Chicago wheat futures fell more than 1 percent to a one-month low on Monday, pressured by generally favourable US crop conditions and expectations of abundant global supplies, traders said.
Corn fell in sympathy with wheat and on outlooks for improved planting weather in parts of the Midwest, and soybeans also slipped.
As of 12:30 p.m. CDT (1730 GMT), Chicago Board of Trade May wheat was down 8-1/2 cents at $4.35-3/4 per bushel after dipping to $4.35-1/4, its lowest since March 12.
CBOT May corn was down 2-1/2 cents at $3.56 a bushel and May soybeans were down 2-1/2 cents at $8.78 a bushel.
CBOT soft red winter wheat futures posted the biggest declines of the three commodities, while K.C. hard red winter wheat and Minneapolis Grain Exchange spring wheat
futures fell to contract lows in nearly every contract month.
Ahead of the US Department of Agriculture's weekly crop progress report due later on Monday, analysts surveyed by Reuters forecast on average that the government would rate 60% of the winter wheat crop in good to excellent condition, unchanged from the previous week.
A year ago, the USDA rated just 31 percent of the crop as good to excellent.
Analysts also expected the USDA to show that farmers were able to plant 7% of their intended corn acres and 2% of their soybeans by Sunday. Analysts pegged the respective five-year averages at 12% for corn and 2% for soybeans.
In Ukraine, farmers have so far sown 2.1 million hectares of spring grain crops for the 2019 harvest, or 93% of the expected area, the agriculture ministry said. Traders were monitoring the spread of African swine fever in China, home to the world's largest hog herd. The disease, which is fatal to pigs but harmless in humans, has spread to every province on the Chinese mainland since its initial detection in August 2018.