It is important to correctly identify your hemlock’s stressor(s) in order to address it properly. In addition to the hemlock woolly adelgid, there are other pests and pathogens you may find on your hemlock trees. Here is a guide to several of the most common ones, produced in collaboration with the Blue Ridge Resource Conservation & Development Council. Unless otherwise indicated, photos are credited to the Hemlock Restoration Initiative.
- Elongate Hemlock Scale
- Hemlock Borer
- Hemlock Looper
- Armillaria Root Rot
- Hemlock Tip Blight
- Fabrella Needle Blight
- Spruce Spider Mites
- Rosellinia Needle Blight
Elongate Hemlock Scale
Origin: Japan
Description: The elongate hemlock scale (EHS), Fiorinia externa, is a soft-bodied, legless, and wingless insect that is a pest of eastern and Carolina hemlocks along the eastern United States.
Symptoms & Impact: EHS causes yellow foliage, foliage drop, and stunted growth. It appears as brown or white ovular marks beneath the needle. EHS feeds on the underside of the needle where it removes mesophyll fluid from the tree. It is not known to be a major health problem in forested stands in North Carolina; however, when found in association with other hemlock pests (e.g., HWA) or natural stresses (e.g., drought), EHS can contribute to hemlock mortality.
Treatment Options: EHS is not effected by imidacloprid, but can be controlled using dinotefuran products. The dosage and timing of treatment can differ from dinotefuran treatment for HWA.
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Hemlock Borer
Origin: Native to Eastern U.S.
Description: The hemlock borer, Melanophila fulvoguttatta, is a secondary pest to eastern and Carolina hemlocks as well as other conifers. The adult borer is a black shiny beetle with yellow to orange spots on the wings. The mature larvae are translucent white and about an inch long.
Symptoms & Impact: Look for sloughing, reddish bark, woodpecker holes, and needle die-back. The hemlock borer mostly infests trees that are already stressed or weakened. Adult borers lay eggs in the bark where the larvae develop, before emerging as adults. When found in association with other hemlock pests (e.g. HWA) or natural stresses (e.g. drought, wind-throws), hemlock borers can contribute to hemlock mortality.
Treatment Options: Maintaining healthy trees is the best way to prevent hemlock borer infestation. When possible, treat HWA and other pests. During drought, water trees if possible.
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Hemlock Looper
Origin: Native to North America
Description: The hemlock looper moth, Lambdina fiscellaria, is a defoliating insect that can cause severe damage to conifers and hardwood trees when in outbreak. The adult moth is gray-cream colored with dark lines across the fore and hind wings. Larvae are very mobile and grow up to 1.25”.
Symptoms and Impact: Defoliation often marked by partial needle consumption; red needles are characteristic of the looper. During outbreaks, tree mortality can be high as the insect is not very mobile, but it is not known as a serious pest in North Carolina.
Treatment Options: No treatment recommended.
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Armillaria Root Rot
Origin: Native to North America
Description: Armillaria root rot is a fungal disease caused by Armillaria species that affects stressed conifer and broadleaf trees. Trees that have experienced drought, extreme freezing, insect infestation, root injury, or recent transplanting may be susceptible.
Symptoms and Impact: Leader growth slowed, branch die-back, stunted and yellowing leaves, white mycelial mats below the bark near the soil line of the trunk, black shoe-string fungi under bark and branches, honey-brown colored mushrooms near the trunk during the fall. Can lead to tree death.
Treatment Options: No treatment is currently available. Preventative measures include: watering trees during drought conditions, treating insect outbreaks, and protecting trunks from damage.
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Hemlock Tip Blight
Origin: Western U.S.
Description: Hemlock tip blight is a fungal infection caused by the fungi, Sirrococcus tsugae. Other fungal twig blights also exist.
Symptoms and Impact: Hemlock tip blight causes tip die-back. Impact on whole-tree health on eastern hemlocks is light, but it is important to monitor and note if the disease worsens over time. There is no treatment option at this time.
Treatment Options: No treatment available
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Fabrella Needle Blight
Origin: Native to North America
Description: Fabrella needle blight is a fungal infection caused by the fungi Fabrella tsugae.
Symptoms and Impact: Needles in the lower part of the tree turn brown and fall in late summer, leaving bare twigs. Yellowing needles may be an early sign. Fungal fruiting structures appear as small dots on the underside of the needle lining either side of the center of the needle. The infection does not harm a healthy tree, but can add to the stress of a sickly or young hemlock.
Treatment Options: Treat the hemlock for other pests and avoid overhead watering and ensure proper spacing for adequate air circulation.
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Spruce Spider Mites
Origin: Native to North America
Description: These mites damage conifer needles when they feed on the plant tissue. Creates speckled brown/tan discoloration at the base of the needles spreading up the twig.
Symptoms and Impact: Can cause defoliation and damage to sick or young hemlocks. Not usually an issue on healthy, large hemlocks.
Treatment Options: Miticides can be used to control, but it is recommended to consult with an arborist before treatment.
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Rosellinia Needle Blight
Origins: Native to North America
Description: Rosellinia needle blight is created by a fungus Rosellinia herpotrichoides. Creates signature ‘matting’ and browning of needles in clumps.
Symptoms and Impact: Rosellinia needle blight can lead to defoliation, and kill young or sick trees, but is not usually fatal in large and healthy hemlocks. It can seriously affect lower and inner needles and can be aesthetically displeasing.
Treatment Options: There are no fungicides for the control of Rosellinia needle blight, so it is recommended to increase air flow by thinning and removing affected branches.
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See this Tennessee Department of Agriculture Forest Health presentation, Insects & Diseases of Eastern Hemlock, for more photos and information.