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.