U.S. wheat futures fell two per cent and hit a six-month low on Wednesday in light technical trading, pressured by end-of-year positioning and a lack of export demand, traders said.
Corn and soybeans also sagged in holiday-thinned volume. Grain markets remained closed in Europe.
At the Chicago Board of Trade, March wheat fell 19-1/4 cents, or 2.4 per cent, at $7.74-1/2 per bushel after dipping to $7.73-3/4, its lowest level since June 27 (all figures US$).
CBOT March corn ended down 11 cents, or 1.6 per cent, at $6.93-1/4 a bushel and most-active March soybeans settled down 17-1/4 cents, 1.2 per cent, at $14.18-1/2 a bushel.
In wheat, early selling accelerated as the March contract dropped below last week's low of $7.82-1/2.
"Right now the path of least resistance is lower, until we find someone who wants to start buying wheat and extending coverage," said Shawn McCambridge, a grains analyst with Jefferies Bache in Chicago.
U.S. soft red winter wheat, the type traded at the CBOT, has become the cheapest milling wheat in the world, but the absence of fresh export sales has kept a lid on futures prices.
"Until we start to show there is some actual business out there, we will continue to see pressure," McCambridge said.
The U.S. Department of Agriculture reported the amount of wheat inspected for export in the latest week at 15.128 million bushels, within a range of trade estimates for 12 million to 17 million.
USDA showed corn export inspections at 13.475 million bushels, within the range of estimates for nine million to 14 million.
Traders were monitoring crop weather in the southern U.S. Plains hard red winter wheat region, where cold temperatures this week raised the threat of crop damage from winterkill. Temperatures in northwest Kansas were in the single digits Fahrenheit (-12 to -17 C) on Wednesday morning.
The Commodity Weather Group (CWG) reported sub-zero (Fahrenheit) temperatures from parts of Colorado into the northern Plains in the past two days, but said protective snowpack would limit any crop damage.
However, CWG said in a daily note to clients, "a few spots in Colorado and western Kansas may incur patchy losses due to thinner snow cover."
Traders were also weighing the impact of cold weather on the winter grain crop in Russia, although CWG said damage from cold temperatures early this week would be isolated.
New-crop corn drops below $6
Corn and soybeans sagged in sympathy with the declines in wheat, with improving South American crop weather adding pressure.
New-crop December 2013 corn fell below psychological support at $6 for the first time since July 11, dipping to $5.98-1/4. U.S. farmers watch the December 2013 corn contract to gauge prices for the next harvest as they consider what to plant this spring.
U.S. corn acreage is expected to expand in 2013. Private analytics firm Informa Economics last week projected plantings at 99 million acres, the most since 1936.
In South America, wet areas of Argentina were expected to turn drier in the next two weeks, easing concerns about excess moisture, while welcome rains were forecast later this week and next week for parts of central Brazil.
"They don't have just a big crop this year; it's a huge crop coming," said Jason Roose, commodity analyst with U.S. Commodities in West Des Moines, Iowa, referring to the South American corn and soy harvests.
Roose said the soybean harvest in Brazil, which is expected to produce a record-large crop, could begin in mid-January.
"All the news that was bullish before is turning more bearish. Harvest is coming up in Brazil," Roose said.
CBOT March soybeans turned lower in the early minutes of trade after failing to hold support above the contract's 200-day average at $14.40.
Export demand for scarce supplies of U.S. soybeans helped underpin the market, limiting losses. USDA on Wednesday confirmed sales of 115,000 tonnes of U.S. soybeans to China and another 108,000 tonnes to unknown destinations, both for delivery in 2012-13.
USDA reported weekly export inspections of U.S. soybeans at 44.486 million bushels, above a range of trade estimates for 37 million to 42 million.
-- Julie Ingwersen covers the commodities markets for Reuters in Chicago.