Soft red winter wheat futures at the Chicago Board of Trade closed lower on Thursday on spill-over selling from a sharp drop in corn and soya, traders said.
China's switch of an order for US soft red winter wheat to hard spring wheat also pressured futures, they said.
CBOT wheat closed 1 to 4-3/4 cents per bushel lower, with May down 4-1/2 at $3.94-1/2. July was down 4-3/4 at $4.03-1/4.
The weakness in wheat futures surfaced despite earlier supportive news from USDA's weekly export sales report which showed US wheat exports last week at 402,700 tonnes for old crop and new crop combined, above estimates for 200,000 to 350,000 tonnes. Shipments of 751,100 tonnes were a third over the four-week average.
But the data also showed that China last week switched an order for 50,000 tonnes of soft red winter wheat to hard spring wheat.
Weather worries also were helping underpin prices but most of that support was in the Kansas City Board of Trade hard red winter wheat market.
KCBT July gained 4 cents on CBOT July Thursday.
"A glut of soft red winter and a shortage of high protein wheat keeps Kansas City gaining on Chicago," a wheat trader said.
Estimated volume was modest at 22,564 futures and 4,982 options.
Meteorlogix weather early Thursday said extremely hot weather this week in the US Plains hard red winter wheat region was probably harming the crop in its critical heading and flowering stage of development.
The hottest and driest weather is in Kansas, the No 1 HRW wheat producer in the United States.
Background support stems from talk that China may be in the market for up to 3 million tonnes of wheat from the United States, Australia and Canada. And wheat traders hoped to land some wheat business for Iraq that had been thought to be going to Australia.
The delivery market also remains supportive to nearby May. No wheat was posted on Thursday for delivery against the May contract.
Technical support in the July contract at $4.05-1/2 per bushel was broken, driving the contract to a session low of $4.01. The nine-day moving average for July stood at 69 prior to the open on Thursday. Chartists view an RSI of 30 or less as an oversold market and 70 or more as an overbought market.