The grain trade continues to sink into the red Tuesday, with corn, soybeans and wheat all trading lower on bearish global economic news, namely regarding the Greek debt situation and a referendum that nation's leaders have called on whether or not they'll accept the EU's bailout package.

At 12:30 CST, December corn was 7 cents lower at $6.40 per bushel, while January soybeans were 21 1/2 cents lower at $11.86 and December wheat was 6 1/2 lower at $6.21 3/4, according to Barchart.com.

On top of the bearish news out of Greece, there's no fresh news on grain export sales so far Tuesday, and that's got the grains "pinned in negative territory," according to a Dow Jones Newswires report.

• Read more: Grains lower amid global unease