My woodlot has HWA, what's next???


My woodlot has HWA, what's next???

This article is a personal account of how we are dealing with recently finding hemlock woolly adelgid (HWA) in our families' woodlot.

We've known for five years that it was coming.  Now that we've found it on our trees I feel an urgency knowing their time could be limited.

The approach described is based on our current understanding and our priorities.  Everyone will be different.  And we will probably learn new things that will adjust our plans.

Have you had any experience dealing with an HWA infestation?  Please COMMENT with any insights you may have learned from your experience on our Social Media ( Instagram or Facebook ).  

With over 30,000 private woodlot owners, many of us in Nova Scotia are/will be going thru this process.

Most HWA infested hemlocks will eventually die.  And because the bug is so prolific, most trees in an infested area will end up getting infested probably within 1-3 years of the first discovery.

On our 150 acre woodlot, there are about 100 mature hemlock trees over 80 inches around (two people can just touch finger tips if they give it a hug).  And about 10,000 more in various sizes.

We could could let nature run its course as most of our hemlocks die over the next 5-10 years.

We could harvest all our hemlocks before the bug kills them.

We believe that our future woodlot should include hemlock.  So we have decided to treat key trees and eventually implement biocontrols to maintain a natural balance.


So far we have found two separate HWA infestations and they were both isolated to individual trees.  But how widespread is the infestation?  And is it in the older trees that we hope to keep alive?  Because older trees respond much slower to treatment so they will have to be treated early if we hope to keep them alive.

So we are conducting a survey of hemlocks throughout the woodlot:

  • around the trees we know have HWA, we inspect all the hemlocks in the immediate vicinity
  • anytime there is a windstorm or branches come down we search the underside of branches looking for  HWA
  • starting now up until the weather warms we will inspect the upper branches using a bright, focusable light around dusk (HWA pops in the beam)
  • in late May/early June, hemlock tips will grow out and should turn a very distinctive lime green colour.  No colour change suggests the tree may be under stress.  This seems like a good job for a drone.
  • throughout the year we will be checking the health of our hemlocks by assessing their crown density -- from the base of the tree, look up into the crown ... with healthy trees you see very little sunlight coming through dense foliage

We see hemlocks as part of our future woodlot.  We expect many will die but it is important to us that some remain.

First up is an ongoing monitoring program.  As described above, we will be looking for HWA throughout the woodlot.  Winter is a good time to look for the cotton-like, woolly sacs,  Spring is a time to assess new growth and thru the summer and fall we will be looking up into the hemlocks to assess their crown density, looking for signs of needle drop and branches without needles.

Second is the treatment plan. We are currently getting certified to apply pesticides.  We will treat select trees to keep them alive until biocontrols are in place.  We expect to treat between 250 and 500 hemlocks over the next couple of years. Our schedule, the pace of HWA spread and cost will determine the specific numbers. 

The selection will be based on outstanding examples that will be important seed trees and hemlocks along watercourses that provide important erosion/water control.

For the short term, we will be continuously monitoring our hemlocks for HWA, treating select trees as soon as necessary and removing some of the hemlocks that are infested that have not been treated. 

Some of the dying hemlocks will be retained for wildlife and eventually decaying onsite.  

There is going to be a lot of lumber milling.

For the longer term, we have to get the Canadian west coast biocontrol insects produced in large quantities ASAP so HWA is kept in check thru natural processes because continuously applying pesticides every 5-7 years to keep trees alive is unsustainable.

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Many thanks to Donna Crossland for proof reading the copy and offering suggestions.