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Bark Beetle Prevention

Tree Mortality in Flagstaff
Tree mortality in Flagstaff

Bark beetles are a common presence on forested land in Arizona. Populations of bark beetle species increase and decrease from year to year. This is a common phenomenon for insect populations. During the summer of 2002 bark beetle populations increased to unprecedented levels and continue to create a problem both for federal and state forested land and for private landowners. The damage caused by bark beetles is exacerbated by drought conditions in Arizona. Trees stressed by drought are especially vulnerable to bark beetle attacks. The spruce-fir forest of the Pinaleño Mountains near Safford suffered severe tree mortality from bark beetle and defoliating insect attacks during the early 2000s. Bark beetle attacks have killed large numbers of trees in the spruce-fir forests of the San Francisco Peaks. An estimated 100,000 pinyon pines are dying in the transition zone east of Flagstaff.

See the Bark Beetles section of the Forest Insect Pests Photo Gallery for photos of bark beetle adults, pupae, and larvae, their galleries (tunnels) under the bark, and the damage they cause.

What can private landowners do to protect their trees against bark beetle attacks?

Here is a short list of preventative measures.
1. Reduce the density of trees in your yard or woodlot by thinning. Most landowners are reluctant to cut down any of their trees. Keep in mind that trees will grow faster and stronger if they have less competition from neighboring trees. Trees that do not have to compete for scarce water will be more likely to survive both severe drought and bark beetle attacks. For the health of your trees, and to curtail the spread of bark beetles, keep the density down.

2. In times of drought or insufficient rain, water your trees. This is particularly necessary during May, June, and October. During a severe drought period, it may be advisable to water at other times as well. Enough water must be provided to penetrate the soil to a depth of two feet. Water in a donut-shaped pattern at the drip-line, or outer edge of the branches. To find out if your tree needs to be watered, check the soil to a depth of 6-8 inches just outside the drip-line at least once a month.

3. A landowner may have certain highly valued trees, treasured because of size, location, appearance, or other reasons. Valued trees that have not yet fallen victim to bark beetles can be protected from beetle attacks by the application of insecticide to the outside of the trunk. The only registered chemicals for use against bark beetles are carbaryl and permethrin. An insecticide specifically formulated for bark beetles is applied to the entire trunk and the base of branches 4" or greater in diameter. Common home and garden insecticides, even those containing carbaryl or permethrin, will not work. Contact your county Cooperative Extension office. Instructions for insecticide spraying are given below in the document Preventative Spraying.

Recognizing bark beetle attacks.

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 the landowner notices. By the time the needles have faded to red, the bark beetle attack has been under way for a considerable time, and the tree is dying. Other signs are many pitch tubes (globules of pitch ¾ to 1¼ " in diameter) on the trunk, and boring dust in bark cervices or at the base of the tree, produced when the beetles bore into the bark.
What can be done for trees already attacked by bark beetles?

The unfortunate answer to this question is that nothing can be done, except to remove the tree.

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 that 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 expeditiously.

You may wish to save the wood from bark beetle-infested trees for use as firewood or poles. In order to kill any bark beetle adults or larvae still in the wood, be careful to follow one of the storage methods described in the Pine Bark Beetles Publication.

Bark Beetle Photo Gallery

Preventative Spraying [PDF document]

Bark Beetle News Release 2004
[PDF document]

Pine Bark Beetles Publication [PDF document]

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Insect Home Page
Arizona Cooperative Extension Forest Health Program
Tree Mortality in Horsethief Basin
Tree mortality in Horsethief Basin
Tree Mortality
Tree mortality
Before thinning

Before thinning
After thinning

After thinning

Spraying insecticide

Last Reviewed and Updated: July 2010January 23, 2013
U.S. Forest Service School of Renewable Natural Resources