The balsam woolly adelgid, Adelges piceae, is a tiny, sucking tree pest first introduced to the United States and Canada, from Europe, in 1900. The assumed method of introduction is afflicted nursery stock. Preferred host trees in Europe appear relatively unaffected by the adelgid’s predation and these insects are not even considered forest pests of significance. In North America, however, the balsam woolly adelgid is devastating true firs, Abies spp., in eastern and western forests. Some areas are seeing near complete removal of firs from the ecosystem.
True firs are the only known host for the balsam woolly adelgid. Susceptibility varies among species; native North American varieties are highly susceptible, some Asian firs are affected while other are not, and European fir species can host large adelgid populations with little to no damage. Trees afflicted with this pest may have “gouting”, which is where the terminal growth appears stunted and buds and branch nodes are swollen; trees with this type of symptom will decline slowly, succumbing to the infestation over several years. Crowns of affected trees may also suffer stunted growth and will appear to take on a fiddlehead shape or curl towards the top. Wood decaying fungi will quickly invade dying or dead upper stems. A more serious adelgid infestation can occur along the main bole; these populations can reach 100 to 200 insects per square inch of bark surface. In this case, the foliage will become chlorotic before turning red and brown and the tree will decline quickly. Severity of symptoms and responses to infestation appear to vary by species and region.
This pest does not differentiate by age, all sizes of tree have been found to be affected. Injuries to the stems and twigs occur due to feeding; the adelgid injects the tree with a substance that appears to interrupt normal hormonal function causing abnormal cell differentiation in the bark and newly formed wood. The cambium is stimulated to produce aberrant quantities of phloem and ray cells and huge parenchyma (ground tissue of non-woody structures) cells develop in bark. Concurrent to this damage, an unusually wide annual ring will be produced, composed of cells with abnormally thick walls.
Initial infestations encounter a veritable pool of host-worthy, susceptible material that has grown for years. All adelgids are female, meaning all individuals have the ability to reproduce and populations increase exponentially. This results in several years of severe tree mortality. After the initial wave, the infestation is less spectacular, having exhausted much of its host material. It takes time for trees to regenerate and grow into a susceptible state, causing adelgid populations to fluctuate. However, it appears once the balsam woolly adelgid colonizes a stand of trees it remains permanently.
There are cultural, manual and chemical controls that effectively manage the balsam woolly adelgid pest. If you have concerns or questions about trees on your landscape contact your arborist and visit: http://www.savatree.com/insect-mite-treatments.html.