Tree Damage from Hemlock Woolly Adelgid

The hemlock woolly adelgid is a sap-sucking insect that feeds specifically on hemlock trees. As the insects feed, they damage the tree by removing sap and disrupting the flow of water and nutrients. Though all species of hemlock are vulnerable, damage is particularly severe in eastern hemlock and Carolina hemlock. When large populations are present, an infested tree can die in just a few years. This invasive insect is native to Asia and the Pacific Northwest. It has now become well established in much of the Eastern United States, killing thousands of trees since its introduction.

signs of hemlock woolly adelgid

The white, cotton ball-like masses that indicate a hemlock woolly adelgid infestation. Small nymphs are also visible.

Signs of Hemlock Woolly Adelgid

Hemlock woolly adelgid is an incredibly small insect. Detecting its presence is made easier by the white coverings of the egg sacs. These have a woolly appearance, hence the name, and look like miniature cotton balls lining the underside of branches.

Typically the insects begin feeding in the lower part of the tree. With that, early signs of their presence can usually be found there. Needles near the base of the hemlock tree will fade in color or fall off. The lower twigs and limbs will eventually begin to die. Hemlock woolly adelgid populations can grow very quickly.  Each female can lay up to 300 eggs on a host tree.

In the native range of the pest, hemlock species are more resistant and populations are further controlled by natural enemies.  Unfortunately, in the non-native areas of the eastern U.S. where the pest is now widespread, these natural checks and balances are not in place.

There are a number of options for controlling hemlock woolly adelgid. Catching infestations early is very important as these insects reproduce very quickly. Regularly monitoring hemlocks for signs of hemlock woolly adelgid is the first step in maintaining plant health and preventing the loss of trees.


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