While there is no cure for Sudden Oak Death or other P. ramorum-associated diseases, there are preventive measures that may protect plants. The publication “Protecting Trees from Sudden Oak Death Before Infection” provides helpful treatment information for areas not currently infested but at risk. More information and links to other resources can be found below. See the 2016 updated treatments for sudden oak death.
If oaks dominate the site and are the preferred species, consider removing California bay laurels within 15 feet of the trunks of valued oaks, as California bay laurels greatly contribute to disease spread. Keep in mind that bays are important for many wildlife species, and should the oaks be lost, bay trees may be the only remaining mature trees. Combining bay removal with chemical treatments may be a viable option if the oaks are very high-value and removal of the California bay laurel will not diminish landscape value. More information about removing bay trees that are growing near susceptible oaks is available at the Phytosphere Research website.
The California Department of Pesticide Regulation approved a special local need registration for Agri-Fos® fungicide in October 2003. It is currently the only chemical treatment approved by the State for use against Phytophthora ramorum infections on oaks and tanoaks. The compound is best used as a preventive measure and is NOT A CURE, but it may help protect trees from infection. Guidance for application and use of Agri-fos® is available at the UC Berkeley Forest Pathology and Mycology laboratory.
Agri-fos®’s,active ingredient is mono- and di-potassium salts of phophorous acid, and has a “Caution” warning label. Pesticides can be injurious to humans, domestic animals, desirable plants. Use all pesticides selectively and carefully. Follow manufacturer recommendations for application and disposal of surplus pesticides and containers.
Agri-fos® is a systemic pesticide, it may be injected or mixed with a surfactant and sprayed on the trunk for absorption through the bark Currently in Northern California one application per year is recommended, preferably in the fall. Applications should be made when the tree is actively transpiring, prior to the onset of very cold temperatures.
Since the treatment is preventive and must be made to healthy trees, and the pathogen’s distribution and activity is patchy and somewhat cryptic it is difficult to determine which trees to treat. Trees under consideration for treatment should be adjacent to known infestations.. Treatment is not recommended in areas where infested plants are not already present within about 0.5 miles.
For isolated infestations (more than 25 miles from known infested areas), an aggressive vegetation management approach may be worthwhile to prevent spread to adjacent areas. Infected and adjacent healthy host trees are removed or treated with herbicides and re-sprouting monitored for re-infection. Guidance from a registered professional forester is recommended, see the contacts section to find guidance available by county.
In heavily infested areas, inoculum levels are thought to be too high to reduce via removal of infected plant material, but in cases where the pathogen appears to be detected at a very early stage these efforts may be worthwhile. P. ramorum sporeloads may be reduced through the removal of known infected trees and neighboring symptomatic hosts and the clean-up of host litter from under the canopy before winter rains enhance spore dispersal. Before implementing any aggressive removal treatments with an aim of reducing innoculum loads, you should first confirm: (1) the presence of P. ramorum through laboratory testing; and (2) the distribution and relative abundance of the pathogen in the area. Guidance from a registered professional forester is recommended, see the contacts section to find guidance available by county.