A recent warm, dry spell had fueled worries that corn could be damaged during crucial pollination stages, after unprecedented delays in planting this spring.

However, Tropical Depression Barry is now expected to bring rain to the Mississippi Valley, Delta region and Ohio Valley, according to Commodity Weather Group.

The September corn futures on the CBOT are down 9-1/4 cents, or 2.1pc at $4.44-3/4 a bushel at 12:05 p.m. (1705 GMT). The most actively traded contract earlier hit $4.64-3/4, the highest level since June 2014 on a continuation chart.

But the most-active contract stayed below contract highs of last month on individual September and December delivery positions.

Traders are awaiting a weekly US Department of Agriculture crop report, due out at 3 p.m. CDT (2000 GMT), for an update on corn conditions.

The agency is expected to rate 56pc of the crop in good to excellent condition, down 1 percentage point, according to a Reuters poll.

Still, "I wouldn't be surprised if conditions stayed the same or if there was a slight increase in the good to excellent ratings," said Mike Zuzolo with Global Commodity Analytics.

Traders remain uncertain about the size of the upcoming harvest. Zuzolo said he expected corn ratings to decline again in next week's USDA condition report.

"Corn is already looking a little stressed," he said.

Traders largely shrugged off the USDA's forecast for UScorn production in its monthly supply and demand report on July 11, holding out for a follow-up survey of plantings by the agency after its previous acreage estimates were viewed as too high for corn and too low for soybeans.

September CBOT wheat futures were down 14 cents, or 2.7pc at $5.09 a bushel after earlier touching their highest level in more than two weeks at $5.31-1/2.

August CBOT soybean futures were down 10-1/4 cents or 1.2pc at $9.02-1/2 a bushel, off a $9.36-1/2 session peak that was its highest since June 2018.

Weather risks for soybean crops in the Midwest were being weighed against demand concerns against the backdrop of a long-running US-Chinese trade dispute and pig disease in China, the world's top soy importer.

China produced 24.7 million tonnes of pork in the first six months of 2019, down 5.5pc from a year earlier, according to figures from the National Bureau of Statistics, amid a severe swine fever epidemic.