U.S. wheat futures are expected to start weaker Wednesday under pressure from the rising U.S. dollar.

Traders predict soft, red winter wheat for September delivery, the most actively traded contract, will start down 8 cents to 10 cents a bushel at the Chicago Board of Trade. In overnight electronic trading, the contract lost 9 1/2 cents, or 1.5%, to $6.26 a bushel.

Strength in the dollar is weighing on prices as it makes U.S. farm goods less attractive to foreign buyers, traders said. Wheat is expected to drop in early trading along with corn and soybeans.

"Strength in the dollar could slow sales from the U.S.," wrote analysts at Doane Advisory Services, an agricultural advisory firm in St. Louis.

Traders are keeping a close eye on demand for U.S. wheat as countries in the Black Sea region are poised to increase exports after limiting grain sales during the past year following a devastating drought. Increased competition for export business from Russia and Ukraine, along with strength in the U.S. dollar, could reduce demand for U.S. wheat.

Concerns about demand are rising as harvest is rolling across the Northern Hemisphere, bringing fresh supplies in from the fields. In the U.S., the winter-wheat harvest was 56% complete as of Sunday, above the five-year average of 52% for that time of year, according to federal data issued Tuesday.

As for spring wheat, which is grown in the northern U.S. Plains and will be harvested in late summer and autumn, crop conditions are improving. The U.S. Department of Agriculture rated 70% of the crop as good to excellent, up one percentage point from a week earlier. Yet, development remains slow due to late planting and soggy conditions. The USDA said 13% of the spring wheat crop was in the headed stage of development, well below the five-year average of 52%.