What are my management options?
No management:
At least 80% of infested hemlock trees are expected to die within 4–15 years. Individual trees may possess some level of resistance to HWA and will be extremely important for the survival of the species. The loss of hemlock will gradually lead to hardwood-dominated stands or a mix of hardwoods, red spruce, and white pine. During this transition, the dead standing, and downed hemlock will provide valuable habitat for a variety of birds, mammals, and invertebrates such as pollinators.
Chemical control:
Hemlock can be protected from HWA by treatment with systemic insecticides. In Canada, only one option is currently available: direct stem-injection of imidacloprid, a neonicotinoid pesticide which spreads via the vascular system of the tree and kills HWA as it feeds. Trees remain protected against HWA for up to 5 years. The injection process is costly, so prioritizing individual trees or valuable stands is strongly recommended. To learn more about imidacloprid and its uses, availability, application regulations and certified applicators visit the Chemical Treatment page.
Silvicultural management:
Long-term stand management should be ongoing to promote overall stand health and resilience against stressors. Prior to HWA impacts, stand thinning may promote hemlock growth, boosting its tolerance to HWA infestation, although this approach alone is unlikely to be sufficient in the long term. Following HWA detection in your stand, removal of highly infested trees (hotspots) may slow down the further spread of the pest. Pre-emptive cutting of healthy hemlock stands in anticipation of HWA is not recommended, as it could result in the loss of resistant hemlock, and dramatically impact the associated habitat. Visit our Silviculture page for more information on silviculture trials.
Biological control:
Biological control is on the horizon! The introduction of specialist natural enemies of HWA is the only long-term, region-wide strategy to ensure persistence of hemlock on the landscape. Canadian Forest Service, Parks Canada, and other members of the HWA Working Group – Maritimes are actively researching the potential for releasing predators of HWA to help control the populations of the pest. Biocontrol is not a simple or quick process; however, we remain optimistic that it will begin to play a key role in the integrated pest management of HWA over the next 10-20 years. Another reason to leave uninfested hemlock in the forest. Visit our Biocontrol page for more information on biocontrol research.