A recent study, completed at The University of Connecticut Department of Natural Resource Management and Engineering in cooperation with the U.S. Forest Service, has found that hemlocks can recover from adelgid infestations. In addition, site characteristics were found to play an important role in the health of the hemlocks and their resistance to long-term damage caused by the adelgid. It attacks hemlocks from the base of the needles. Because individual adelgids are so small, the first indication of infestation is usually the discovery of the white, cottony egg sacs. In addition to protecting the eggs, the fibrous sacs help transport the adelgid by sticking to bird feathers or mammal fur.
Wind also carries the sacs between trees, spreading infestations further.
Because the hemlock woolly adelgid is an exotic species, it has no natural predators in our region. Researchers have looked for natural predators of the adelgid in Japan and China in an attempt to find a biologic control. Insecticidal soaps and horticultural oils provide effective control if branches are thoroughly soaked, including the undersides of each branch. While this form of spraying is virtually impossible in most forest applications, it can be used to protect infested hemlock hedges or individual ornamental trees. This study examined changes in hemlock health over an eleven year period.