Managing aster yellows phytoplasma (Candidatus Phytoplasma sp.) and its leafhopper vectors is complex and requires better control methods than those currently used and a greater understanding of the phytoplasma-insect relationship. In this thesis, I determine the effectiveness of a decision support tool focused on managing phytoplasma infected leafhoppers and determine whether leafhoppers in celery and carrot field edges contribute to phytoplasma transmission within the crop fields.We informed farmers about phytoplasma infectivity on their farms via a web-based text messaging system to shift county-level management of Macrosteles quadrilineatus from using leafhopper abundance to infectivity. We found that infected M. quadrilineatus abundance decreased after farmers were informed about their numbers, suggesting that our decision support tool allowed growers to successfully manage infected M. quadrilineatus. We also identified temporal differences in infected and uninfected leafhopper peak abundance in celery but not in carrot cropping systems, suggesting that farmers should account for these phenological shifts across crops and over time.In the field edge surveys, leafhoppers were collected from celery and carrot fields and field edges. I identified leafhoppers through DNA barcoding and conducted real-time PCR to determine phytoplasma infection status. The most abundant species were M. quadrilineatus (57%) and Empoasca fabae (23%). Our results confirmed that M. quadrilineatus was the primary vector in celery and carrots, although there is evidence that E. fabae may also vector this pathogen.
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