(Updates U.S. market activity to close)
By Michael Hirtzer
CHICAGO, July 28 (Reuters) - U.S. corn and soybean futures eased on Thursday, pressured by ample existing supplies and largely favorable growing conditions that will likely lead to huge harvests this autumn, traders and analysts said.
Chicago Board of Trade corn futures led the declines, with technical selling weighing further after prices failed to rise above their 10-day moving average.
CBOT December corn futures settled 4-1/4 cents lower at $3.38-3/4 per bushel. Prices trimmed their losses late in the session but the declines of roughly 1 percent were biggest in a week. CBOT November soybeans finished down 8 cents at $9.78, after rising the past two sessions.
U.S. Department of Agriculture weekly U.S. export sales for the current marketing season of a negative 1,400 tonnes of soybeans were below expectations for sales of 250,000 to 450,000 tonnes. Export sales of 438,800 tonnes of corn were within the range of estimates.
"The export sales were a little disappointing," said Ted Seifried, analyst at brokerage the Zaner Group.
Seifried added that some traders were betting the USDA will boost corn yield estimates in its monthly supply and demand report due on Aug. 12 due to historically high U.S. crop condition ratings.
Plentiful rain this summer has developing corn and soy crops in good shape, boosting yield potential. The Commodity Weather Group in a note to clients said showers expected during the next 15 days should aid much of the U.S. crops.
"Soybean plants are in an excellent condition so far," Commerzbank analysts said in a note. "Concerns about yield losses therefore seem overstated, particularly since the weather outlook can change again quickly."
Wheat futures also were lower but holding just above their nine-year lows from earlier this month. CBOT September wheat declined 4-1/2 cents to $4.10-1/4 per bushel, notching their third straight session of lower prices.
After the close of trading, an annual tour of the top spring wheat growing state of North Dakota projected wheat yields there would be lower than the record-large yields seen in 2015. (Additonal reporting by Colin Packham in Sydney and Gus Trompiz in Paris; editing by Dan Grebler and Marguerita Choy)