Combating Sudden Oak Death

Incidences of Sudden Oak Death in California are being monitored to combat the disease. Residents in Los Altos and Los Altos Hills recently gathered to learn how to treat and protect trees from the disease, where so far few trees have been infected. Researchers at UC Berkeley have predicted that the disease could eliminate 90% of California’s black oak and live oak trees with 25 years if steps aren’t taken to control it. A survey of the area’s trees conducted in May showed that nearly 10 times more trees were infected with the disease than the previous year, with the highest incidence in East Bay, Saratoga, and Sonoma. Los Altos and Los Altos Hills are thought to have a low disease incidence because of the landscaped nature of the area with less native vegetation.

Sudden Oak Death showed up in California less than 25 years ago when infected California bay laurels and other infected plants were introduced into the landscape. Laurels can have the disease without dying, but once an oak gets the disease, it will die. Oak trees can be treated with an annual injection or bark application of phosphite, which has minimal environmental impact and increases resistance to the disease.

Residents can help stop the spread of the disease by cleaning garden tools and vehicles of soil and debris from infection sites and buying ornamental plants from nurseries that test for the disease.


Mapping to Proactively Reduce Sudden Oak Disease and Death

Designed to help protect historic heritage trees, a comprehensive map, called SODMAP, details the spread of sudden oak death – a tree-killing microbe. The disease is spreading from the forested hills into residential areas all over the Bay Area, and it has already killed hundreds of thousands of oak trees from southern Oregon to Big Sur. The map is to be updated annually to track the movement of the disease, which will help cities and counties plan projects to keep the disease from spreading and to preserve healthy trees.

The disease, most aggressive during the rainy season, was discovered in Mill Valley in 1995. It kills both big oak trees and the smaller tan oaks. Other plants, like the California bay laurel, camellia, and rhododendron, are host plants of the disease. Any oak less than 0.6 miles from the disease is at a high risk of becoming infected. The disease is also spread through the water. Arborists and ecologists predict that in 25 years, 90% of California’s live oaks could die from the disease.

This map may counteract this worst-case scenario. “People need to know that if they can take action before their trees are infected, then they can really slow down the rate of infection and minimize the number of trees that are infected,” says MatteoGarbelotto, a UC Berkeley forest pathologist who helped create the map. “The biggest hindrance to protecting oaks is that people don’t think about it until the trees are infected, so the more we let people know there are these tools, the more they will know they can do things to make things better.”

There are three recommendations to help mitigate the spread of the disease:
1. Remove California bay laurels that are near oaks – this increases the survival rate of oaks tenfold.
2. Use phosphonate spray – it’s effective against the disease.
3. Avoid big projects like soil removal, grading, or tree pruning during the rainy season in infected areas.