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College of Food, Agricultural, and Environmental Sciences


Cooler Weather Playing a Positive Role in Wheat Development

June 2, 2008

WOOSTER, Ohio -- Cool weather is slowing the development of Ohio's wheat crop, but lower-than-average temperatures are keeping diseases under control and may even result in bumper yields.


Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, said that wheat is behind in development by about two weeks. While the crop has flowered in southern Ohio, the remainder of the crop in some parts of central and northern Ohio has just reached heading, and it could still be another week before the crop is fully flowering.

"It's been cool by Ohio standards for this time of year. The temperatures have not been low enough to hurt the crop itself, but it has slowed development," said Paul, who also holds an Ohio State University Extension appointment. "The upside to cooler temperatures is less disease development. With the exception of powdery mildew on some susceptible varieties, we've seen few foliar diseases and the most important disease, head scab, doesn't develop well under these cooler conditions."

Head scab, also known as Fusarium head blight, is likely to occur when warm, wet weather persists during the crop's flowering stage in May and June. The disease infects the wheat heads, causing shrunken, lightweight kernels, thereby reducing the quality and feeding value of the grain. The fungus that causes the disease also produces a chemical compound in the infected grain called vomitoxin that is toxic to livestock and humans.

Paul recommends that growers refer to the Fusarium Head Blight Prediction Center ( to evaluate the potential risk of head scab development. Using such information as the flowering dates of a grower's wheat, the type of wheat planted and data from National Weather Service weather stations, the system predicts the level of risk a grower may face from head scab. Currently, head scab risk throughout the state is low.

"We are hoping that the game being played between weather, fungal development and wheat development will result in us not having a major concern in terms of scab development," said Paul. "Right now, infections will likely be low because of cooler temperatures. But we did receive quite a bit of rain the past two weeks in southern Ohio, which was perfect for spore production. If we get warmer temperatures, conditions will be ripe for infection."

The next two weeks will be critical for the wheat crop in central and northern Ohio, which has yet to complete the flowering stage.

The only foliar disease currently being reported is powdery mildew, and much of the infection is being found on the lower leaves of susceptible wheat varieties.

"For those fields in which the crop flowered before the disease reached the leaf below the flag leaf, powdery mildew should not be a concern. However, for some of the later fields that are still at early head emergence, growers should scout, and if they find the disease has spread to the leaf just below the flag leaf, then they should apply a fungicide if the variety is susceptible," said Paul. "Most of the fungicides that are effective against powdery mildew cannot be applied after full head emergence. The warmer weather forecasted for the next few days will slow down the development and spread of powdery mildew."

Not only are the cooler temperatures keeping wheat diseases at bay, but the weather conditions could also pave the way for high yields.

"Once pollination takes place, the cooler temperatures should extend the grain fill period and we should have a bumper wheat crop," said Paul. "So the weather is playing a positive role in low disease development and a longer grain fill period. I hope we have a good wheat crop and everybody's happy."

According to the Ohio Agricultural Statistics Service, 33 percent of the wheat has headed, down from 71 percent this time last year. However, 80 percent of the crop has been rated in good to excellent condition.

For further updates on Ohio's wheat crop, refer to the OSU Extension Agronomy Team Web site at


Candace Pollock
Pierce Paul