Technical Abstract: The epidemiology of Pierce¿s disease of grape in California has changed over the last 10 years due to the introduction of an exotic vector, Homalodisca vitripennis (Germar). Although this insect is highly polyphagous, citrus is considered a preferred host of H. vitripennis and proximity to citrus has been implicated as a significant risk factor in recent epidemics of Pierce¿s disease in southern California. Consequently, a detailed knowledge of the distribution and management of citrus in relation to grape is needed to improve insect and disease management. Analysis of data on the area planted to these two commodities indicates that only 5 counties in California concomitantly grow >1,000 hectares of grape and >1,000 hectares of citrus: Riverside, Kern, Tulare, Fresno, and Madera Counties. Within these 5 counties, the proximity of grape to citrus was greatest for Riverside County compared to the other four counties. The use of carbamates, organophosphates, and pyrethroids as part of the typical citrus pest management program for the control of key insect pests was compared among the same five counties plus Ventura County from 1995-2006. These insecticide classes were investigated because each is known to kill H. vitripennis. The use of these broad-spectrum insecticides was lowest in Riverside and Ventura Counties compared to the other four counties. Analysis of historical trapping data indicates a strong negative effect of broad-spectrum insecticides on glassy-wing sharpshooter abundance. These results are discussed in context of the spread of the glassy-winged sharpshooter throughout California and are used to retrospectively analyze the Pierce¿s disease outbreaks in Kern and Riverside Counties.