What to look for – Needle discoloration

Often the symptoms of a spruce aphid infestation are noticed before the insects themselves are observed. Unfortunately, the symptoms can sometime occur well after the damage has been done. Yellowing and browning of older needles followed by premature needle drop are the two main symptoms of spruce aphid infestation. Needle yellowing may appear on all or parts of individual needles, depending on the extent of the infestation. Individual needles may appear yellow or brown at different rates than surrounding needles. This discoloration is often observed in the summer after the majority of aphid feeding has ceased from the spring.

spruce tree with brown damaged needles — Damage to Sitka spruce resulting from spruce aphid feeding.
(Region 10, US Forest Service)

What to look for – Presence of aphids

Confirming that spruce aphid is the cause of your tree health issues can be difficult based on symptoms alone. Finding actual aphids is important in determining proper control measures for the pest.

close up damaged needles on stem — Aphids on spruce needles and individual needles with aphid feeding damage.
(Region 10, US Forest Service)

Visually inspect trees for the presence of aphids. Check previously infested trees and nearby trees starting in mid to late winter when temperatures are mild. Check the undersides of needles and older needles for the presence of adult and immature aphids. Monitor weekly through spring to note any increases in numbers of aphids on the tree. This method is good for small to medium sized trees where many branches are within reach or at eye-level.

a bright green insect on stem — Single aphid on a spruce needle. Note the yellow and orange discoloration due to feeding damage.
(Region 10, US Forest Service)

Using a Beat Sheet

Another method for monitoring for spruce aphid is referred to as the “beat sheet” method. Traditionally, this method uses a large piece of fabric stretched over a sturdy frame which is held beneath vegetation. A pole or stick is used to tap on the branches to dislodge insects which fall onto the fabric and can then be collected, counted, observed, etc. This method may be easier on larger trees with higher branches. If the goal is simply to determine if the pest is present, a simple set up using a clipboard or other sturdy surface with a piece of plain copy paper can substitute for the traditional gear. Simply hold the paper beneath the branches and tap them with a pole or stick to dislodge anything onto the paper where it can be further examined.

This short video shows how to use a beat sheet. While it is geared toward trees in orchard production, the principles of use and equipment are the same.

Whether visually inspecting individual branches or trying the beat sheet method, monitor trees weekly through the spring. Check trees again in the fall for autumn populations.