Monday, May 13, 2013

Freeze Damage on Winter Wheat

Chad Lee and Jim Herbek, Extension Agronomists, University of Kentucky

The cold temperatures experienced yesterday in many areas and the cold temperatures expected tonight could damage the wheat crop. Wheat in the boot or heading stages generally needs temperatures at or below 30 F (-1.1 C) for at least two hours to cause severe damage. The Kentucky Mesonet reported lows of 45.1 F for Fulton County, 38.0 F for Graves County, 41.1 for Hopkins County, 42.7 F for Simpson County, and 39.6 F in Mercer County) for Sunday, May 12, 2013. None of these temperatures are low enough to severely damage wheat, but localized temperatures across fields may have been lower. 

Bleached wheat head exhibiting freeze

damage symptoms. Photo taken in 2012.
Usually, a week to ten days of warm, sunny weather is needed before the full extent of a freeze damage becomes evident. So, while we all want to scout fields today and tomorrow, a true assessment of freeze damage should not occur for about a week. Cool, cloudy days will slow wheat growth and slow the development of freeze symptoms.

Freeze injury in wheat.*
(From the Winterkill and Freeze Injury portion of the Comprehensive Guide to Wheat Management)
Table 3-3. 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
Jointing (6-7) 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.

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