March 29, 2001 | By: Laura Skillman
PRINCETON, Ky.

Cold temperatures earlier this week may have farmers worried about winter wheat crop damage.

Wheat had broken dormancy and resumed growth so there was some very young, tender tissue, said James Herbek, University of Kentucky Extension agronomist.

"It's a little early to say if we had damage," he said. "We are likely to see some burning to the leaf, but that's not a concern. The wheat plant will shoot out new leaves and resume growth, so that will not have a bearing on permanent damage."

The real concern is damage to the growing point which is the developing wheat head. If it has been killed or seriously damaged, there is a good chance the plant will not develop a head of grain.

At least three factors must come into play before freeze damage to the growing point occurs. Herbek says temperatures have to be around the mid 20s or lower to cause damage to the growing point. Temperatures dipped to those levels on March 26 and March 27 when they got down to 18 to 20 degrees in some recording areas.

The second criterion is that those temperatures must be maintained for at least two hours to cause damage. Records show that at the UK Research and Education Center in Princeton temperatures were at 24 degrees or lower for five to six hours so there was enough time for the freezing of the tissue to occur.

A third criterion is that the plant has to be at a susceptible growth stage. When it has jointed, it becomes the most susceptible. That occurs when the growing point has moved above the soil surface.

"What our saving grace may be this year is that most of the wheat had not yet jointed, so hopefully we didn't have extensive damage, at least in western Kentucky where the majority of the state's wheat is grown," he said. "The only concern may be in the southern tier of the state where wheat growth may be further along in the growth stage."

There may be some fields that have just jointed - where the growing point is at or slightly above the soil line. If it was around the soil level, the growing point probably didn't get damaged either, Herbek said.

Soil temperatures around the state are running in a temperature zone of 40 to almost 50 degrees which is probably warm enough to buffer air temperatures right at the soil line. In fields where the plant has jointed two to three inches above soil line, there may be cause for concern.

To determine damage, split the stem and use a magnifying glass to check the small growing point. If the head is glossy looking, with a white to light green color and very turgid, damage likely did not occur. If the point is cream to tan in color, flaccid and limp, and not growing anymore, it is probably killed.

Herbek notes that it is hard to tell healthy tissue from damaged tissue right away so it is best to wait seven to 10 days before checking the crop.

If a random sample of the field shows damage to 20 percent or less of the crop, it is probably not a major concern, he said. Wheat has tillers that are likely undamaged and will continue to develop into grain heads.

For more information on detecting freeze damage in wheat contact your county office of the UK Cooperative Extension Service.