On a day when most of the market slipped, prices for wheat, corn and soybeans moved higher.

Wednesday was a down day for prices for most stocks, metals and energy commodities, as investors worried about the still-sluggish U.S. economy and were underwhelmed by the Federal Reserve’s latest plan to boost it. The investors who sent agricultural commodities higher weren’t any more optimistic — they were just fearful that poor weather could crimp crop supplies.