Written by Brandon Gerrish, Ph.D., AgriLife Small Grains Extension Specialist
Freezing Temperatures Experienced Across Texas
Recent freezing conditions have led to some concern of winterkill in Texas wheat fields. Temperatures dipped under 0°F in the northern Panhandle and below freezing as far south as Corpus Christi. Freeze damage in wheat is dependent on several factors and severity can range from minor leaf tip burn to plant death. After several days of warm temperatures, now is a good time for wheat farmers to be checking fields for damage.
What Main Factors Affect Freeze Damage Severity in Wheat?
1. Temperature and Duration
How low temperatures descend as well as the duration of low temperatures are two contributing factors. In general, plant parts need at least two hours of freezing conditions before injury occurs. The colder it gets and longer it persists, the more potential there is for plant damage.
2. Wheat Growth Stage
The stage of growth is a major contributing factor. During the period shortly after emergence, wheat has some potential for freeze damage but quickly becomes more tolerant as the plant develops and begins to tiller. As colder weather sets in during the fall and winter, wheat in most of the state will enter dormancy and during this period it is most resistant to freeze damage. However, as temperatures rise in late winter and early spring, wheat breaks dormancy and shortly after will begin the process of transitioning from vegetative growth to reproductive growth (grain head development). After this transitioning phase begins, wheat becomes increasingly sensitive to freezing temperatures. Wheat is most sensitive during the flowering stage, at which point even a short period of freezing temperatures can result in severe yield losses.
3. Soil Moisture or Snow Cover
Conditions that help to insulate plants, such as snow cover or soil with higher water content, can help to reduce freeze damage. Cold temperatures can more easily penetrate to the wheat growing point without these forms of insulation.
4. Genetics
The genetic components of plants, both within and across plant species, will affect winter hardiness. Most winter wheat varieties grown in Texas provide enough winter hardiness to endure freezing conditions during dormancy. While differences in the level of leaf burn across winter wheat varieties have likely been observed across the state this past week, severely damaged wheat is more likely due to advanced growth stages or other cultural practices rather than variety selection. However, differences among small grain species vary widely as wheat and triticale generally offer better tolerance to freeze damage than others such as oats.
How to Evaluate Freeze Damage
Wheat is a resilient crop and growers should not easily give up on it. It is possible that even wheat with severe foliar damage, such as in the photo above, may still be alive. Prior to checking fields, it is important to allow some time for freeze damage symptoms to develop. Allowing several days of warmer temperatures will make it easier to identify dead tissue. Properly checking plant viability requires dissecting plant stems and checking the growing point. To do this, growers will need a sharp knife or razor blade and possibly a small shovel to dig up plants. Feeling for a slight bulge in the stem, likely near the base of the plant, and carefully cutting into the stem at that point will reveal the growing point as shown in the image below.
Growing points that appear green are likely healthy and will begin to regrow with warmer temperatures assuming adequate moisture and nutrients are available. Growing points that appear yellow or brown are likely dead and will not regrow. Plants with growing points that are pale green or white may be partially damaged. Allow another day or two and recheck fields in these situations.
As most wheat across the state was still in dormancy or younger vegetative growth stages during the past week, widespread damage resulting in plant death is unlikely. The potential for severe damage will continue increasing with any freeze events during the next 4-8 weeks.
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