Pests and Diseases

Certain insects and diseases are commonly associated with specific tree species and forest types. Most of these (99%) have only minor impacts on our trees and don’t require any specific treatment. The others are the ones to keep an eye out for and take action against once found on your property. Visit the DNR forest health website to learn more about the insects and diseases to be aware of and see if they are a potential problem for your forest.

Many times we don’t see the agent that is causing the illness in our trees, or we may only be seeing a secondary cause for the illness. The real agent may not be apparent, so you need to know how to deduce the cause from the evidence at hand. To do that, you need to be able to recognize symptoms (such as wilting leaves or a deformity on the trunk) and signs (for example, tunnels in the wood or mushrooms on the trunk) of the pest to determine the primary cause of the illness. Use the University of Minnesota Extension website to match the signs and symptoms you are seeing to the appropriate insect or disease.

Our forests and trees are constantly under attack by insects and diseases, so it is not uncommon to find trees infested with some kind of pest. If you have completed the first two steps in this process, then you know which pests are important to keep an eye out for and how to identify them. Now you need to put any kind of insects or diseases you find in your forest into perspective. If it just one tree that is infected with an insect or disease and the surrounding trees seem healthy, then this might not be a concern. If instead it is a group of trees that are infected or there are a number of trees scattered throughout your forest with this infection, then you may need to be concerned. At this point, it would be a good idea to get a professional opinion on your situation.

Start with your local DNR Forester. You can find those who work in your county by visiting the DNR website. They can help to diagnose your problem and offer solutions. They may also work with DNR regional forest health specialists. If the problem you have is limited to a yard tree, then you need to contact your local Extension office, a local arborist, or an urban forester to figure out what the problem is.

If you have questions about pests and diseases in your woods, contact:

Page last updated January 2026.