While some damage is caused by nymphal and adult feeding, the most serious problem is the viral disease, curly top, that is vectored by beet leafhoppers.
Infected plants turn yellow and stop growing.
Leaves roll upward and turn purplish in color. Leaves and stems become stiff. Spring plantings are the most susceptible. The insect migrates from overwintering hosts in the foothills, and is mostly a problem in the San Joaquin Valley. Insecticides applied directly to fields do not prevent leafhoppers from transmitting curly top virus and do not reduce the incidence of the disease.