Corn was trading below a one-year high struck on Tuesday, while soybeans slipped for the first time in eight sessions to edge back from a four-month peak. Wheat was consolidating below last year's two-year peak linked to damage to spring wheat.
Investors were squaring positions before the US Department of Agriculture's (USDA) monthly supply-and-demand outlook for US and global crops which is attracting greater interest given concern of weather stress to US crops.
"Climatic conditions are remaining a core concern for US traders, with a focus on the hydric deficit that affected spring wheat and which could now spread on the corn belt," consultancy Agritel said in a note.
The most active corn futures on the Chicago Board of Trade were down 1.5 percent at $4.08 a bushel by 1148 GMT, after reaching their highest since June 2016 at $4.17-1/4 in the previous session.
Despite some scattered showers early on Tuesday across parts of Iowa and Illinois, the top US corn states, forecasts call for continued hot, dry weather over the rest of the week, while some models also pointed to hot weather later in the month.
"July is a key development month for corn, so the timing makes prices acutely sensitive to hot weather during this period," said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia.
While the USDA may not revise its US corn and soybean yield forecasts significantly at this stage, traders will be looking closely at other supply-and-demand changes to gauge potential tightness in supply next season.
The most active soybean futures declined 1.1 percent to $10.31-3/4 a bushel, easing from Tuesday's four-month high of $10.47.
A weekly USDA crop progress report on Monday had supported price strength in soybeans by rating 62 percent of the US soybean crop in good-to-excellent condition, down from 64 percent the previous week and below an average analyst estimate.
The most active wheat futures dropped 1.0 percent to $5.47-1/4 a bushel.
Severe weather in the northern US spring wheat belt has fired up wheat markets in the past month, although traders are waiting to see if harvests under way in western Europe and the Black Sea region will offset reduced US supply.