Wheat able to withstand cold

It has been a long and very cold winter. The office has received many calls the past several weeks asking about the effects the extreme cold has had on the wheat crop.
Winter wheat is a cool-season grass that can tolerate fairly harsh weather. Wheat “hardens” in the fall to acclimate to cold conditions.
This hardening period is variety-dependent and occurs when plants are exposed to temperatures between 30 degrees and 60 degrees, followed by slowly declining soil temperatures. After hardening, wheat can tolerate temperatures between zero and 10 degrees.
The reason why wheat can survive these cold temperatures is because the growing point, cells that produce new growth, are below the soil surface until warmer conditions arrive in spring.
Extreme cold may still kill the growing point if soil temperatures drop below these critical levels. One may believe that we dropped below these critical temperatures after several days of air temperature between minus 10 and minus 20 degrees.
However, we had abundant snow cover during these periods. Snow is a great insulator. Although air temperatures were below zero, soil temperatures remained in the upper 20s to lower 30s.
Loss of stand generally occurs during the winter months from extended periods of standing water or ice on exposed plants rather than extreme cold.
The crown (lower stems) “breathes” during the winter months and does not go completely dormant, though the rate is greatly reduced with lower temperatures.
Plants covered with standing water or ice for an extended period basically suffocate, become weak and often die. Generally, these periods of standing water or ice occur during late fall before winter conditions change from rain to snow, during mid-winter thaws, or as the snow melts in late winter.
Another time that wheat stands may become damaged and lose plants is during the freeze-thaw of late winter. If a farmer planted wheat too shallow, the crowns may become pushed above the soil surface during this freeze-thaw process.
The exposed crowns and upper roots may become desiccated from drying winds, which may cause death of plants. Farmers describe plants being pushed out of the ground, exposing the roots. Agronomists call this heaving damage.
Farmers may have unwisely planted shallower last fall because of a late planting date or improper setting of the drill or planter. Wheat should be planted at 1.5 inches deep to lessen the risk of heaving damage.
Fields should be assessed this spring for loss of stand. However, fields should not be evaluated until completely green from warmer temperatures for at least 10 to 14 days. Stand evaluations will be more accurate when made during weather periods that promote growth.
Select about 10 to 15 spots in a field for evaluation. Count the number of plants per foot of row. A stand with an average of about 12 plants per foot of row should still result in a good population of head-bearing tillers per acre.
Fifteen tillers per square foot is considered the minimum for an economic crop. Yield potential will be reduced if tiller numbers fall below 25 per square foot after greenup.
The number of tillers per square foot is equal to the number of tillers in 19.2 inches of row in fields planted at 7.5-inch-wide row spacing. Ohio studies have shown that under adequate weather conditions, spring tillering may still compensate for thin stands at greenup.
Soon, wheat fields will be greening up from warmer spring temperatures. Stands should be evaluated to assess winter damage. Areas of thin stands probably occurred from periods of standing water or ice on a field rather than from extreme cold temperatures.
Lentz is extension educator for agriculture and natural resources for The Ohio State University Extension Service in Hancock County. He can be reached at 419-422-3851 or via email at lentz.38@osu.edu.
Lentz can be heard with Vaun Wickerham on weekdays at 6:35 a.m. on WFIN, at 5:43 a.m. on WKXA-FM, and at 5:28 a.m. at 106.3 The Fox.


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