Skip Navigation
MI.gov
DNR - Department of Natural Resources | DNR Department of Natural Resources | DNR
Department of Natural Resources | DNR
close print view
Printer Friendly Page
Email this Page
Share this Link on Facebook
Tweet this page on Twitter!

Forest Pests

Be on the lookout for a few very destructive pests. Pests are grouped by the pest, or location and type of the symptoms. To learn more about a forest pest, simply "click" on one of the images found below.

Asian Longhorned Beetle
Balsam Woolly Adelgid
Hemlock Woolly Adelgid

Asian Longhorned Beetle

Balsam Woolly Adelgid (Firs Only)

HemlockWoolly Adelgid (Hemlock Only)

Oak Wilt

Oak Wilt

Beech Bark Disease
Beech Bark Disease

Beech Bark Disease

Sudden Oak Death


Forest Insect Pests

Asian Longhorned Beetle (Anoplophora glabripennis)
  • Trees Affected
    Norway, sugar, silver, and red maple, horsechestnut, aspen (poplar), willow, elm, mulberry, and black locust and other hardwoods.
  • Symptoms
    Very round rust colored holes (entry and exit wounds) about 3/8 to 1/2" in diameter along the branches or trunk of the tree.
  • Importance
    Extremely destructive exotic pest that once established can kill hardwoods very rapidly.
  • Prevention
    Early detection and prompt removal of dead or dying trees.

  • Learn More
    Current Status, Research, and Management of the Asian Longhorned Beetle
Asian longhorned beetle

Adult Asian longhorned beetle on a hardwood tree.

Asian longhorned beetle

Round rust colored holes left by the Asian longhorned beetle.

Asian longhorned beetle

Click to view a larger poster for printing


Balsam Woolly Adelgid
  • Trees Affected
    All true furs, Abies spp., including balsam and fraser fir.

  • Symptoms
    Infested crowns with abnormal drooping of current shoots and gouting of outer twigs. Crown becomes increasingly thin and dieback may occur. Stem attacks with conspicuous presence of white woolly masses often giving the lower bole a whitewashed appearance. Sapwood of infested wood swells causing gouting of twigs and increased heartwood formation.
  • Importance
    A serious pest of forest, seed production, landscape, and Christmas trees. Stem infestations are usually more serious, causing greater levels of damage and mortality. Persistent crown infestation can kill a tree over a number of years.
  • Prevention
    Early detection and prompt removal and destruction of dead or dying trees. Prescribed fire is often used to sanitize the site.
balsam whooly

Balsam fir bark infected with Balsam Woolly Adelgid.

balsam whooly

Gall-like formation on the twigs, due to Balsam Woolly Adelgid feeding.

balsam whooly

Balsam fir needles infected with Balsam Woolly Adelgid.


Hemlock Woolly Adelgid
  • Trees Affected
    Eastern hemlock (Tsuga canadensis) & Carolina hemlock (T. caroliniana).
  • Symptoms
    White cottony masses at the base of needles.
  • Importance
    Destructive disease that can quickly kill hemlock.
  • Prevention
    Early detection and treatments to avert establishment of populations.
  • Learn More
    USDA Forest Service Hemlock Woolly Adelgid Site
Hemlock Woolly Adelgid

Eastern Hemlock needles infected with Hemlock Woolly Adelgid.

Hemlock Woolly Adelgid

Dieback on Eastern Hemlock due to Hemlock Woolly Adelgid.


Foliage Dieback

A number of forest pests directly or indirectly affect the foliage on trees. Some pests eat or chew on the leaves or needles while other pests may injure parts of the tree which led to foliage dieback.

Oak Wilt

    Trees Affected
    White, and Red Oak

  • Symptoms
    Bronzing or browning of green leaves from the tips/margins toward the leaf base.
  • Importance
    Destructivedisease that can kill oaks very rapidly.
  • Prevention
    Early detection and prompt removal of dead or dying trees. Avoid trimming, or cutting live oak trees during spring (May - June).
oak wilt

Oak wilt symptoms on red oak leaves.

oak wilt defoliation

Oak wilt defoliation.


Trunk/Bark

The affects of some pests are most noticeable on the bark or trunk of the tree. Often times scales or wholes are left by the pest on or within the bark.

Beech Bark Disease
  • Trees Affected
    American Beech
  • Symptoms
    Small white scales are present on the bark of the tree.
  • Importance
    Very destructive disease that can kill large stands of beech trees.
  • Prevention
    Early detection and prompt removal of dead or dying trees. Avoid touching the infected tree or trees.
beech bark scales

Scaling associated with beech bark disease.

White lichen

White lichen often confused with beech bark disease.


Sudden Oak Death
  • Trees Affected
    (Quercus sp., Lithocarpus densiflorus); rhododentrons; huckleberry (Vaccinium ovatum); bay laurel (Umbellularia californica); and California buckeye (Aesculus californica); Big leaf maple (Acer macrophyllum); CA honeysuckle (Lonicera hispidula).
  • Symptoms
    Cankers are formed on stems. Cankered trees may survive for one to several years, but once crown dieback begins, leaves often turn from green to pale yellow to brown within a few weeks.
  • Importance
    Exotic lethal disease of oaks. Likely difficult to eradicate once established. Prevention
    Early detection and prompt treatment of site which includes prescribed fire.
  • Learn More
    California Oak Mortality Task Force
sudden oak death, dark spots

Dark spots on bark with exuding brown to tar black
thick sap.

Bleeding or seeping

Bleeding or seeping from the main stem or trunk.


QR code



Copyright © 2001-2014 State of Michigan