NEW YORK—Corn closed below $7 a bushel for the first time in a month Monday as near-perfect growing weather in the Midwest boosted hopes that crops will shrug off last month’s floods and produce a good yield.

Other commodities traded mostly higher, with crude oil inching up and gold, silver and copper prices rising.

Weather forecasts show rainfall this week for western Corn Belt states of Minnesota, the Dakotas, central Nebraska and northern Iowa, offering relief to parched crops as they enter the critical pollination period. In eastern Corn Belt states, warm, dry weath...