God Help the Canadian Hemlock



by Susan
Warning:  Reading the recent New Yorker article about Canadian hemlocks will break your heart.

Tsuja canadensis, considered the redwoods of the East, range from Georgia to New Brunswick and west to Wisconsin.  The tallest are 170 feet and the oldest 600+ years old.  And according to the New Yorker, they create whole ecosystems.

Hemlocks create deep shade and cover the ground with beds of needles, altering the temperature, moisture, and chemistry of the soil around them, and creating a distinctive habitat for certain animals and plants.  Some ecologists believe these coves contain – or, until recently, contained – the last examples of primeval rain forest in eastern North America.  Only small fragments of old-growth forests remain in the East.

Foresters started worrying about them in the late ’80s, when stands of hemlocks
were discovered to be 90 percent dead, turned into "groves of
sunbleached ruin by the adelgid".

Seems that a wealthy gardener in my hometown of Richmond, VA is responsible for a whole lot of destruction.  What’s now Maymont Park was the first garden to import evergreens from all over the world, including at least one that carried a hemlock-killing insect, the wooly adelgid.  A single female can generate as many as 90,000 clones of itself in a year.

Plenty of people are concerned, like The Friends of the Smokies.  They have a small lab that’s breeding a kind of lady beetle native to Japan that eats woolly adelgids, and it’s shown promising results.  But it’s waaay underfunded, so don’t expect that lady beetle to arrive on the scene Laura Croft-like and rescue thousands of trees.  And haven’t we learned lessons about importing one species to solve problems caused by other imported species?  How do we know it won’t cause other problems?

Then there’s an insecticide treatment called Imidacloprid brought to us by the folks at Bayer.  It’s injected into the soil around the root system of hemlocks, where the adelgids suck it into their bodies and die.  It’s an artificial kind of nicotine with one big advantage: it migrates very little through the soil and degrades quickly in sunlight.  However, it kills not just adelgids but many grubs.  Here’s one expert’s reaction: "I wouldn’t want to see chemical treatment be the only way to save hemlocks, but nothing else is ready right now."  And this one: "Either you get some invertebrate kill around the treatment site or you get an ecosystem collapse – that’s the choice."  That’s some crappy choice!  And the hemlocks that are successfully protected by this product need to be re-treated every few years.  So "what you get is a forest on life support."  And funding for hemlock-saving measures competes with demands for fire-fighting monies – something no worthy program should ever have to compete with.

I know it’s not a big deal like the death of whole forests, but I’d sure like to save the 5 Canadian hemlocks growing in my garden, so if I see symptoms I’ll start using that pesticide or spraying with oil every year.  Actually, after they get too tall to spray, the only option would be injecting that insecticide into the soil, so a few grubs may have to be sacrificed to save the trees.

The New Yorker piece went on to compile this horrifying list:

  • Chestnut blight, a fungal disease from Asia, kills American chestnuts.
  • The misnamed "Dutch elm disease", an Asian fungus that’s carried by
    a beetle from Europe, has "pushed into oblivion" American elms.
  • The majority of wild flowering dogwoods have been killed off by the Asian fungal disease anthractnose.
  • Sudden Oak Death has killed hundreds of thousands of oaks in the
    West and is moving eastward.  Though the source of this fungal
    killer hasn’t been proven yet, scientists suspect imports from
  • Another fungal disease that’s carried by a European insect is killing massive numbers of American beech trees.
  • Emerald ash borers, which arrived here in 2001 via packing wood from China, are now devastating  American ash trees.

Now just reading about hemlocks was enough to turns me into a "close-the-borders" anti-immigrant crusader, so this list is pure pile-on.  Tancredo for president!

But seriously, the death of hemlock, if it were to happen on one day, would be the 9/11 of the plant world.  We’d turn against all imports, not just plants, because one of those killers came here in packing material.

By disposition I’m inclined to favor inclusiveness and open borders, but the plight of these trees makes me totally understand the demonizing of "alien" plants.  I’m heartsick, too.  And the solution is?

Photo by  Wade Franklin.  Thanks, Wade, for the stunning and absolutely perfect photo for this story.


  1. I think the Genie has been let out of the bottle on this one or if you prefer Pandora’s Box has been opened. Yes it looks like the Wooly Adelgid came in on imported conifers and in the past, plants or plant products were the most likely source of introduced pests.

    Global Free Trade has changed everything. I have seen dozens of giant spiders in ceramic tile from Turkey and big yellow scorpions in tile from Mexico. Any product that is not manufactured, packaged and transported in a sterile environment is very likely to pick up small hitch hikers.

    When I mentioned the big bugs I saw in imported tile to an Agricultural inspector on Maui whose job is generally to look at plant products, he visibly blanched, knowing there was no way they could inspect all cargo, household goods, cars, planes and ships that arrive in the islands from around the world.

    We are headed towards a kind of unitary global environment. The only thing that will stop it is an economic collapse that shuts down the global transportation system.

  2. What an excellent post. It’s so hard to limit our gardens to plants that naturally grow in our region. We want all the beautiful plants and flowers that we see in other folks’ areas and we forget that there is a reason these plants don’t grow where we are! Either they will take over or require too many resources for their survival. Or…they bring foreign pests with them that our plants cannot handle.

    Was that rant enough to be posted on this blog???

  3. There is important work going on to preserve some of these threatened trees. I have links on my blog to sites for the American chestnut, elm and dogwood trees. Disease resistant strains of elm and dogwood are now available and researchers with the chestnut projects are making progress. It would be great to support their work by planting these trees.

  4. A researcher at the Ag Experiment Station in Connecticut is also working on an adelgid predator — the research took a long time because he had to be sure the predator would not turn into a pest. I saw a whole hillside of hemlocks in the Naugatuck River valley die during a single summer several years back — it was heartbreaking. Sometimes it feels like we won’t have anything left but the damn Norway maples.

  5. As soon as we unpacked the moving boxes in spring 2006 (50 miles north of Manhattan) I was calling around for what to do to help the incredibly beautiful hemlocks on our property. We had them sprayed (cooler temps, never in summer!) twice at a not-inexpensive cost…but what else can one do? Good news is that there are a lot of seedings that, for want of doing something, I have added our compost around them and have been spraying with a mixture of vegetable oil and cloves so Bambi stays clear.

  6. I’m also afraid Christopher is right.
    The emerald ash borer, which has been in Windsor in the southwestern part of Ontario, is now reported in Toronto, and heading east. Of course, when politicians are more interested in increasing global consumption than about natural ecosystems…trees are going to lose out.

  7. If you go up to Clingman’s Dome in the Smokies you can see the devastation these bugs caused. I was there several years ago and it looked like shattered telephone poles stuck in the ground. It’s amazing that something so small can be so devastating. The hemlock is a beautiful tree and I’d hate to see it lost. I started several in my yard this year hopefully they will be safe from the pests until a good predator bug is found.

    I think the best thing to do for now is to keep the species alive by planting and propagating trees until a cure can be found. Preserving some seed as a precaution for the future might be wise.

  8. Actually the country’s plant 9/11 happened 100 years ago with the appearance of chestnut blight. The recent pests are more of the same, but not as destructive to the Northeast as chestnut blight was. Having said that, yes, Canadian Hemlock is a climax tree and the forest changes when it dominates. Once it’s the dominant tree, you know the forest has reached maturity.

    I hope they are able to find a predator that will target the adelgid exclusively.

    One huge, huge way gardeners can help keep a lid on things is NOT to grow plants known to be invasive. This is hugely important! Whenever possible CHOOSE NATIVES FOR YOUR GARDENS!

  9. This article itself was moving, with much historical information on the hemlock woolly adelgid (HWA) that is not readily available – so much of the HWA literature is just a rehash of information that was not worth much to begin with.

    But in addition to the historical content (and the very sad story), this also appears to be a propaganda-piece for Bayer and those in the chemical gardening industry. (Despite his presentation here as a do-gooder tree climber, Will Blozan is also the owner of a large chemical arborist business in the Asheville area and a major USFS contractor.)

    And on the subject of biological control of HWA, Blozan is dead wrong. The USDA-approved HWA predator beetle Sasajiscymnus tsugae (which is this HWA’s native predator – at its point of origin in Japan) turns out to be a very effective predator that can knock back the adelgid population to the point that the Canadian hemlock can re-foliate and return to health (coexisting with lower HWA densities).

    I am watching this happen on 2- year sites with my own severely defoliated forest hemlocks, on 1st year sites in neighborhoods in the Brevard NC area and in 4-5 year sites in NC National Forest areas.

    So a biological control agent is available, though “official” awareness of this has a ways to go.

  10. Wow, I’ve been a designer afraid – afriad to recommend Canadian Hemlocks and even Carolina Hemlocks, because the the scurvy adelgids. These are such lovely trees at the National Arboretum that it breaks my heart we can’t plant such a useful native in our surburban gardens. I have been at too many houses where I’ve seen the damage done. But I think I will change my approach having seen this article. For the true native loving clients, maybe they are willing, especially in the age of sustainable gardens, to take care of their trees to retain a native of their own. I will try to convince them armed with this advice. Thank you.

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