The Trail Companion

Fall 2000

Sudden Oak Death

...continued.

Protecting Our Trees

What treatments are available to protect our trees? As a practicing arborist, I can tell you the best recommendation for healthy trees is proper. It is not always feasible to protect trees in a forest setting, though it is done in some cases. Trees of importance should receive proper care, which includes:

Proper pruning, removing dead, dying and damaged branches.
Discouraging other insect defoliators, which are on the rise.
Irrigating drought stressed oaks and seedlings during summer to maintain vigor (during normal rainfall years, established oaks do not generally need extra water) Slow water away from the trunks inside the dripline once every 3-6 weeks for about an hour. Do not overwater and keep water off the trunk of the tree.
Avoid soil compaction or grade change around the base of the tree.
Regularly checking tanoaks and other oaks from March to October for bleeding from the bark and boring dust (frass) from beetles.

If trees show symptoms, measures should be taken to protect still healthy trees, including proper handling of infected wood:

Promptly cut down trees showing advanced symptoms. They are breeding grounds for future beetle attacks on additional trees. Chip the brush and immediately cover firewood for six months to prevent further beetle emergence. Stump grinding is recommended, as beetles are attracted to stumps as well.
Do not remove infected wood and brush from the site! The pathogen can be transported to a previously unaffected area through firewood, chipped wood, or even soil on equipment, tires or boots.

Coast live oak (Quercus agrifolia)

Proper care is the only option now available to maintain susceptible trees. Spraying the trunks of individual trees to eight feet above the ground with the insecticide Astro™ (permethrin) may slow decline of infected oaks by preventing beetle attacks, but will not prevent death. The syndrome is not fully understood and there is no remedy once a tree has advanced symptoms. Often trees are beyond saving even at the earliest stages. Hopefully the mystery of Sudden Oak Death will be solved, or like most plant disease/insect epidemics, this one will run its course and recede in time.

For additional information, see the CAMFER (UC Berkeley's Center for the Assessment and Monitoring of Environmental Resources) website and the UC Cooperative Extension Sudden Oak Death website.

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Sudden Oak Death

Oak Mortality Syndrome