Hemlock Woolly Adelgid found in Grafton, ON
[Parts of this article were adapted from CFIA communications]
A new, established population of the hemlock woolly adelgid (HWA) was found in Grafton area in August 2022. The CFIA requests that woodlot owners begin surveying for HWA, making it a regular part of your walks in the bush. The CFIA’s survey approach is summarized further down in this post.
What is HWA?
HWA is similar to aphids in that they suck fluid from their hosts. They feed on cells storing nutrients and water at the base of hemlock needles, causing the needles to die and the trees to eventually take on a grey cast. There are two forms of the insect, each of which lay up to 300 eggs each year. This can result in exponential population growth due to the absence of natural enemies. A heavy infestation can kill a tree in as little as 4 years.
Why is it a problem?
In the States, HWA has caused widespread death and decline of hemlock trees, which in turn negatively impacts the types of animals, plants, and other organisms living in the ecosystem. Eastern hemlock in the southern Appalachian Mountains may be virtually eliminated in the coming years.
How does it spread?
The primary means of HWA spread is through the movement of infested nursery stock and by natural spread by wind, birds, and small mammals.
Though anyone with hemlock trees on their property can consider scouting, the following parties should thus prioritize scouting for HWA:
- nurseries importing hemlock from infested or regulated areas
- hemlock forests within 100 km of known infestations: Fort Erie, ON; Grafton, ON
- stands of at least 4 hectares with a strong hemlock component
Signs and Symptoms
Egg sacs – white, cottony, and occurring at the base of needles on the underside of branches. They resemble cotton swab tips and can remain on the tree for up to a year.
Nymphs and adults – very small and difficult to detect. Nymphs can be long ovals, flat, black and may have a slight white fringe around their bodies.
Twig dieback and discoloration of hemlock needles – HWA feeding causes these symptoms. In an advanced infestation, swollen growths occur at twig tips and no new branches or twigs will form. The crown of heavily-infested trees become yellow-green-grey and transparent from needle loss
- Review images of the signs and symptoms of HWA in this article and familiarize yourself with what to look for. At this time of year, you’ll be looking for individuals rather than large-scale damage.
- Select a hemlock tree whose branches you can reach from the ground, without a ladder. In mature stands where this is not possible, use a pole pruner to remove two branches from the mid-upper canopy of selected trees. Binoculars or the ball sampling technique are also good alternatives.
- Select a branch with green needles
- Flip the branch over and look for evidence of egg sacs and nymphs. Focus your exam on the outer 1m of the branch.
- If no woolly masses or nymphs are found, walk to the opposite side of the tree and examine a second branch
- Examine the lower portion of the trunk for evidence of HWA before proceeding to the next tree. (Note: The folks that found the new population found the woolly balls on tree boles)
While walking to the next tree, look on the ground for hemlock branches that may have broken off from tree crowns, and examine all shoots for HWA signs.
- Mark suspect trees and sample branches to obtain an insect sample for lab confirmation
- When walking along roads or open trails, use binoculars to scan hemlocks for signs and symptoms of HWA
- If you find HWA, or something that you think is HWA, record the location of your find and take photos of the HWA and the trees. Please contact Nicole Mielewczyk Nicole.Mielewczyk@inspection.gc.ca and she will send a survey crew to confirm. Don’t worry about being wrong with you identification, in this case its much better to report.
A more detailed and systematic HWA survey protocol can be found here, beginning in section 6.3 on page 7.
How to report a sighting
If you find HWA, or something that you think is HWA, record the location of your find and take photos of the HWA and the trees. Please contact Nicole Mielewczyk Nicole.Mielewczyk@inspection.gc.ca and she will send a survey crew to confirm. Don’t worry about being wrong with you identification, in this case its much better to report.
Alternatively, please call Jenny at 519-835-5872 if you do not have access to email.
PLEASE BROADCAST THIS MESSAGE TO YOUR NETWORKS, especially your contacts in the Durham, Northumberland, Peterborough, Kawartha Lakes and Hastings Regions.
For more information and photos, click here.
HWA Q&A today (Sept 29th) at 2:30pm
The Invasive Species Centre is holding a HWA question and answer session with an expert panel: Chris MacQuarrie and Victoria Fewster from Canadian Forest Service, Nicole Mielewczyk from CFIA, and Kathleen Ryan from Silv-Econ Ltd. This is the perfect time to ask all your HWA-related questions!
Click here to register.
Past HWA webinars and how-to videos on sampling can be found on the Invasive Species Centre website here.