Watch for aphids on conifers
Predators such as lady beetles are often helpful in keeping aphid numbers low, usually disappearing after several weeks.
Aphids feed on conifers by sucking juices from branches, shoots and needles. Feeding from aphids can cause the foliage to become curled; distorted or affected trees may lose their needles.
Aphids on stem of spruce leader.
Close-up of aphids
Some of the common conifer-feeding aphids produce lots of honeydew, which leads
to black sooty mold. On the other hand, there are many insect predators who
relish aphids. Often, aphid problems take care of themselves – the predators
knock the population way down fairly rapidly. The exception is when ants are
present – they will protect the aphids from the predators.
Cinara are a group of several species of large, brown or black aphids that feed on many conifers. This week I have seen branches of spruce that had several hundred of these aphids covering the branch. The foliage glistened with honeydew (excrement produced by the aphid). In most cases, when we find these in a Christmas tree field, there are only a few trees with aphids while the rest remain aphid-free. Usually, they are not a problem and disappear after several weeks.
Cinara aphids feeding
on the stem.
Scout your fields and if you are finding large numbers of aphids, keep monitoring the trees weekly. If you have high populations and the trees will be harvested this year, you may want to apply an insecticide.