Sudden Oak Death

Sudden oak death, caused by the pathogen Phytophthora ramorum, is a potentially devastating disease. Recently, P. ramorum has been found in nurseries in the eastern United States. Sudden oak death has not been found in the eastern United States nor has the pathogen, P. ramorum been found escaped in the eastern United States. The impact this disease could have on the southern Appalachians is unknown but it has the potential to severely alter the biodiversity and decimate the populations of oaks, one of the most abundant group of trees in the eastern United States. The disease, first found in coastal California in 1995, was thought to be restricted to California but in April 2004, P. ramorum was detected in 14 nurseries in Georgia. In the eastern United States, it has also been detected in Florida. Whether the disease is in other eastern states or spread beyond the nurseries is as of yet undetermined.

Sudden oak death causes cankers on the stems of oaks. Trees often bleed a reddish or black ooze from the cankers. Under the bark of infected trees, necrotic tissue surrounded by black zone lines often can be found (USDA - Forest Service 2002). Cankered trees may survive for one to several seasons. Once crown dieback begins, leaves turn brown within a few weeks.

The disease usually does not spread from oak to oak since it rarely produces spores from infected oaks. However, the pathogen infects many species of shrubs. Two common genera for host plants are Rhododendron (common in the Appalachians)and Camellia (USDA - APHIS 2004). These shrubs are not killed, but spores are readily produced on infected leaves, which display spotting and blighting symptoms. Another common symptom is twig dieback. For more information as well as an updated host list click here.