The recent cold temperatures experienced on March 15-16 were enough to potentially cause freeze damage to winter wheat in parts of Kansas. The actual freeze damage will be region-specific, depending on crop growth stage and minimum temperatures. While there is nothing we can do immediately, growers can prioritize the fields they sample for freeze-damage symptoms based on conditions more likely to result in freeze damage.
According to Kansas Mesonet Weather Data for Barton County. Hours below 12 degrees was 3 and for Ellis County it was 4 hours of below 12 degrees. According to the K-State Spring Freeze Injury to Kansas Wheat publication, the approximate injurious temperatures for tillering and jointing wheat are two hours at 12 and 24°F, respectively. These are not hard numbers, as many factors influence freeze injury.
There are several factors that can affect the potential for freeze damage to wheat in the spring. 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 greater risk of injury because air can penetrate them more easily. If the plants were wet before the freeze, a coating of ice may form, protecting the growing point to some extent. However, if temperatures drop too low, the cold will penetrate the ice.
No-till fields can often sustain more freeze damage because the residue acts as a blanket, preventing the soil's heat from radiating up into the plant canopy.
There is often less freeze injury at a given temperature when soils are wet than when they are dry. Wetter soils tend to radiate a little more warmth than dry soils. On the other hand, drought-stressed plants tend to be more tolerant of cold injury, and their lower leaf water content tends to reduce the severity of freeze injury.
Windy conditions during the nighttime hours, when temperatures are at their lowest, will reduce the amount of heat radiating from the soil and increase the risk of injury.
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.
Although the sensitivity to freezing temperatures at a given growth stage is very similar across all varieties, Kansas wheat varieties can differ in their release from winter dormancy by up to 3 weeks. Because of differences in winter-dormancy release, late-release varieties may escape freeze injury due to delayed development.
Injury symptoms to look for in the coming days. There are many possible scenarios after a freeze, and producers should not make any immediate decisions. 10 to 14 days of warm temperatures are needed to allow the wheat to resume growth and to properly assess freeze damage, which will depend strongly on the crop stage.
Greenup - wheat that hasn’t started to joint yet will likely show damage to the existing foliage. This wheat will have damage that causes the leaves to appear dark green to blackish, and it will turn brown and crispy. Splitting the wheat stem to identify the growing point (tiny wheat head) and determine whether it is above or below the soil surface can help assess the risk of freeze injury.
This information has been summarized and taken from the K-State Agronomy eUpdate weekly newsletter. To read the full version search in your browser for KSU Agronomy eupdate, also you can subscribe too.
More information on freeze damage to wheat is available in Spring Freeze Injury to Kansas Wheat, K-State Extension publication C646, available at: http://www.ksre.ksu.edu/bookstore/pubs/C646.pdf.
If you need any assistance or have any questions, please give me a call at 785-628-9430 or email me scampbel@ksu.edu
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Extension. You can contact him by e-mail at scampbel@ksu.edu or by calling 785-628-9430.