Q. Dear Peter: I have a large Douglas fir tree. About a month ago I noticed that the needles on the end of a branch looked as if they had been spray-painted white. Now it’s spreading to other branches at different parts of the tree. What’s going on and how do I treat it? Marilyn Boyle – Tacoma, wa
A. It sounds to me like you are dealing with an early flocking of your Douglas fir by some wooly adelgids. Adelgids are related to aphids and live off of the sap of the host trees. They also excrete a waxy substance that protects them. This is likely what looks like the white spray paint. Most likely you have the Cooley Spruce Gall Adelgid. This species of adelgid alternates between the Colorado Spruce and Douglas Fir. This is seen very often at Christmas Tree Farms where the two species may be in close proximity. But the adelgids can stay on the Douglas Fir without alternating to the spruce for many years. Unless the Fir tree is otherwise compromised the infestation is usually not fatal. You can wait to see if natural predators will take care of it or you can start a spray program. You will likely want to contract out the spraying if the tree is large. There are multiple generations (which can travel from other areas) so you will need to monitor the tree after a summer spray. September-October is the next best time to spray and get newly hatching adelgids that are hatching from eggs (which are resistant to spraying).