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Spring Freeze Injury to Wheat
5/18/2004
Ron F. Meyer
Area Extension Agent
(Agronomy)
Colorado State University Extension
Golden Plains
Area |
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Freeze injury can cause crop losses through reduced leaf area,
weakened stems and lodging, sterility, uneven maturity, and shriveled
kernels. However, the severity of freeze injury and resulting crop losses
are quite variable. Crop growth stages become progressively more cold
tolerant through winter dormancy and increasingly freeze susceptible from
spring regrowth through flowering. Heading and flowering are the most
vulnerable stages. Crop condition is also important, with lush, rapidly
growing plants more susceptible than drought stressed plants. Plants
located in low parts of the field and other areas where cold air tends to
accumulate also are more at risk. Wind, precipitation and adequate soil
moisture also can reduce the amount of freeze damage to
wheat.
Growth stage yield responses to freezing*
temperatures.
|
Reductions in
Yield |
Growth
Stages |
|
Slight to Moderate |
Tillering |
|
Moderate to Severe |
Jointing, Boot, Milk |
|
Severe |
Heading, Flowering |
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* Losses generally occur following two or more hours
of temperatures below 24° - 30°F, depending on growth stage.
Wheat plants in the tillering stage can tolerate temperatures as low as
12°F for two hours without damage. |
The temperature
reached and the amount of time the crop is exposed to that temperature are key
determinants of freeze injury. Predicting crop loss from observed
temperatures is difficult because crop response is so variable.
Generally, two hours of exposure to temperatures in the 24-30°F range will
damage plants that are beyond the tillering growth stage. Keep in mind
that temperatures reported at official weather stations are taken several feet
above the soil surface and may be quite different from those the crop was
exposed to during the same time period. This is due to the transfer of
stored heat within soil to the air immediately above the ground surface.
However, soil surfaces that are dry or insulated with large amounts of crop
residues have reduced heat exchange to the air near the surface.
Consequently, freeze injury can be more severe with these field
conditions.
Freeze damage symptoms vary with the plant part and with the
severity of the injury. Freeze damaged leaves show tip burn and yellowing
a few days after the freeze event. More severe symptoms include
completely yellow-to-grey, limp leaves and a detectable silage odor.
Injured stems may be discolored, show lesions, or have swollen nodes.
Severely injured stems may be split and lodge easily.
Freeze injury
during flowering kills anthers, resulting in sterility. Freeze damaged
heads will turn partly to completely white within one week of the freeze.
White portions of the head will not produce seed.
Options for freeze
damaged wheat include:
* Harvesting the crop for grain if it is only
partially damaged. Lodging and shattering may be problems and test weight
may be reduced. However, freeze damaged grain does make good cattle
feed.
* Freeze damaged wheat can be cut before soft dough stage to make
good quality hay or ensilage. Nitrate content should be checked. If
the crop is cut after heading, then animals should be monitored for big jaw or
lumpy jaw, a condition caused when awns injure mouth tissues.
* The
damaged crop could be abandoned, the field fallowed and this year’s summer
fallow ground planted to a spring crop. This option may be limited by
herbicide plantback restrictions and by available soil moisture. Compare
expected returns from the summer crop to those from harvesting the wheat crop
for grain to decide which makes more economic sense.
|
Temperatures causing wheat freeze
injury and symptoms |
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GROWTH STAGE |
|
2 HOUR TEMPERATURE |
|
YIELD EFFECT |
|
PRIMARY SYMPTOMS |
|
Tillering |
|
12°F* |
|
Slight-Moderate |
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Leaf
chlorosis; burned leaf tips; odor; bluish cast |
|
Jointing |
|
24°F |
|
Moderate-Severe |
|
Death of
growing point: leaf yellowing or burn: lesions, splitting or
bending of lower stem, odor |
|
Boot
|
|
28°F |
|
Moderate-Severe |
|
Floret
sterility; head-trapped in boot; lower stem damage; leaf discoloration;
odor |
|
Heading
|
|
30°F |
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Severe
|
|
Floret
sterility; white awns or heads; lower stem damage; leaf discoloration |
|
Flowering |
|
30°F |
|
Severe
|
|
Floret
sterility; white awns or heads; lower stem damage; leaf discoloration |
|
Milk
Stage |
|
28°F |
|
Moderate-Severe |
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White awns
or heads; lower stem damage; leaf discoloration; shrunken, roughened or
discolored kernels |
|
Dough
Stage |
|
28°F |
|
Slight-Moderate |
|
Shriveled,
discolored kernels; poor seed germination |
|
* 3-5
degrees for certain very winter hardy varieties. |
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Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
5/24/2004 |
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Colorado
State University, U.S. Department of Agriculture, Kit Carson, Phillips,
Washington and Yuma counties cooperating. Extension programs are
available to all without discrimination. Where trade names are used, no
discrimination is intended and no endorsement by Colorado State University
Extension is implied. |
