The positive spell cast by external markets helped Chicago crops – but only for so long.
After a firm start to live trading, prices fell back as traders booked profits.
"The turnaround from strongly higher prices across the floor early in the session to mixed and falling prices this afternoon continues in very light volume trading, making it easy for the bears to push prices down," Vic Lespinasse, the GrainAnalyst.com analyst, said.
"Long liquidation by earlier buyers coupled with a growing number of short sellers has put increasing pressure on most pits."
This was a significant disappointment to many investors, given the upbeat conditions on share markets – where New York and London stocks added more than 2% - and oil – where New York crude for August stood 3.6% higher at 17:15 GMT.
Chicago corn for September was 5.25 cents down at $3.33 ¼ a bushel – 10 cents off its high - amid expectations of ideal weather for the US crop's pollination phase.
Soybeans for August, which had touched $10.63 ¾ a bushel, stood at $10.22 ¼ a bushel, down 12.75 cents on the day.
US soybeans, besides promising weather, have the potential of stronger competition from South America to deal with, amid talk that opposition politicians may remove powers to set soybean taxes from Argentina's president.
Traders believe that would lead to lower taxes, raising the incentive for Argentine farmers to boost soybean production.
Wheat carried the standard for Chicago's main crops, adding 2 cents to $5.32 a bushel for the September contract.
Still, that was small beer compared with juice, which continued its phenomenal winning streak, adding 4.4% to a 10-month high of 102.10 cents a pound for New York's September contract.
Nearest-contract juice has not traded above $1 a pound since September last year, with traders saying that the breaking of the buck-barrier had encouraged investors focused on technical factors to raise positions even further.
White sugar was also in demand, closing up 1.5% at $449.9 a tonne for London's August contract.
However, London cocoa dipped 1.5% to £1,724 a tonne, weakened by soft data on Malaysian grindings.