My pines are infested with bark beetles – now what?

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Driving into the Collins Forest early last winter I glanced up into the canopy and saw a disheartening sight.  A dozen large ponderosa pine trees had “bark shavings” and red foliage from top to bottom or tops that appeared to be dying.  These were the familiar signs and symptoms of a bark beetle infestation.  What to do?  This unfortunate situation is one that many forest landowners are confronted with from time to time.  The basic options are:

  • Do nothing
  • Cut down the trees and dispose of the material by burning or chipping
  • Cut down the trees and remove them from the site

Each of these can be an appropriate response, depending on the situation.  Is there a market for the wood?  Will it pay its way out of the woods?  How much volume is there – enough to interest a logger?  Is there good access?  Is the terrain steep?  Is disposal of the material by burning or chipping feasible?  Are there nearby dwellings or structures at risk from a falling beetle-killed tree?  Are bark beetle larvae or adult beetles still present in the standing trees?  What are the consequences of not removing the infested trees – or removing them?   The answers to these questions will help determine which option is chosen.

In SW Oregon, the western pine beetle (WPB) and the ips beetle are the bark beetles of greatest concern for ponderosa pine.  Mountain pine beetles and red turpentine beetles may also be present.  Sometimes a single tree may host more than one species of bark beetle. 

The western pine beetle infests ponderosa pine greater than 6” DBH, usually trees that are stressed from drought, root disease or other factors and/or are growing on overly dense sites.  The foliage of infested trees turn light green, then yellow, then rusty brown and finally falls off.  A tell-tale sign of WPB infestation is the “bark-shaved” look – caused by woodpeckers hunting for beetle larvae.  The ips beetle attacks the tops of larger trees and smaller, pole-sized trees. 

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Do nothing?  For some, this idea may appear heretical – an invitation for the problem to spread and grow worse.  However, in many cases when the issue is discovered, the trees are already dead and the bark beetles are long gone.  It can be difficult to tell if a tree still harbors bark beetle larvae.  During the summer months, when there can be multiple generations of the WPB, the beetles often leave the tree before the foliage fades in color.  If the tree turns color in winter, the beetles usually are still present. 

Many recently killed trees will contain other beetle larvae – typically, those of wood borers.  These insects are not tree killers but rather are the “clean-up crew” that initiate the process of wood decomposition. 

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Felled beetle-killed ponderosa pine tree.  Note bark shaving and blue stain in sapwood.  The staining is caused by a fungus carried by the beetle.  The fungus plus up the water conducting tissues of the tree, hastening tree death. 

Removal of trees no longer containing bark beetles does not provide a forest health benefit.  Left standing, the trees will provide valuable wildlife habitat.  Removal is warranted if there is a fuels concern or if they would damage something if they fell. 

Cutting down beetle-killed trees is a common practice.  If bark beetles are still present in the trees before they are felled, cutting down the tree won’t by itself prevent beetle emergence.  Knocking off the bark, cutting up the tree and piling and burning it, or chipping it, are all ways of destroying bark beetle “habitat” and preventing beetle spread. 

In our case, about half the trees had bark shavings, indicating WPB attack, and the other half had dead or dying tops, indicative of ips beetle attack.  The trees were all in the 18” to 32” diameter range – nice large trees that we just hated to lose.  However, they were growing along a driveway and a few were located near a large storage shed, so there was a definite hazard to consider.  The trees started to fade in color in the late fall, and close examination of affected trees suggested that beetle larvae were still present inside at least some of the trees.  Removal of the trees could then – in theory – prevent spread to adjacent ponderosa pine trees that we were concerned about. 

But it was late January, only a month or two before beetle emergence, so we would have to act quickly.  A rough tally suggested that the dozen trees totaled about 7,500 board feet – three loads on a self-loading log truck. 

Which local mills wanted ponderosa pine trees?  Not many, apparently.  In fact, it appeared that basically no one was interested in ponderosa pine at that time.  Finally, we secured a local logger who was skilled, conscientious and, fortunately, had a purchase order for ponderosa pine that was about to expire.  The price was not great, however.

An additional complicating factor in this “sanitation-salvage” operation was the risk posed by generating fresh ponderosa pine slash.  The ips bark beetle is known to infest fresh pine slash, generally material in the 3” – 10” diameter range that is generated from January through July.  The beetle then emerges from the slash and may attack standing green trees.  The risk is greatest in drought years. 

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Ips beetles attack the tops of large trees and pole-sized trees.  Fresh pine slash, as in the foreground, is breeding material.  The problem is worse in drought years.  Photo: Donald Owen, California Department of Forestry and Fire Protection,

We would remove the boles of the trees down to a 6” small end diameter and take the logs and any resident beetles to the mill.  But what about all of the leftover material, the tree tops and large limbs that are 3” in diameter and larger?  This turns out to be quite a volume of potential ips habitat.  We dealt with this by including removal off-site of the leftover 3” – 10” material in the logging contract.   Since this had no value, it was an additional cost.

In the end, the operation was completed by early March.  We were very lucky to find someone who could do the work and had a market for the pine logs, and who was willing to do all the extra cleanup.  We didn’t make any money – in fact, there was a relatively small net cost.  But, we were able to salvage the logs, reduce the potential falling hazard, and reduce the risk of beetle spread to nearby trees.  The fact that the trees were close together and access was easy made a big difference.  Had the affected trees been on a remote, steep hillside, our approach would likely have been different. 

A final note: Your best bet to reduce the threat of bark beetles is to maintain healthy, vigorous trees.  That is usually accomplished by thinning to reduce stand densities.  Sanitation/salvage of beetle-infested trees can play a role in specific situations, but is not a viable long term strategy for improving forest health. 

Some great resources from the Oregon Department of Forestry:

Video-Bark Beetles Intro Part 1

Video-Bark Beetles in Pine

Fact sheet-Western pine beetle

Fact sheet-Ips beetle

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