Phytophthora species, including P. ramorum, typically produce spores that allow them to survive in soil. Media in containerized nursery stock can become contaminated from infested soil or plant material, resulting in the spread of these pathogens. Phythophthora species are projected to be a continuing issue for the nursery industry through unknown introductions as a result of international plant trade.
Steam treatment has been shown to be effective at removing inoculum of these pathogens from soil, pots, and media if the temperature is held at 50C (122 F) for at least 30 minutes.
Elliott, M. and Chastagner, G. 2019. A Technique for Treating Contaminated Soil with Steam for Eradication of Phytophthora. Poster presented at the 7th Sudden Oak Death Science Symposium June 25-27 2019 San Francisco, CA.