Effects of solarization and biocontrol on soilborne Phytophthora spp. in container nurseries
F. FUNAHASHI (1), J. L. Parke (1). (1) Oregon State University, Corvallis, OR, U.S.A.
Infested nursery beds are an important source of <i>Phytophthora</i> spp. in container nurseries. Soilborne inoculum of <i>Phytophthora</i> spp., shown to be located mostly in the top 10 cm, can initiate disease through movement with surface water or splashing onto foliage. We investigated soil solarization, alone or with subsequent amendment with a <i>Trichoderma</i> sp. biocontrol agent, on the survival of <i>Phytophthora</i> species. In field trials conducted with <i>P. ramorum</i> in San Rafael, CA or with <i>P. pini</i> in Corvallis, OR, infested rhododendron leaf inoculum was buried 5, 15, and 30 cm below the soil surface. Solarization for 2 or 4 weeks during summer 2012 eliminated recovery of <i>Phytophthora</i> buried at 5 cm in CA and OR, and at 15 cm in CA. Maximum soil temperatures exceeded 50°C in CA and 45°C in OR. The biocontrol treatment was added to solarized and non-solarized plots, but there was no effect on <i>Phytophthora</i> recovery 2, 4, or 8 weeks later. Populations of the introduced <i>Trichoderma</i> sp. and of indigenous <i>Trichoderma</i> spp. were significantly greater in solarized as compared to non-solarized plots. Data from lab experiments at controlled, stable temperatures will be combined with field data to establish a model to predict the minimum time period required for solarization to eliminate <i>P. ramorum</i> and <i>P. pini</i> from different soil depths in container nurseries. Soil solarization appears to be a promising technique for disinfesting the upper layer of soil in container nurseries.
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