GRAINS-CBOT corn extends retreat, wheat and soy also lower

* Rains may improve weekly US winter wheat crop ratings

* Strong demand from China should underpin corn prices

* (Adds quotes, updates prices)

LONDON, Nov 2 (Reuters) - Chicago corn futures fell on Monday, as funds scaled back long positions against the backdrop of a decline in crude oil prices and improved crop weather in South America.

U.S. wheat prices fell for a sixth consecutive session to their lowest since mid-October while soybeans also lost ground.

The most-active corn contract on the Chicago Board Of Trade (CBOT) was down 0.9% at $3.94-3/4 a bushel, as of 1010 GMT, extending its retreat from a 14-month peak of $4.22-1/4 set on Oct. 27.

Speculators had built up a large net long position during the recent run-up in prices, with sentiment buoyed by strong demand for corn from China.

Dealers said, however, they had begun to scale back long positions during the last few days.

“While we appear to have seen some profit-taking in recent days...the fundamentals remain constructive for corn, with robust Chinese demand,” ING said in a market update.

Improved weather in parts of South America also added pressure on prices.

“The market has lost impetus from the shrinking areas of concern for South America crops,” said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia.

The most active wheat contract on the CBOT was down 0.9% at $5.93-1/4 a bushel after dipping to a low of $5.91, its weakest since Oct. 14.

Dealers said the wheat market was weighed partly by rains in the U.S.

“This could lead to an improvement of the weekly wheat crop rating that will be released tonight,” analysts Agritel said in a note.

The U.S. Department of Agriculture last week rated only 41% of the winter wheat crop in good or excellent condition, down from 56% at the same stage a year ago.

December milling wheat on Paris-based Euronext fell 1.1% to 203 euros a tonne.

Soybean prices also fell with the most active CBOT contract down 0.7% at $10.49 a bushel. (Additional reporting by Naveen Thukral in Singapore, Editing by Sherry Jacob-Phillips and Ed Osmond)