SINGAPORE: Chicago soybeans and corn futures slid to their lowest in four years on Monday, dropping below $10 and $4 a bushel respectively, ahead of a U.S. supply-demand report that is expected to show bumper production.

Wheat prices slid 1% after closing higher on Friday, although losses were limited by expectations of lower output in Russia and France.

"There is a lot of bearishness in corn and soybean markets on expectations of higher U.S. output and overall global supplies," said one trader in Singapore.

The most-active soybean contract on the Chicago Board of Trade (CBOT) was down 0.3% at $9.99-1/2 a bushel, while corn gave up 0.3% to $3.94 a bushel, both at their weakest levels since late 2020.

The U.S. Department of Agriculture's (USDA) monthly World Agricultural Supply and Demand Estimates and crop reports are forecast to show higher production, according to a survey of analysts, which would add to large global supplies. The reports are scheduled for release at 1600 GMT.

Wheat prices fell with the most-active contract down 1% at $5.37-1/4 a bushel.

Russian agricultural consultancy Sovecon revised its forecast for the country's 2024 wheat crop down to 82.9 million metric tons from 84.7 million tons on Friday, citing lower yields and a smaller seeded area as reasons for the downgrade.

Extreme weather events, such as early spring frosts, floods, and summer heat, have affected this year's harvest outlook in some key producing areas of the world's largest wheat exporter.

Ratings of French soft wheat showed 48% of the crop in "good or excellent" condition by Aug. 5, down from 50% the previous week and the lowest since the poor harvest of 2016, farm office FranceAgriMer said on Friday.

France's farm ministry on Friday lowered its estimate of the country's 2024 soft wheat output, now expected to be 25% below last year's volume.

An oilseed workers' strike in Argentina is set to carry on into its seventh day on Monday as wage negotiations with firms remained stalled, affecting shipments from one of the world's major grain exporters.

The strike has affected terminals located north of Rosario along the Parana River, where more than 80% of Argentina's agricultural and agro-industrial exports are shipped.

Large speculators trimmed their net short position in CBOT corn futures in the week ended Aug. 6, regulatory data released on Friday showed.

The Commodity Futures Trading Commission's weekly commitments of traders report also showed that non-commercial traders, a category that includes hedge funds, trimmed their net short position in CBOT wheat and trimmed their net short position in soybeans. (Reporting by Naveen Thukral; Editing by Sherry Jacob-Phillips and Rashmi Aich)