Winter wheat has so many joking epithets about its ability to survive adverse conditions that this characteristic is taken for granted. However, if conditions are right -- usually, if the combination of crop stage and cold temperatures comes together -- then some major damage to even this crop is possible.
Such a combination indeed is what we had this past weekend, the Palm Sunday weekend of March 19-20, 2016. Overnight low temperatures Saturday and Sunday plummeted into the hard-freeze category of the upper teens to low 20s Fahrenheit (-7.8 to -5.6 deg Celsius) in a large portion of the Southern Plains. The area with this kind of cold included the southwestern crop district of Kansas, and almost all of central and western Oklahoma. I mention these two locales specifically because of the progress stage of the winter wheat crop. In southwestern Kansas, the winter wheat crop was assessed at 10 percent jointed during the weekend of Sunday, March 13. In that same time frame, 10 percent of the entire Oklahoma wheat crop was listed as being in the joint stage. Jointing is the first definite stage in the wheat plant's development after it exits dormancy.
And that's where the significance of this past weekend's cold spell comes into play. Very mild February and early March temperatures caused wheat to move out of dormancy and into spring development on the way to harvest. In many areas, this post-dormancy activity occurred around two weeks ahead of normal.
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With that move to jointing, winter wheat starts losing its tolerance to cold weather. When the wheat is dormant, even bitter-cold temperatures of as much as 10 below zero Fahrenheit (-23 Celsius). Even after dormancy, when the plant is sending out the auxiliary tillers, the wheat plant can withstand temperatures as low as +12 F (-11 C) with no significant damage. From the joint phase on, however, that resilience drops off notably as the plant moves more into the actual grain production sequence. And, when the wheat plant is jointing, a mere 24 degrees F (-4.4 C) for a couple hours is all it takes to produce the following damage: death of the growing point; leaf yellowing or burning; lesions, splitting, or bending of the lower stem; odor. The extent of damage that is possible is termed "Moderate" to "Severe."
That kind of cold indeed happened, as we noted. And, Monday morning, numerous social media comments referred to a "silage smell" when somebody was walking around a wheat field -- the pungent aroma of frozen wheat. (It's the same olfactory sensation that a hailed-out cornfield has. I've experienced both along with the "real McCoy of silage.")
From here, it's the usual round of checking for a couple weeks -- wait and see -- before a definite evaluation can be made. Nonetheless, Palm Sunday weekend 2016 may be recorded as a weekend when the Southern Plains wheat crop sustained a major round of freeze damage.
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