Corn has pulled back 10 percent since the beginning of the month, settling at an 11-month low on Friday as traders worried an economic slowdown will curb demand for it and other commodities. Wheat settled at a 16-month low, while soybeans reached a new 13-month low near $11 a bushel.
Losses accelerated ahead of the close as the grain markets felt pressure from a downturn in equities, traders said. Traders will keep their eyes on outside markets and Europe next week in the absence of any fresh supply or demand items.
"After today, we're going to be again at the mercy of what's going on in Europe," said Brian Splitt, senior broker at Allendale.
Concerns about the global economy continued to hang over the markets as agencies cut credit ratings for European countries. Standard & Poor's downgraded Belgium's credit rating to double-A from double-A-plus on Friday, citing concerns about funding and market pressures, while Fitch downgraded Portugal's credit ratings to junk status.
The "EU debt crisis continues to act as the anchor to this sinking ship," Benson Quinn Commodities said in a note about the grain markets.
So far, the decline in grain prices has not led to a strong increase in export demand.
US export sales of corn last week at 350,000 tonnes were below trade expectations for 400,000 to 600,000 tonnes.
"That's been the main problem with the grains as a whole. We just have not been getting good export business," Splitt said.
Traders largely shrugged off better-than-expected demand for wheat and soybeans.
The US Department of Agriculture said exporters struck deals to sell 614,400 tonnes of wheat last week, above expectations for 300,000 to 500,000 tonnes, and 921,600 tonnes of soybeans, above expectations for 500,000 to 750,000 tons.
"You'd think that, with these price levels, somewhere along the line we're going to pick that (demand) up," said Tom Leffler, owner of Leffler Commodities.
Chicago Board of Trade (CBOT) corn futures for December delivery fell 1.1 percent, or 6-1/4 cents, to $5.82-1/2 per bushel. Prices closed down 4.5 percent for the week.
December wheat slipped 0.8 percent, or 4-3/4 cents, to $5.74-1/2 a bushel. January soybeans fell 1.4 percent, or 16 cents, to $11.06-1/2 per bushel.
Trading was choppy as market participants returned from the Thanksgiving holiday. US grain futures markets were closed for the holiday on Thursday and traded an abbreviated session on Friday.
Grains also fell after the International Grains Council on Thursday said it still expected farmers to produce a record global corn crop in 2011/12. The council trimmed its output estimate by two million tonnes to 853 million, but that is still up from 826 million tons in 2010/11. The council lowered its forecast for global wheat production in 2011/12 by one million tonnes to 683 million, still well above the prior season's 653 million.