What Is Wrong With My Hemlock Tree?

are there any white, cotton-like masses on the underside of Hemlock needles?

Are the needles discolored?

Are there any small bumps on the needles?

Did the tree become girdled, sawdust material may be present?

Are there any spiny bags dangling from branches?

Were the lower branches and needles eaten?

An aphid-like insect, the Hemlock woolly adelgid (Adelges sugar) is the most serious pest of Canadian and Carolina Hemlocks, killing whole forests of them from New England to North Carolina. Adelgids feed on the sap at the base of Hemlock needles primarily on new twig growth. Needles turn gray than yellow and then drop off. Branches die back, and growth is slowed. The newly hatched nymph stage is very vulnerable to control by sprays of neem soap or light horticultural oil.

Two-spotted spider mites and spruce spider mites cause discoloration of Hemlock needles. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray plants with insecticidal soap or pyrethrin.

Hemlock scale and Hemlock fiorinia scale attack Hemlocks. Scale insects feed beneath small bumps or blister-like protective shells that they form as they crawl on stems and leaves. These shells may be white, yellow, or brown to black. Scrape off minor infestations with your fingernail. Prune out badly infested growth, or use a soft brush and soapy water to gently scrub the scales off the stems. Control scales by spraying insecticidal oil during the growing season.

Hemlock borer larvae are half an inch long worms that damage the bark of living, injured, and dying trees. They make sinuous interlacing, flattened galleries in the inner bark and sapwood, girdling infested limbs or trunk and interfering with the tree's circulation. If you see borer holes in your trees, probe into them with a flexible wire or inject a solution of parasitic nematodes.

Bagworms are small, brown caterpillars that feed on inside the silky, white bags they create. Camouflaged with browned needles, these bags hold eggs over the winter and enlarge to protect the caterpillars that hatch in May or June as they feed. Handpick and destroy all the bags. If you notice crawling caterpillars you may have to use insecticide as they are really hard to get rid of.

Hemlock needles and twigs are tasty to deer. As the pressure of development restricts their habitats more severely than ever, deer and other animals are forced to feed in residential landscapes. Here they often find plants that are tastier than the wild ones they normally forage on. Barriers provide the most reliable long-term protection from deers.

Sometimes the lower branches on Hemlocks turn brown and die. Assuming the trees have sufficient moisture and nutrition, and no obvious insect problems, this is probably due to environmental factors. Most commonly it is because the lower branches are denied sufficient light by nearby plants that have grown large and shade them. Prune adjacent trees and shrubs to permit light to reach the bottom of the Hemlock.