Persistance Of Phytophthora Ramorum After Eradication Efforts In Oregon Tanoak Forests

E. M. Hansen and W. Sutton, Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR USA 97331

In Oregon, P. ramorum is confined to a small area of forest land in the SW corner of the state, where it is subject to an ongoing eradication effort. Infected trees and adjacent host plants are destroyed. Intensive monitoring of the sites for the presence of the pathogen follows treatment. Here we report part of that monitoring effort, focused on rainwater and streams flowing out of treated areas, and persistence of P. ramorum in soil and on plants growing around the stumps of infected tanoak trees. Rainwater and streams were baited with leaves of tanoak and rhododendron, soils were baited with pear fruits and tanoak and rhododendron leaves, and susceptible Douglas-fir and redwood seedlings were planted around stumps. In addition, other sprouting host plants were examined for infection. P. ramorum is still recovered from streams 30 months after site treatment, although no new plant infections have been associated with these streams. The pathogen was initially recovered from tanoak sprouts around 88 % of the 43 sampled stumps, from soil around 14% of the stumps, and from other sprout plants around 7% of the stumps. Douglas-fir and redwood seedlings were not infected. Recovery rates after 30 months are currently being assessed.

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