University of Maryland Extension

Dogwood Insect Pests: Identification and Management

Key Points

  • Selecting a tree appropriate for your site, planting it correctly, and providing regular care are essential steps to prevent common pest problems of dogwoods (Cornus spp.).

  • Dogwoods planted too deeply, inadequately watered during the first two years of establishment and drought periods, or physically wounded at the trunk (e.g., mower damage), are more susceptible to pest infestations.

  • The most common pests of dogwoods in Maryland are sawflies, borers, and scales.

  • Refer to Diagnosing Problems of Flowering Dogwood to identify symptoms and possible causes.

Common Pests of Dogwoods (Cornus spp.) in Maryland

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Dogwood Sawfly (Macremphytus tarsatus) larvae. Photo: Bruce Watt, University of Maine, Bugwood.org

Dogwood Sawfly (Macremphytus tarsatus)

The dogwood sawfly is an occasional pest of dogwood. The larvae (young insects) resemble caterpillars and  feed on the foliage of several species of dogwood and are most commonly seen on shrub dogwoods [e.g., silky dogwood (Cornus amomum), redosier dogwood (C. sericea)]. Adult sawflies, which resemble tiny wasps, emerge during late spring and early summer. The female lays eggs on the undersides of the leaves. Upon hatching, the young larvae feed together and chew the leaf. As they grow, they will eat all of the leaf except the midrib.

After the second molt, the larvae become covered with a white powdery material. After their final molt they lose the powdery covering and change color. The mature larvae are yellowish with a shiny black head and black spots. These mature larvae will wander about in search of an overwintering site, generally in soft or decaying wood. There is one generation each year.

Management: 

  • Management is seldom needed, but if desired, wear gloves and manually remove and discard the larvae. 

  • If an infestation is heavy, particularly on a young plant, the larvae may be sprayed with horticultural oil registered for landscape use. Apply according to the label instructions.

dogwood-borer
Dogwood Borer (Synanthedon scitula) Adult. Photo: David Laughlin, Horticultural Student, Bugwood.org

Dogwood Borer (Synanthedon scitula)

The dogwood borer is the major pest of dogwood. It most frequently attacks trees that are stressed or injured. The adult is a day-flying clearwing moth. It is about 3/8 inch long, blue-black with two yellow bands around the abdomen, and resembles a wasp. 

Adults emerge from dogwood trees around mid-May, and continue throughout most of the summer. The female moth lays her eggs on the bark of the tree, and is particularly attracted to injured bark, scars, and other rough areas on the trunk. 

Upon hatching, the young caterpillar finds a suitable place to enter the tree such as a wound, scar, woody gall, or branch crotch. It will feed just under the bark in the cambium layer. The full grown caterpillar is white with a pale brown head, and about 5/8 inch long. There is one generation eacha year. The caterpillar overwinters in its burrow under the bark and pupates in the spring. When the dogwood borer moth emerges, the brown pupal skin is frequently left behind in the exit hole, indicating the presence of this pest.

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Dogwood Borer Damage at the Base of Flowering Dogwood. Photo: James Solomon, USDA Forest Service, Bugwood.org 

Small, wet areas on the bark, dead branches, adventitious growth (water sprouts on trunk and large branches), or sloughing and cracking of bark can all be symptoms of dogwood borer attack. Small trees or individual branches can be girdled and killed in one to two seasons. Larger trees with ongoing infestations often develop rough, knotty areas on the trunk and large branches, and may lack vigor.

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Dogwood Twig Borer (Oberea tripunctata) Larva. Photo: Terry S. Price, Georgia Forestry Commission, Bugwood.org 

Dogwood Twig Borer (Oberea tripunctata)

The dogwood twig borer is a less serious pest of dogwood. The adult is an elongate (5/8 inch long) beetle with long antennae. This beetle has yellow/tan wing covers with a black line down the center and along the margins. There are two distinctive black dots just behind the head. The adult beetle emerges from infested twigs in the spring and the female lays her eggs in healthy twigs.

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Flagging of a branch caused by Dogwood Twig Borer infestation. Photo: James Solomon, USDA Forest Service, Bugwood.org

The yellowish larva that hatches from the egg begins tunneling in the pith, boring down the center of the twig, occasionally making a series of holes to the surface through which it expels sawdust. As the larva tunnels, the twig may break off or wilt behind it. There is only one generation each year, with the larva overwintering inside the twig.

Management:

  • Infested twigs should be clipped off several inches below the girdled or infested portion and destroyed. This should be done after wilting occurs and before adult emergence in the spring. This insect usually does not cause serious problems.

Flatheaded Apple Tree Borer (Chrysobothris femorata)

The flatheaded apple tree borer attacks a wide variety of shade and fruit trees. On dogwood it can be a serious problem on young trees that are planted too deeply and on stressed, older trees. 

The adult beetle is 1/2 inch long, oval, flattened, greenish bronze above and brassy below. The wing covers have wavy, light colored indentations. The adults may be seen running over the bark of trees and fly when disturbed. Adults appear in summer and feed on the foliage of host trees. They lay eggs under bark plates or in bark crevices on the main trunk or larger branches. 

The larvae bore into the tree and feed in the phloem (tissues that move plant foods produced by leaves) and outer sapwood. Larvae are called flatheaded borers because of the enlarged, flattened area behind the small, black head. They are creamy colored and excavate large, irregular tunnels in the phloem on the main trunk and larger branches which die back first. Mature larvae overwinter in cells in the outer wood and pupate in the spring. There is one generation each year.

The larvae may be found boring into the base of these trees. Small trees are often killed.

Large trees are seriously injured from dieback of branches and loss of large patches of bark over mined areas on the trunk.

Management: 

  • Maintaining good tree health is the best way to prevent flatheaded apple tree borer. Plant trees at the proper depth and in the best conditions possible. It is essential that young trees receive adequate water during establishment.

Scale Insects

There are several scale insects, such as calico scale, cottony maple scale, and oystershell scale, that can become pests on dogwood. These insects attach themselves to branches or leaves where they suck juices from the tree. Heavy infestations may cause leaf yellowing, stunting and dieback. Calico scale and cottony maple scale are both soft scales and produce honeydew (a clear, sticky substance).

calico-scale
Calico Scale (Eulecanium cerasorum), females. Photo: John A. Davidson, University of Maryland, Bugwood.org

Calico Scale (Eulecanium cerasorum)

Female calico scale insects are very conspicuous in May. They are large (1/4 inch long), black and white-spotted and swollen. They are found on twigs and branches. 

By mid-June they die, shrivel and turn brown. Eggs hatch at this time and tiny white crawlers settle on leaf veins. These immature scales turn yellow and feed on the leaves during the summer. They move onto the bark to overwinter.

Management:

  • This scale is usually controlled by beneficial insects and generally does not require spraying. 

  • If it is necessary to control high populations, apply a horticultural oil (2% summer rate) or insecticidal soap spray during the summer. 

  • During the dormant season (when leaves have fallen from deciduous trees)  apply a horticultural oil (4% dormant rate) to control overwintering immature scales.

cottony-maple-scale
Cottony Maple Scale (Pulvinaria innumerabilis). Photo: Kansas Department of Agriculture, Bugwood.org

Cottony Maple Scale (Pulvinaria innumerabilis)

The cottony maple scale is easiest to find in May and June. During this time, ¼ inch long white ovisacs may be found on branches and twigs. Ovisacs are white, cottony masses that contain eggs. Crawlers hatch in June and settle on leaves to feed. 

Examine the undersides of leaves for the flat, yellow, immature scales along the leaf veins. They will be found where honeydew and/or sooty mold (a fungus that grows on honeydew) are present. Adult female scales are 3/16 inch long, black, flat, and oval. There is one generation each year and immatures overwinter on the twigs.

Management:

  • If it is necessary to control cottony maple scale, apply a horticultural oil (2% summer rate) or insecticidal soap spray during the summer. 

  • During the dormant season (when leaves have fallen from deciduous trees)  apply a horticultural oil (4% dormant rate) to control overwintering immature scales.

oystershell-scale
Oysershell Scale (Lepidosaphes ulmi). Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Oystershell Scale (Lepidosaphes ulmi)

This is an armored scale and, unlike the cottony maple and calico scales, it does not produce honeydew. Heavy infestations of this scale may cause yellowing, wilting and eventually branch dieback.

To monitor for this pest, look for tiny (1/8 inch long), oystershell shaped, and brown to gray scale covers on the bark of wilting or dead branches. There may be one or two generations a year. 

Crawlers are present in May. They are about the size of a pinhead and light colored. Look for the crawlers near the old scale covers. They do not settle on the leaves, but stay to feed on the twigs and branches.

Management:

  • Prune out heavily infested branches. A dormant oil spray may be applied in late winter. Be sure to thoroughly cover all of the branches. 

  • It is much easier to spray the trees for all of the scale insects listed in late winter to control the overwintering scales. Spraying during the dormant season also lessens the impact on beneficial insects that are present during the spring and summer.

  • A summer rate (2%) spray of horticultural oil may be used in summer, if necessary.

dogwood-club-gall-midge
Dogwood Clubgall Midge. Photo: Terry S. Price, Georgia Forestry Commission, Bugwood.org

Dogwood Clubgall Midge (Resseliella clavula)

The dogwood club gall midge is responsible for spindle shaped swellings near the tips of dogwood twigs. The adult midge is a small, delicate, brown fly. The adult midges emerge in May and the female deposits eggs in new terminal leaves. The newly hatched larvae, or maggots, work their way into the developing twig. As the yellow-orange maggots grow, the tissue swells around them forming the characteristic gall. 

The first evidence of the presence of the club gall midge may be a wilted, deformed leaf. A light infestation will cause little harm, but a heavy infestation can stunt a tree. The galled twigs and terminals die prematurely and flowering is reduced. 

Prune out and destroy the galls in summer before the maggots drop to the ground to pupate in the fall. This insect usually does not cause serious problems.

Symptoms on dogwoods may also be caused by diseases or abiotic (environmental) factors. Refer to our pages on common dogwood diseases, abiotic problems, and tree care.

By Mary Kay Malinoski, Principal Agent, University of Maryland Extension. Edited and revised by Christa K. Carignan, Coordinator, University of Maryland Extension, 12/ 2019.

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