Hemlock Woolly Adelgid (Adelges tsugae) is an aphid-like insect that attacks and kills hemlock trees. Its egg sacs, which look like cotton balls or clumps of snow, can be found at the base of needles. It can be spread by wind, animals and human movement of nursery stock, logs, firewood and other wood products.
Hemlock Woolly adelgid is still a new pest in Ontario but in the United States, whole tracts of hemlock forest have been lost. Hemlock is one of our few shade tolerant evergreens and an important part of Ontario’s ecosystems. Many birds and other wildlife species rely on hemlock. Hemlock shades forest streams from summer sun and allows cold-water fish like brook trout to survive, and it provides shelter and cover for deer and birds in winter.
Hemlock woolly adelgid was first reported in Canada in British Columbia in the 1920s, and in the United States in the 1950s. It has been found in the Niagara Falls area since 2019 and has recently found to be spreading. Unfortunately it is a common pest in the neighbouring US so it is very important for us to continue monitoring for this pest.
At any time of year, look for premature bud and shoot dieback, premature needle loss, thinner, greyish-green crown (healthy crowns are a shiny, dark green colour), dieback of twigs and branches, discoloured foliage, tree mortality within 4 to 15 years.
In late winter and spring, signs include white “woolly” sacs resembling tiny cotton swab ends at the base of hemlock needles on young twigs; these are most obvious in early spring.
The small, white, woolly masses contain the tiny eggs that give rise to the next generation of hemlock woolly adelgid (Photo magnified: Julie Holmes, CFIA). Unlike most other insect pests, Hemlock Woolly Adelgids are active in late winter. Females lay eggs in February and March. Beginning in March, look for small, white, woolly tufts on the twigs of hemlock (Photos: Julie Holmes, CFIA). The white, waxy covering on the egg masses protects the eggs from predators and desiccation. The egg mass stage is the only stage that is easily visible to the naked eye, making late winter/early spring an important scouting period for this pest.
Injectable applications of insecticides are registered to help protect hemlocks from this adelgid pest. Injectable applications must be performed yearly and are time-consuming, making them more costly to deliver compared to other methods of pest management. Horticultural oils are also registered to help smother the nymphs stage of this adelgid in spring and summer.
Research is being conducted of releases of a tiny ladybird beetle (Pseudoscymnus tsugae) that feeds on adelgids (the introduced ones, and the native balsam woolly adelgid and pine bark adelgid). Results are promising and may lead to natural control of the hemlock woolly adelgid. Laricobius nigrinus is another beetle in western North America that feeds on the hemlock woolly adelgid and is being investigated as a biocontrol agent. Some predatory beetles found currently only in Asia are also being tested, to see if they can be safely imported and released in North America. The future of hemlock woolly adelgid control will probably be a mixture of natural enemies and well-timed applications of specific pesticides, called integrated pest management.
Injectable applications of insecticides are registered to help protect hemlocks from this adelgid pest. Injectable applications must be performed yearly and are time-consuming, making them more costly to deliver compared to other methods of pest management. Horticultural oils are also registered to help smother the nymphs stage of this adelgid in spring and summer.
Research is being conducted of releases of a tiny ladybird beetle (Pseudoscymnus tsugae) that feeds on adelgids (the introduced ones, and the native balsam woolly adelgid and pine bark adelgid). Results are promising and may lead to natural control of the hemlock woolly adelgid. Laricobius nigrinus is another beetle in western North America that feeds on the hemlock woolly adelgid and is being investigated as a biocontrol agent. Some predatory beetles found currently only in Asia are also being tested, to see if they can be safely imported and released in North America. The future of hemlock woolly adelgid control will probably be a mixture of natural enemies and well-timed applications of specific pesticides, called integrated pest management.
Scout your hemlock trees regularly for symptoms and signs of hemlock woolly adelgid. This pest is regulated by the Canadian Food Inspection Agency and should be reported, please REPORT to CFIA if you detect this pests in Ontario. You can also contact the toll-free Invading Species Hotline at 1-800-563-7711 or report it on the EddMaps App. Infested trees are removed and destroyed in an effort to protect our beautiful hemlock trees.
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