In the past week, the area experienced freezing temperatures for several nights during the week and weekend. It is still several weeks before the normal dates of the last spring freeze in the state, and a freeze during the week of March 14-20 normally does not cause any problems for wheat. However, this year the wheat is much more advanced in development than normal.
Warmer-than-normal temperatures in February and March (about 6 and 9 degrees F, respectively) coupled with increased day length has sped up wheat development this winter. The most advanced wheat fields in Kansas are currently about Feekes 7 (second node) in selected fields in southern
Kansas. However, many fields have not jointed yet across the state, especially in northwest Kansas and other northern areas of the state.
The developmental stage of wheat is directly affected by temperature and varies within a region. Factors that influence current stage of development include variety selection, tillage practice (soil temperature), and planting date. In general, early-maturing wheat tends to be more susceptible to freeze injury than later-maturing wheat as the probability of a freeze event matching more sensitive stages of development is greater.
There are many possible scenarios after a freeze, and producers should not take any immediate decision following a freeze event. Several days of warm temperatures are needed to properly assess freeze damage to the wheat crop. Where wheat was at the jointing stage, producers should watch their fields closely over the next 7 to 10 days from the freeze event for the following:
1. The color of newly emerging leaves. If they are nice and green, that probably indicates the tiller is alive. If newly emerging leaves are yellow, that probably indicates the tiller is dead. The color of existing leaves is not terribly important, except for the flag leaf, which should not have emerged at this point in time yet. Existing leaves will almost always turn bluish-black after a hard freeze, and give off a silage odor. Those leaves are burned back and dead, but that in itself is not a problem as long as newly emerging leaves are green.
2. The color of the developing head or growing point in wheat that has jointed. As long as heads are light green, crisp, and turgid, the head in that tiller is fine. If the head is whitish, flaccid, and mushy, it has died.
3. Ice in the stems. If there was ice in the stems below the first node the morning of the freeze, those tillers may be damaged (although not always) and may not produce grain. You may see split stems from ice accumulation.
4. Stem integrity. If the wheat lodged immediately after the freeze, that indicates stem damage. Later tillers may eventually cover the damaged tillers. Even if there is no immediate lodging, look for lesions or crimps anywhere on the stems. If these symptoms are present, it usually means the wheat will lodge at some point during the season. If the stems look undamaged, that’s a good sign.
A number of key factors determine freeze damage: the stage of development of the wheat, the density of the stand and condition of the plants, the amount of residue on the soil surface, the extent and duration of low temperatures, temperature gradients within the field (position on the landscape), soil moisture, and the wind speed.
The best thing producers can do for the first few days is simply walk the fields to observe lodging, crimped stems, and damaged leaves. Producers should not take any immediate actions as a result of the freeze, such as destroying the field for recropping. It will take several days of warm weather to accurately evaluate the extent of damage.
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-state Research and Extension. One can contact her by email at aboor@ksu.edu or calling 620-793-1910