Hemlock Woolly Adelgid: What Is It?

This is a brief, informative article to give general information on the Hemlock Woolly Adelgid and the effect it is having on our forests.

The Hemlock Woolly Adelgid (adelges tsugae) is a very tiny insect that is posing a huge threat to our hemlock trees, mainly in the eastern United States.

The Hemlock Woolly Adelgid (HWA) has been referred to as a microscopic vampire. This insect has been in the United States since 1924, brought here, presumably, accidentally from Asia.

How can such a small insect destroy such a large tree? The HWA positions itself at the base of the needles on a hemlock tree. They insert their feeding tubes, called stylets, into the twigs and suck the sap out from the tree. This sap is the tree's food supply and once it is siphoned out the tree will starve. (The death of the tree will happen within a few years.) During the slow death the growth of the tree slows or stops and the needles turn colors from green to gray and then drop. Most of the damage occurs in the spring and the HWA are spread by birds and winds.



Whay are hemlocks important? According to the USDA Forest Service, hemlocks provide important shelter for various animals including deer, rabbits and turkey. 90 species of birds use them as a food source as well as roosting and nesting sites. They also help plant species flourish and brook trout flourish in streams they border.

The infestation of HWA extends from North Carolina, up into New England, all of New Jersey (which has suffered heavy damage) and is spreading through Western PA and New York.

If we don't stop the HWA it has been estimated that we could lose our hemlock trees within 20 - 25 years. So how do we stop them? If you have an ornamental hemlock in your yard the most effective way to protect it is to keep it healthy. Be sure it gets plenty of water during dry spells and trim off dead or dying branches. If you notice the HWA on the branches (they leave white cottony sacs at the base of the needles) the most effective way to protect it is with chemical insecticides. Insecticidal soaps and horticultural oils are effective and commonly used materials.

So, since this pest is from Japan do they have the same problem we do? No. And one of the reasons is a different climate, but another reason is natural predators. One of them is the coccinellid beetle or ladybird beetle. The Department of Agriculture has received shipments of this beetle and have been experimenting with it. So far it has survived severe winters and seems to be slowing the progress of the Hemlock Woolly Adelgid.

Hopefully, we will hear a followup soon that will bear a good report on the use of ths natural predator.

© High Speed Ventures 2011