Root Diseases

Root/Butt Rot is one of the most common diseases affecting Northwest trees. Many fungi are capable of causing considerable decay in the roots and butts of trees. Trees are most prone to this when their health is compromised either by root damage or pests. Infected trees usually display a combination of signs such as crown die back, loss of foliage and discoloration of leaves. Conks near base of declining trees are possible indicators of root rot.

Armillaria can often be identified by their honey yellow mushrooms. These fungi are seen at the base of Oregon White Oak trees. Identifying this disease can be troubling because the canopy of the tree may appear healthy even though it is severely infected.

The following sites provide further useful information:

Foliage Diseases

Blight is a general term used to describe a symptom that occurs in trees when any number of pathogenic organisms infects them. They all exhibit a browning affect on the leaves that progresses to a complete death of twigs, branches and floral organs.

Anthracnose is an organism that induces blight on many species of trees. In the Northwest it is common to see Dogwood Anthracnose. It is identified by the small, purple-rimmed spots and large blotches on the leaves.

Verticillium Wilt is not a true foliage disease; it is a fungus that lives in soil, although it is most apparent in the crown of infected trees. A prime example is seen in maples, where half the crown has been stripped of its foliage. This is a very prominent sign that a tree has been infected by verticillium.

Insects and Pests

Bronze Birch Borer is a slender metallic-bronze colored beetle that inhabits all varieties of birch trees. The European white and grey birches are the most vulnerable. The damage caused by this insect is inflicted during its larval state. These larvae bore into the bark to reach the phloem and cambium layer for sustenance. It is this boring and tunneling that weakens and kills trees by interrupting the flow of sap.

Progressive thinning of the crown, beginning at the top is one sign of infestation. Also, small “D” shaped holes on trunk can be an indication of their presence. If caught early enough, the infected tree can be treated. Trees with advanced crown loss will not benefit from insecticide use and should be removed.

Aphids are small pear-shaped insects most commonly green, brown, yellow or white. They are most commonly found on rose, ash, oak, maple, willow and fruit trees. Aphids damage plants by sucking the sap from leaves, twigs, stems, or roots. They sometimes transmit plant diseases in the process. Leaves attacked by aphids have spotty yellow discoloration which may later dry out and wilt or curl. Some species of aphids form galls – swellings of plant tissues. The galls, which are often brown, contain many aphids in different stages of development. One of the biggest annoyances from these tiny insects is the sweet, sticky sap that they produce. The “honeydew” accumulates on anything found under the infested tree or plant (such as your car!).

Pruning infested leaves or plant sections can help prevent he spread and development of new colonies. The use of high-pressure water can be a possible simple solution if they are not extremely embedded. Lady beetles, parasitic wasp and the lacewing can also be used to keep aphids in control.
Further aphid info


The Eastern Fox and Gray Squirrels are non-native species to Oregon. The fox squirrels are reddish-brown in color with tan undersides. Eastern gray squirrels are small gray squirrels with a white underside. Both have managed to almost completely cause the Western gray squirrel to disappear (an Oregon native species). The abundance of these rodents raises the competition for food which leads to an increase of squirrels feeding on the cambium layer of trees. The trees most often targeted are maples and oaks. This can be seen as spots of brown in the canopies of trees. Simple measures to deter squirrels from your trees are not feeding squirrels and using bird feeders that do not allow access for squirrels.