Hemlock Woolly Adelgid

Submitted photo

Pennsylvania’s State Tree, the Eastern Hemlock, is under attack from the woolly adelgid.

Pennsylvania’s State Tree, the Eastern Hemlock, is under attack. This beautiful and important tree of our mature forests and native ecology is being attacked by yet another foreign invasive insect that could, if allowed to advance, decimate our hemlocks.

The foreign insect comes from Asia. It is a tiny bug with a funny name – the woolly adelgid. “Woolly” comes from the white fuzzy shelters that the female insects cover themselves with and “adelgid” from the family of sap sucking insects to which they belong.

Sapsuckers they are! These insects gather in great numbers to attach themselves to hemlock branches at the base of the needles. They suck the life juices right out of those branches, causing the needles to turn brown and the tree to die back. In some instances a healthy tree can fight off the damage but the subsequent stress typically causes the tree to die completely in about 4 years.

Here in Fayette County, hemlock trees are found in the wild and most often in the older growth woods in ’the mountains’ in places like Ohiopyle State Park and Bear Run Nature Reserve. Elsewhere, the evergreen hemlock is a popular choice for many property owners who enjoy incorporating native plants in their landscaping. Since its arrival in eastern Pennsylvania in the late 1960’s, the woolly adelgid has made its way to our area and has been attacking Fayette County’s hemlocks since about 2013.

So, what should you do if you find the white, cottony clusters on the branches of your hemlock? If the tree is small enough, it can be sprayed with insecticidal soap or oil. Timing is important though, due to the life cycle of the insect. The treatment is best applied from late September through October when the insects are active. Spraying needs to be thorough and repeated a couple of times to be effective. If the tree is large, soil treatment, or drenching, is the best option. A liquid concentrate or tablet form of the insecticide is placed directly in the soil around the affected trees. The treatment will be taken up by the roots and dispersed through the tree, whereupon the adelgids will suck it out of the branches. The key ingredient in this method is Imidacloprid, and it is best used in the Spring from late March through early June. If treating by this method, it is necessary to keep the soil moist for the duration of the treatment.

The woolly adelgid has no predators in the eastern U.S. but scientists are testing natural predators from the Pacific Northwest, most notably the “Ln” beetle. Locally, the Western Pennsylvania

Conservancy and the PA Bureau of Forestry are experimenting with insectaries – nursery habitats for the woolly adelgid and its predators in a natural setting – with the hope of establishing the Ln beetle quickly enough to fight the spread of the adelgids in the region. It also has been observed that the woolly adelgid spread slowed down and the general population thinned out after several days of zero-degree weather. Unfortunately, the nature of our current climate change has reduced the occurrence of those colder temperatures and, therefore, it is less reliable in helping to eliminate this pest.

Through the efforts of the scientists and our own diligence, let us hope that we can prevent further decimation of our Eastern Hemlock trees. They are an important part of Pennsylvania’s environment and ecosystem. If you have and treasure hemlock trees, be on the lookout for the woolly adelgid.

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