Soybeans and corn were also lower, pressured by a further rise in the dollar, making them less competitive on export markets.
However, soybeans were supported by rains in parts of the US Midwest threatening to slow the harvest and reduce crop quality and a rise of the real in competitor Brazil after a strong first-round showing for far-right presidential candidate Jair Bolsonaro raised hopes for much-needed economic reforms.
The most-active wheat contract on the Chicago Board of Trade was down 0.2 percent at 1050 GMT to $5.13 a bushel, after falling earlier in the session to its lowest since Oct. 2 at $5.12 a bushel.
Soybeans fell 0.3 percent to $8.67-1/4 a bushel, having climbed to their highest since Aug. 22 at $8.74-3/4 on Monday. Corn was nearly unchanged at $3.66-1/4 a bushel, down 0.1 percent, having closed down 0.5 percent in the previous session.
Russian grain exports quickened last week, SovEcon said, citing preliminary customs data. Russia exported 15.7 million tonnes of grain over July 1-Oct. 4. That was up 26 percent from a year ago and included 13.5 million tonnes of wheat.
Recent rains in parts of Australia and Argentina - both key southern hemisphere grain exporters - added pressure to wheat.
"The strong pace of Russian wheat exports is adding pressure on wheat prices," said Phin Ziebell, agribusiness economist at National Australia Bank.
"There have been beneficial rains in Western Australia."
Traders squared positions ahead of Thursday's monthly US Department of Agriculture (USDA) crop supply and demand report that is expected to show larger US corn and soybean crops and bigger supplies of corn, soy and wheat.
Wet weather across key corn and soybean states - including Iowa, Nebraska and Minnesota - stalled the harvesting of both crops, but the rains have boosted soil moisture for hard red winter wheat planting in the central and southern US Plains.
Due to the Columbus Day federal holiday, the USDA's weekly harvest progress and crop condition report normally released on Monday afternoon was delayed by a day.