There are many tree diseases out there right now, in both our forests, where millions of trees are dying from a variety of tree diseases, and in our cities, where street trees are being killed by many of the same tree diseases.

One of the most pervasive of these is called Sudden Oak Death (Phytopthora Ramorum). This fungal disease has killed over 60 million trees and counting.  It has now been declared as "Unstoppable" by experts as UC of California, Davis.  This tree disease, classified as a "water mold",  was first identified in  California in 1995, and quickly spread,  as the trees had no natural defenses against the disease, which they believe was brought into the country as nursery stock from possibly Asia.

Trees develop resistance to tree diseases and insects over many years, decades, even centuries, so when a new disease suddenly shows up, they are not able to develop tree disease resistance compounds rapidly enough to defend themselves.  There are many tree diseases that have making trees sick in our forests for centuries, but for the most part trees can defend themselves against these as they have evolved defenses over time, so the diseases are usually only able to invade trees that are weak, or stressed,  such as from drought.
Although this disease has spread to the point in our forests, that it cannot be eradicated, it is possible for the private property owner to protect their trees. Live oak, Tan oak, and other Oak trees can be treated for this disease, and the tree disease treatment is most effective if done preventatively.

The treatment can be done by either a tree professional, such as an ISA certified Arborist, or by the homeowner using a technique called a "Basal Drench", which is just a term for spraying around the lower section of the trunk, below the lower branches. This is the "Basal"  section of the tree.
By applying the product here, it  is taken systemically into the tree and protects and defeats the tree disease organism.