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Freeze Concern Hits Kansas Wheat Farms

Temperatures below freezing mark could impact northwest Kansas wheat crop.

Ambient air temperatures dropped to below 32˚F. in several locations in northwest Kansas Thursday night, prompting concern from wheat farmers about potential damage to the 2019 crop. 

Temperatures dropped to 31˚F. in Plainville, Kansas, and 31.9˚F. at the Kansas State University Western Kansas Agriculture Research Center in Hays, where the wheat is just beginning to push a head out of the boot. Hill City had a low of 30˚F. Wheat yields in this region are generally expected to be very good, based on this month's Wheat Quality Council Hard Wheat Tour.

Wheat in these locations ranges in maturity to flag leaf, to boot, to heading – which is when the crop is most vulnerable to extended temperatures below 32˚F.

According to KSU studies, moderate to severe yield impact is possible at the following stages and extreme temperatures lasting at least two hours:

  • Boot: 28˚F. Causes floret sterility; spike trapped in boot; damage to lower stem and leaf discoloration.
  • Heading: 30˚F. Causes floret sterility; white awns or white spikes. Damage to lower stem and leaf discoloration.
  • Flowering: 30˚F. Causes floret sterility; white awns or white spikes. Damage to lower stem and leaf discoloration.

On Twitter, Romulo Lollato, Extension wheat specialist at KSU, explained the potential damage of floret sterility. “Florets that are sterile will not form a grain. The actual impact on yield at a field level will depend on several other factors (position on the landscape, soils moisture, amount of crop canopy, etc.). Parts of the field might be more affected than others.” 

KSU research shows there are several factors that influence the extent of freeze damage to wheat. These include: 

  • Density of the stand and condition of the plants. 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 are at higher risk of injury because the air can penetrate the stand more easily. If the plants were wet before the freeze, this can result in a coat of ice on the plants that may protect the growing point to some extent. If temperatures get too low, however, the cold will go through the ice.
  • Amount of residue on the soil surface. No-till fields can often sustain more freeze damage 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 temperaturesSignificant 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 have more moisture present. Wetter soils tend to radiate a little more warmth than dry soils. On the other hand, drought-stressed plants tend to be more hardened against cold injury and their lower leaf water content tends to decrease the severity of the freeze injury.
  • 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 (position on the landscape). 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.
  • Wheat variety. Although the sensitivity to cold temperatures at a given growth stage is very similar across all varieties, varieties can differ in their release from winter dormancy as much as three weeks. Because of differences in winter dormancy release, late-release varieties may escape a freeze injury for being delayed in their development. For instance, a late-release variety at Feekes 4 or 5 is less sensitive to freeze damage than an early-release variety planted at the same date which might have reached Feekes 6. For more detailed information of different varieties release from dormancy during the current growing season, please see the accompanying eUpdate on first hollow stem.   
     

Injury symptoms

There are many possible scenarios after a freeze and producers should not take any immediate action following a freeze event. Several days of warm temperatures are needed to properly assess freeze damage to the wheat crop. Thus, producers should watch their fields closely over the next seven to 10 days after the freeze event for symptoms like color of new leaves (if they are green, tillers are in good shape); color of developing head (if it’s green, that head is fine); ice in the stems (identified by split stems), and stem integrity (if lodged, chances are there is damage). 

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

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