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Sudden oak death is a new disease capable of causing a range of symptoms from leaf spots to plant death on many woody hosts, not just oaks. It has changed the ecology of coastal California forests and is spreading in larch plantations in the United Kingdom. Because its host range has been unpredictable, there are surveys and monitoring programs for the pathogen throughout the southeastern U.S.

CAUSES and GEOGRAPHIC DISRTIBUTION

Sudden oak death is caused by Phytophthora ramorum (a water mold). The historical origin of the pathogen is unknown but it was first described in Europe on ornamental Rhododendron sp. and Viburnum sp. in 2001. In 2002 the pathogen was reported in California and Oregon and has since been found in western Canada.

HOST RANGE

Many woody hosts are affected. Oaks are dead end hosts for the pathogen because they do not sporulate from the lesions produced on the tree trunks. On other hosts the disease is foliar and these hosts may drive epidemics.

SYMPTOMS

Symptoms of this disease vary from host to host. Symptoms may progress rapidly after infection or may not be visible for significant periods of time. Symptom progression is favored by temperatures near 20 degrees Celsius (68 degrees Fahrenheit).

SPREAD of PATHOGEN AND CONTROL OPTIONS

The pathogen can be spread by movement of infected host material, infested soil, irrigation water, and wind-blown rain. Unintentional movement of infected but asymptomatic nursery stock is also a potential means of pathogen dissemination

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Prepared by Philip F. Harmon and Carrie Harmon, UF/IFAS Department of Plant Pathology. Revised by Erica Goss, EPI and UF/IFAS Department of Plant Pathology.