Sawdust around tree may be sign of trouble

Q: My large old maple tree has some sawdust on the trunk; should I be worrying about it?

A: Mature trees can exhibit many different symptoms of disease or insect infestation.

If no one has climbed up with a chain saw when you weren't looking, the appearance of sawdust on the trunk or larger branches can indicate insect activity from beetles or borers. This symptom certainly requires investigation.

Here are some suggestions.

Sawdust generally emerges from holes bored by bark beetles. Unfortunately, a nickname for these beetles is "nature's undertakers" because they seldom attack fully healthy trees.

Some trees, in fact, will exert pressure from sap and veins that keeps bark beetles from being able to bore into the core. If the plant is diseased, the "pitch power" that repels beetles will be reduced and the insects can penetrate the tree. Look for holes and other evidence of insects along with the sawdust.

Late summer, while leaves remain on the branches, is a good time to check trees. (Also, it's sensible to get professional assistance with tree problems before storm season starts pruning their limbs or knocking them over.)

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The reason you want to look at the tree while it still has leaves is simple: a number of symptoms of tree decline will show up as alterations in the appearance of the leaf canopy. Browning or dead leaves in the crown (top range of branches) can be a serious sign of tree disease. It usually indicates that fluids from the tree's veins aren't reaching the top, and this may imply root disease or interruption in the vascular system.

Large trees can survive for a number of years with crown decline, but it's often the first sign of significant tree problems.

Individual branches can die one at a time, which can also be symptomatic. This can be caused by insects, birds or disease, such as verticillium wilt in maples.) It's often possible to prune out one branch with success, but if the pruning doesn't reveal healthy wood, suspect a larger problem.

After looking at the crown, check the trunk and major branches. Old wounds such as lawn-mower or string-trimmer damage, an open hollow cavity in a trunk, or a rotten, split area where branches attach will all lead to severe problems.

Mushrooms and fungal growths appearing on the bark definitely mean trouble.

The common hard, shelf-shaped fungus called "conks" will indicate decay within the trunk. (These are sometimes called "artist's fungus" because of the smooth white undersurface that irresistibly calls for engraving with a fingernail or pointed stick. Children enjoy finding these, but they bode evil for tree life.)

Any tree in a high-traffic area, or near a dwelling, should be taken down if it has extensive trunk decay. To get a professional diagnosis, consult with a certified arborist. Look for people whose qualifications indicate "certified arborist: or ISA" (International Society of Arboriculture).

Mary Robson is area horticulture agent for Washington State University/King County Cooperative Extension.