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C.O.R.N
Newsletter
2007-08
April 10, 2007 -
April 16, 2007
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What Will Cold Temperatures Do To Our Wheat?
by
Pierce Paul, Jim Beuerlein, Dennis Mills
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Over the last few days, average temperatures have dropped considerably, with lows between 20 and 29F and highs between 34 and 40F. The wheat in now greening up across most of the state, but in some southern counties, early planted wheat is already jointing. Growers, especially in southern Ohio, are concerned that the cold temperatures may have damaged their crop. Whether or not the crop is damaged by cold spring temperatures and the extent of the damage depend on three main conditions: 1) how cold it gets, 2) the length of time the crop is exposed to the cold temperatures and 3) the growth stage of the crop at the time of exposure. Freezing temperatures are most damaging when the crop is at more advanced stages of development. Once it warms up in the spring and the wheat starts to grow, it looses its cold-temperature hardiness, making it more prone to injury from freezes. Such injuries are most severe when freezing temperatures occur during boot and heading growth stages.
We have certainly had extended periods of temperatures below freezing over the past 5 days or so, however, at our current growth stage (tillering to jointing), freeze injuries will likely be less than they would have been if we were at boot or heading. Based on information coming out of a Kansas State University publication http://wheat.colostate.edu/freeze.pdf temperatures below 12 F are injurious during tillering, where as, during jointing 2 hours of exposure to 24 F may be injurious. At these growth stages, injuries tend to be greatest if the wheat is lush and actively growing (especially after spring nitrogen application) and are more common in low areas of the field.
Frost injury during tillering appear as light green to yellow discoloration (burning) of the tips of the leaves (early symptoms may be confused with those caused by some viruses and nutrient deficiency). Although these injuries may reduce tiller numbers, at this early growth stage, the wheat crop still has time to recover and produce new leaves and tillers once it warms up. In addition, since the growing points are still close to the soil line, they are protecting from cold temperatures injury.
Once the wheat starts to joint, which may be the case in some southern counties, the growing point is no longer protected by the soil, but is somewhat protected by the vegetation and its nearness to the soil surface. Also wheat is a cool season crop and can tolerate temperatures well below freezing. In addition to discolored leaf tips, the growing point of injured plants will become brownish, with a water soaked appearance. To assess the extent of the injury, remove the leaves, split the stem longitudinally (lengthwise), and examine the growing point, which is located above the uppermost node. Examine both main and secondary tillers from different areas of the field and determine the average number of healthy and injured tillers per foot of row. A healthy growing point is usually white to yellowish-green in color as opposed to off-white or brown. When the growing point is severely damaged, growth of the affected stem stops, even on healthy-looking plants. In extreme cases, the leaves in the whorl die and the affected tiller may not produce a head, however, secondary tillers may remain unaffected and should develop normally and produce grain.
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C.O.R.N. is a summary of crop observations, related
information, and appropriate recommendations for Ohio
Crop Producers and Industry. C.O.R.N. is produced by
the Ohio State University Extension Agronomy Team, State
Specialists at The Ohio State University and Ohio Agricultural
Research and Development Center. C.O.R.N. Questions
are directed to State Specialists, Extension Associates,
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and the Ohio Agricultural Research and Development Center
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Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in
cooperation with the U.S. Department of Agriculture,
Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800)
589-8292 (Ohio only) or (614) 292-1868
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