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PPO Home > WSU Sudden Oak Death Program > Sudden Oak Death Research > Steam treatment to sanitize soils, pots, and media

Steam treatment to sanitize soils, pots, and media

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.

Soil temperatures at 5, 15, and 30 cm during steaming in a sandy loam field soil. The steamer (Sioux SF20) was shut off at 3 PM when the soil at 30 cm reached 50°C. The soil cooled rapidly at 5 cm but held above 50°C at 30 cm for about 14 hrs. The steamer operated for a little less than 5 hrs.
Soil temperatures at 5, 15, and 30 cm during steaming in a sandy loam field soil. The steamer (Sioux SF20) was shut off at 3 PM when the soil at 30 cm reached 50°C. The soil cooled rapidly at 5 cm but held above 50°C at 30 cm for about 14 hrs. The steamer operated for a little less than 5 hrs.

How the process works

Steam generators

Effectiveness of steam treatment

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.