Pests and Diseases: Hemlock Woolly Adelgid


Today’s Pest and Disease topic is the Hemlock Woolly Adelgid. Unless you are familiar with them, you may not be sure if it’s a fungus or an insect. Hemlock Woolly Adelgids are little white fluff balls that attack one of our most beautiful native evergreens, the Eastern Hemlock (Tsuga canadensis). Let’s look at how this insect came to be one of the most dreaded of all pests in the eastern forests.

Hemlock Woolly Adelgid was accidentally introduced to the United States in the early 20th century but it wasn’t until the middle of the 1900’s that it became a true pest. It found its way to the Eastern Hemlock and fell in love…it starting having lots of babies and without a predator to keep its population in check, it became a force to reckon with. It’s depressing to know that the Hemlock Woolly Adelgid is responsible for the death of Eastern Hemlocks and studies have estimated that it could wipe out the hemlocks in some southern areas within 10 years.

hemlock woolly adelgidLet’s look at how a small, little fluff ball can wreak so much havoc. The Hemlock Woolly Adelgid literally sucks the life out the trees and the trees are so weakened by the damage that they succumb to starvation. It doesn’t happen overnight…that would be too easy. It usually takes years to kill the trees and in those years, the population of the adelgids continue to climb and they just move right on over to the next tree to begin their devastation again.

While hemlock is a common sight in northern U.S. forests, its presence is mostly in the mountainous areas of Virginia and Maryland where it enjoys the cooler temperatures. In fact, I remember a story from my Woodies professor at Virginia Tech where a student had been on a hike up to the popular Cascades waterfall. The student came back excited to tell Dr. Niemeira that he found a variegated hemlock. Unfortunately, the “variegation” ended up being a heavy infestation of Hemlock Woolly Adelgid.

So what can you do if you have Eastern Hemlocks? Scout regularly for the pest. Be sure to check the undersides of the foliage as this is a favorite hiding spot. I don’t like to just pass you off to someone else, but if you spot the little fluff balls on your hemlocks, I recommend that you consult a Certified Arborist. They will be up-to-date on the latest recommendations for controlling them and they will probably be able to apply the insecticides for you. While I’m not a fan of pesticides, if you have to use them let someone who has been certified in the application process do the work for you. I need to hear from the Mid-Atlantic Gardening readers if you have encountered Hemlock Woolly Adelgid. Leave me a comment below or e-mail me at Happy gardening!

March 6, 2012Permalink Leave a comment

Leave a Reply

Your email address will not be published. Required fields are marked *