Farm Talk

Crops

April 22, 2014

Freeze could damage some Kan. wheat

Parsons, KS — The hard freeze throughout Kansas in the early morning hours of April 15, could cause some damage to wheat, said Jim Shroyer, K-State Research and Extension crop production specialist. Wheat in the jointing stage is most at risk, he said.

There are a number of key factors in determining 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, soil moisture, and the wind speed, Shroyer explained.

 Stage of development

Wheat that hasn't started to joint yet might suffer damage to the existing foliage, but the growing points will be protected by the soil and should escape injury. This wheat will have cosmetic damage to the leaves that will show up almost immediately. Jointing wheat can usually tolerate temperatures in the mid to upper 20's with no significant injury. But if temperatures fall into the low 20's or even lower for several hours, the lower stems, leaves or developing head can sustain injury.

Density and condition

If the stand is thick, that will tend to reduce the extent of freeze damage as the warmth of the soil will radiate up into the canopy. On the other hand, well-fertilized succulent wheat has often sustained more freeze injury than wheat that is not as well fertilized. Thin stands, which are common this year, are at higher risk of injury because the air can penetrate the stand more easily.

 Residue

Many times there is more freeze damage in no-till fields because the residue acts as a blanket and doesn't allow the heat from the soil to radiate up into the plant canopy.

 Extent and duration of low temperatures

Significant injury becomes much more likely if the temperatures in the damaging range last for two hours or longer.

 Soil moisture

There is often less freeze injury at a given temperature when soils are wet than when dry. Wetter soils tend to radiate a little more warmth than dry soils.

 Wind speed

Windy conditions during the nighttime hours when temperatures reach their lows will reduce the amount of warmth radiating from the soil and increase the chance of injury.

 Temperature gradients within the field

Low spots in the field are almost always the first to have freeze injury. The coldest air tends to settle in the low areas, especially under calm wind conditions.

There are many possible scenarios after a freeze, and things do not always go according to "the book," Shroyer said. He advised producers to keep watching their fields closely over the next 7 to 10 days for the following:

•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. 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.

•The color of the developing head or growing point in wheat that has jointed. As long as heads are light green and turgid, the head in that tiller is fine. If the head is whitish and flaccid, it has died.

•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.

•The integrity of the stem. 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 you see that, it usually means the wheat will lodge at some point during the season. If the stems look undamaged, that's a good sign.

The best thing producers can do for the first few days is simply walk the fields to observe lodging, crimped stems and damaged leaves, the K-State agronomist said.

"Be patient. Do 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," he said.

After several days, producers should split open some stems and check the developing head, he said.

"Where stems and/or growing points were killed by the freeze, start looking for new tiller growth coming from the crown area. In fact, look for new tiller growth even if you think the stems look okay. Sometimes tillers can be killed but will not show any symptoms for quite a while. In those cases, the first sign that the tillers are dead is the sudden growth of new tillers at the base of the plant," Shroyer said.

If secondary tillers begin growing normally and fill out the stand, the wheat may look ragged because the main tillers are absent, he added. Watch out for bird cherry oat aphids and other potential insect or disease problems on these late-developing tillers, he said.

"Enough tillers may survive to produce good yields, if spring growing conditions are good.  If both the main and secondary tillers are injured, the field may eventually have large areas that have a yellowish cast and reduced yield potential," he said.

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