The condition of corn in the 18 states that produce most of it has deteriorated due to widespread drought.
The latest report from the U.S. Department of Agriculture says 30 percent of the crop is now considered in poor or very poor condition. A week ago, it was 22 percent.
Indiana and Illinois have been particularly hard hit.
The USDA said Monday that Indiana's corn is now 61 percent poor or very poor compared to 50 percent last week.
In Illinois, 48 percent of the corn is rated as poor or very poor, compared to 33 percent last week.
The amount of corn rated good to excellent also is dropping, to 40 percent this week from 48 percent a week ago.
Corn surged 31 cents to $7.74 in afternoon trading.