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Tips for wheat freeze damageBy D. Bruce Bosley CSU Extension agent, cropping systems Colorado Cold morning temperatures during the past couple of weeks have raised concerns over freeze damage to area wheat crops. A useful handout on wheat freeze damage has been developed by Ned Tisserat, Colorado State Extension plant pathologist, and others Wheat varieties vary in their susceptibility to freeze injury, mostly due to differences in plant growth stages. Freeze injury on winter wheat may happen at any stage of growth but low temperatures at heading or flowering growth stages are more susceptible to severe crop injury than at other growth stages. Temperatures of 30 degrees Fahrenheit lasting two hours or more at heading and flowering are enough to cause severe damage. It takes cooler temperatures of 28 degrees for two hours at boot, milk, and dough stages to cause moderate to severe damage. During jointing, temperatures may have to drop to 24 degrees or lower for two hours to damage wheat. Freeze injury can be expressed in floret sterility, white awns or whole spikes, damage to the lower stem, leaf discoloration at growth stages leading up to the flowering stage. Damaged fields often develop a rotten odor a few days after a hard freeze. Freezes from flowering growth stage on can cause shrunken, roughened, or discolored kernels, and damage to the germination potential of the wheat seed. Warm soil temperatures can create a microclimate in the wheat canopy above the soil surface that is higher than air temperatures measured in the general atmosphere. Dry soil surface conditions and fields with a high amount of previous crop residues are more at risk than fields with moist soil and no to low levels of residues. Dry soils and crop residues insulate warmer soil temperatures and reduce the warming of air immediately above the soil line. Scouting fields for freeze injury shouldn't be done until three to four days following the freeze event in order to be able to determine the extent of tissue damage. Healthy wheat heads will remain greenish; damaged heads may turn white; and severely affected heads will turn a watery tan color. It should be noted that when primary tillers are killed by frost, it is possible that undamaged secondary and tertiary tillers may be able to complete grain filling to produce a reduced but acceptable yield. Corn can also sustain freeze damage but, at this time of the year, the growing point is below the soil surface. Freeze recovery is probable even when all surface tissues look frozen. Regrowth should be examined after three to four good growing days before deciding whether to replant. Early growth corn that has been frozen off will often out yield replanted corn if the damage is restricted to the above ground plant tissues. Please contact me, Bruce Bosley about this or other cropping systems or natural resource topics at 970-522-3200 extension 285 at Sterling or 970-542-3540 at Fort Morgan. 5/26/08 Date: 5/21/08
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