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Hemlock woolly adelgid is now in Ontario and our hemlocks need your help

By Colin Cassin, Policy Analyst at the Invasive Species Centre

This article was originally written for the Biodiversity Education and Awareness Network blog. Check it out here!

Hemlock fans, I have some bad news for you. There is a new forest pest in Ontario that requires your attention. Now, if the name hemlock woolly adelgid sounds familiar to you, it may be because in the last decade two populations of HWA were detected and eradicated in Ontario. Immediate action was taken in both instances and our woodlots have enjoyed several HWA-free years as a result.

If HWA is new to you, here are the basics. First, HWA is an insect. It feeds on the phloem of our native hemlock trees. Second, HWA is a highly-effective hemlock killer. Typical populations of HWA can kill a healthy, mature hemlock in as few as 3 to 4 years. Third, HWA is an exotic species in Eastern Canada and is certainly worthy of “invasive” status. These invasive insects have been found in 5 counties in Southwest Nova Scotia. Interestingly, HWA is not considered invasive in Western Canada as its native range has traditionally included parts of the Pacific Northwest and Eastern Asia. Within this native range it has developed natural enemies which limit populations and damage to more traditional levels.

Protecting our hemlock trees from this serious invasive species threat is important for a few reasons. First, the tree’s dense foliage provides a unique set of conditions for many wildlife, such as overwintering deer. Secondly, hemlocks have provided a number of important cultural assets such as use of hemlock bark and other parts of the tree for dyes, teas and other uses. Lastly, this versatile species can be formed into a shrub or tree, making it a valued species for use in horticulture and landscaping. Unfortunately, those features and many others are being lost in neighbouring states and those provinces where HWA is established.

Hemlock woolly adelgid uses many pathways for local and long distance spread including on clothing, wildlife such as bird feet, or possibly on infested landscape material.

During the summer of 2019, the Canadian Food Inspection Agency (CFIA) identified two new populations of HWA in Southern Ontario. Both locations are in the Niagara region, not far from New York State where HWA has been established for a number of years.

These two Ontario locations are the only known occurrences of this forest pest in the province and are thought to be relatively new introductions. CFIA detected these populations using a systematic surveying program where they look for HWA and other notable forest pests that threaten Ontario. The fact that they are here is a bad thing, but the fact that the survey located them is a great thing.

Hemlock fans in Ontario now find themselves at a critically important time in the story of HWA, and we must collectively take decisive action to prevent the spread of this pest. The threats posed to our hemlocks are real and without action we will lose large stands of hemlock in Southern and Central Ontario to HWA. Given the low-diversity nature of these late-succession communities, it’s reasonable to assume these forests will not recover gracefully. What’s more is that we have the tools available to provide ourselves with the best possible chance to spot HWA early and increase the likelihood of “successful” HWA eradication efforts.

Hemlock woolly adelgid uses many pathways for local and long distance spread including on clothing, wildlife such as bird feet, or possibly on infested landscape material.

The Invasive Species Centre has been working with our partners at CFIA and Silv-Econ Ltd. to ensure our professional forestry and arborist communities are able to spot HWA. In November, we brought nearly 80 participants from across Southern Ontario to see HWA in person and try their hand at some basic sampling techniques. Increased familiarity with this “new” invasive species will result in several additional conservation authorities, municipalities, and private woodlot owners including HWA sampling in their own forest health monitoring activities.

We have a lot of ground to cover, and with multiple pathways of introduction (ex. bird hitchhiking, contaminated nursery stock, etc.) being possible, we need as many eyes on our hemlock trees as possible. Taking a few minutes to watch an HWA webinar, or sharing an HWA fact sheet with a colleague will enable us to increase our collective chances to score another HWA “win” and eradicate this invasive species.

To learn more about hemlock woolly adelgid and the threat it poses to hemlocks, check out our hemlock woolly adelgid webpage. 

Be sure to follow @invsp and @forestinvasives on Twitter to keep up to date on HWA and other invasive forest pests, and to participate in upcoming invasive species training events