CBOT prices dropped 1.8 percent from their highest level in two months.
Traders were closely watching US Federal Reserve's policymaking committee's two-day meeting, which started on Tuesday. Chairman Ben Bernanke to hold news conference at close of meeting.
The US Agriculture Department late on Monday said 35 percent of the US wheat crop was in good to excellent condition, down from 36 percent a week ago and down from 69 percent a year ago.
USDA also said just 6 percent of the spring wheat crop had been planted, up from 5 percent a week ago, down from 39 percent a year ago and below the 25 percent five-year average.
Showers this week will boost crop prospects in the northern and eastern portion of the US Plains hard red winter wheat region but dryness continues to stress the crop in the southwest, leading to crop losses.
Canadian plantings of wheat are expected to climb 17.4 percent to 24.7 million acres in 2011, according to Statistics Canada's first report on 2011 crop plans released on Tuesday.
Dryness in North China Plain also becoming a concern because the wheat crop is in or near its reproductive stage of development and is in need of rain. Dry weather similarly a concern in western Europe.
Rain in parts of west Europe over the weekend was not enough to bring major help to parched wheat crops in key producers France and Germany and fears of crop damage are growing, analysts and traders said.