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College of Food, Agricultural, and Environmental Sciences


Wheat and Heat Don't Mix

June 13, 2005

WOOSTER, Ohio — Wheat is a cool weather-loving plant. It doesn't respond too kindly to the heat and lately in Ohio the crop's been showing it.

Pat Lipps, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that the warmer-than-normal temperatures (as high as the lower 90s in some cases) are stressing the crop — and during a critical time of grain filling which can make or break yields.

"The wheat crop has just finished flowering. It's in its early stages of grain development and grain filling. This is an extremely critical time for kernel development and plumpness of kernels," said Lipps. "When we get to the mid-stage of ripening and we get several days of 90-degree weather, the wheat begins to shut down. Our concern is that the plant may decide to give up filling grain earlier than expected."

The stress on the crop is likely to affect yields, but by how much is still uncertain. One bright spot shines out through the situation, however.

"The good thing is that disease levels are very low. Probably in the past 20 years, I've seen disease levels this low perhaps only one other time," said Lipps. "When you have high temperatures and high levels of disease you have a worse situation. Despite the weather, with low disease levels, we think we will still have a pretty reasonable crop."

Lipps said most of the crop throughout Ohio is already suffering from the warm weather, with the plants, in some cases, ripening prematurely and the lower leaves turning brown.

"In hot weather the plant respires 24 hours a day. Whenever you have respiration, the plant is using up its carbohydrate reserves which can go to two places: either into filling the grain or to keeping the plant alive," said Lipps. "We'd like to see the plant use its reserves for grain filling, but with higher temperatures photosynthesis is not occurring very quickly, so fewer carbohydrates are being manufactured and the plant is using up what it has faster. So there is a problem with the crop being able to keep up with the higher temperatures."

Lipps said that in southern Ohio, where the crop is entering the later stages of grain development, grain filling will probably only be 14 to 16 days, down from the usual 21-day period.

"Every day of grain filling is worth between a bushel and a half and four bushels of yield, depending on the temperature," he said.

Candace Pollock
Pat Lipps