wpe5.jpg (2127 bytes)U.P. TREE  IDENTIFICATION  KEY
from Michigan State University Extension


Identifying some of the more common tree health issues will be the main purpose of this portion of the Tree ID website. The geographical focus is the Upper Peninsula of Michigan. Please don't expect every pest to be found on these pages. Certainly, tree health is an important part of forest health. However, a healthy forest will have a certain degree of insect and disease activity that may harm individual trees. This is good and "healthy". After all, many animals depend upon structures such as tree cavities and tree tissues in order to survive. Therefore, insect and disease activity within a forest is not necessarily a bad thing. In most cases, these organisms are endemic and interesting. There are, of course, exceptions. Also, forest trees are the focus, not residential trees.

Forest health will be defined differently by people from various perspectives. And, forest health is different than tree health. A forest is an ecosystem, while a tree is a single organism within an ecosystem. The functions and presence of biological taxa such as insects and fungi are essential to the life of a forest. For the most part, this website will describe insects and diseases that are harmful to trees, although it's important to recognize that they may still be beneficial to the forest.

From this page, click on the word or image below (and left) to learn more about insects, diseases, and other forest damaging agents.
Or, click here to visit a page that lists pests by host species.




  • Species of tree - it's usually critical to correctly identify a tree in order to help identify a pest.
  • Are the symptoms from an insect or disease? It's not always clear.
  • What part of the tree is affected?
  • How widespread is the problem? Within the tree? Across the forest?
  • When did the problem begin?
  • Has there been any soil disturbance lately?
  • What, exactly, does "it" look like?
  • Are there underlying conditions that may be more important?
  • Is the problem damaging the tree, or is it a secondary event related to the real cause?
  • Sometimes, it's just plain tough to correctly ID a pest!
  • There are thousands of possibilities!


1. A cedar, larch, spruce, or fir is NOT a pine.
2. Nothing is gross or icky (well, almost nothing).
3. If it looks scary, it probably is not.
4. Larvae are the immature stages of insects. Worms live in the ground.
5. Trees cannot heal wounds. They are there until the tree dies.
6. Leaf diseases in the late summer are almost never a problem.
7. Conifers lose needles every fall. Tamarack loses all of them.
8. Exotic pests are a special problem, and becoming more frequent.
9. Active forest management provides a vigorous forest, the best defense.
10. The "problem" may be worse for you than for the tree or forest.
11. In seeking help, a downsized image or two, or a sample in a zipper bag can help.


Regularly, and with increasing frequency, North American forests are host to damaging insects and diseases from other continents. Historically, most came from Europe but, recently, more have come from China and east Asia. Most exotic introductions fail. Nevertheless, some of the species that have been successful have caused damage to forests and the threats continue to occur. Some of the more notable examples include chestnut blight, oak wilt, Dutch elm disease, white pine blister rust, beech bark disease, gypsy moth, emerald ash borer, hemlock woolly adelgid, sudden oak death, and Asian longhorned beetle. These exotics have nearly removed (or may do so) tree species from forests. These infestations are not trivial matters. Through 2012, the EAB had the single largest economic effect in forest health history, with a price tag of about $1.7 Billion.  In addition to insects and diseases, exotic plants, such as garlic mustard and buckthorn, can harm forests. Lastly, native species can "go invasive" when balances are disrupted. Examples would be white-tailed deer, ironwood, and Pennsylvania sedge. Many scientists place exotic and invasive species among the top threats to North American forest health.


DNR Forest Health
DNR annual forest health reports
Emerald Ash Borer
US Forest Service Eastern Forest Threat Center
Asian Longhorned Beetle
Deer Damage
Oak Wilt
Hemlock Woolly Adelgid


Other Damages







Selections on this website were made by Bill Cook, with the help of several forest health experts. Many of the images were obtained from the excellent collections at ForestryImages.com, a product of the Bugwood Network. Above, Bill is sharing a moment with friends (forest tent caterpillars) during an outbreak at the Ouimet Canyon, Ontario.


Click HERE to return to the U.P. Tree ID home page.

This site created and maintained by Bill Cook, MSU Extension Forester for the Upper Peninsula of Michigan.   Editing and modification is ongoing.  Submit suggestions, questions, and corrections to cookwi@msu.edu or call 906-786-1575.