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Forest health

Aerial photo of forest beginning to show autumn color

Forest health

Protecting Michigan's forests

Protecting the health of Michigan's forests is a challenging task that requires collaboration. Our forest health professionals work with other state and federal agencies and universities to prevent, evaluate and manage the occurrence and impacts of both native and exotic forest insects and diseases. Email the forest health team with questions about pests and diseases.

Seeing spots? It could be spongy moth.

The sight of red-and-blue spotted caterpillars munching on backyard trees is a sure sign of spongy moth (lymantria dispar dispar,) an invasive species formerly known as gypsy moth. There are steps you can take to protect trees and minimize the damage done by these hungry pests.

Learn more about this species and how to protect trees
Gray, fuzzy lymantria dispar caterpillar with blue and red spots

Species of concern

asian longhorn beetle

Asian longhorned beetle

Watch list - not detected in Michigan.


The Asian longhorned beetle can attack and kill many tree species. Its favorite host is maple trees, and it also poses a threat to hops and grapes. Beetle larvae feed in tunnels in trees, eventually killing the tree.

beech bark disease thumbnail

Beech bark disease

Present in Michigan.


Beech bark disease is caused by a sap-feeding scale insect and a fungus. Trees are first infested with whitish beech scale, allowing infection by the Neonectria fungus. The fungus kills trees by blocking sap flow. Infected tree limbs can break in heavy winds.

Emerald Ash Borer

Emerald ash borer

Present in Michigan.


The emerald ash borer is a metallic green insect with purple abdominal segments under its wing covers. The larva are worm-like. Adults feed on the foliage of ash tress and the larvae tunnel and feed on the underside of the bark.

hemlock woolly adelgid infestation

Hemlock woolly adelgid

Present in Michigan.


Adelgids are tiny insects that secrete white wax as they feed on sap from hemlock shoots and branches. Hemlock woolly adelgid feeding can kill needles, shoots and branches, resulting in tree death.

Oak Wilt Thumbnail

Oak wilt disease

Present in Michigan. 


Oak wilt disease can quickly kill healthy red oaks and can damage white oaks. Avoid pruning oaks April 15-July 15 when the infection can be spread by beetles in tree wounds.

A spotted lanternfly with its wings open

Spotted lanternfly

Watch list - not detected in Michigan.


The spotted lanternfly sucks sap from the stems and leaves of orchard trees, grape vines, oaks, pines and other plants. Feeding can weaken the plant and eventually contribute to its death. Trees will develop weeping wounds that attract insects and cause mold growth.  

Thousand Cankers Disease

Thousand cankers disease

Watch list - not detected in Michigan.


Thousand cankers disease involves a twig-beetle insect native to the southwestern U.S, and a fungal pathogen. The disease affects black walnut trees, a valuable economic and ecological resource in Michigan.

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