Curly top of sugar beet was among the first plant viral diseases recognized (with tobacco mosaic) in the late nineteenth century. It was also the second disease shown to be associated with a leafhopper vector, the beet leafhopper (Circulifer tenellus) (Fig. 1), the dwarf disease of rice from Japan being the first. Since its discovery, beet curly top has likely been the most intensively studied of all the leafhopper-transmitted virus diseases owing to its past and continuing impact on multiple economically important crops