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Freeze damage update

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Amanda De Oliveira Silva

Amanda De Oliveira Silva

I have served as an Assistant Professor and Small Grains Extension Specialist at Oklahoma State University since August 2019. I believe that close interaction with producers is vital to understand their production strategies and to establish realistic research goals. My program focuses on developing science-based information to improve the agronomic and economic viability of small grains production in Oklahoma and in the Southern Great Plains.

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Amanda de Oliveira Silva, Small Grains Extension Specialist

It has been almost one month since the freeze event on April 21, and we are now obtaining a better picture of potential freeze damage on wheat fields across Oklahoma. As I have indicated, the extent of the freeze damage will depend on several factors, including the growth stage of the plants, how low the temperature will get, and how long it stays at those cold temperatures. Wheat growth stage ranged from flag leaf emergence to heads starting to or fully emerged when the freeze occurred, and number of hours and temperature varied across the state (Figure 1).

Figure 1. Hour below freezing two days after the freeze event.

Traveling around the state for plot tours these past weeks, I have seen and heard about damage ranging from minimal to quite severe. Some fields seem to be fine with only scattered damaged heads and the grain appears to be filling as expected. Other fields however, show much more significant damage with discolored and sterile heads.

At the plot tour at Chickasha on April 30, there was a mix of freeze and hail damage with several abnormally growing heads (due to head trapping). Anthers seemed to be fine at that point (Figure 2).

Figure 2. Abnormally growing wheat heads at the Chickasha variety trial on April 30.

On May 7, I checked some wheat fields around Sentinel with Gary Strickland (Jackson County Extension Educator and SW Regional Agronomist) and we observed almost no freeze damage with a few heads in the field showing a pale color and partial sterility (Figure 3). I have observed this symptom commonly in fields I have visited, and many producers have described this to me as well.  Although common, it typically has been found at a low incidence.

Figure 3. Freeze damaged heads with partial sterility and pale color near Sentinel, OK on May 7.

We observed a few spots with freeze damage while at Alva on May 12, especially in low spots of the field and on the tops of terraces. Again, relatively few spots in the field showed damage. The wheat was looking good at Alva, but really needing a rain (Figure 4).

Figure 4. Freeze damage on wheat in low spots of the field at Alva, May 12.

The most severe freeze damage that I have seen so far was yesterday near Morris in eastern OK. The heads were green but there was no grain present (i.e. sterile). Damaged heads had glumes with a chocolate discoloration, which is similar to the discoloration caused by the bacterial disease called black chaff. In some cases, Dr. Hunger and I felt these discolored heads were the result of this bacterial disease but that the majority of the heads showing these symptoms were the result of freeze damage (Figure 5).

Figure 5. Freeze damaged heads without grains inside and showing a chocolate color on the outside (top photos). Heads showing no freeze damage and black chaff bacterial disease (bottom photos).

At the plot tour at El Reno today, we also observed a few varieties with pale colored and “empty” heads due to the freeze (Figure 6). We observed more freeze damage on wheat that was planted earlier and grazed as compared to the grain-only (ungrazed) wheat in that same field. Another noteworthy item is related to my earlier observation that the February freeze hurt some of the varieties in the dual-purpose plots by severely reducing tillering that would cause a loss of stand. That observation in those varieties was confirmed as the stand loss was quite evident today.

Figure 6. Wheat at El Reno. Same variety under grain-only (left) and dual-purpose (right) systems.

In conclusion, the freeze damage I am seeing is variable within and across fields, but overall I would say is minimal in most of the state. However, continue to keep scouting as it will now be easier to identify freeze damage.

Please let me know what you are seeing out there! My email is silvaa@okstate.edu.

Also, contact your County Extension office for more information.


3 Comments

  1. Doug Hisken says:

    Hi, How much of a threat do we have if we are just now seeing stripe rust show up. Can the crop out run it until harvest? Southern Sedgwick Co Ks.

    Sent from my iPad

    >

    • Amanda De Oliveira Silva says:

      Hi Doug, that will depend on the susceptibility of the variety to stripe rust and the stage of the wheat. What stage is your wheat now? If it is already flowering, the crop will out run it until harvest and we would hope for stripe rust to start shutting down. Also if the wheat is flowering, it would be too late to spray due to harvest interval of most fungicide products.
      Thanks for the question! Feel free to reach out to me via email (silvaa@okstate.edu) or Dr. Hunger the OSU Wheat Extension Pathologist (bob.hunger@okstate.edu) if you have any other questions.

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