With some pests, no matter how closely one looks at the foliage, no signs of active infestation come to light. Slide the same tree out of its pot and it’s another story.
Root adelgid on young black pine roots
Root aphids and adelgids are insects that feed primarily on their hosts’ roots. There exist numerous species that feed solely on the roots of conifers. Deciduous varieties too succumb to their own root adelgid and aphid species.
Treatment isn’t exactly like it is for their above-ground counterparts as you can’t always remove the trees from their pots. And because roots are sensitive, it’s important to consider the phytotoxicity of any pesticides.
As with other infestations, keeping trees healthy is the best preventative. I often find infestations in overgrown specimens that dry out quickly, but root-feeding insects can show up anywhere.
Systemic pesticides can work well when necessary, though I usually scrape away what I can during repotting and watch the watering carefully through winter. If the tree is healthy, that will often do the trick. Additional stress caused by radical root work or severe cutback and bending can slow a tree’s recovery from infestation, so I’m likely to take a light approach when I see lots of the critters and postpone more stressful work for when the tree is healthy.
