Studies in San Bernardino County showed that 95 to 100% of slips grown from sweet potato roots that were heavily infested with root-knot nematodes also became contaminated. A simple, effective treatment consisting of dry heat—first, at 60° to 100° F for six to eight hours, then at 108° to 110°F for 24 hours—successfully killed nematodes and nematode eggs inside infested roots.