By Jason Kelley, Wheat and Feed Grains Agronomist
On the morning of April 8thmuch of the state had a frost/freeze with temperatures at or near freezing to as low as 25 degrees F in localized areas. Approximately 20% of the state’s wheat was in the process of heading on April 8thwith a majority of wheat in South Arkansas in the Mid –late boot stage depending on variety and location. Wheat in Northeast Arkansas was less developed with the flag leaf emerging at early boot. Fortunately these growth stages would be approximately 10-14 days behind last year’s growth for this date, but near the long term average.
Estimated temperatures and duration to cause damage are listed below:
Diagnosing Damage: It will take several days before we can begin to determine the extent (if any) of freeze damage. Temperatures are forecast to be warm which will speed growth and make accessing damage easier. Lower stem damage (soft, broken over stems) and damaged heads are two areas to evaluate. Below is a description of several types of freeze damage that we may see if temperatures were indeed low enough to cause damage (hopefully they were not).
Leaf burn is the most common and most easily recognizable injury symptom that may be seen (Figure 1 below). The leaf burn in the photo was from an area where the temperature dropped to approximately 27 degrees F in 2017. Leaf burn itself should be considered cosmetic injury, but it does indicate that temperatures were cold enough to potentially cause other forms of damage including head and stem damage and further investigation is needed to verify any damage.
Damage to the developing head is also something to look for in the coming days to weeks. Figure 2 (Photo by Chris Elkins, Poinsett Co. in 2017) shows a white and dead head on an otherwise healthy looking plant. In this instance, temperatures were cold enough to freeze the small developing head and killed it, even though the plant itself looks healthy.
Stem damage is another form of damage that could be seen. Temperatures may have been cold enough in some areas to cause stem damage. Stem damage can be found in several forms, but a soft, rubbery or flat spot on the stem typically between the first and second or second and third nodes is often seen. The photo in Figure 3 shows a stem that is soft and rubbery and the tiller will eventually die. Non-lethal stem damage that does not kill the tiller and head may cause the stem and or nodes to be brittle and could increase lodging potential later in the season near harvest.
On wheat that was heading or flowering, damage to the flowers can occur. The head for the most part does not show damage, but closer examination shows that the flower portion in the head was damaged. Anthers should be a light green color prior to emerging. If anthers are white or a light brown prior to emergence, the anther was likely killed and the floret will be sterile, Figure 4.
I think overall given the stage of the wheat and the temperatures, freeze damage should be limited, but keep in mind reported temperatures for a given area may or may not be consistent with temperatures in the field. As with any freeze damage it will take several days or weeks to determine the full extent of any injury that may have occurred.
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