Applications of Fungicides to Protect Four Hosts from Foliar Infection by Phytophthora ramorum in Curry County, Oregon

Ellen Michaels Goheen, USDA Forest Service, Forest Health Protection, Central Point, OR, USA 97502; (541) 858 6126; egoheen@fs.fed.us; Alan Kanaskie, Oregon Department of Forestry, Salem, OR USA 97310; Jennifer Parke and Melody Roth, Oregon State University, Department of Crop and Soil Science, Corvallis, OR USA 97331; Nancy Osterbauer and Aaron Trippe, Oregon Department of Agriculture, Salem, OR USA 97310

Oregon’s Phytophthora ramorum eradication effort in tanoak/conifer forests of Curry County has greatly reduced levels of infection, but has not completely eliminated P. ramorum from some affected sites. Two fungicides, Stature® and Agri Fos®, were tested for their ability to protect Rhododendron macrophyllum, Vaccinium ovatum, Umbellularia californica and Lithocarpus densiflorus from foliar infection. Fungicides were applied at 1x and 2x their recommended rates in February and April. New foliage was treated in May. Leaves were collected after treatment, taken to the laboratory, wounded, and inoculated with A1(N11A) and A2(4143) isolates of P. ramorum. Inoculated leaves were placed in a sealed moisture chamber for one week. Visual analysis of disease incidence and leaf necrosis was done using ASSESS. No fungicide treatment provided complete protection from foliar infection by P. ramorum for tested hosts. Data suggest that significant differences between the fungicide-treated leaves and controls for both older and new foliage depended upon the host treated and the P. ramorum isolate used. For example, significantly greater leaf necrosis was observed on new Vaccinium foliage inoculated with 4143 than on older foliage inoculated with the same isolate (P<0.001). However, no difference was observed on new versus old Vaccinium foliage inoculated with N11A (P=0.90).

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