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Home  > Tree Care  > Tree Diseases  > Sudden Oak Death

Sudden Oak Death

Phytophthora ramorum

California forestry officials began to notice a significant decline in the Tanoak population in 1995. In 2000 scientists isolated and identified the cause of the decline to be a new disease in California called Sudden Oak Death. The disease was quickly confirmed in eight counties by 2001 and has now been confirmed to be present in southwest Oregon.

Sudden Oak Death is a canker disease that has been found to infect and kill several species of oak. The most susceptible oak species is the Tanoak. The disease has also been found to infect over 100 other plant species, but often with less significant consequences. Sudden Oak Death is an aggressive disease that will infect and kill healthy oak trees.

Sudden Oak Death is most active, and most likely to infect new trees, during periods of cool, moist weather. Spores of the disease may be windblown to healthy trees or may be present in the soil. Spore build-up may occur in an area where plants other than oak trees are infected with the disease. Whenever possible work on oak trees should be performed from June to October when the weather is generally drier and warmer.

A quarantine zone has been established due to the aggressive nature of this disease and the potential for damage to other areas of the country. Movement of regulated materials is allowed within the quarantined area, but movement outside of the quarantine zone is by permit only. The California counties quarantined due to Sudden Oak Death include Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and Sonoma counties.

 

Black zone lines under infected oak bark

 

Trees infected with Sudden Oak Death



Sudden Oak Death has been confirmed in California Black Oak, Canyon Live Oak, Coast Live Oak, Shreve Oak, and Tanoak trees. A Sitka Spruce in Ireland was confirmed to have been infected with Sudden Oak Death by an infected Rhododendron growing under the tree.

Symptoms of Sudden Oak Death



One of the first symptoms of Sudden Oak Death is dark spots on the tree that exude a dark, thick sap. Infected trees may also be infested with bark beetles or experience a sudden change in the color of the foliage from green to brown.

How to control Sudden Oak Death



Proper cultural methods such as mulching, fertilizing, and watering to keep trees healthy does not guarantee a tree will not be infected with Sudden Oak Death. This disease can infect and kill healthy oak trees.

Arborists do have a fungicide treatment that can be used on healthy oak trees to reduce the potential for infection of Sudden Oak Death. The product, called Agri-Fos, can be injected into the tree or used with a surfactant called Pentra-Bark and sprayed on the trunk of the tree.

Removing infected Oak trees with Sudden Oak Death




Arborists need to exercise extreme caution when removing oak trees infected with Sudden Oak Death. Trees infected with the disease appear to be more prone than normal to rapid decay and tree branches, or the entire tree, may fail unpredictably. Wood failures have occurred on trees within a few months of dying and in some cases even when the trees were still green. Homeowners should consider hiring a professional arborist to remove any trees infected with Sudden Oak Death.

Stump grinding is not recommended for trees infected by Sudden Oak Death. Stump grinding may result in the stump grinder becoming contaminated with soil which could then spread the pathogen to another location.

Bleeding ooze from Sudden Oak Death canker

Leaf and twig dieback on Tanoak

A hillside in Big Sur devastated by Sudden Oak Death

Canker on oak tree infected with Sudden Oak Death

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