How much do you know about the Hemlock Wooly Adelgid?

In New England, hemlock trees play an important ecological role.  They are important for limiting erosion along stream beds and provide food and shelter for deer and other wildlife.  The hemlock is valued as an ornamental tree as well as a source of lumber.  Unfortunately, hemlock trees are vulnerable to infestation by a pest called the Wooly Adelgid.

Wooly Adelgid

The Wooly Adelgid is a destructive insect that was accidentally introduced to the United States from Japan.  Wooly Adelgid infestations have been noted from Georgia to Massachusetts and can have drastic effects on hemlock populations.  Trees infested with the Wooly Adelgid become desiccated and typically die within ten years.  Specimens that survive the pest are often so weakened that they eventually die of secondary causes.  Westchester County’s tree care professionals, Westchester Tree Life want to keep your trees safe!

“Adelges tsugae 3225077” by Connecticut Agricultural Experiment Station Archive, Connecticut Agricultural Experiment Station / © Bugwood.org. Licensed under CC BY 3.0 us via Commons –

Wooly Adelgid infestations can be identified by the presence of the insect’s egg sacs.  These sacs look like fluffy tufts of cotton clinging to the underside of the hemlock’s branches.  Infested branches change from a healthy dark green color to a paler greyish-green shade.  This pest reproduces asexually and in North America can have two generations a year.  The Wooly Adelgid feeds on the hemlock’s sap and probably injects a toxin into the tree while feeding.  This results in a loss of needles and a lack of new growth.

There are a few options for addressing an infestation of the Wooly Adelgid.  Insectcides that are sprayed on the tree, injected into the tree, or applied to the soil around the tree can be effective in treating individual trees.  This sort of treatment will remain effective for two or three years.  However, such treatments can only be used when there is no risk of the insecticide contaminating nearby bodies of water.

Another option is use a non-toxic insecticidal soap or horticultural oil.  These products are applied to the hemlock’s affected foliage and work by smothering the pests.  Trees treated in this manner will need to be retreated annually.

When multiple hemlock trees are affected by the Wooly Adelgid, a biological approach to eradicating the pest may be best.  The Wooly Adelgid can be controlled by introducing a natural predator to the area.  There are two beetles that feed on the Wooly Adelgid and are highly effecting at keeping the pest’s numbers at a manageable level.  These are P. tsugae, a black lady beetle, and the larva of the L. nigrinus.  Releasing these beetles into areas where Wooly Adelgids threaten the health of hemlock trees has proven to be an effective and safe method of control.

P. tsugae and L. nigrinus

If you have hemlock trees on your property and suspect they are infested by the Wooly Adedgid, contact Westchester Tree Life today for a consultation.  We can examine your trees and advise you on the best way to eradicate this pest in your unique situation.