Last week I received an email from Evelynn Von Feldt, one of the long-time Master Gardeners, and she thought I should do a column on a problem the Tillamook County Master Gardeners have been working on for the last few months. Upon reading the email, I realized this is something I should write about as it seems to be affecting spruce trees in Oceanside and other parts of the county.
Apparently, local Sitka spruce needles have been turning brown and dropping their needles. This gives the appearance they are dead. The damage was diagnosed by Joy Jones, former OSU Extension Office Agent for Horticulture, as being Spruce aphids. It is so much of a problem in coastal Spruce forests that the Oregon Department of Forestry is now looking into the matter and monitoring the damage. Dr. Christine Buhl, one of the Forest Entomologists from ODF came out to the coast to see what is going on. She reports that the problem is so severe that ODF has issued a Forest Health Pest Alert that explains the infestation and the ways to manage it.
Spruce aphids (Elatobium abietinum) are non-native insects that have been evident in west coast forests since the 1920’s. They feed voraciously on the sap in needles of its favorite food source, the spruce. They like Sitka spruce but also will feed on Colorado Blue Spruce that many gardeners like to plant in their yards. Aphids feeding causes spruce needles to turn brown or prematurely shed. The damage is seen first at the beginning of spring in February and March when the aphids have their peak feeding season. Older needles and those lower in the tree’s canopy are the first targets. The aphids do not affect the trees’ buds and new needles will open and flush out during the same growing season. This is true even on trees that seem to be irrevocably harmed. The population of the Spruce aphids declines during the summer due to natural enemies and lack of nutritious foliage for them to eat. But by May and June, the affected needles will turn brown and drop off the branches.
The Spruce aphid infestation can eventually cause trees to lose height and diameter as the growth slows. Since the trees still put out new growth, they can survive aphids unless the favorable-for-the-aphids weather conditions continue for several years, in which case the trees become so stressed they will eventually die.
So, what can we do about Spruce aphids? The thing most ODF publications suggest is to wait out the aphids. A colder winter, natural enemies and loss of food will decrease populations. Of course, we have no control over the weather, but we can refrain from fertilizing the spruce trees as the aphids love the nitrogen-rich trees. Once the nitrogen levels drop off in the summer, the aphids will drop off, too.
A blast of strong water from a hose may also dislodge many of the aphids. Chemical sprays aren’t advised because spraying an entire forest with insecticides is prohibitively expensive and will affect other desirable insects. But smaller ornamental trees may be sprayed. To be most effective, this should be done in late March or early April, before the affected needles have dropped. Be sure and read the labels on the insecticides to be sure they can be safely used on spruce and are effective against aphids. And always follow the label directions to the T!
Soil drenches and tree injections of insecticides may be a last resort. ODF suggests contacting one of their entomologists to discuss treatment and monitoring options. They also have a website with information on forests and how to contact ODF. Find it at: http://tinyurl.com/ODF-ForestHealth. Dr. Buhl also lists her contact info on the Pest Alert, so I feel I can give you that info, too: email@example.com with her phone number 503.945.7396.
As to the piles of fallen needles, well they will take years to decompose. If you find them around acid-loving plants – like the spruce trees – you can probably leave them. If they have been blown and blanketed around more alkaline plants, you might want to rake them up for the compost pile. We don’t have many native plants that don’t like acid, so this would only be an issue around ornamental trees and shrubs.
In short, this seems to be a potential problem only if our winters continue to be mild and not cold enough to keep the aphids under control. But this is something worth monitoring and looking for if you have spruce trees.
Thanks to Evelynn for making me aware of this issue so I could share the potential problem with my readers. I also thank Evelynn for these photos that she took of some damage along Route 131 this spring.