10 Common Tree Diseases in Oregon and How to Spot Them

Oregon’s lush landscapes and diverse tree species make it a beautiful place to live, but it also means trees are exposed to a variety of diseases. Identifying tree health issues early can help prevent the spread of disease and save your trees. Here are 10 common tree diseases in Oregon and how to recognize them.

1. Anthracnose

What It Is: A fungal disease that affects leaves, stems, and fruits.
Signs to Watch For:

• Irregular brown spots on leaves.
• Premature leaf drop.
• Twigs with cankers.
  Commonly Affects: Ash, oak, maple, and sycamore trees.

2. Dutch Elm Disease

What It Is: A deadly fungal disease spread by elm bark beetles.
Signs to Watch For:

• Wilting leaves that turn yellow or brown.
• Defoliation starting at the tree’s crown.
• Brown streaking in the tree’s vascular system when bark is peeled back.
  Commonly Affects: Elm trees.

3. Apple Scab

What It Is: A fungal disease affecting apple and crabapple trees.
Signs to Watch For:

• Olive-green or black spots on leaves and fruit.
• Premature leaf drop.
• Deformed or cracked fruit.
  Commonly Affects: Apple and crabapple trees.

4. Armillaria Root Rot

What It Is: A fungal disease that attacks tree roots, leading to structural instability.
Signs to Watch For:

• Honey-colored mushrooms growing near the tree base.
• Decaying or discolored roots.
• Canopy dieback and yellowing leaves.
  Commonly Affects: Conifers and hardwoods.

5. Phytophthora Root Rot

What It Is: A water mold that thrives in poorly drained soil.
Signs to Watch For:

• Stunted growth or wilting.
• Dark, water-soaked bark near the soil line.
• Dieback in the upper branches.
  Commonly Affects: Rhododendrons, maples, and dogwoods.

6. Powdery Mildew

What It Is: A fungal disease that leaves a white, powdery coating on foliage.
Signs to Watch For:

• White or gray powder on leaves, stems, and buds.
• Distorted or stunted leaves.
• Reduced flowering or fruiting.
  Commonly Affects: Oaks, maples, and fruit trees.

7. Leaf Spot Diseases

What It Is: A group of fungal and bacterial infections that cause spots on leaves.
Signs to Watch For:

• Brown, black, or yellow spots on foliage.
• Leaves with a scorched or burnt appearance.
• Premature leaf drop.
  Commonly Affects: Ash, dogwood, and sycamore trees.

8. Sudden Oak Death (Phytophthora ramorum)

What It Is: A serious disease caused by a pathogen that kills oaks and other species.
Signs to Watch For:

• Cankers on the trunk that ooze dark or reddish-brown sap.
• Wilted foliage and rapid tree death.
• Spots or lesions on leaves.
  Commonly Affects: Tanoak, oak, and madrone trees.

9. Cedar Rust

What It Is: A fungal disease that alternates between cedar trees and other hosts like apple trees.
Signs to Watch For:

• Orange, gelatinous growths on cedar branches.
• Yellow or orange spots on leaves of alternate hosts.
• Early leaf drop or fruit deformation.
  Commonly Affects: Cedars, apples, and crabapples.

10. Verticillium Wilt

What It Is: A soilborne fungal disease that blocks water flow in the tree.
Signs to Watch For:

• Wilting and yellowing leaves, often on one side of the tree.
• Discolored or streaked wood under the bark.
• Slow dieback over several seasons.
  Commonly Affects: Maples, ash, and fruit trees.

How to Prevent and Treat Tree Diseases

1. Regular Pruning: Remove dead or diseased branches to prevent the spread of infection.
2. Good Watering Practices: Avoid overwatering, as many fungal diseases thrive in wet conditions.
3. Proper Mulching: Mulch around the base of trees to maintain soil health, but keep it away from the trunk.
4. Fertilization: Keep your trees healthy and resilient with proper nutrients.
5. Professional Inspections: A certified arborist can diagnose and treat tree diseases effectively.

Trust North Woods Tree Service to Keep Your Trees Healthy

At North Woods Tree Service, we specialize in tree health assessments and treatments for common diseases. Our certified arborists can help you identify problems early and develop a plan to protect your trees.

Contact Us Today for a Free Consultation!
📞 Call us at (503) 656-5802
📧 Email us at jbccustomsllc@gmail.com

Don’t let tree diseases compromise your landscape—let us help your trees thrive!