I have had the great honor and pleasure of working with Sandy Purcell for my entire scientific career, first as his graduate student at UC Berkeley and later on numerous collaborative projects during my tenure at UC Davis. Our collaborative research on plant pathogenic phytoplasma, non-cultiviable, wall-less prokaryotes that are transmitted primarily by leafhoppers and psylla, is focus of this presentation. As a graduate student, Sandy provided the knowledge, experience and facilities that allowed me to the prepare antiserum and cloned DNA probes specific for the X-disease phytoplasma (XP), a pathogen that had ravaged California cherry orchards for years. We used these molecular diagnostic tools to identify the major insect vectors and plant reservoirs of XP and with other colleagues devised orchard management strategies that greatly reduced losses to X-disease. Another California phytoplasma disease, peach yellow leaf roll (PYLR), caused epidemic losses during the 1980s. Based on insect trapping and epidemiological data, Sandy proposed that pear psylla were likely the vector of PYLR and he was able to transmit PYLR using field-collected pear psylla. Although the PYLR phytoplasma was thought to be a strain of XP, PYLR-infected tissues tested negatively with our XP diagnostic reagents. Work by students in my lab showed that PYLR was caused by a strain of the pear decline phytoplasma; collaborative UC Berkeley/Davis research showed this pathogen is only transmitted by pear psylla and pear trees are its primary reservoir. This information resulted in management guidelines that have all but eliminated losses to PYLR in California.