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This year there were several reports of dead tops developing on larger ponderosa pines in the southern Willamette Valley. When a tree’s top turns from green to orange relatively quickly, it indicates an abrupt shut off of moisture flow to the foliage. Animals such a porcupines or tree squirrels can cause top-kill by stripping off a tree’s bark and girdling the upper bole. However, during periods of below normal precipitation, such as western Oregon has experienced in 2001 and 2002, attacks by a bark beetle, the California fivespined Ips, are often the cause of top-kill in pines. Damage is most noticeable in large trees growing on droughty, exposed sites where they are subject to higher temperatures and levels of evapotranspiration (water loss). Various forms of human disturbance such as house construction and road building can damage tree roots and increase susceptibility to bark beetle attack and top-kill.
Tops infested with beetles generally turn color in the late summer or fall of the year of attacked, or during the following spring.
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Most signs of a beetle infestation in the top of a tree are difficult or impossible to observe from the ground. Early indications of Ips attack are orange-brown boring dust in bark crevices and the presence of wishbone shaped gallery chewed by the beetles under the bark. The presence of a blue stain in the sapwood of the dead top is also characteristic of Ips attacks. The only obvious sign of beetle attack that is usually visible from the ground is the removal of bark by woodpeckers feeding on beetle larvae. In some cases woodpeckers strip bark from infested trees while the tops are still green.
The prognosis for large pines with dead tops is not good. Often trees with top-kill become infested by another bark beetle, the red turpentine beetle. Between attacks on the upper bole by Ips and attacks on the lower bole and root collar area by red turpentine beetle, many trees die completely within a few years. Since dead tops eventually fall out of pines, these tops should be removed if they pose a hazard to people and nearby structures. Dead tops can be disposed of at leisure, since by the time the damage is visible, the Ips outbreak is over.
