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Like many other pests and parasites that have devastated plant populations in North America and worldwide, the hemlock woolly adelgid did not originate in Michigan, but that doesn’t mean that it’s not our problem. If left unaddressed, it’s very possible that the hemlock bug could devastate the hemlock tree population here as it has on the East Coast and into Kentucky and Tennessee.

The hemlock woolly adelgid originated in southern Japan and was first reported in Virginia in 1951. It had been described as being problematic to West Coast hemlocks nearly 30 years prior to that. This small aphid-like insect develops and reproduces on all species of hemlock, but it only threatens the survival of the eastern and Carolina hemlocks. Less than 1/16th of an inch long, this bug ranges in color from reddish brown to purplish black and feeds on young twig tissue. The stored starches that it consumes are necessary for the nourishment of the hemlock and, without them, makes it more vulnerable to other stresses and, therefore, shorter lived.

What Spreads The Hemlock Woolly?

The hemlock woolly adelgid primarily spreads by wind or by being carried by birds or animals, and, under normal circumstances it is slow. In Japan, natural predators within the environment keep it under control, and it’s not considered especially dangerous. It’s spread to Michigan can be blamed on infested nursery stock being transported here from eastern states.

If you have hemlock trees on your property, what should you be on the look out for? White cottony masses on the branch tips of the hemlock. These are the ovisacs that the new insect will hatch from, conveniently located next to their most desired food source.

The hemlock bug has been eradicated in three Michigan counties: Ottawa, Emmet, and Macomb. The state passed a quarantine law in 2014 to stop nursery stock being shipped in from any state with HWA infestations which hopefully means that tree professionals should only be dealing with localized outbreaks already in existence. The treatment involves removing infested trees and treating adjacent trees with pesticides.

While there are no established hemlock bug populations in Michigan, it is important for arborists, landscapers, and nursery owners to be aware of this problem so that it can be dealt with immediately if and when it crops up again. Two out-of-state shipments of hemlock stock arrived in Kent County this March, and one tree was found infected. Fortunately it was destroyed before it could be planted.

If you are concerned about the hemlock woolly adelgid or any other pest posing a danger to the trees on your property, please do call Chop. Our trained staff of arborists can deal with any tree problem and help keep your trees healthy and beautiful.