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Bark Beetle Control

Most species of bark beetle are very small, and not commonly seen unless bark is removed from an infested tree. They are not found flying around or crawling on branches or the outside of the trunk.

Fading foliage (changing from green to yellowish-green to sorrel to red and finally to rusty brown) is frequently the first sign of attack. By the time the needles have faded to red the tree is dying. Other signs are many pitch tubes (globules of pitch ¾ to 1¼ " in diameter) on the trunk, and reddish-brown boring dust in bark cervices or at the base of the tree, produced when the beetles bore into the bark.

The only known direct control method is the removal of infested trees. A good rule to follow is “If the tree is brown cut it down -- if in doubt cut it out.” Finding boring dust means that even if the tree is still green it should be cut down. If dead trees are left standing they may provide a new generation of beetles to attack more trees.

Thinning overly dense stands is a good long-term strategy to prevent future bark beetle damage. Thinning can increase individual tree vigor provided the remaining trees are healthy. Thinning should be done in the fall after most beetles have completed their flight period.

Improper logging and tree thinning activities can actually contribute to bark beetle outbreaks. If thinning is done in the spring and early summer, immediate slash removal is critical. Bark beetles breeding in slash, stumps and other debris can spread to standing live trees from 3 to 6 miles away.

If slash is left on site, even in the fall, it should be bucked into short sections or chipped to accelerate drying to reduce the suitability for bark beetles. The bark from all logs and slash should be peeled and burned or piled and covered with plastic sheeting and stored in the sun for an extended period of time.

Even firewood removal can spread bark beetle infestation by transporting infested wood to new areas. Gathering firewood from forests infested with bark beetles should be discouraged.

Injection of insecticides or systemics has been shown to be completely ineffective in killing bark beetles or larvae already in the tree. Sometimes a tree will have a fading crown but the lower branches will still be green. Topping the tree, or removing the crown, will not save the tree. The tree has already been weakened from the attack to its upper trunk. If bark beetles are not yet in the lower part of the tree, it will soon be attacked by beetle species that target the lower trunk. Prevent the spread of bark beetles from this tree to others by removing it as quickly as possible.

There are several miracle cures being promoted to save trees from bark beetles. These materials may not have gone through extensive research to test their effectiveness. Buyer beware! Often, if what is being marketed sounds “too good to be true” it generally doesn’t live up to its billing. It is against the law to use unregistered pesticides and using pesticides for insects not listed on the label is unwise.

J.G

References

DeMars CJ and BH Roettgering. 1982. Western pine beetle. Forest insect and disease leaflet 1. USDA Forest Service.

Massey CL and DL Parker. 1981. Arizona five-spined ips. Forest insect and disease leaflet 116. USDA Forest Service.

Wilson JL. 1997. Engraver beetles in Southwestern pines. USDA Forest Service.

Preisler HK and RG Mitchell. 1993. Colonization patterns of the mountain pine beetle in thinned and unthinned lodgepole pine stands. Forest Science 39(3):528-545.

USDA Forest Service Region 3. 2002. Memo. "Early alert: western bark beetle activity."

Last edited June 25, 2003

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