Hemlock Woolly Adelgid Now in Ontario and Our Hemlocks Need Your Help

Blog & Photos by Colin Cassin, Policy Analyst with the Invasive Species Centre

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 (HWA) sounds familiar to you it’s likely 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.

But let’s back up a minute. If HWA is new to you there are the basics you should know:

  1. HWA is an insect. It feeds on the phloem of our native hemlock trees.
  2. 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.
  3. HWA is an exotic species in Eastern Canada and is certainly worthy of “invasive” status. Interestingly HWA is not considered invasive in Western Canada as its native range is thought to include parts of the Pacific Northwest and Eastern Asia.

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 attractive for many wildlife species, such as overwintering deer. Secondly, hemlocks provide 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 provinces where HWA is established.

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 the survey’s located them is a great thing.

We now find ourselves at a critically important time in the story of HWA in Ontario. We are at a crossroads where we can collectively take decisive action to prevent the establishment of this pest in Ontario or allow it to spread beyond its current footprint.

I believe we should take the former. The threats posed to our hemlocks are real and without action we will loose 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 us to provide ourselves with the best possible chance to spot HWA early and increase the likelihood of “successful” HWA eradication efforts.

The Invasive Species Centre has been working with our partners at the CFIA and Silv-Econ to ensure our professional forestry and arborist communities have an opportunity to train their eyes to spot HWA. In November we were able to bring nearly 80 participants from across Southern Ontario to see HWA in person and try their hand at some basic sampling techniques. This 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 (Bird hitchhiking, contaminated nursery stock, etc.) 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 from Ontario.

To learn more about hemlock woolly adelgid and the threat it poses to Ontario’s hemlocks, visit us online at www.forestinvasives.ca. Be sure to follow us on twitter (@forestinvasives) to keep up to date on this and many other invasive forest pests, and to participate in upcoming invasive species training events.

Photo Captions:

Photo 1: The opportunity for participants to observe live specimens of HWA is a particularly effective means for ensuring the key messages have a lasting impact. It also provides an opportunity for participants to take their own photos which can be used in developing their own outreach tools.

Photo 2: Surveying for HWA using the ball sampling method is an interactive way to complete hemlock surveying. This method enables surveyors to assess HWA presence in the upper part of the canopy.

Photo 3: The black adhesive tape is surprisingly effective at capturing the white woolly egg sacks indicative of HWA presence. This sampling method involves up to 10 “shots” per tree. 

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