During the past few weeks, our weather has been less than ideal for our developing wheat crop. There have been several instances of frost and freezing temperatures reported, and a few fields have sustained freeze damage. This past weekend, we in Barton County were spared the winter storm that caused significant damage to crops in Western Kansas. The wheat in our area may still show signs of damage from the colder temperatures even though we did not get quite as cold, or have snow as in other portions of the state. Below is a little more information about freezing temperatures and its effects on different stages of wheat. As always, if you have any questions, feel free to get a hold of me, and I will be happy to help.
In this stage, wheat can be injured if temperatures drop down into the mid to upper 20’s for several hours. Injury is more likely if this occurs repeatedly and if it is windy at night – conditions experienced over the course of April 29–May 1, when below-freezing temperatures were experienced during three consecutive nights for the western third of Kansas.
To detect injury to wheat at boot stage, producers should wait several days then split open some stems and look at the developing head. If the head is green or light greenish in color and seems firm, it is most likely going to be fine. If the head is yellowish and mushy, that’s a sign of freeze injury. 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.
Usually, it is possible for some of the spikelets to be alive and a healthy dark green while other spikelets on the same head are damaged due to the difference in pollination timing within the wheat head. This is especially true following one single freezing event. If a spikelet flowers normally and the kernels on that spikelet develop normally, then the head is at least partially viable and will produce grain (unless it freezes again, of course). However, the three consecutive nights with below-freezing temperatures during the April 29 – May 1, period might decrease the chances that earlier of later pollinating spikelets survive
Awns beginning to appear
If the awns have begun to appear, there can be significant injury to the heads if temperatures reach about 30 degrees or lower for several hours. The heads may fully exert from the boot, but few, if any, of the spikelets may pollinate normally and fill grain. Damaged heads from a freeze at this stage of growth may seem green and firm at first glance, but the floral parts will be yellowish and mushy. Additionally, yield loss from stem damage will be greater at this stage than at boot stage.
Several fields in the southwest portions of Kansas were flowering as of April 29 – May 1. In this stage of development, wheat is particularly vulnerable to damage from freezing weather. Temperatures of 30-32 degrees or lower for about 2 hours or more, can damage anthers.
If the wheat was in the flowering stage at the time of the freeze, you can determine if the anthers are damaged by examining them with a magnifying lens. Healthy anthers will first be lime green, then yellow. If they are damaged by a freeze, they will begin twisting within 2 to 3 days. Shortly afterward, they will begin to turn whitish or brown. The stigma in the florets may or may not also be damaged by a freeze. If the anthers are damaged by freeze, the flowers may fail to develop a kernel.
Wheat doesn’t flower all at the same time on the head. Flowering proceeds from florets near the center of wheat spikes to florets at the top and bottom of the spikes over a 3- to 5-day period. This small difference in flowering stage when freezing occurs can produce some odd-looking heads. The center or one or both ends of the spikes might be void of grain because those florets were at a sensitive stage when they were frozen. Grain might develop in other parts of the spikes, however, because flowering had not started or was already completed in those florets when the freeze occurred.
If you are unsure whether there has been freeze damage to the anthers, wait several days and determine whether kernels are developing normally. A week after flowering, kernels should be well-formed up and down the head under normal conditions.
In addition to this, be watching for any freeze damage to lower stems. If the damage is severe enough, the plants will eventually lodge.
The comments above are general guidelines. Actual damage, if any, will not become apparent until temperatures have warmed back up for several days and growth has resumed.
For more information on freeze damage to wheat, see Spring Freeze Injury to Kansas Wheat, K-State Research and Extension publication C646, at ksre.ksu.edu/bookstore/pubs/c646.pdf.
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-state Research and Extension. Contact her by email at firstname.lastname@example.org or call 620-793-1910.