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Studies in the use of heat to control Phytophthora tentaculata.
W. SCHWEIGKOFLER (1), K. Kosta (2), S. Sharma (1), A. Santiago (1), S. Ditta (1), V. Huffman (1), K. Suslow (1). (1) Dominican Univ of California, San Rafael, CA, U.S.A.; (2) California Department of Food & Agriculture, Sacramento, CA, U.S.A.

<i>P. tentaculata</i> is a pathogen of herbaceous plants and has been found in nurseries in Europe and China. In fall of 2012, <i>P. tentaculata</i> was isolated from Sticky monkey flower, <i>Mimulus aurantiacus</i> (Phrymaceae), in coastal California. Since then, <i>P. tentaculata</i> was found in several native plant nurseries and restoration plantings. Most probably, the pathogen can spread via infected nursery material. Recently we have shown that thermal treatment by steaming can be used to inactivate <i>P. ramorum</i>, the causal agent of Sudden Oak Death and Ramorum blight, from nursery plants, soil and equipment. In order to test if heat treatment could also be used to control <i>P. tentaculata</i>, we tested the effect of dry and wet heat on the survival rate of <i>P. tentaculata</i> in the lab. Two other Phytophthora species recently isolated from Rhododendron at NORS-DUC, namely <i>P. syringae</i> <i>and P. cf. fallax</i>, were included in the study. Whereas<i> P. syringae</i> is a well-known nursery pathogen, <i>P. fallax</i> was previously only described from Eucalyptus trees in New Zealand. Because <i>P. tentaculata </i>does not grow on Rhododendron leaves (the leaf baiting material for <i>P. ramorum</i>), we tested the survival of <i>P. tentaculata</i> grown on agar plugs. Incubation at 50 °C inactivated all tested Phytophthora strains. The effect of steaming was tested successfully at the NORS-DUC research nursery using a commercial steaming unit (SIOUX Steam-Flo SF-1); no Phytophthoras were re-isolated from the post-steaming soil.

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