I have been getting some reports about a strange looking insect on hemlocks. It is the hemlock elongate scale, Fiorinia externa. This scale is a yellowish brown, flat, elongated insect with a shell-like waxy covering that is primarily a pest of eastern hemlock and Carolina hemlock in the Eastern United States including Connecticut, Maryland, Massachusetts, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, and Virginia. Other trees affected are northern Japanese hemlock, fir, and spruce trees.
This is a serious pest, so make sure you identify it correctly. It helps to look at the damage on the tree. This scale pierces the underside of the needles with its mouthparts and removes the fluids from the needles causing needle yellowing/dropping, thinning canopy, and branch dieback starting at the bottom of the tree and moving upward. Death of the entire tree can occur within ten years with a heavy infestation. Also note that hemlock elongate scale is often found on the same trees as hemlock woolly adelgid, another hemlock tree killing insect. I think many people mistake this insect for other types of fungi or mites, so use the above information to make sure you know what you’re dealing with.
There are multiple options when it comes to battling hemlock elongate scale. Management may be difficult with contact insecticides (Up-Star® Gold, Distance®, and/or RTSA Horticultural Oil) that are sprayed directly on the tree/pest because the life stages overlap throughout the growing season, making application timing difficult. A systemic insecticide like Transtect™ is easier to use than contact insecticides because proper timing is less of an issue. Transtect™ is applied to the soil and absorbed by the tree. Transtect™ should be applied early in the spring, as the 1st generation is emerging from their shells, or in September/October for the second generation. Transtect™ will also work on hemlock woolly adelgid for the same trees. Also, maintaining healthy trees with supplemental watering during drought can decrease susceptibility. DO NOT fertilize with nitrogen. This can increase hemlock elongate scale populations.
I hope that helps you save your hemlock tree!