James Herbek and Chad Lee, University of Kentucky
April 2004

The relatively warm fall caused much of the wheat in Kentucky to grow faster than expected. The fluctuation of freezing and warm temperatures this spring has caused some damage to wheat. The symptoms from cold temperature damage to wheat appear as leaf burn, where the leaf blades appear yellow to reddish brown at the leaf edges. The reddish brown fades into yellow closer to the leaf mid-rib. The leaf burn often occurs on the upper portion of the leaves. Stem damage can occur from cold temperatures. The stems will be weak at the point of damage and may bend or break. Often the wheat will compensate for the damaged stalk and return to an upright position. However, the wheat may be more likely to lodge at later growth stages.

Wheat yield losses from cold temperatures depend on the wheat growth stage, temperature and duration of temperature. Table 1 includes the conditions required for freeze injury to wheat as well as the expected impact on yield, while Table 2 describes each growth stage of wheat. Table 1 is a copy of Table 3-3 from ID-125: A Comprehensive Guide to Wheat Management in Kentucky and Table 2 is a copy of Table 2-1 from the same publication.

The vague yield effects in Table 1 indicate that predicting yield from wheat injured by freezing temperatures is not an exact science. In addition to wheat growth stage and temperatures, yield losses depend on the weather conditions following freeze injury. Cool, damp conditions will slow recovery from the freeze injury, while warmer conditions will accelerate recovery.

One factor that will help to determine the severity of damage to wheat is the condition of the developing wheat head. A healthy developing wheat head is light green in color, glossy and turgid. A damaged head will be pale white to tan with a limp appearance. To help determine potential yield impacts, investigate the quality of several developing heads in the field. If most of the wheat heads are damaged, then expect moderate to severe yield losses. If very few of the wheat heads are damaged, then expect slight to moderate yield losses.

For questions about freeze damage to wheat, contact your county extension office.  

 

Table 1. Freeze injury in wheat.
Growth Stage Approximate injurious temp. (two hours) Primary symptoms Yield effect
Tillering (1-5)a 12°F Leaf chlorosis; burning of leaf tips; silage odor; blue cast to fields Slight to moderate
Jointing (6-7) 24°F Death of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odor Moderate to severe
Boot (10) 28°F Floret sterility; spike trapped in boot; damage to lower stem; leaf discoloration; odor Moderate to severe
Heading (10.1-.5) 30°F Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration Severe
Flowering (10.51-.54) 30°F Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration Severe
Milk (11.1) 28°F White awns or white spikes; damage to lower stems; leaf discoloration; shrunken, roughened, or discolored kernels Moderate to severe
Dough (11.2) 28°F Shriveled, discolored kernels; poor germination Slight to moderate

a Numbers in parentheses refer to the Feeke's scale (see Table 2.)

Wheat Growth Stages Identified by the Feekes Scale.

Table 2.A Tillering
Stage Description
1 One shoot (number of leaves can be added), first leaf through coleoptile.
2 Beginning of tillering; main shoot and one tiller.
3 Tillers formed; leaves often twisted spirally. Main shoot and six tillers. In some varieties of winter wheat, plant may be "creeping," or prostrate.
4 Beginning of the erection of the pseudo-stem; leaf sheaths beginning to lengthen.
5 Pseudo-stem (formed by sheaths of leaves) strongly erected.
Table 2.B Stem Extension
Stage Description
6 First node of stem visible at base of shoot.
7 Second node of stem formed; next-to-last leaf just visible.
8 Flag leaf (last leaf) visible but still rolled up; ear beginning to swell.
9 Ligule of flag leaf just visible.
10 Sheath of flag leaf completely grown out; ear swollen but not yet visible.
Table 2.C Heading
Stage Description
10.1 First spikelet of head just visible.
10.2 One-quarter of heading process completed.
10.3 Half of heading process completed.
10.4 Three-quarters of heading process completed.
10.5 All heads out of sheath.
Table 2.D Flowering
Stage Description
10.51 Beginning of flowering.
10.52 Flowering complete to top of head.
10.53 Flowering completed at base of head.
10.54 Flowering completed; kernel watery ripe.
Table 2.E Ripening
Stage Description
11.1 Milky ripe.
11.2 Mealy ripe; contents of kernel soft but dry. Soft dough.
11.3 Kernel hard (difficult to divide with thumbnail).
11.4 Ripe for cutting. Straw dead.