The problem is, it doesn't just infect oaks, but several other plant species like California bay laurel. The pathogen lives as an endophyte in the leaves of bay laurel without killing the host or even causing significant damage, yet still spreading the disease. In fact, one method to control the disease is to physically remove all the bay laurel trees from an area you would like to protect. How well this actually works is not clear to me, but I haven't kept up with the literature.