The Tree Diseases Most Commonly Seen in Portland

Trees provide a multitude of benefits, such as supplying food and habitat for wildlife, purifying air, abating noise, supplying shade, increasing privacy, cooling air temperatures, intercepting stormwater, and reducing runoff.

They also provide many aesthetic benefits that make the otherwise gray infrastructure and densely populated conditions of the urban environment a beautiful place to live. A simple Google search of the benefit of trees gets 218,000,000 results.

he Tree Diseases Most Commonly Seen in Portland

It’s these benefits that make it imperative to take care of our trees and ensure they live on for many generations to come.

Unfortunately, just like people, trees can become ill and if not properly treated, are susceptible to requiring removal. Tree diseases can have a plethora of negative effects on a tree and depending on what ails your plant it just might be time to reach out to a Portland tree service.

Is the Tree Alive?

Some trees, for reasons of disease, may already be dead or past the point of saving. While it’s best to consult with an arborist, a simple “twig test” can quickly lead you down the right path.

Break off a twig and see what it looks like on the inside. As long as the tissue is green, the tree is still living. However, if it’s dark and brittle, that twig is dead and further investigation of the tree from which it came is needed.

If healthy tissue is found among dead twigs, prune any branches broken off during testing as improper wounds will attract more diseases and pests. If a mixture of dead and healthy branches is found, it is necessary to remove the dead wood as soon as possible.

When working with mature trees, a Portland tree service should be called since a professional will have the knowledge needed to effectively heal and remove dead branches and twigs from such trees. The same call is probably a good idea if it seems all of the twigs during the test are dead so that the appropriate steps to remove the tree carefully can be made.

Is the Tree Sick?

If the tree in question seems to be alive, the next inspection should be for disease. There are many common tree diseases in Portland and it is quite helpful to know what to look for when identifying whether a tree is in need of professional care.

Some of the most common tree diseases include Dothistroma, Fire Blight, Armillaria root rot, Powdery Mildew, Anthracnose, and, specific to stone fruit trees, Apple Anthracnose, Bull’s Eye Rot, and Perennial Canker. The following descriptions will help you diagnose most sick trees.

Dothistroma needle blight

A fungal infection, Dothistroma needle blight causes premature defoliation in mature trees and severe stunting and death in young trees. It has been detected in more than 35 pine species throughout North America.

In Oregon, dothistroma infects plantings of lodgepole and Monterey pines. Early symptoms of dothistroma include darker-green bands and yellow and tan spots on needles. The dark green bands do not last long and will be missed if not observed at the onset of the infection.

Over time, the spots and bands turn brown or reddish brown. A dothistroma needle blight Infection is typically most severe in the lower crown of the tree.

Fire Blight

Fire Blight is a bacterial disease affecting apples and pears. Blight cankers is noticeable diseased bark tissue. Leading up to and during bloom, bacteria will ooze from the cankers and is spread by rain as well as insects, which are drawn to the ooze.

One active overwintering canker can produce enough bacteria to infect a significant portion of flowers in a one acre area, so it is important to cut out cankers in the dormant season and remove damaged wood from all trees.

Armillaria root rot

This disease attacks trees and kills shrubs, and vines. The fungi infect healthy trees, either weakening them or killing them directly. This disease is so common that only larch trees and birch trees are resistant to armillaria root rot.

One of the most noticeable indicators of an Armillaria infection are the clusters of mushrooms that tend to form at the base of the infected tree. Other symptoms include the appearance of lighter, bleached wood, yellowing foliage, and dieback of twigs and branches. Deciduous trees can sometimes develop sunken cankers on the trunk.

Powdery Mildew

Powdery Mildew is a fungal disease that affects cherries, apples, pears, peaches, plums, nectarines, and many other ornamental trees. Unlike many other diseases, powdery mildew doesn’t require moist conditions to grow and is limited by wet springs.

Powdery mildew is recognized easily by the white to gray mycelium and fungal spores that form on leaves, flowers, fruit and shoots. In order to prevent Powdery Mildew, it is important to provide good air circulation and sunlight by pruning excess foliage. Pruning out infected buds in the dormant season and severely infested shoots as they appear in early spring will also help protect trees from this disease.


While Anthracnose is most common in the Eastern U.S., it is still known to affect a variety of shade and ornamental trees in Oregon. The infection can be particularly severe on American sycamore and several trees in the white oak group.

The most common symptom of anthracnose is dead spots or blotches on the tree’s leaves. The spots or blotches may be black, brown, or purple and are often found along the veins of the leaves. Infected leaves frequently become distorted or oddly shaped due to the irregular growth between the healthy and infected portions of the leaf.

Because they are such an integral part of Portland, it is important to take care of the city’s trees. Knowing what to look for is the first step in working to maintain beautiful, and healthy, trees and ensures they are around for generations to come. It is also important to make use of professional Portland tree services, like Mr. Tree Services, to decide the best solution for a diseased or dead tree.

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About Mr.Tree, Inc.

We take pride in our quality service and complete and total customer satisfaction. Our professional and certified arborists have the knowledge and experience to take care of all your tree service needs. We have a highly trained team that is always up to date on all the latest techniques and equipped with the most state of the art tools to handle all your tree care needs. Feel free to browse through our website for more information about the services we offer.

We can help you with everything from lot clearing to tree pruning. We would be more than happy to help you turn your residential or commercial property into something you can be proud of. If you want to use a company that offers the most comprehensive tree services in the area, call Mr. Tree today.

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