What’s Going On?

We’ve had several years of drought here in California, with the result that in January 2015 it was estimated that 22 million trees were dead then and tens of millions were likely to die by end of 2015. Another estimate listed 20 percent of California’s forests, up to 120 million trees were doomed.

A side effect of this has been an explosion of bark beetles and other insects that feed on stressed trees. 

A Bark beetle is described as "... not much larger than a piece of cooked rice. Not only are they small and difficult to see, their activity is often scattered and hardly noticeable. They survive in trees that are stressed, diseased, or injured; either by human activity or during storms or wildfires. Occasionally, small groups of standing trees may be killed but over the landscape they are often unnoticed. Bark beetles can increase dramatically when sufficient food is available. Typically this is in the form of drought-stressed trees. High numbers of these small beetles (outbreak populations) attack trees en mass. Often many trees are killed over the landscape; likened to that of wildfire. In many years, more trees are killed by bark beetles than by fire!"

Interestingly once a beetle finds a target tree it exudes a pheromone that attracts other beetles to the same tree for a mass attack. The beetles carry a fungus into the tree that also attacks the tree. The fungus seem to be the final straw that kill the tree.

The articles I've read describe attacks on large percentages of Monterey Pines and other native pines. There are a variety of bark beetles native to northern California. Most will attack any pine they find. 

How Trees Fight Back

When attacked by the beetles the trees produce pitch, aka resin, and attempt to drown the beetle. The tree may not be able to produce enough pitch to drown all the beetles in a mass attack. When a tree is stressed, such as in a drought, it may not be able to produce much pitch at all. 

Because our bonsai are much smaller I suspect they are more easily killed than trees in forests. 

Prevention, Not Treatment

I found references to two different types of airborne fungui that are attacking pines. They are Heterobasidion annosum and Fusarium circinatum. The references I've found say there is no treatment once the fungus has become established.

To prevent bark beetles from attacking your trees and bringing a fungus inside the wood you need to spray with an insecticide or use a systemic like Bayer All-in-One. There are a few variations of these products, including liquid and pellets. Rose & Flower All-in-One combines a low nitrogen fertilizer with neonicotinoid insecticide and a fungicide. The insecticide is supposed to kill beetles and other boring insects while the fungicide attacks the fungus infection. 

The advice is to sprinkle a couple of tablespoons of the pellet version on top of your soil and then water. You'll need to add more in a month or two because by watering every day the product will quickly be disolved.

Neonicotinoids are very effective against a lot of insects, but unfortunately are implicated in the mass death of bees. No final word on this yet, but it's a good idea to be careful in how widely you use this product.