Technical Abstract: The beet leafhopper is the only known vector of the beet leafhopper-transmitted viresence agent (BLTVA), a plant pathogenic phytoplasm that infects potato and is causing large economic losses in the Columbia Basin. The leafhopper acquires BLTVA from winter annual weed hosts (mostly mustards) that provide overwinter survival for both the vector and BLTVA. It spreads BLTVA from the overwintering weeds to potatoes and other crops during leafhopper migrations that occur in late May and June. Thus, efforts to control the disease by killing beet leafhoppers must be implemented during this crucial period. Because potato is not a good host of the beet leafhopper and because the processes required for transmission require extended periods of time, nearly all BLTVA infection within potato fields originates from sources outside the field, and secondary spread within the fields rarely, if ever, occurs. Potato volunteers and seed potatoes are not important sources of BLTVA since the disease agent rarely survives from one tuber generation to the next in the tuber.