Wheat Freeze Injury

The overall wheat crop is in poor condition and has been subjected to harsh environmental conditions since the day it was seeded. Extreme to exceptional drought, high winds and extreme temperature swings have been the norm and have taken their toll on the area wheat crop.  Recently freezing temperatures have caused significant injury to area wheat; low temperatures reached potentially damaging levels on four occasions since March 25. The following table provides low temperatures in degrees F recorded at 4 local NOAA weather stations on dates where potentially damaging low temperatures occurred.

Date	Clovis	Friona	Muleshoe	MWR*
3/25	13	17	15	16
4/10	16	20**	21	23
4/19	n/a	19	20	19
4/25	15	20	20	20
*Muleshoe National Wildlife Refuge, **Mesonet data

Stem, head, and growing point damage as well as leaf burn has been observed. The following table outlines established freezing temperature injury thresholds as well as potential yield impact for wheat at current crop stages of area wheat.

Growth Stage	Temp (2 hours)	Yield Effect
Jointing	24oF	Moderate to severe
Boot	28oF	Moderate to severe
Heading	30oF	Severe

Inspection of growing points and stems are necessary to evaluate potential injury prior to heading. A normal, uninjured growing point is bright white to yellow-green and turgid; freeze injury causes it to become white or brown and water soaked in appearance. Injury to the lower stems in the form of discoloration, roughness, lesions, splitting, collapse of internodes, and enlargement of nodes frequently occurs at the jointing stage and the following stages after freezing. Severe stem injury can affect plant-water relations during the late season. Affected plants can suddenly dry down as evaporative demand exceeds the capacity of the stem to uptake water. Lodging of plants is the most serious problem following stem injury. The most apparent symptom in the heading stage is usually chlorosis or bleaching of the awns so that they are white instead of the normal green color. Freezing temperatures that injure the awns will usually kill the male flower parts.