Australia's unique flora has evolved in isolation from many of the world's major plant pathogens. As these pathogens have made their way into Australia, their impact on plant species and communities has been dramatic. Two plant diseases, Phytophthora root rot and myrtle rust, are used as examples to illustrate the impact diseases can have on individual species, on plant communities, and on the species that depend on those plants. Botanic gardens have a key role to play in protecting plants and enhancing conservation outcomes through surveillance, education, and ex situ conservation programs.