Pests image: Hemlock Woolly Adelgid


Hemlock woolly adelgid (HWA – Adelges tsugae) is a serious forest pest that attacks and kills hemlock trees (Tsuga spp.). It has been present in the mid-Atlantic region of the United States since the 1950s but has spread to many states in the eastern US, as well as southwestern Nova Scotia and parts of southern Ontario. Most recently, an infestation was confirmed in the Hamilton, ON, area in March 2023.

Sign and Symptoms

Spring is an excellent time to monitor for HWA, when trees are free of snow and fresh egg sacs may be visible. In April and May, trees may be assessed for nymphs, which resemble grains of pepper, and egg sacs, which are small, white woolly masses found on twigs. Infested trees may also exhibit decline, twig dieback, and discoloured needles.

HWA_Survey Ball
HWA_Close Up
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HWA_Tree Trunk
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Symptoms of attack

  • Premature bud and shoot dieback
  • Premature needle loss
  • Thin, greyish-green crown
  • Dieback of twigs and branches
  • Discoloured foliage
  • Mortality

Signs of HWA

  • Eggs
  • Nymphs
  • Adult

The good news is that trees in the early stages of HWA infestation can be protected by applying TreeAzin® Systemic Insecticide treatments. Treatments may be applied in spring (April-May) or fall (late October-November). LPC’s Urban Forest Health Department also offers HWA field surveys for early detection and management of this destructive pest. Contact our support team at for more information.

Results of TreeAzin treated trees

  • TreeAzin significantly reduced HWA densities at 5, 8 and 12 months post-treatment.
  • Healthy trees!
Hemlock Woolly Adelgid Management using TreeAzin in an IPM Program

Hemlock woolly adelgid (HWA) is an aphid-like insect that is a devastating pest for eastern Canada’s hemlock trees. TreeAzin is the only product available in Canada for rapid control of HWA, and is the only botanically-based solution. In this webinar, we discuss the mode of action, our research projects, as well as the method of application.

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