Silvicultural Control

In general, silvicultural management designed to improve hemlock health shows promise - vigorous hemlock appear to be less vulnerable to HWA. Forest thinning is found to improve hemlock carbon balance and is associated with lower HWA abundance. There is evidence that leaf chemistry is associated with susceptibility to HWA. In particular, high nitrogen and potassium levels were associated with increased vulnerability to HWA, so nitrogen fertilizers are not recommended. A silvicultural guide for Ontario will be available soon.

Chemical control
TreeAzin (azadirachtin) and ImaJet (imidacloprid) are registered for use against HWA in Ontario. Both products are individual tree systemic insecticides injected directly into the tree’s trunk. Treatments would need to be repeated on a regular basis and  must continue indefinitely, as long as HWA is present in the area. Horticultural oil is registered as well but is only useful for smaller trees. Two basal bark sprays, Xytect (imidacloprid) and Starkle (dinotefuran), have received emergency registration in Nova Scotia. It is unknown whether they will receive emergency registration in Ontario, or full registration in either province

Biological control (US)
There are no know parasitoids of HWA, so work on HWA biocontrol in the US has largely focussed on prey-specific predators.  Several predators have been identified for HWA control, and some have been released. However, results have been inconsistent and release of some species have since been discontinued. Two species of Laricobius beetles, L. nigrinus from western North America and L. osakensis from Japan show promise. On their own they are unlikely to provide HWA control but Leucopis, a silver fly native to western North America, may compliment predation by Laricobius beetles. Currently, there are no biological control predators being released in Canada.

General resources for HWA management

Hemlock woolly adelgid management

This page presents an overview of available management options. At this time only silvicultural approaches and injected, systemic insecticides are available as management tools in Ontario.