Wow……only in Kansas! We can easily go from 70 degrees F one day to below freezing the next! Our wheat crop likes these abrupt temperatures about as much as we do!!!! Which is not at all!!! So the temperatures during the morning of April 27 dropped below freezing and into the lower 30’s or upper 20’s in most of the state. The lowest measured temperature was 24 degrees F in north central Kansas (Scandia, Republic Co.), where temperatures were below 32 degrees F for as long as 7.3 hours. The Post Rock Extension District has three weather stations which are in Jewell, Mitchell and Osborne counties. At these locations, temperatures were below 32 degrees F for 3.8 hours in Jewell Co., 6.2 hours in Mitchell Co. and 7 hours in Osborne Co.
The effects of a freeze event on the wheat crop will depend on whether the event matches critical sensitive stages of crop development and on several micro-climate factors which are field-specific according to Dr. Romulo Lollato, K-State Research and Extension Wheat specialist. So the areas of the state that would be the most vulnerable to injury based on the wheat development stages, would be northcentral, central and southwest Kansas. These counties reported temperatures cold enough to potentially damage the wheat due to their current growth stages.
Lollato explains that the actual freeze damage potential will be very field specific and depend on several micro-climate factors. Low areas of the fields might experience colder temperatures than those reported at nearby weather stations. Similarly, increased wind speed might help warmer air make its way into the canopy, decreasing freeze injury potential. On the other hand, low wind speed might allow the canopy’s micro-climate temperatures to decrease more than those measured at nearby weather stations. Similarly, warm soils might help buffer some of the cold temperatures experienced in certain fields.
Soil temperature, which is affected by soil moisture status and by the presence of crop residue on the soil surface, can potentially help buffer cold temperatures. Moist soils will be able to hold warm temperatures better than dry soils. The majority of our area has good soil moisture in the profile due to the recent rainfall events, which could help decrease the actual cold damage experienced.
Below are a few guidelines for each of the growth stages of the wheat and freeze damage symptoms to look for:
Boot. 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. Temperatures at these levels were measured in parts of southwest Kansas and in north central Kansas. In north central Kansas, the majority of the fields are at boot stage currently and could sustain injury, as temperatures were as low as 24 degrees F. To detect injury, producers should wait several days, after it has warmed up, and 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.
It’s possible for some of the spikelets to be alive and a healthy dark green while other spikelets on the same head are damaged. 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).
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. Field reports from north central Kansas indicate that more advanced fields were at this stage as of April 25; thus, the low temperatures measured during the morning of April 27 could most likely have caused damage to fields in this situation.
In addition to all the information provided above, be watching for any freeze damage to lower stems. If the damage is severe enough, the plants will eventually lodge. Actual damage, if any, will not become apparent until temperatures have warmed back up for several days and growth has resumed.
K-State Research and Extension has an excellent publication, “Spring Freeze Injury to Kansas Wheat” that is available either online or at one of our Post Rock Extension District Offices in Beloit, Lincoln, Mankato, Osborne or Smith Center. The publication, at NO COST, is an excellent resource that explains the potential injury to wheat at different growth stages and at different temperatures along with color pictures.
Post Rock Extension District of K-State Research and Extension serves Jewell, Lincoln, Mitchell, Osborne, and Smith counties. Sandra may be contacted at firstname.lastname@example.org or by calling Smith Center, 282-6823, Beloit 738-3597, Lincoln 524-4432, Mankato 378-3174, or Osborne 346-2521. Join us on Facebook at “Post Rock Extension” along with our blog site at “postrockextension.blogspot.com. Also remember our website is www.postrock.ksu.edu and my twitter account is @PRDcrops.