The causal bacterium of almond leaf scorch (ALS) disease was transmitted from almond to almond and to grape, and from grape to almond by several species of leafhoppers known to transmit the same bacterium from grape to grape: Graphocephala atropunctata (Signoret), G. confluens (Uhler), Draeculacephala minerva Ball, and Carneocephala fulgida Nottingham, and by the meadow spittlebug, Philaenus spumarius L. Surveys of commercial orchards detected only very low populations of known or suspected ALS vectors in areas which had a high incidence of ALS. In contrast, many almond-growing districts in central California which had a high incidence of Pierce’s disease in grapes but only rare infections of almond trees with ALS had much higher populations of D. minerva and C. fulgida. These findings are consistent with the hypothesis that D. minerva is not the principal vector of ALS in California.