June 20 (Bloomberg) -- Wheat may rise on speculation that diseases caused by wet weather will curb yields of the winter crop being harvested in the U.S.

Head scab, a fungal disease that can attacks plants late in the growing season, may cause losses as high as 70 percent in some parts of eastern Kansas, a report from Kansas State University said. Wheat prices have climbed 18 percent this month, partly on concern excessive rain will delay the harvest.

``When it warms up, that creates humidity under the leaves, and diseases can proliferate,'' said Vince Boddicker, a manager of Farmers Trading Co. in Mitchell, South Dakota. ``Scab can be found right at the end if the conditions are right. If you don't get it taken care of early, the head won't produce anything.''

Wheat futures for September delivery fell 0.5 cent to $8.9825 a bushel in overnight trading on the Chicago Board of Trade. The price has climbed 48 percent in the past year, reaching a record $13.495 on Feb. 27.

Wheat is the fourth-biggest U.S. crop, valued at $13.7 billion last year, behind corn, soybeans and hay, according to government data. Kansas is the biggest winter-wheat producing state.

To contact the reporter on this story: Tony C. Dreibus in Chicago at Tdreibus@bloomberg.net.

Last Updated: June 20, 2008 10:00 EDT