Ensure your Hemlocks are safe from this invasive pest with proper HWA treatment practices.
Hemlocks are wonderful trees to have in your landscape, and their density makes them a great choice for planting in privacy screens. However, without proper care, Hemlocks are very susceptible to Hemlock Woolly Adelgid, which can seriously damage and eventually kill your Hemlocks.
Unlike other insects, such as Winter Moths, that feed on the leaves, needles, twigs, or new buds of trees, the Hemlock Woolly Adelgid (HWA) does not damage Hemlocks by feeding. Instead, the Hemlock Woolly Adelgid causes damage to Hemlocks because its saliva is toxic to the tree. As the HWA feeds on the Hemlock, its saliva is spread through the needles and slowly disperses throughout the tree.
Unhealthy Hemlocks, particularly those infested with HWA, usually stick out like a sore thumb, as the rich green color is replaced by a grayish or yellowish hue. In a group of Hemlocks, you can usually pick out one infested with HWA fairly easily.
Controlling and preventing HWA is relatively straight forward, and the insects can be killed quickly; however, the toxin from their saliva has already infiltrated the tree and it may take a while for the tree to rebound. It can take an entire year or more until the toxicity in the tree is reduced.
The common misconception among homeowners with treated Hemlocks is that the tree is still infested because they see the small “white spots” on their trees. What really happens when treatments are applied correctly is that the insects are killed, but their woolly protective covering remains on the tree. Over time the woolly covering will fall off.
Hemlocks need to be treated for HWA every year. Even if your Hemlocks have not been infested, these pests have spread so rapidly that there is no way to ensure your trees will remain free of infestation. There really is no rhyme or reason to when HWA will infest, but it is well-known that they are force to be reckoned with for Hemlocks in our region. A topical treatment of Horticultural oil in the spring and fall, coupled with an injection treatment in between will do the job.
If you think you may have Hemlock Woolly Adelgid, or have Hemlocks that are not treated regularly you should consider consulting with a Certified Arborist to learn how to keep your Hemlocks safe.