Josh Lofton and Steve Harrison- LSU AgCenter
Louisiana has experienced a relatively mild winter across much of the state. This has allowed for some “catch-up” growth for a winter wheat crop that was planted in poor conditions early in the season or with better conditions very late in the fall. However, recent colder conditions have all but stopped growth. This is typically not an issue but with the increased over-winter growth, questions always arise as to the potential damage that cold temperatures might have on a more advanced wheat fields. This is especially true with temperatures forecast in the lower 20’s for two consecutive nights this week. While this is a very reasonable question to ask, the answer is not as straight-forward and depends on growth stage, duration of cold temperatures, amount of foliage covering the growing point, soil temperature, soil moisture, and wind, among other factors.
The two most important factors are the potential low temperatures and the duration of these cold temperatures. Critical cold temperatures for the wheat depend on the growth stage of the crop when the cold occurs. As can be seen from the table below (Kansas State University Extension Service), the wheat crop is least susceptible to cold temperatures during the tillering. Wheat becomes more susceptible to cold damage as the crop progresses towards the heading stage and is very susceptible to cold temperatures during heading. Most of the state’s wheat crop is probably at or near jointing but some fields clearly showing one or two nodes. During jointing, 24°F for greater than 2 hours can cause moderate to severe negative effects on growth and yield for the current crop. The most detrimental impact of these temperatures will be death of growing points resulting in loss of those. This will often occur on the main stem of the tillered wheat as it is the most advanced. Death of growing points will effectively terminate any yield that could have been expected from that tiller and may lead to development of new tillers from the base of the wheat plant. While extensive tiller death would only occur if the crop was greatly advanced or temperatures get down to the mid-teens for an extended amount of time, which is not expected.
Growing points should be evaluated about a week after the hard freeze occurs. This allows damaged tissues to start showing symptoms of discoloration and damaged stems to wilt. Health of the growing point can be evaluated by removing the most advanced stem at the soil level and splitting the stem. A growing point can be identified by locating stacked plant tissue that looks similar to a beehive above the current visible nodes. If this tissue is white, firm and fleshy, the growing point is still active and productive. However, if the growing point is discolored and limp, the growing point is no longer active and that tiller will cease to grow and produce.
Determining the extent of the damage from this cold spell and potential yield losses will be difficult until plants have time to start recovering. Severely damaged field will put up new tillers from the soil line in about 10 – 14 days. The damaged tillers will wilt and bleach out. However, evaluation of the crop following the weather will give a better indication of the total damage. There will be some superficial leaf damage and leaf discoloration in less advanced fields, but this is not likely to cause yield losses. The hope is that the crop has adequate foliage covering the growing points, thus limiting tiller death. For questions or concerns following these temperatures contact your local extension agent or state-specialist.
Josh Lofton- State Wheat Specialist, firstname.lastname@example.org