Wheat followed corn higher but soybeans were choppy, turning lower at times as the market struggled with rising global inventories.
As of 12:37 p.m. CDT (1737 GMT), Chicago Board of Trade July corn was up 5-1/2 cents at $3.72-1/2 per bushel after reaching $3.76-1/2, its highest since May 22.
CBOT July wheat was up 1 cent at $4.30-1/2 a bushel and July soybeans were down 1/4 cent at $9.12-1/2 per bushel.
Corn posted the biggest advance. The market climbed after the USDA late Tuesday, in its first weekly corn condition ratings for 2017, rated 65 percent of the crop as good to excellent.
The figure fell below an average of analyst expectations for 68 percent and was down from 72 percent a year ago. It raised concerns that the crop might not be able to meet the government's initial yield projection of 170.7 bushels per acre, based on historical trends.
Ratings were lowest in the eastern half of the Midwest, where excessive rains swamped fields this spring.
"Historically we have a limited chance to make trend-line yields when our good-to-excellent ratings are below 70 percent at this time of year. So the market is really forced to add some premium into prices," said Brian Hoops, analyst with Midwest Marketing Solutions.
Soybeans were choppy after the July contract dipped to $9.09-1/2, the lowest price for a most-active contract since early April 2016.
Strength in corn lent support, along with worries about port strikes that could limit the flow of soy from Argentina, the world's top soymeal exporter.
Yet CBOT soybeans were on track for a monthly decline of more than 3 percent, pressed by a record-large Brazilian harvest, poor soy crush margins in top buyer China and an expected jump in US soybean seedings.
Wheat firmed after the USDA rated 50 percent of the US winter wheat crop in good to excellent condition, down from 52 percent the previous week. Analysts surveyed by Reuters had expected no change.
Egypt's state grain buyer GASC bought 180,000 tonnes of wheat in an international purchase tender, including 120,000 tonnes of Russian and 60,000 tonnes of Romanian origin. GASC passed on offers of US hard red winter wheat.