Corn bids eased by 5-6 cents per bushel along Midwest rivers and soy bids by 4-13 cents. Rainfall delayed the early phases of the harvest in parts of the region, limiting deliveries so far this week.
Corn bids were narrowly higher at some inland processing plants, supported by light farmer sales, while soybean bids were largely flat at processors and elevators.
Farmers largely delayed sales as Chicago Board of Trade corn and soybean futures fell as much as 1 percent on technical selling.
The US Department of Agriculture late on Monday said 7 percent of the US corn crop was harvested, down from the five-year average pace of 11 percent. Thirty-four percent of corn was mature, down from the average of 47 percent.
USDA said soybeans were 4 percent harvested, below the average of 5 percent, while 41 percent of soybean plants were dropping leaves, compared with 43 percent normally.