CBOT September soft red winter wheat settled down 7-1/2 cents at $4.83 a bushel while the nearby July contract dipped to $4.66-3/4, the lowest spot price on a continuous chart since April 24.
K.C. September hard red winter wheat ended down 12 cents at $4.75-1/2 a bushel and the front July contract hit $4.54, the lowest spot price since Jan. 29.
MGEX spring wheat futures set across-the-board contract lows and September finished down 5-3/4 cents at $5.45-1/2.
Commodity funds hold a net long position in K.C. wheat, leaving the market prone to bouts of long liquidation.
The US Department of Agriculture late on Monday said the US winter wheat harvest was 41 percent complete while the Kansas harvest was 52 percent finished, ahead of the state's five-year average of 32 percent.
Forecasts for beneficial rains in eastern Australia's wheat region added pressure.
Egypt's state grain buyer purchased 120,000 tonnes of Russian wheat in an international tender. No US wheat was offered.