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Sudden Oak Death

Sudden Oak Death

An exotic pest that we do not want in Michigan
(Information Provided By: Andrew J. Storer, Assistant Professor of Forest Insect Ecology, Michigan Technological University)

Tens of thousands of oaks have been killed by a new disease known as Sudden Oak Death (SOD). SOD was first reported in California in 1995. As of fall 2001, the disease has been confirmed in eight counties along the central California coast, and now in an isolated area in southern Oregon.

What is the Sudden Oak Death pathogen, (Phytophthora ramorum)?

This species has only recently been named following its discovery as a pathogen on rhododendrons in Germany in 1992. The pathogen, isolated in 2000 from dead and dying oaks in California, is the same species as that found in Germany on rhododendrons. This pathogen causes a canker disease in oaks referred to as Sudden Oak Death along with numerous other diseases, including leaf spot and shoot dieback in a number of other hosts.

Symptoms of Sudden Oak Death

  • Bleeding or sapping from the main steam or trunk

  • Wilted shoots

  • Bark beetle infestation

  • Rapid change in foliage color from green to brown

Bleeding or sapping from the main steam

The first symptom is bleeding, an oozing or seeping of a reddish-brown to tar black thick sap. Bleeding typically occur first in the lower bole of trees


seeping of a reddish-brown to tar black thick sap

Dark spots on bark with exuding brown to tar black thick sap.


Black Zone Lines

Black "Zone Lines" are found under cut away bark.

Transmission of Phytophthora ramorum

Field observations suggest that the pathogen is transmitted through the air.  Therefore leaf infections of other hosts is associated with increased likelihood of disease in neighboring oaks. Much, however, remains to be learned.

Defining the threat in the Great Lakes Region

Pin oak (Quercus palustris) and northern red oak (Quercus rubra) are equally or more susceptible to this pathogen than the three oaks affected in California suggesting that species in the Great Lakes Region are at high risk to the disease.
The pathogen favors cool, moist conditions and further research is needed to determine if environmental conditions and other factors in eastern and northern forests are suitable for establishment and spread of the pathogen

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