Steaming is a sustainable method to eradicate the quarantine pathogen Phytophthora ramorum from infested nursery soil
W. SCHWEIGKOFLER (1), K. Kosta (2), K. Suslow (1), V. Huffman (3), S. Ghosh (4). (1) Dominican University of California, San Rafael, CA, U.S.A.; (2) CDFA, Sacramento, CA, U.S.A.; (3) Dominican University of California, San Rafeal, CA, U.S.A.; (4) Dominican University of California, San Rafel, CA, U.S.A.
The long-distance spread of <i>Phytophthora ramorum</i>, causal agent of Sudden Oak Death, through infected nursery plants is a serious thread for environments not yet affected by the pathogen. Nurseries tested positive for the presence of <i>P. ramorum</i> are required by federal and state regulations to eradicate infested plants and to disinfest soil and water. At NORS-DUC we study environmental friendly methods to eradicate <i>P. ramorum</i> from infested soils, among them biological control, solarization and steaming. Research beds (surface 9.1 x 3.7 m, depth 30 cm) filled with high clay content soils were treated with hot steam at a target temperature of 50°C for 30 minutes. As controls, teabag sachets containing Rhododendron leaf disks colonized by <i>P. ramorum</i> were buried at various depths in the soil. Leaf disks collected before and after steaming were assessed for <i>P. ramorum</i> by plating on PARPH-V8 medium. All leaf disks were <i>P. ramorum</i>-positive pre-steam and negative post-steam. Seasonal effects of environmental temperature on the steaming process and temperature gradient were measured by steaming at different times of the year. Additionally, soil at a commercial nursery tested positive for <i>P. ramorum</i> was steam-treated and -after eradication of the pathogen- released from quarantine. Soil texture and water content play an important role for the dynamics of the steaming process. Our results confirm that steaming can be used to eradicate quarantine pathogens from nursery soils.
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