The Adelgids Are Coming. How Can We Save Our Hemlocks?
Marlene Gioia Smickle: ISA Certified Arborist - PA Certified Pesticide Applicator - Penn State Master Gardener – Pike County
There are Bits of Cotton All Over My Hemlock Trees. What can I do?
Hemlock Wooly Adelgids may be killing your trees, and you are not alone. Most of the Northeastern United States is being affected. The Hemlock Wooly Adelgid (HWA) was introduced in this country in 1924 and has been contained in the west from California to Alaska for over seventy years. Although they pose no threat to the Western Hemlock, they have been devastating the Eastern Hemlock (Pennsylvania’s State Tree) since their arrival. A recent study was done at Mount Minsi in Delaware Water Gap National Recreation Area. In a three-year period, new growth on Hemlock went from 80% to 0%, while the Adelgid population increased from 2% to 88%.
This small, reddish brown insect, about 0.8mm, roughly half the size of a pinhead, overwinters as an adult and lays its 50-300 eggs in March and April. These eggs appear as white tufts at the base of each needle. The nymphs hatch in April and May and continue to live on the Hemlock needles, feeding almost entirely on new growth. The wingless mature adults are ready to leave home by June and are easily transferred by birds, deer, and other third parties, like wind. Every year, two generations of HWA are produced. Now, here’s a scary thought … every one of them is female, capable of producing 50-300 offspring without a male.
The HWA is first be seen on lower branches working its way up until it has infested the entire tree. Heavily infested Hemlocks will most likely die within one year. Some stands of affected Hemlocks have lasted as much as seven years. Once HWA has weakened a tree, the tree becomes susceptible to a host of other problems, for example diseases and other insects.
What can you do? There are an awful lot of Hemlock trees in Pike and Wayne County. You might think we could probably stand the loss of a few. You are right. Your primary concern should be the specimen trees, trees that surround your home and add value to your property, or the ones on park trails that help attract tourists to our area.
If you notice HWA eggs this Spring, you should: First, investigate how many trees on your property are actually affected. Second, accept the fact that you may not be able to save them all. Third, decide which trees you must save.
What you can do:
- Discourage birds and other animals from the area by moving bird feeders and birdbaths away from your Hemlock trees.
- A strong stream of water will dislodge immature insects — use care to avoid helping them onto a different Hemlock.
- Prune out heavily infested branches and burn them.
There are professionals who can help you. Penn State Cooperative Extension can send you literature and answer questions. There has been success in fighting this pest using micro-injections of insecticide followed by a nutritional fertilizer. Applying horticultural oil in Spring and Fall has shown to be effective for controlling this insect. Advantages to using microinjection techniques include removing weather restrictions, containing the pesticide to the affected tree, targeting the insect using the necessary amount of pesticide, assuring the pesticide will be brought to every needle, and removing the potential of chemical drift affecting people, pets, beneficial insects, nearby streams and lakes.
You can search these websites for more information:
As a concerned homeowner, you should:
- Be aware of the Hemlock Wooly Adelgid.
- Accept what you cannot change.
- Be proactive in fighting back where you can.
- Save some of those beautiful trees.
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