Corn futures followed wheat lower. Soybeans were firmer, but pared gains on a smaller-than-expected monthly US soybean crush figure.
As of 12:59 p.m. CDT (1759 GMT), Chicago Board of Trade July wheat was down 9 cents at $4.23-3/4 per bushel after dipping to $4.21-1/2, its lowest since April 25.
CBOT July corn was down 2-1/4 cents at $3.68-3/4 a bushel, while July soybeans were up 3-1/2 cents at $9.66-1/2 a bushel, snapping a three-session slide.
Wheat posted the day's biggest move on a percentage basis. The July contract session high at $4.31 was below Friday's low of $4.31-1/4 and formed a gap in the contract's chart, a bearish technical signal.
"Wheat prices face seasonal and chart-related selling as harvest approaches in the southern (US Plains) belt," INTL FCStone chief commodities economist Arlan Suderman said in a note to clients.
"All the talk about lower planting in the United States and then storm damage have had limited impact on wheat supplies," said Phin Ziebell, an agribusiness economist at National Australia Bank. "We don't see much upside to prices as there are plenty of supplies."
Corn followed wheat lower, pressured in part by improved US weather in recent days that allowed for planting progress in the Midwest before showers return this week.
Analysts expected a US Department of Agriculture report later on Monday to show that 68 percent of corn seeding had been completed as of May 14, close to the five-year average for this time of year of 70 percent.
"As long as it's sunny and warm in Chicago, I think that puts a damper on corn prices," said Terry Reilly, senior commodity analyst with Futures International.
CBOT soybeans got an early boost from a surge in the value of the Brazilian real, which tends to discourage Brazilian farmers from selling their dollar-denominated soybeans.
But soybeans pared gains on a smaller-than-expected monthly US soybean crush figure.
The National Oilseed Processors Association said its members crushed 139.1 million bushels of soybeans in April, down from 153.06 million bushels in March. Analysts had been expecting an April crush of 145.7 million bushels, based on an average of estimates in a Reuters survey.
NOPA's crush figure suggests the USDA may make another downward revision to US soy crush estimate for the 2016-17 marketing year, Reilly said.