Infection byXanthomonas axonopodispv.manihotis(Xam) of the perennial rangeland weed leafy spurge was tested to see whetherXammight serve a potential biological control agent for this invasive weed. Although leafy spurge was susceptible toXaminfection, it recovered within 21 d after inoculation (DAI). Microarray resources available for leafy spurge allowed us to follow the physiological and signaling pathways that were altered as leafy spurge was infected and then recovered fromXaminfection. The first physiological effect ofXaminfection was a down-regulation of photosynthetic processes within 1 DAI. By 7 DAI, numerous processes associated with well-documented pathogenesis responses of plants were observed. Although some pathogenesis responses were still detectable at 21 DAI, other processes associated with meristem development were noted. Ontological analysis of potential signaling systems indicated jasmonic acid plays a significant role in the recovery processes.