Spruce Bark Beetle Control

CONTROL OPTIONS FOR THE HOME OR LOT OWNER

Spruce beetles are always present in spruce forests, and it is only when an abundance of breeding material is available to them, along with favorable weather conditions, can they increase to epidemic numbers. Spruce beetles prefer to attack, and can kill, large diameter spruce. These trees are often valued ornamentals. Other trees such as aspen, birch and hemlock are not attacked by spruce beetles.

This short guide presents suggestions for reducing the possibility of spruce beetle caused tree mortality, and control options which may be useful in the home or small lot setting.

I. Suggestions for reducing the possibility of spruce beetle infestation

  1. Maintain the health of the trees on the lot; spruce beetles prefer to breed in weakened standing or windthrown trees. Fertilizing and watering each tree early in the growing season helps to promote tree vigor. Removing windthrown trees helps eliminate potential sources of infestation. These trees should be split or debarked immediately to help dry out the material.
  2. Avoid importing infested material, such as firewood containing live spruce beetles, to the homesite or the lot.
  3. During home construction, avoid damaging trees with mechanical equipment, placing excess soil over tree roots, or altering drainage.
  4. Consider the health of the tree and all options before making a decision on control measures. Fast growing, healthy trees are more resistant to spruce beetle attacks than are slower growing or unhealthy trees. These may need more attention and protection.

II. Spruce Beetle Damage

First, using this flow chart, determine whether your tree is attacked or unattacked. Control and management options are then listed on the following pages.

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KEY TO SPRUCE BEETLE DAMAGE

SPRUCE,

IF UNATTACKED

GREEN NEEDLES

NO visible rust-colored boring dust on bark, in bark crevice, especially at eye-level and below, or on the ground

NO rust-colored, opaque globules of pitch mixed with boring dust on bark especially at eye-level and below

=Unattacked tree (See A)

IF ATTACKED

GREEN NEEDLES

Reddish-brown boring dust PRESENT on bark, in bark crevices, especially at eye-level and below, or on the ground
Reddish-brown, opaque globules of pitch and boring dust PRESENT on bark, especially at eye-level and below.
Woodpecker activity may be present.
 

=Tree attacked this season (See B)

OR

FADED YELLOW OR BRIGHT RED NEEDLES

Evidence of previous beetle attacks as described above

Beetle larvae, pupae, and/or adults present under bark

Woodpecker activity may be present.

=Tree attacked this season (See C)

OR

NO NEEDLES REMAINING ON TWIGS

Tree appears reddish-brown in overall color

Evidence of previous beetle attacks as described above

Beetle larvae, pupae, and/or adults present under bark

Woodpecker activity may be present.

=Tree attacked last season or before(See D)

OR

NO NEEDLES AND NO TWIGS REMAINING--TREE SILVER-GRAY

Loose bark with evidence of previous beetle activity on the underside

No live beetles present

=Tree attacked 3 or more seasons ago(See E)

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III. Control Options

A. UNATTACKED TREE

Fertilize and water each individual tree early in the season to encourage vigor. A fertilizer high in phosphorous such as 8-32-16 may help in root production which in turn helps the tree in water and nutrient uptake. An application of one pound of fertilizer per inch tree diameter is suggested. Incorporate fertilizer into root zone area and water well.

Prune the lower branches on full-crowned trees; no more than one third of the total tree height should be removed. Based on Forest Service research findings, removing these lower branches may be an effective step in reducing the possibility of spruce beetle attack. Pruning should be done in the fall, and the branches should be removed from the area and disposed of.

Spray the tree with an insecticide registered for use on spruce trees to prevent spruce beetle attacks. This should be done in spring before the end of May in order to protect the tree prior to the beetle's emergence and dispersal flight. Currently three chemicals are registered for preventative use against spruce beetles:

carbaryl or chlorpyrifos or lindane

Follow all label directions when using any pesticide

All recent windthrown trees should be removed from the area prior to mid-May. They should be debarked or split immediately for firewood to encourage drying of the phloem tissue beneath the bark, therefore discouraging the beetles from attacking the material. Seriously damaged trees should be either removed or sprayed a previously described. Stumps should not be left above ground, or if so, should be debarked down to 2 inches below the soil surface.

FOR HOME OR LOT OWNERS WITH MANY TREES:
  • Thinning trees reduces competition and increases vigor.
  • Select valued trees for individual protection, using one or more of the options presented in this outline.
  • Contact State of Alaska Service Forester for more information.

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B. TREE ATTACKED THIS SEASON

Recently attacked trees can become next spring's infestation source, so it is important to determine the degree of initial attack. One or two beetle attacks don't necessarily mean the tree will die; however, it is important to realize: 1) you may not notice all the attacks; and 2) there is a good chance that the tree will be attacked again, successfully, next season. It helps to be observant, but when in doubt, it also helps to ask a qualified person such as your area Extension Pest Scout.

A heavily attacked tree should be removed during the coming fall, or before May of the following spring, to avoid infestation of surrounding trees. The tree should be debarked or fire-scorched immediately upon felling to destroy the beetles and larvae within. Scorched wood may then be used as firewood since it is not fully burned. Stumps should not extend above ground, and if so, should be debarked down to 2 inches below the soil surface. (Note: heavily attacked trees which are removed in the fall following new attacks may also be split for firewood and allowed to dry out over the winter. This may prevent the young, newly hatched larvae from developing into adult beetles).

C. TREE ATTACKED LAST SEASON

Trees that were attacked last season are the sources for attacking beetles this season and the next. Because of the beetle's 1- or 2-year life cycle, these infested trees are important to identify as they contain the new generation of beetles which are ready to emerge and attack new trees.

Determine if beetles are present by removing a section of bark near the lower portion of the trunk.

Remove the infested tree prior to upcoming May and debark or fire-scorch the material immediately upon felling. This will prevent the beetles from emerging and attacking surrounding trees by killing any adults and larvae within the material. The wood may then be split and used for firewood.

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D. TREE ATTACKED LAST SEASON OR BEFORE

Usually only adult beetles remain under the loose bark, and these will be ready to emerge and find new host trees as soon as mid-May or early June.

Determine if beetles are still present by removing a section of bark from the lower portion of the trunk and examining the underside. If no beetles are under the bark - see section E.

Remove the infested tree prior to the upcoming spring and debark or fire-scorch the material immediately upon felling. This will prevent the remaining adult beetles from emerging and attacking surrounding trees. The wood may then be split and used for firewood.

E. TREE ATTACKED 3 OR MORE SEASONS AGO

This dead tree will have no spruce beetles remaining under the bark. Other beetles and larvae may be observed, but they are of little concern as they are beneficial wood decomposers, and not tree killers.

Cut the tree down to use as firewood.

Leave the tree standing to serve as wildlife habitat. (The tree should be removed however, if it is unstable or endangering persons or property.)

For more information contact our Forest Health Protection staff.

 

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https://www.fs.usda.gov/detail/r10/forest-grasslandhealth/?cid=fsbdev2_038903