Wheat also slipped for a second day, pulling away from multi-month highs touched earlier this week, as a tender being held by top importer Egypt shifted attention back towards stiff overseas competition in a well-supplied global market.
Soybeans, which had reached their highest in over three months on Tuesday amid concerns over US planting delays and renewed hopes surrounding US-Chinese trade negotiations, ticked lower.
The most-active corn contract on the Chicago Board Of Trade was down 0.7pc at $4.46-3/4 a bushel, as of 1103 GMT.
That took the contract further away from Monday's five-year peak of $4.64-1/4.
The US Department of Agriculture (USDA) said on Monday that 2019 US crop was 92pc planted, matching trade expectations, and a dry start to the week in parts of the US Midwest has also increased chances some farmers will be able to round off field work.
Weather worries have also been tempered by large US inventories and bumper harvests in South America.
"US corn was overvalued as compared with the international market to the point that it was almost possible for the United States to import South American corn," said Ole Houe, director of advisory services at brokerage IKON Commodities.
Amid uncertainty over the extent to which US farmers were able to carry out their intended corn plantings, attention was turning towards the USDA's June 28 acreage report.
CBOT soybeans were down 0.4pc at $9.09-1/2 a bushel, having climbed to their highest since March 4 at $9.21-1/2 on Tuesday.
In the previous session, soybeans had been supported by comments from US President Donald Trump indicating that Washington and Beijing would restart trade talks after a recent lull, and confirming he would meet Chinese counterpart Xi Jingping at a G20 summit later this month.
US soybean planting, which takes place later than planting for corn, was 77pc completed by Sunday, lagging the average trade estimate of 79pc and the five-year average of 93pc.
CBOT wheat was down 1.5pc at $5.23-1/2 a bushel.
The wheat market has been curbed by decent crop ratings for winter wheat, despite uncertainty over harvest delays and potential quality damage caused by torrential rain in US grain belts.
Egypt's General Authority for Supply Commodities (GASC) is holding a tender on Wednesday to buy wheat for July 22-31 shipment, with Black Sea origins such as Russian wheat expected to confirm their early-season price advantage over US and western European supplies.