Bark Beetle Prevention
 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 the drought Arizona has suffered for many months. Trees stressed by drought
are especially vulnerable to bark beetle attacks. The spruce-fir forest of the
Pinaleño Mountains near Safford have suffered severe tree mortality from bark
beetle and defoliating insect attacks for the past several years. 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. Ponderosa pines are suffering severe attacks in the Flagstaff
area. Some neighborhoods in Flagstaff have lost nearly 100% of their pines. 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. For more detailed information, view or download the PDF documents Bark Beetle News Release and Pine Bark Beetles Publication, listed below. (Adobe Acrobat is required to open these documents.) 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. The Bark Beetle News Release below explains how to determine the proper spacing for your trees. 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 such as we have recently experienced, 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. See the Bark Beetle News Release for more information, or 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. See the Pine Bark Beetles Publication for additional information. 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 Bark Beetle News Release or the Pine Bark Beetles Publication. Bark Beetle Photo Gallery Preventative Spraying [PDF document] Bark Beetle News Release [PDF document] Pine Bark Beetles Publication [PDF document] |
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 Tree mortality in Horsethief Basin | ||
 Tree mortality | ||
 Before thinning |  After thinning | |
 Spraying insecticide | ||
| Last Reviewed and Updated: February 14, 2006 Questions/Comments:azfh@cals.arizona.edu |
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