Wheat prices are soaring their maximum allowed amount on the Chicago Board of Trade after Russia banned grain exports for the rest of the year.

Prices shot up 60 cents, or 8 percent, to $7.8575 immediately after the open of trading on Thursday. It's the highest price since August 2008.

CBOT rules stipulate that prices can rise a maximum of 60 cents in one day, although they are allowed to rise more the following day if the 60-cent limit is hit.

The price of wheat has been soaring since early June, and notched its biggest monthly gain in July in at least 51 years.

Russia, one of the world's biggest grain exporters, cut off wheat exports because a severe drought has already destroyed one-fifth of that country's crop.