NEW YORK—Corn prices sank to a seven-week low Monday as crops extended their rebound from last month’s flooding, promising some relief at the grocery store for consumers who had faced higher prices for meat, dairy and other foods.

Other commodities traded mixed, with crude oil, gold, silver and copper rising. Soybeans, wheat and other agriculture futures fell.

Corn has plunged 20 percent in the last month, driven lower by ideal growing weather in the U.S. Corn Belt and a big drop in oil prices last week. The grain soared to record-highs near $8 a bushel in June as the w...