A field of wheat shows signs of yellowing a common symptom of freeze damage In this field the symptom did not appear for a more than week after a late freeze in April 2013

A field of wheat shows signs of yellowing, a common symptom of freeze damage. In this field, the symptom did not appear for a more than week after a late freeze in April 2013.

April freeze puts wheat in jeopardy

A mid-April freeze that turned temperatures from balmy high 70s degree readings to several points below freezing likely caused damage to a significant portion of the Southwest wheat crop.

A mid-April freeze that turned temperatures from balmy high 70s degree readings to several points below freezing likely caused damage to a significant portion of the Southwest wheat crop, according to crop specialists across the region.

Jeff Edwards, Oklahoma State University Extension wheat specialist in Stillwater, in a blog following the April 15 freeze, said much of the state’s wheat crop could be vulnerable. “Most of Oklahoma spent at least four hours below freezing last night and some areas spent an extended period of time below 28 degrees,” he wrote. “While temperatures in the wheat canopy might have remained slightly higher than reported air temperatures, they were still probably low enough to result in significant injury to wheat.”

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Much of the state’s wheat crop was at risk, says Clark Neely, AgriLife Extension small grains and oilseed specialist, College Station. He said wheat in the Panhandle and Rolling Plains, even with lower temperatures — mostly in the mid-20s —was not as likely to have been injured as in the Central and West Central regions because the wheat in those areas was not as far along in development.

Some isolated south Plains areas, with even lower temperatures—mid-20s to upper teens—could see significant damage. Temperatures that low pose a high chance of wheat in any stage, Neely said.

“Based upon what I’ve seen, I would anticipate potential freeze injury anywhere from the Waco to Dallas area and westward to the Concho Valley and San Angelo area,” he said. “Primarily because that’s where the crop was flowering, and flowering is when the crop is most susceptible to freeze damage.”

A later than usual wheat crop—delayed because of a cool spring and ongoing drought—may have helped avoid some cold damage. Most Texas High Plains wheat was still in the jointing stage.

Generally, when wheat is flowering, freeze damage can occur when temperatures are as high as 32 degrees and stay there for two hours or more, he said.

It was very “touch and go, and flirting with the freezing mark” in those central parts of the state, Neely said. Soil moisture, plant-moisture content, whether it’s windy or calm, and field terrain also affect cold damage.

“Wind can be good or bad, depending upon how cold it gets,” Neely said. “If it’s a still night, the cold will settle down in the low-lying areas. So it’s good in the sense that wind keeps the air stirred up, but it can also spread freeze damage across a wider area.

“Unfortunately, one county over — or even one field over — there can be a degree difference. Anytime you get down to that 32-degree mark, it gets kind of tricky with flowering wheat. He recommended that farmers scout their fields and pay attention to what the weather conditions were like.

Too early to assess damage

Neely and other specialists across the region expect no realistic evaluations freeze damage for a week, perhaps two.

“It really depends upon the weather after the freeze. If it becomes hot and dry, we’ll see symptoms a lot sooner. If it stays cool, it’ll take a little bit longer for those symptoms to show up.”

Kansas wheat may be damaged as sell, according to Jim Shroyer, K-State Research and Extension crop production specialist.  He said wheat in the jointing stage is most at risk.

Shroyer explained how specific factors affect damage potential.

  • 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 20s with no significant injury. But if temperatures fall into the low 20s or even lower for several hours, the lower stems, leaves or developing head can sustain injury.
  • Thick stands tend to reduce the extent of freeze damage as the warmth of the soil will radiate up into the canopy. But well-fertilized, succulent wheat may sustain more freeze injury than wheat that is not as well fertilized. Thin stands, common this year, are at higher risk of injury because air can penetrate the stand more easily.
  • Often more freeze damage occurs in no-till fields because residue acts as a blanket and doesn't allow heat from the soil to radiate up into the plant canopy.
  • Significant injury becomes much more likely if the temperatures in the damaging range last for two hours or longer.
  • Often less freeze injury occurs at a given temperature when soils are wet than when dry. Wetter soils tend to radiate a little more warmth than dry soils.
  • 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.
  • Low spots are almost always the first to have freeze injury. The coldest air tends to settle in the low areas, especially under calm wind conditions.

“Over the next few days growers will need to inspect fields closely to determine the extent of injury,” Edwards said. “Symptoms may start to appear later this week and will likely be clearly identifiable by early next week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against. I anticipate that we will not have any partial “blanking” of wheat heads and that most wheat heads will either be okay or a complete loss.

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“New tillers might emerge, but it is already April 15. Also, we have very dry soil conditions. For these reasons I am doubtful that newly emerging tillers will have much yield potential in areas south of I-40. IF (and that is a big if) weather conditions remain favorable, late emerging tillers in northern Oklahoma might still have a shot at producing grain.”

 

 

Also of interest:

Most of SW wheat acreage escapes freeze damage

El Niño: As the world turns the weather changes

Weather continues to bedevil Texas crops

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