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.
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
can be done for trees already attacked by bark beetles?
unfortunate answer to this question is that nothing can be done, except to remove
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.
Beetle Photo Gallery
Spraying [PDF document]
Bark Beetle News Release 2004 [PDF document]
Bark Beetles Publication [PDF document]
Insect Home Page
Arizona Cooperative Extension Forest Health Program