Sudden Oak Death

Robyn Cole
Frederick County Master Gardener Program

Sudden Oak Death (SOD) is a tree and plant disease which mostly affects Oaks. It began to appear in California and in Europe in 1995. SOD has spread through 16 counties in California, even infecting redwood trees. SOD was first discovered in Oregon in 2001. Oregon recently reported the good news that the disease has been contained on 88 acres of land. Currently there are around 39 states affected by this disease. Its origins are not known. SOD is made up of three parts: the first is a fungus pathogen called Phytophthora ramorum; it destroys the vascular system of the tree. The second part is actually three beetles: two different types of Oak ambrosia beetles and one Oak bark beetle. They weaken the health of the tree. And the third is another fungus called Hypoxylon thouarsianum; this decays the tree.

It can spread from mud on peoples' shoes, bike tires, cars, and forest animals. Even from irrigation water from infected streams. The most common way it is spread though, is through rain splashes from other infected trees.

Why should we worry about SOD here in Maryland? Some of the nurseries from California that are importing plants to Maryland may have been infected by SOD. There are over 60 different species of plants that are affected by SOD. Maryland has many possible hosts, including Douglas fir, oak, western starflower, rhododendron, lilac, mountain laurel, camellia, and viburnum. Because Maryland has so many hosts for this disease, SOD could kill thousands of our trees and plants, devastating our forests, and changing the landscape. However, only plants bought and planted within the last two years could be hosts.

For trees, symptoms of bleeding or oozing can occur on the outer bark-usually on the lower 6 feet of the trunk. Cankers in the inner bark could occur as well, surrounded by a black line. For other plants, there could be leaf spots, leaf drop, tip dieback and stem lesions. These are symptoms of many other diseases, so unless you have bought and planted one of the host plants within the last two years, it is unlikely that your plant has SOD.

What treatments are there for SOD? One way is to use chemicals on trees and plants, which is helping slow down the disease; California uses this method. Oregon's method is to cut and burn around the perimeter where plants and trees are affected, stopping the disease from spreading elsewhere. Since, (in Maryland) very few infected plants have been reported, Maryland is using prevention as a control. To prevent the disease from spreading throughout the country, all nursery plants known to harbor the disease in California and Oregon are inspected before being shipped to other states. Some nurseries have been quarantined. Any plants that are found infected will be destroyed.

In May, 2006, the House of Representatives passed an agricultural bill allocating $7.7 million for research targeting Sudden Oak Death.

What should I do if I suspect I have an infected plant or tree?

Some options for getting treatment would be to contact the Maryland Home and Garden Information Center at 1-800-342-2507, 8 A.M. - 1 P.M. M-F, or or the Maryland Department of Agriculture at