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Ramorum Blight & Sudden Oak Death

Phytophthora ramorum, a water mold, is a pathogen that causes rapid declines in multiple species of oak, usually in the form of Sudden Oak Death and foliar blights. This species falls into the same genus as the more well-known Phytophthora infestans, the cause of the Irish potato blight and subsequent famine. P. ramorum was first discovered in the United States in coastal California, in 1995, on a declining tanoak tree. Since then, the pathogen has spread to fourteen counties in California as well as Curry County, Oregon.

P. ramorum is spread through the movement of infected plant material, soil and rainwater. The "sickly six" most susceptible nursery stock genera are magnolia, kalmia, camellia, peiris, viburnum and rhododendron. Symptoms of P. ramoruminclude large cankers on the bark of tree trunks or the main stems of herbaceous plants and secondary infection by other pests. The bark cankers often “bleed,” where the infected bark exudes black fluid that dries into a crust. This water mold can also cause dark grey or brown lesions, with indistinct edges, to appear on the leaves of the infected plant and twig dieback. Infected trees can die within months of the initial infection.

DPI regulates the movement of plant materials into and out of South Carolina to prevent the introduction of nonnative pest species. DPI, in coordination with USDA-APHIS-PPQ, surveys for P. ramorum through water and foliage samples. 

Ramorum blight is a foliar blight on nursery stock that typically does not kill the plant P. ramorum develops into bleeding cankers in trees, causing sudden oak death

If you think you have a plant infested with P. ramorum that exhibits symptoms of sudden oak death or foliar blights, please send images to invasives@clemson.eduor call the Invasive Species Program at 864-646-2140.

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