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Sudden Oak Death

Phytophthora ramorum Werres et al. (Peronosporales)

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Phytophthora ramorum is one of several species of fungus-like water molds (oomycetes) that are can infect to plants. The origin may be from Asia, but this is uncertain. In California Sudden Oak Death was first reported in in 1994 in Marin and Santa Cruz counties, after which it spread through most of Northern California into Oregon and south along the Pacific coast. However, there is a possibility that it could invade the eastern United States as well.

How the pathogen is transmitted is uncertain, but insects are not believed to be involved. Infection results in spores that may be spread by wind and rain. Plant nurseries may also inadvertently be instrumental in spreading the infection. P. ramorum is now a major threat to California woodlands.

Symptoms are cankers on a tree's trunk, foliage dieback, and eventual death. There is a wide host range including over 40 California tree and shrub species with variable susceptibility to infection. Some trees, like tanoak (Lithocarpus densiforus) and coast live oak (Quercus agrifolia), show high systemic infection and high mortality. The most susceptible species exhibit browning foliage and death within one year. Others species like California bay laurel (Umbellularia californica), show only foliar lesions and mild twig dieback, and they continue to spread the pathogen. The United States Forest Service estimates that by 2022, Sudden Oak Death killed over 1 million trees in central & northern California.

REFERENCES:

Brasier C. & J. Webber. 2010. Sudden larch death. Nature 466: 824-825.

Cobb R. C., R. K. Meentemeyer, & D. M. Rizzo. 2010. Apparent competition in canopy trees determined by pathogen transmission rather than susceptibility. Ecology 91 (2): 327-333.

Davidson J. M., H. A. Patterson, & D. M. Rizzo. 2008. Sources of inoculum for Phytophthora ramorum in a redwood forest. Phytopathology 98:860-866.

Davidson J. M., H. A. Patterson, A. C. Wickl, E. J. Fichtner & D. M. Rizzo. 2011. Forest type influences transmission of Phytophthora ramorum in California oak woodands. Phytopathology 101: 492-501.

Eyre, C. A., K. J. Hayden, M. Kozanitas, N. J. Grünwald & M. Garbelotto. 2014. Lineage, temperature, & host species have interacting effects on lesion development. In: Phytophthora ramorum. Plant Disease 98: 1717-1727.

Fichtner, E. J., S. C. Lynch & D. M. Rizzo. 2007. Detection, distribution, sporulation, & survival of Phytophthora ramorum in a California redwood-tanoak forest soil. Phytopathology 97: 1366-1375.

Frankel, S. J. 2008. Sudden oak death & Phytophthora ramorum in the USA: a management challenge. Australasian Plant Pathology 37: 19-25.

Goheen, E. M., E. Hansen, A. Kanaskie, N. Osterbauer, J. Parke, J. Pscheidt & G. Chastagner. 2006. Sudden Oak Death & Phytophthora ramorum: a guide for forest managers, Christmas tree growers, & forest-tree nursery operators in Oregon & Washington. Extension Publication EM 8877, Oregon State University. 16 pages.

Grünwald, N. J., M. Garbelotto, E. M. Goss, K. Heungens & S. Prospero. 2012. Emergence of the sudden oak death pathogen Phytophthora ramorum. Trends in Microbiology 20: 131-138

Grünwald, N. J., E. M. Goss & C. M. Press. 2008. Phytophthora ramorum: a pathogen with a remarkably wide host range causing sudden oak death on oaks & ramorum blight on woody ornamentals. Molecular Plant Pathology 9: 729-740.

Kamvar, Z. N., M. M. Larsen, A. M. Kanaskie, E. M. Hansen & N. J. Grünwald. 2015. Spatial & temporal analysis of population of the sudden oak death pathogen in Oregon forests. Phytopathology 105: 982-989.

Kline, N., S. Navarro & D. C. Shaw. 2018. Sudden oak death: prevention, recognition, restoration. Extension Publication EM 9216, Oregon State University. 12 pp.

Parke, J. L. & C. Lewis. 2007. Root & stem infection of rhododendron from potting medium infested with Phytophthora ramorum. Plant Disease 91: 1265-1270.

Peterson, E., E. Hansen & J. Hulbert. 2014. Source or sink? The role of soil & water borne inoculum in the dispersal of Phytophthora ramorum in Oregon tanoak forests. Forest Ecology & Management 322: 48-57.

Rizzo, D. M. & M. Garbelotto. 2003. Sudden oak death: endangering California & Oregon forest ecosystems. Front. Ecol. Environ. 1: 197–204.

Venette, R. C. & S .D. Cohen. 2006. Potential climatic suitability for establishment of Phytophthora ramorum within the contiguous United States. Forest Ecology & Management 231: 18-26.

Vercauteren, A., M. Riedel, M. Maes, S. Werres & K. Heungens. 2012. Survival of Phytophthora ramorum in Rhododendron root balls & in rootless substrates. Plant Pathology 62 (1): 166-176.

Webber, J F., M. Mullett & C. M. Brasier. 2010. Dieback & mortality of plantation Japanese larch (Larix kaempferi) associated with infection by Phytophthora ramorum. New Disease Reports 22: 19.

Werres, S., R. Marwitz, W. A. Man, T. Veld, A. W. A. M. de Cock, P. J. M. Bonants, M. de Weerdt, K. Themann, E. Ilieva & R. P. Baayen. 2001. Phytophthora ramorum sp. nov., a new pathogen on Rhododendron & Viburnum. Mycological Research 105: 1155-1165.