Injury to Kansas Wheat," or check the Web at http://www.oznet.ksu.edu/library/crpsl2/C646.pdf.