Dr. Calvin Trostle, Extension Agronomy, TAMU Dept. of Soil & Crop Sciences, Lubbock, (806) 746-6101, ctrostle@ag.tamu.edu

Dr. Fernando Guillen-Portal, State Extension Small Grains Specialist, TAMU Dept. of Soil & Crop Sciences, College Station, (979) 845-4826, fernando.guillen@tamu.edu

February 26, 2021

The cold temperatures in Texas in February’s cold snap range from as low as -12° F in the Panhandle to mid-single digits as far south as the Austin region.  A few locations in Texas set all-time low records (Tyler, TX for one).  Lubbock recorded -6° F, only the third time below 0° F since 1980, and the coldest since 1963.  Furthermore, the temperature was below freezing for a full seven days at Lubbock (and much of that below 10° F, allowing temperatures to potentially penetrate any canopy and into the ground.

Below are key points about this pronounced freeze on Texas wheat and other small grains.  Our key points about the effects on the recent freeze on growth and development in wheat are taken from Texas A&M AgriLife’s “Wheat Freeze Injury in Texas” document at http://wheatfreezeinjury.tamu.edu This document comments on the conditions and effects of prolonged freeze on wheat in the tillering stage and at other stages of growth.

The Texas wheat crop in South Texas and possibly into Central Texas (especially for early maturity varieties) was possibly at some stage of growth of jointing.  We believe this wheat was the most susceptible to injury as the growing point would be at or above the soil surface.  You can best tell by looking for hollow stems.  If you find a hollow stem, then the growing point is above the hollow area.

Other small grains in Texas are also susceptible to the freezing conditions.  Rye and triticale, however, are generally more cold tolerant than wheat, but oats and barley less so.

Key Considerations

• Temperatures were below freezing over much of Texas wheat for 6-7 days.
• We know of no wheat in the Texas High Plains that was close to jointing at the onset of the freeze. Probably not in the Rolling Plains either.  So, this lessens injury potential.  South, Central, and possibly Northeast Texas might have some wheat that was beyond the tillering stage (jointing, or further development).
• Essentially all wheat varieties in the Texas High Plains and Texas Rolling Plains are grown several hundred miles to the north, so they do have cold tolerance.
• The fact that it had been so warm might make wheat more susceptible to freeze. For example, it was tied a record high of 80° F in Lubbock on Super Bowl Sunday (Feb. 7).
• If you received some snow in the early part of the freeze, if it is not blown off the field then that can help protect the wheat. This is common cold protection for winter wheat in the Central Great Plains.  This protection is good, and there is moisture for the wheat crop when it warms up.

• Additional comments from “Wheat Freeze Injury in Texas” on the conditions and effects of prolonged freeze on wheat in the tillering stage. These include:
  • The document suggests temperatures below 12° F for at least two hours could cause some damage (leaf yellowing, leaf tip and leaf tip burn, silage odor, bluish color). These symptoms have only slight to moderate impact on yield.  We do not think 12° F is that important as much winter wheat in the Texas High Plains is well below this temperature in different years.
  • Low temperature and its duration, soil moisture, and wind can influence injury potential. Soils that are very dry enable the cold to penetrate further into the soil to the crown.  This is more likely in the droughted areas of Texas, especially in the High Plains region where the Drought Monitor shows some extreme and exceptional drought (http://droughtmonitor.unl.edu).  If soil moisture is high then the foliage likely has a high moisture content and is more susceptible to freeze damage.  So, for Texas, which factor in the recent freeze was more important.  For North Texas, the Rolling Plains, the High Plains, and possibly the Concho Valley, the importance of the growing point—still below the soil surface—is much more important than possible loss of leaves due to freeze and burn.
  • Leaf burn usually does not have a great impact on yield potential at the current stage of growth for most Texas wheat. The plants will develop new leaves.  This may be less so for wheat in South Texas.  But even there, if much of the foliage is lost, and even a few growing points, the wheat can compensate with new tillers.  Inspect the base of the wheat plant (crown) below the soil line.  If it is turgid and green, there is no reason for concern.
• An aspect of major concern in the northern and High Plains part of the state is drought-stressed wheat that is being grazed. Grubbing the wheat down too much will curtail its ability to recover if moisture becomes available.  This is a case of “less is more.”  Less grazing—hopefully, cattle can be moved off the wheat for a couple of weeks (do you have a place to go with them?), then return after moisture and jointing to catch the burst of early spring growth.

Regional Updates

Central Texas—Tyler Mays, AgriLife Extension Agent-IPM, Hill & McLennan Counties, tyler.mays@ag.tamu.edu

Winter storm Uri hit the Central Texas area with severe cold temperatures.  Some areas in the region got as low as -2°F degrees.  Thus, I anticipated severe freeze damage in wheat. Field scoutings in wheat fields in Hill County and northern McLennan Counties showed a varying degree of damage from negligible to severe leaf burn and growing point injury. The snow received in the area early in the storm along with most producers having finished N topdressing the week before the storm prevented further damage. An assessment on the degree of injury at the growing point of the plant indicated only 10% of plants with growing point damage (Figs. 1 & 2).  Scouting one 1,700-acre fields of wheat indicated

• 79% of acres suffered minor damage with just the tips of the upper leaves being burned.
• 15% suffered severe leaf burn but no damage to the growing points.
• 6% suffered severe leaf burn with some growing point damage.

Figure 1. Effect of freezing temperatures observed during Uri storm on growing point in the plant. Healthy (A) and (B) dead growing point.

Figure 2. Overall view of leaf burn damaged cause by the freezing front. Hard red winter wheat variety “WB Cedar” (A), Soft red winter wheat variety “TA8861” (B).

Central Texas—Dr. Fernando Guillen-Portal

Winter wheat fields around College Station were exposed to freezing temperatures during the period of February 12 to February 19 (average of 26 °F).  Minimum temperatures within that period ranged from 6 °F to 30 °F.  Freezing conditions caused leaf burn damage in the crop to a varying degree.  Given that wheat was still at the vegetative stage and was covered by at least 4 inches of snow on Feb 10, freeze damage might not be of significance.  Preliminary observations at 10 days after the freeze on a winter wheat variety test at the TAMU Farm Lab (College Station) indicated a varying degree of sensitivity to leaf burn damage among varieties (Tables 1 & 2, Figure 3). It is likely these differences in leaf damage relate to differences in variety growth rate, the most affected ones being the early maturity.  Overall, early observations suggest levels of damage caused by this unprecedented freezing front on wheat in South Texas was minimal.

Table 1.  Leaf burn damage caused by freezing temperatures in hard red winter wheat genotypes at the TAMU farm near College Station, TX (Feb 24, 2021).

^†Oklahoma State University.

Table 2.  Leaf burn damage caused by freezing temperatures in soft red winter wheat genotypes at the TAMU farm near College Station, TX (Feb 24, 2021).

Figure 3. Varying leaf burn damage observed Feb 24, 2021 in a field trial including hard red and soft red winter wheat genotypes planted Nov 11, 2021 at the College Station Farm Lab.

Northeast Texas—Dr. David Drake, AgriLife Extension Agent-IPM, Hunt County, david.drake@ag.tamu.edu

Temperatures have returned to normal and the snow melted.  A common question:   “Are my fall planted crops damaged?”  The short answer is probably not.  There was a gradual hardening off by low temperatures.  During the coldest temperatures (-1 or -2 F°) there was an insulating blanket of snow.  Lastly the wheat and other small grains should have still been in the vegetative stage where they are more cold tolerant.  Some oat plants that are less winter hardy have freeze-burned leaves, but the crowns are still green (Fig. 4).  Annual ryegrass, barley, wheat, triticale, and cereal rye all should be fine. The more cold tolerant species are listed last.

South Plains—Dr. Calvin Trostle

Wheat appears to not have been significantly damaged.  The leaf burn observed is typical during winter (Fig. 5).  On the fields I looked at no more than 20% of leaf matter has been lost to freeze burn.  All wheat appears fine at the crown.  Some fields are showing “pseudo” stems, which are rolled leaves.  This is a precursor to jointing and the hollow stem stage (Fig. 6).  Once the first few hollow stems appear, if cattle are grazing but grain harvest is planned then cattle need to be removed.  Most of the

wheat is at Feekes 4 growth stage (beginning of erect growth).  For Feekes growth stages, see https://wheatfreezeinjury.tamu.edu/files/Growth%20Stages%20of%20Wheat.pdf  The growing point is below the soil surface and insulated from the coldest temperatures.

Figure 4. Wheat partially insulated by snow, left; oats with upper leaves damaged by cold temperatures but plant tissue in the center above the crown is still green, right.  (Hunt Co., Texas, Feb. 2021)

Figure 5.  Modest leaf burn of Nov. 8 planted wheat, Lubbock Co. (left).  Some leaves have curled and are dried out.  The core of the plant at the soil line is green and undamaged.  Dryland field with light leaf burn but otherwise healthy.

Figure 6.  More advanced dryland wheat growth showing a ‘pseudo’ stem, which consists of rolled leaves.  This is not jointing though it may be a week or so away (Lubbock Co.).

Panhandle—Dr. Jourdan Bell, Extension Agronomist, Amarillo, Jourdan.bell@ag.tamu.edu

I have checked wheat at Bushland Research Farm.  Fortunately, wheat is at only Feekes 4 to Feekes 5 (strong erect growth, presence of pseudo stems) so it was less susceptible to freeze injury than if it was at a more mature growth stage.  We do have leaf burn, but the crown looks good.  However, dryland and grazed fields in the Bushland area exhibit greater injury as noted for the South Plains. Essentially if the wheat condition was poor prior to freezing temperatures, drought stress and over grazing compounded freeze injury.  Fortunately, the snow was received before we dropped to subzero temperatures as low as -15°F.  The snow stabilized soil temperatures (Fig. 7) and provided a blanket that protected the wheat from subzero air temperatures.  It is amazing that although during and after the lowest air temperatures, soil temperature at the 2” depth never dropped below 34°F.

Figure 7.  Soil temperatures at the 2” depth at the Texas A&M AgriLife Research Farm, Bushland, TX remained above freezing during the entire winter blast from Feb. 13 to Feb. 21.  This protected wheat crowns.  The lowest air temperature was -15°F the morning of Feb. 15.  Once snow fell the 2” soil temperature rose 2 degrees.