TREE SAVERS: Why are my Hemlocks Dying

Invasive Hemlock Woolly Adelgid (HWA) is decimating America’s Eastern Hemlock Forests.

Dead Needles Closeup Before Maura

TREE SAVERS: Why are my Hemlocks Dying


Eastern and Carolina hemlocks are dying because of an invasive hemlock-eating pest transplanted from Japan. The pest – Hemlock Woolly Adelgid (HWA) – kills hemlocks by sucking the nutrients from the tree, killing it in as little as 3-5 years. Sadly, this voracious adelgid destroys entire hemlock forests in as little as 6-10 years. HWA is what’s killing your hemlocks.


Hemlock Woolly Adelgid was first discovered in 1951 in a Virginia hemlock forest. Since their discovery, HWA has now established itself in Minnesota, Wisconsin, Michigan and every state along the upper eastern seaboard and the entire Appalachian range all the way to the Great Smoky Mountains. Fully infested forests extend from Maine to Georgia.If your hemlocks are dying, they’re death is part of a massive and rapid HWA infestation killing entire hemlock forests.


In fact, HWA has become an environmental disaster. As hemlocks die, the death of the entire forest ecosystem is put in motion.

All those species that depend upon the hemlock also disappear. The hemlock is an arboreal backbone that provides critical habitat for over 96 bird and 47 mammal species. Streams with hemlock forests contain a higher richness and diversity of aquatic invertebrates and significantly greater trout populations. As hemlocks die, stream-side shading disappears, water temperatures rise, and trout die.

The hemlock canopy traps and retains moisture, increases humidity, and reduces evaporation. As trees die, the natural ability of the soil to retain moisture diminishes (hydrological failure). Erosion happens and streams and waterways become clogged with sediment. Guess where that sediment ends up? It ends up in lakes. And as trees die, fire hazard rises. Dead trees and underbrush become fuel for forest fires.

Finally, a dead hemlock forest is more than just an eyesore. Local economies that depend on a lush hemlock forest decline. Hemlock forests provide aesthetic beauty, tourism, increased property values and wood products.


The most commonly used pesticide is Imidacloprid, a neurotoxin that is selectively toxic to insects, including bees. But though Imidacloprid has proven to be an effective pesticide for HWA, it is also toxic to mammals, causing mortality when exposed to high doses. Worse, studies have shown that this pesticide is toxic to humans.

It’s also expensive, labor intensive requiring repeated applications, and has been relatively ineffective in halting the spread of HWA. Another limitation is the fact that once HWA is poisoned; when the tree recovers there’s nothing to prevent HWA from reestablishing itself on the tree. In reality, Imidacloprid is effective in the short term, but not in the long-run as a sustainable approach.


There is a solution – biological control. Biological pest control means using another living organism to control the pest. When people use ladybugs to control aphids on rose bushes instead of using a pesticide, they’re using biological control. In the case of HWA infestation, there’s been no other living organism to biologically control HWA – until now.

The S.tsugae beetle – Sasajiscymnus tsugae – is the natural ladybug predator of HWA. After rigorous lab and field testing, in 1995 the USDA approved the implementation of the S.tsugae beetle as THE method of biologically controlling HWA in public forests. Research determined that S.tsugae beetles pose no threat to any other living organism other than HWA.

“The best option for managing Hemlock woolly adelgid in forests is biological control.”
U.S. Department of Agriculture 2005

The S.tsugae beetle is the perfect biological control agent. Infested hemlocks can significantly recover in just one year. Once released and allowed to do its predatory work, hemlocks stay recovered. The biological control of HWA using its natural predator is proving to be not only the most effective solution, but the most economically and environmentally friendly sustainable solution.


To learn more about Sasajiscymnus tsugae (S.tsugae beetle), how and why it works, and how you can get these voracious HWA eating beetles on your hemlocks, visit our website: or call us today at (570) 871-0088. On our website you can download our free “Guide to Saving Hemlocks.”

Together we can save the majestic hemlock – starting with your trees.

(570) 871-0088

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