Russet crack disease of sweet potatoes (Ipomoea batatas) was first reported in New Jersey in 1961 and it was suggested a virus might be the cause. Soon after, the disease was in California; probably it had been imported with propagative roots from the east coast. The present paper reports studies done at the University of California at Davis and in Merced County, California, to clarify the cause of russet crack and its method of transmission.