Question and answer: Common arbor illnesses and maladies | Evergreen Aborists

Several common maladies in landscapes are coming into their full splendor as the summer progresses.

Several common maladies in landscapes are coming into their full splendor as the summer progresses.

The wet, cool spring was ideal for the development of many fungi.  However, it is too late to spray for most problems at this time. Details of the following diseases and recommended fungicide treatments are available on the WSU Cooperative Extension “hortsense” website under the “ornamentals” link.

Q. What is going on with all the dead twigs and needles in my Atlas cedar or weeping blue Atlas cedar?

A. This cedar needle blight has affected many such trees during the past three years.

According to Jenny Glass, diagnostician at the WSU Plant Clinic, the fungus is most likely Sirococcus conigenus. The wet, cool spring has been ideal for the development of the disease. It attacks the new growth in the spring and early summer. The spores overwinter in the dead needles. Unfortunately, no fungicides are registered for this disease. Removal of as many of the dead twigs, dead needles and debris from under the trees as possible may help reduce the problem for next year.


Q. What is causing the dead leaves in my cherry trees?

A. The most common disease is the brown rot fungus on cherries and flowering plums. This is first noticed in the spring when blossoms seem to collapse or become limp, but do not fall off the tree. Presently, the most visible signs of the disease are the small twigs and leaves that have been infected and died. Most trees have minor infections that either can be ignored or treated by spraying the tree three times during the spring blossom season. However, it is a difficult fungus to treat successfully. Several fungicides are registered, so read labels carefully and follow the instructions.

Q. What is causing the brown blotches on the leaves of my dogwood, maple, willow, lilacs, Lombardy poplars and other trees?

A. Several fungi may be involved. The most common on dogwoods and maples is likely anthracnose. The leaves may turn brown, wither up and premature leaf drop may occur. Again several fungicides are registered but must be applied in the early spring to protect the new leaf growth. A bacterial leaf blight has attacked various species of willows, lilacs and the tall Lombardy poplar trees and caused leaves to wither and drop. Blighted shoots often turn black and appear scorched as they die back. New growth that occurs later may not be infected after the spring spore dispersal season has passed.

Fall applications of fungicides before fall rains and again before bud break in spring are recommended.  Commercial pesticide applicators should be consulted on trees over 10 feet tall.

Q. My tree just looks sick. What is the problem?

A. If you inquire at a Master Gardener clinic or with some type of professional, be prepared to answer several questions. First, what kind of a tree is it? What does the damage look like? When did you first notice it? Do you see any tiny insects on the leaves? Is the problem occurring on one tree or several similar trees?

Ideally, take a sample to a Master Gardener clinic near you. An infected branch should have healthy and diseased tissue on it. Or you can contact a professional and request a visit your yard to observe the tree.

Remember, the more information and samples you can furnish, the more likely you are to have a proper diagnosis made.


Dennis Tompkins is a certified arborist, certified hazard tree risk assessor and Master Gardener from the Bonney Lake-Sumner area. He provides small tree pruning, pest diagnosis, hazardous tree evaluations, tree appraisals and other services for homeowners and businesses. Contact him by phone at 253-863-7469 or email at His website can be found at