My research focuses on two related aspects of Pierce’s Disease (PD) epidemiology in California vineyards. The first concerns the transmission ecology of PD’s causal agent, the xylem limited bacterium Xylella fastidiosa, by native and non-native leafhopper vectors. Because of the wealth of data available from prior transmission studies of this economically important vector-pathogen-crop system I am using it as a model system to tease apart the contributions of various ecological factors (e.g., vector species, vector density, inoculation duration, temperature) to the probability that a given plant becomes infected. The second aspect of my research concerns the importance of Glassy-winged sharpshooter (Homalodisca vitripennis; GWSS)-mediated secondary spread for PD dynamics. The leading hypothesis for why this non-native vector can promote devastating PD outbreaks is that, unlike native sharpshooters, GWSS may be able to rapidly spread Xylella from vine-to-vine (= chronic secondary spread) during a single growing season. Yet this hypothesis remains untested. I am investigating (using models and field experiments) how seasonality in acquisition efficiency and vine recovery from infection may diminish the strength of vine-to-vine spread –especially in colder regions of the state.