Wheat’s growth stage determines severity of freeze injury

With the variable weather this spring, many producers are questioning Mother Nature, asking, “Has spring already sprung?” Or “Is this a trick and we will be receiving our winter cold later than desired?” The weather this time of year can prove to be very unpredictable, and in some cases, this can be detrimental to the wheat growing in the spring.

Freeze injury of wheat through the winter is uncommon due to variety tolerance and good management practices, however; once wheat begins growing in the spring, it has little resistance to low temperatures. The stage wheat is in also dramatically affects the severity of injury to the crop. According to a K-State Research and Extension freeze injury publication, the following is a breakdown of wheat stages and their tolerance to freeze injury in the spring:

Tillering—While wheat is in the tillering stage, the approximate temperature in which injury occurs is 12 degrees F, with temperatures at this level for at least two hours. At this stage, there is only a slight to moderate yield reduction. Symptoms can include leaf chlorosis, burned leaf tips, a silage odor and often a blue cast to the field.

Jointing—After two hours of temperatures at or below 24 degrees F, yields can be reduced moderately to severely. If this occurs, there may be death to the growing point, burned or yellowing leaves, lesions, splitting, bending of the lower stem and possibly an odor.

Boot—The temperature of concern for the boot stage is 28 degrees F. Yield reduction and symptoms are very similar to those in the jointing stage, but there may also be cases where the spikes get trapped in the boot as well as floret sterility.

Heading and flowering—At these stages, there can be severe yield reductions when temperatures stay at or below 30 degrees F for two or more hours. Symptoms include floret sterility, white awns or white spikes, damage to the lower stem, and leaf discoloration.

Milk—With a moderate to severe yield reduction at 28 degrees F, again, look for white awns or spikes, damage to the lower stems and leaf discoloration. Other primary symptoms include shrunken, rough and discolored kernels.

Dough—At the dough stage, a slight to moderate yield reduction can occur at 28 degrees F. Look for shriveled and discolored kernels as well as potentially having poor germination.

Determining how wheat is affected by late freezing temperatures will provide a starting place for future management decisions. Although the weather is unpredictable and sometimes likes to remind us of old man winter, it is an indicator of changing seasons and that the new life of spring is right around the corner.

For more information, contact Jeri Geren, Diversified Agriculture and Natural Resources, at [email protected] or 620-331-2690.