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In this four-part series, we will introduce the Hemlock Woolly Adelgid problem, explore solutions, and highlight the work that SWMLC and our project partners are doing locally to stop HWA here, and keep it from spreading there.
Because this one, the hemlock woolly adelgid (pronounced a-dell-jid) (aka HWA) is especially bad, doing huge amounts of damage to one of our most admired trees (eastern hemlock). But we should also care because ingenious people are figuring out ways to get rid of it – and that’s inspiring!
To get started, there’s the victim in this story, the eastern hemlock (Tsuga Canadensis). It’s a stately, graceful, evergreen tree that can grow up to 100 feet tall and live for more than 500 years. It’s admired for its tiny cones and soft sprays of flat, shiny green needles with silvery undersides – and many yard-sized versions have been developed for landscaping. In the past, people used various parts of the tree to make medicines, and its bark was used to make dye.
Hemlocks are the nesting tree of choice for many birds that need the safety of high branches and heavy foliage, including kinglets and a whole bunch of different warblers, like Blackburnians and black-throated greens. In the winter, the seed cones provide food for birds like crossbills and pine siskins, porcupines munch on small twigs, and deer like to sleep under the sheltering boughs where the snow isn’t as deep.
You wouldn’t think a tree would have much effect on fish but hemlocks play an important role here, too, creating good spawning habitat for trout and other cold-water fish. By growing alongside creeks, hemlock shade cools the water and the dense foliage softens the impact of rain before it hits the ground – reducing the muddy runoff that ruins streams – helping to keep streams cold and clear.
In the wild, hemlocks aren’t usually the dominant tree in the forest, but they are an important part of the forest ecosystem. They seem to show up in small groves, where their dense foliage creates “micro-climates” that are relatively dry and extra shady in the midst of the cool, moist conditions that hemlocks prefer. These special spots are home to salamanders, fungi, lichens, and unique plants (like certain orchids).
Hemlocks grow best in damp climates, which means they thrive in parts of Canada, the Appalachian mountains, and creek ravines near the lakeshore in southwest Michigan, like those at SWMLC’s Wau-Ke-Na, William Erby Smith Preserve.
Or at least they did thrive in these places. Hemlocks are now struggling, having to deal with quickly warming temperatures and new drought/flood extremes.
A favorite book that’s sadly out of print, but worth searching out a used copy:
The Book of Forest, Yard, and Thicket by John Eastman
HWA are soft-bodied insects that create a layer of white, waxy “wool” to protect themselves while they grow – and while they suck the life out of hemlock trees. That’s literally what they do: jam their mouthparts into the soft tissue at the base of the needles and buds to suck sap, robbing the tree of nutrients and water. First the branch withers then, slowly, the entire tree dies. “You’ve heard of death by 1,000 cuts . . . how about death by 1,000 tiny straws?” asks SWMLC Stewardship Director Mitch Lettow.
Because eastern hemlocks and HWA didn’t evolve together, the trees have no natural defense against the insects (HWA was imported in the 1950’s on nursery plants from Asia). The results have been devastating. HWA has wiped out hemlocks in eastern Canada and the US, especially in the Smokies where the dead trees are obvious on the mountainsides. HWA spread slowly on their own, reliant on wind and their waxy bods sticking to bird feet. But humans give them a boost when we move firewood around, or plant infected nursery trees.
Cold temperatures used to keep HWA from our area, but the last few mild winters have changed that. HWA recently turned up in Michigan and five lakeshore counties have issued quarantines against moving hemlock wood, nursery trees – even yard waste that contains the needles. Thanks go to Travis Wilcox, a member of the MI Civilian Conservation Corps Forest Health Crew (and SWMLC volunteer!) who detected a new population of HWA based on ONE individual! “. . . I had just completed a careful binocular survey of a large tree. I turned around to another, smaller hemlock and saw the ovisac right away,” said Wilcox. “We spend a lot of time looking at these trees. Anything white on the underside of a branch catches our attention.”
Travis is talking about that layer of waxy wool that the insects create – and that’s what to look for: small white blobs stuck to the underside of needles, singly or in groups. Inside those blobs are baby HWAs, called “nymphs”, but not cute like the mythological nature spirits.
You can help by checking for HWA on any hemlocks you encounter and reporting any you find to one of the agencies listed at the bottom of this article. Take some photos to ID and be ready to provide a location. But please don’t collect samples – that just spreads them!
Found some HWA?
• Email the Michigan Department of Agriculture and Rural Development (MDARD).
• Call the MDARD Customer Service Center at 800-292-3939.
• Use the Midwest Invasive Species Information Network (MISIN) online reporting tool.
• Download the MISIN smartphone app and report from your phone.
Identification and information on Hemlock Woolly Adelgid:
University of Florida, Institute of Food and Agricultural Sciences
Midwest Invasive Species Information Network (MISIN) website
Quick video on identifying HWA
Details on the story about Travis Wilcox and the Michigan Civilian Conservation Corps Forest Health Crew.
Breeding HWA-resistant strains of eastern hemlock trees looks promising and may turn out to be the best long-term solution. Scientists grew baby trees from cuttings from trees that had survived an HWA attack that otherwise crushed a grove of hemlocks. They planted the young trees near infested forests and found that 96% of the new trees made it, compared to just 48% of the other trees!
There are also experimental hybrids between eastern hemlocks and other hemlock species being bred for the nursery industry. The hybrid trees are sterile and can’t make seeds – so this method won’t work in natural areas – but it could be a great solution for those who want majestic, HWA-free trees in their yards.
Researchers are also looking into “bio-controls” – finding predators that will reduce HWA populations by eating them. The fuzzy bug has its own insect enemies in the parts of the world where it’s a natural part of the ecosystem, so scientists are studying these predator species to see if they can reduce HWA populations on eastern hemlocks, too. They didn’t all pan out – in fact, one type of ladybug just kept flying away! But there’s promise in pairing up a certain fly with some of the beetle species, and research goes on to make sure these predators could be released without unintended side effects.
Chemical insecticides are probably the most effective way short-term way to control HWA – and new focused applications where the poison is injected directly into the tree bark are much more environmentally-friendly than earlier methods.
“Hope for hemlocks: New tactics found to fight deadly pest”, Ad Crable, Bay Journal
That’s the attitude that SWMLC’s Stewardship Crew (Mitch, Dave, Megan, Jess, and Alex) took when they stomped out into the woods looking for wild and woolly foes – hemlock woolly adelgids, that is.
HWA isn’t just a rumor in west Michigan: it’s here. It’s been spreading slowly north along the Lake Michigan coast through Allegan, Ottawa, Muskegon and Oceana Counties for a while now. But when it reached Bass Lake just south of Ludington this past spring, the alarm went up a notch.
We hadn’t seen it in any SWMLC preserves yet but we knew it was just a matter of time before it did: Ottawa County Parks had already seen it and private landowners just to the north of Wau-Ke-Na, WE Smith Preserve North Tract were already dealing with it.
Earlier in the spring, SWMLC received grant funding (along with project partners Ottawa County Parks, The Nature Conservancy-Michigan, Chikaming Open Lands, and Shirley Heinze Land Trust) from the Wildlife Conservation Society’s Climate Adaptation Fund (which is generously supported by the Doris Duke Charitable Foundation). With this support, we’re able to explore new ways to keep forests healthy in the face of threats like climate change – and HWA.
As part of a suite of forest health projects supported by the grant, our goal was to survey, measure, tag, and treat Eastern hemlock trees with HWA-targeted insecticide at Wau-Ke-Na North and neighboring properties. So we sent a letter to nearby landowners to ask if they would like to be included in the project. 25 neighbors said “yes”! They had purchased hemlock trees from nurseries to landscape their yards, or hemlocks occurred naturally in their woods, and they weren’t happy watching HWA turn their shining green trees into dull gray husks.
Our first step was just to find the trees. Eastern hemlocks are not as common in our areas as trees like maples and oaks, so the Stew Crew searched the back dune forests and glacial ravines near the lakeshore where conditions are right. They explored over 300 acres on foot and found more hemlocks than expected. We were delighted, even if it meant more work, because hemlocks are great indicators of high-quality habitat and their presence reflects well on the surrounding natural area.
Once a hemlock was found, Crew members gave each tree its own unique tag, measured how big around it was (“DBH” or “diameter at breast height”), took GPS coordinates so they could find it again, and looked for signs of HWA. All the info went into a database.
Our plan was to treat the trees with a preventative insecticide that has been proven to allow infected trees to regain health, and prevent HWA infections in healthy trees. Chemicals are never an easy choice but new direct-to-bark treatments and targeted trunk injections have replaced the old soil-drenching methods, which vastly reduces the chances of accidentally hurting good-guy species. Also, because the trees usually grow in deep shady forests with few flowering plants, negative effects on pollinators are even more unlikely. So we felt pretty safe in having the treatments done. Our partners at Ottawa County Conservation District conducted the insecticide injections and they were like a swat team, treating 1,101 trees in 40 hours! Huge thanks, you guys!
The insecticide treatments will only last for 5 to 7 years but that will buy us some time. After seeing how quickly HWA has crushed hemlocks in other parts of the country, taking action now seemed like the right thing to do.