Have you noticed some of the Sitka spruce trees at North Coast Land Conservancy’s Circle Creek Conservation Center—or other locations in the region—looking a little brown? That’s the doing of spruce aphids, which suck the sap from the tree needles. They are back this season, feeding off a small portion of the property’s tree population.
As a result of this outbreak, the infested trees will start to look discolored and sickly, or even dead later in the season, stewardship director Melissa Reich says.
“Most of them will be just fine and will put out enough new growth this year to make it through,” she adds. “We won’t do anything different from a management perspective—just observe and learn.”
A little bit about spruce aphids: They are small, soft-bodies insects measuring about 1 to 1.5 mm in size, according to the U.S. Forest Service. They can embody either winged or wingless forms, and they feed off the sap of the trees by inserting their needle-like mouthparts into host foliage. If a population increase occurs, discoloration often intensifies, while affected needles turn brown and drop prematurely. However, spruce aphids essentially feed only on old needles and not new growth.
“Weather is believed to strongly affect spruce aphid abundance, and prolonged periods of cool temperatures or early spring frosts can result in lower populations,” the Forest Service states.
A similar spruce aphid outbreak took place in the Oregon North Coast region in 2019, causing quite a bit of community concern. Jeff Roehm, the volunteer site steward at Circle Creek, noticed the insects were back on the property in early April.
At that point, the aphid outbreak hadn’t spread too far throughout the tree population. However, those that were infested, especially the small trees growing in the open field at Circle Creek, showed somewhat severe symptoms. The good news?
“The aphids won’t kill too many trees, just look awful,” Jeff says.
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