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 StageApproximate injurious temp. (two hours)Primary symptomsYield effectTillering (1-5)a12°FLeaf chlorosis; burning of leaf tips; silage odor; blue cast to fieldsSlight to moderateJointing (6-7)24°FDeath of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odorModerate to severeBoot (10)28°FFloret sterility; spike trapped in boot; damage to lower stem; leaf discoloration; odorModerate to severeHeading (10.1-.5)30°FFloret sterility; white awns or white spikes; damage to lower stem; leaf discolorationSevereFlowering (10.51-.54)30°FFloret sterility; white awns or white spikes; damage to lower stem; leaf discolorationSevereMilk (11.1)28°FWhite awns or white spikes; damage to lower stems; leaf discoloration; shrunken, roughened, or discolored kernelsModerate to severeDough (11.2)28°FShriveled, discolored kernels; poor germinationSlight 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 TilleringStageDescription1One shoot (number of leaves can be added), first leaf through coleoptile.2Beginning of tillering; main shoot and one tiller.3Tillers formed; leaves often twisted spirally. Main shoot and six tillers. In some varieties of winter wheat, plant may be "creeping," or prostrate.4Beginning of the erection of the pseudo-stem; leaf sheaths beginning to lengthen.5Pseudo-stem (formed by sheaths of leaves) strongly erected.Table 2.B Stem ExtensionStageDescription6First node of stem visible at base of shoot.7Second node of stem formed; next-to-last leaf just visible.8Flag leaf (last leaf) visible but still rolled up; ear beginning to swell.9Ligule of flag leaf just visible.10Sheath of flag leaf completely grown out; ear swollen but not yet visible.Table 2.C HeadingStageDescription10.1First spikelet of head just visible.10.2One-quarter of heading process completed.10.3Half of heading process completed.10.4Three-quarters of heading process completed.10.5All heads out of sheath.Table 2.D FloweringStageDescription10.51Beginning of flowering.10.52Flowering complete to top of head.10.53Flowering completed at base of head.10.54Flowering completed; kernel watery ripe.Table 2.E RipeningStageDescription11.1Milky ripe.11.2Mealy ripe; contents of kernel soft but dry. Soft dough.11.3Kernel hard (difficult to divide with thumbnail).11.4Ripe for cutting. Straw dead.