Freeze-Damaged Wheat? Too Early to Tell

Wheat crop could be okay; first-cutting alfalfa may lose tonnage.

Freezing temperatures in much of Kansas Tuesday and Wednesday nights have farmers fearing the worst for a 2007 wheat crop that shows a great deal of promise.

At Kansas State University agronomy experiment stations near Scandia, Colby and Tribune, temperatures dipped to 25 degrees Wednesday night, according to the Kansas State University Weather Data Library. In Garden City, Hays, Rossville and Ottawa, temps plummeted to 28 degrees. The WDL data is online at: www.oznet.ksu.edu/wdl/  

The question is, just what is the effect of below-freezing temperatures on the winter wheat crop?

"We don't know," says Barney Gordon, agronomist in-charge at K-State's Belleville and Scandia experiment stations. "It's green, actively growing and it will take a fairly low temperature to affect that.

"We do think that the first cutting of alfalfa will lose a lot of leaf tissue and may be hurt pretty badly," Gordon says. "The cold temperatures didn't hurt the alfalfa crown roots, so it will come out of it. But that first cutting may be toast."

Back to wheat, which Gordon admits is very unpredictable: "We know that it's not dead, and it can come back from cold temperatures," he explains. "Right now, we'll have to wait and see. I don't think there is major damage here. Further south, where the wheat is farther along, there may be more cause for concern."

Keith Janssen, agronomist in charge at the Ottawa Experiment Field, says there may be some leaf burn, but yield potential should not be impacted. "The crop is farther along than normal, but still not to a stage that the cold weather will be hurt yet."

This year's crop has progressed faster than normal, due to higher than normal temperatures this spring. This, coupled with a general soaking rainfall the last week of March throughout much of the state, has resulted in much more spring growth than usual.

According to the Kansas Agriculture Statistics weekly Crop Weather report issued April 2, 46% of the state's wheat crop has jointed, well ahead of the five-year norm of 19%.

When wheat reaches the jointing stage, moderate to severe yield losses can occur when the temperature dips to 24 degrees for two hours, based on Kansas State University's "Spring Freeze Injury to Winter Wheat" report, on the Web at www.oznet.ksu.edu/library/crpsl2/C646.pdf  

Keep in mind, however, that temperatures at the soil surface typically are a few degrees warmer than the ambient temperature recorded at the agronomy fields.

So, where do you go from here?

Begin scouting, suggests Jim Shroyer, extension agronomist at K-State. If the crop is freeze-damaged, symptoms will show up when the temperature reaches 60 to 70 degrees fairly regularly.

Pay close attention to the growing point, which is just above the uppermost node. Split the wheat stem longitudinally with a sharp blade. A normal, uninjured growing point is bright white to yellow-green and turgid; freeze injury causes it to become off-white or brown and water soaked in appearance. This injury can exist even in plants that appear otherwise normal because the growing point is more sensitive to cold than are other plant parts.

Damaged tillers remain green, but growth of stems in which the growing points are injured stops immediately. A chlorotic, or dead leaf may appear in the whorl, indicating that the growing point is dead. Growth from later uninjured tillers may obscure damage.

Partial injury at this stage may cause a mixture of normal tillers and late tillers and result in uneven maturity and some decrease in grain yield. Injury to the lower stems in the form of discoloration, roughness, lesions, and enlargement of nodes frequently occurs at the jointing stage and the following stages after freezing. Injured plants often break over at the affected areas of the lower stem so that one or two internodes are parallel to the soil surface.

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