Invasive Species Spotlight: Sudden Oak Death

Sudden Oak Death (SOD) or ramorum blight was first identified in the United States in 1995 in coastal forests in Northern California. Since then it has spread to another relatively isolated area in Southwest Oregon. It has also been identified in some areas of Europe; scientists are unclear to the origins of this disease. It has been responsible for the death of thousands of western Oak trees.

Figure 1. Forest with oak trees dying of Sudden Oak Death. (Photo credit: David Rizzo)

This disease is caused by Phytophthora ramorum a ‘fungus-like’ organism that spreads by producing spores transported locally by wind and water or regionally through insect infestations and the sale and acquisition of ornamental trees and shrubs.

Some of the first symptoms of the presence of SOD include: a dark red to black tar like sap oozing from the trees bark and wilting and dieback of foliage and stems. Often new branches will resprout on the dying tree in large numbers but will eventually wilt and die too. Once the tree is in this state of decline it is further susceptible to other insect and environmental problems like bark beetles and drought. An infected tree can die in as little as one year from these compounded problems. Although SOD has been found on other plants like Rhododendrons and Viburnums it has not shown to be as fatal to them. Serving as hosts for the pathogen, these plants may suffer leaf spot and twig blight.


Two common Oak trees in Illinois, Northern Red Oak (Quercus rubra) and Northern Pin Oak (Quercus paulustris), are known to be extremely susceptible to this disease which could lead to severe problems for the state. Invasive fungal diseases can be very dangerous. Although this disease has not yet been found in Illinois, it is of great concern for two main reasons. It has the potential to eliminate hosts – much of eastern North America is covered with deciduous forests that include oaks and shrub species that serve as disease reservoirs. Secondly, this pathogen infects several shrub species that grow in the wild and in domestic settings. Ornamental shrubs grown horticulturally could carry the disease to uninfected areas.

There are several other pests and diseases which can cause the decline of Oak trees but not many of them that are potentially as troubling as Sudden Oak Death. All suspect trees should be properly diagnosed by pest management specialists.