Friday, April 6, 2012

Winter Wheat and Potential Freezing Weather

Chad Lee, Extension Agronomist, University of Kentucky

Recent weather forecasts include the potential for temperatures to dip into the low 30's or upper 20's (Fahrenheit) for the next couple of days. Much of the wheat around Kentucky is somewhere between the boot stage and heading, which means temperatures around 28 to 30 degrees could cause damage.

Wheat sensitivity to cold temperatures depends on the growth stage (Table 1). If a freeze event occurs, the wheat will need about a week to ten days of good growing conditions before we can assess damage. At that point, we will need to examine the developing heads for noticeable signs of damage or death, the stem for signs of girdling (which could lead to lodging) and the tillers which could produce viable heads.

Remember that Table 1 is a general guideline. If temperatures get low enough to cause damage, close monitoring of the crop is needed to determine actual damage.

Table 1. Freeze injury in wheat.*
Growth stage Feekes Zadoks Approximate injurious temp. (2 hrs)
Primary symptoms
Yield effect
Tillering** 1-5 20-29 12°F Leaf chlorosis; burning of leaf tips; silage odor; blue cast to fields Slight to moderate
Jointing6-7 31-32 24°F Death of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odor Moderate to severe
Boot 10 41-49 28°F Floret sterility; spike trapped in boot; damage to lower stem; leaf discoloration; odor Moderate to severe
Heading 10.1-.5 50-58 30°F Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration Severe
Flowering 10.51-.54 60-71 30°F Floret sterility; white awns or white spikes; damage to lower stem; leaf discoloration Severe
Milk 11.1 75 28°F White awns or white spikes; damage to lower stems; leaf discoloration; shrunken roughened or discolored kernels Moderate to severe
Dough (11.2) 11.2 85 28°F Shriveled discolored kernels; poor germination Slight to moderate
*Information in this table assumes timely rainfall events occurring after the freeze event.
**See Section 2 for more information about growth stages.
See the Section on Winterkill in the Comprehensive Guide to Wheat Management


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