The most active corn contract for December delivery went down 2.25 cents, or 0.58 percent to close at 3.8275 dollars per bushel. September wheat delivery fell 5.5 cents, or 0.96 percent to close at 5.645 dollars per bushel. November soybean delivery dropped 6.5 cents, or 0.71 percent to close at 9.04 dollars per bushel.
Temperatures in France are expected to ease later this week following a round of intense heat. Cooler air is expected Friday and into the weekend after temperatures in France and Germany reached almost 100 Fahrenheit degrees, according to Accuweather.
In Argentina, growers who are finishing planting reported moist soils and cool weather that's giving crops a boost. The Buenos Aires Grain Exchange has projected a wheat output of 19 million tonnes.
The U.S. Department of Agriculture(USDA) has pegged wheat output in Argentina at 19.5 million tonnes, which would top a record set in the 2007-2008 marketing year.
CBOT soybean futures retreated after two sessions of gains in a profit-taking and position-squaring setback ahead of Friday's USDA monthly supply and demand report.
Corn also slipped as traders moved to the sidelines ahead of the closely watched report, the first of the season to include field surveys of U.S. crops that have been hurt in some areas by hot, dry weather.