Information from COMTF
COMTF (California Oak Mortality Task Force)
“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 CA 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 CA 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 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 preventative measure and is NOT A CURE, but it can help protect trees from getting infected, as well as suppress disease progression in very early infections.
The phosphonate compound may be injected or mixed with a surfactant and sprayed on the trunk for absorption through the bark.
Both application methods take four to six weeks for the material to be assimilated by the plant. So, it is recommended that initial applications be applied either in the fall after temperatures drop (usually November to early December) or in the spring after new leaves emerge (late March to April). The first year the treatments should be applied once in the fall and repeated again in the spring or vice versa. Every year thereafter the treatment should be administered in the fall (note: if the first treatment is administered in the fall and the second in the spring, the first follow-up annual treatment should begin in 1.5 years in the fall and then annually in the fall thereafter).”
Tree Solutions: The preference for the fall timing of Agrifos applications is related to the benefits of having a recent application of the systemic fungicide, with enough time for uptake and distribution throughout the tree tissues, to be in place for the rainy season infection cycle. But the material is only effective if the tree can absorb it at the time of application.
This general recommendation does not take into account important specifics about dormancy of black oaks which is well underway in November and also drought conditions that prevail in the fall of the year on the California coast. These factors should be considered in deciding on the timing of application for best uptake by the tree of the fungicide solution, spray or injection.
If the property has no black oaks, only coast live oaks, then an application in November may be effective. Black oaks should be treated while they are still transpiring (before they lose their leaves), so that means early to mid October spray timing. It is not practical or cost-effective to treat one species and then make a second trip for application to the other species on the property, so in an area where the species are mixed, the October timing should be considered.
Injection should be considered for the spring timing, due to prevailing drought conditions in the fall and limited uptake of solution.
Waiting for 1 ½ years to re-apply, just to get in synch with a fall application routine, doesn’t make sense when research personnel have stated that the material is most effective for one year . The scientists and agencies have to come up with very general recommendations and often don’t take into account the individual property, species mix, micro-climate, and soil moisture situation.
Have your on-site arborist make the final recommendations for application timing, which for cost effectiveness must include materials availability, geographical grouping of applications and seasonal scheduling issues.