Tree Pests

Tree in skyline

Become Pest Aware   

Have you noticed something is different with a tree that you care about? Is there a tree in your yard that had leaves a few weeks ago but now many are missing, others have holes, and leaves are turning brown like the photo above?

Have you noticed a new orange fungus covering the bark of the street tree in front of your school or business? These can all indicate that your tree is being impacted by an invasive pest.

Most invasive pests are first observed and reported by residents and not by scientists, so we need your help. Simply watching your trees and taking note of any changes is an important step in preventing the spread of invasive pests. 

If you think your tree may affected by an invasive pest: 

  • Identify your tree: this will help you narrow down possible problems. Free Apps like iNaturalist and our free services: The Garden Hotline and Ask an Expert can support you in this. If you think you may have an ash tree, check out this link. Also, you can use our Street Tree Inventory to check your street trees. 
  • Take note of stress symptoms that you see on the tree. Are there new holes in the leaves or bark? Are the leaves drooping or changing color? 
  • Look for insects and take photos if you find one. These insects can be hard to identify so seek help. There are many resources such as The Garden Hotline, the University of Washington’s Plant Answer Line, or Washington State Cooperative Extension.
  • Consider the extent of damage. Trees can tolerate small amounts of damage depending on the insect or disease. If an insect’s chewing damage has only removed about 5% of a tree’s leaves, that won’t have long term repercussions for the tree.
  • Care for your tree: An insect might attack your tree because it is unhealthy (not enough water, root damage, soil compaction). Healthy trees can better withstand a small amount of damage from an invasive pest.
    • Water your tree twice per week in our hot summer months.
    • Improve soil conditions through mulching. 
  • Report and seek help. If you have significant tree damage, obvious signs of invasive pests, or even an invasive insect, contact the Washington State Invasive Species Council. You may consider having an International Society of Arboriculture Certified Arborist access and care for your tree. The Pacific Northwest Pest Management Handbook is a helpful resource for support in caring for your tree.