Soybeans also fell, giving up the last session's gains, as a rapidly advancing harvest in top exporter Brazil boosted global supplies.
Wheat is under pressure from stiff global competition as well as the technical selling that took prices to contract lows for the second straight day.
"The Europeans and the Russians have been undercutting our prices to make sure they get some sales on the books and it's been working," said Jack Scoville, a futures market analyst at the Price Futures Group.
Condition ratings for winter wheat declined from late November to late February across much of the US Plains, the US Department of Agriculture said on Monday.
The May wheat contract on the Chicago Board of Trade fell 4-1/2 cents to $4.68-1/4 a bushel. It fell to the lowest for a most-active contract since April 17 at $4.63-3/4 a bushel.
May corn fell 4 cents to $3.76 per bushel.
May soybeans fell 8 cents at $9.17 per bushel, having firmed 0.2 percent on Monday.
Soybeans dropped as investors waited for signs of Chinese buying. China committed to buy an additional 10 million tonnes of US soybeans in a meeting on Friday, US Agriculture Secretary Sonny Perdue said on Twitter.
"Traders are disappointed they didn't see any USDA announcements this morning of China buying soybeans from the United States. That immediately triggered selling in soybeans," said Terry Reilly, senior agriculture analyst for Futures International.
Soybeans drew support on Monday after US President Donald Trump said he may soon sign a deal with China, but offered few details.
The USDA confirmed on Tuesday sales of 120,000 tonnes of US soybeans to Mexico for shipment in the current and next marketing years.
The global market remains amply supplied with beans.
Brazilian soybean farmers have harvested about 45 percent of fields so far in the 2018/19 season as the work is progressing quickly in top-producing state Mato Grosso, consultancy AgRural said in a statement on Monday.
Harvesting of Brazil's soybean fields is 20 percentage points above last year's levels and significantly above a five-year average of 27 percent of planted area. Farmers in Mato Grosso have harvested about 80 percent of fields, AgRural said.