Freeze and drought concerns for western Nebraska wheat

The degree of injury to wheat from spring freezes is influenced by the duration of low temperatures as well as the low point they reach in the crop canopy. During the jointing stage, when heads are moving up the stems, it takes about two hours at 24°F to cause moderate to severe injury to wheat. Injury symptoms at this stage include: death of the growing point; leaf yellowing or burning; lesions, splitting, or bending of the lower stem; and silage odor. Stem growth stops immediately when the growing points are injured, but growth from later tillers may obscure damage. Partial injury at this stage may cause a mixture of normal tillers and late tillers and result in uneven maturity and some decrease in grain yield.

Since it is difficult to know what the air temperatures were in the wheat canopy, it is often necessary to wait five days or more after the freeze event to assess plant damage. The growing points can be located by splitting stems lengthwise with a sharp knife. A normal, uninjured growing point is bright yellow-green and turgid; freeze injury causes it to become white or brown and water-soaked in appearance. It takes several days of warm weather for freeze injury to become apparent.

Temperatures in a dense wheat canopy with moist soils are likely to cool off more slowly than surrounding air temperatures. Damage within a dense wheat canopy is likely to be less than in a thin stand of wheat. For wheat that was headed or close to heading, check the male parts (anthers) of the flower in the developing kernel. Frequently they are the only parts killed.