Seems the greater LA area is ground zero for the introduction of yet another exotic beetle which is killing our our beautiful native oaks and sycamores, our landscape trees, even our beloved avocado trees.
The good news is that the fungal disease propagated by the beetle can be treated if detected early. You’ll need the services of a professional arborist, but the cost of treatment will likely be less than the cost of tearing out a mature tree.
Look at this link to UC Riverside’s Eskalen Lab. Here they have several PDFs on identifying and treating the disease. They also have a map showing the spread of the disease. Of course, these are only reported infections–it could be much more widely spread.
(Note: a separate invasion was recently detected in the commercial avocado groves of San Diego county, so folks further south should be on alert too.)