DOGWOOD BORER
Photo courtesy of John Neal, USDA, Beltsville
Order: Lepidoptera
Family: Sesiidae
Scientific Name: Synanthedon scitula
Description: The most damaging insect pest of dogwood is the dogwood borer. Adult dogwood borers are dark blue-nearly black, with occasional yellow markings. Wings are clear toward the base and have a span of about 15 millimeters.
The egg is elliptical, blunt on both ends, and very small. When first laid it is pale yellow, turning only slightly darker prior to hatching.
DOGWOOD BORER LARVAE
Photo courtesy of Dr. Jim Baker, North Carolina State University
Biology: The dogwood borer is found in southeastern Canada and throughout the eastern half of the United States wherever dogwood are grown.
Although dogwood is the preferred host, this pest has also been found on oak, chestnut, hickory, elm, willow, and pecan.
In the south, adult emergence occurs from late April through late October, peaking in mid-May. Females lay their eggs singly on the bark of dogwoods with cankered or injured trunks and on injured pecan and on the twig galls of oaks. Sometimes most of the woody galls on oaks are secondarily infested with dogwood borer caterpillars. This tendency to oviposit on galls and wounds of various trees has led some entomologists to believe that only cankered or wounded dogwoods are susceptible to the dogwood borer. Incubation usually requires 8 to 9 days.
Tiny caterpillars hatch from the eggs and bore into the bark. Newly hatched larvae become established if they encounter a bark wound or a cracked callous area. Each larva can consume from 2 to 3 square inches of cambium as it tunnels around under the bark, and it causes ugly scars. Their tunneling may kill small trees. The larva then hibernates within its tunnel throughout the winter. Pupation takes place the following spring. Although there is only one generation per year, borers may be found in various stages of development thoughout most of the year because eggs are laid over a period of several months.
Control: The best control measure for dogwood borer is to plant dogwood trees that do not have cankers on the trunks. Dogwoods can also be protected from dogwood borers by applying an insecticidal spray in late spring or early summer. Consult the North Carolina Agricultural Chemicals Manual for current recommendations.
COTTONY MAPLE LEAF
SCALE
Photo courtesy of Dr. Jim Baker, North Carolina State
University
Order:Homoptera
Family: Coccidae
Scientific Name: Cottony Maple Leaf Scale.
The most conspicuous life stage of the cottony maple leaf scale is the fluffy, white egg mass. Winter is a good time to treat these scales as the lady beetles that specialize on feeding within the egg sacs of the scales are not active. Demonstrations have shown that during the winter, pyrethroids are more effective for this soft-scale insect than are oils and other types of pesticides. Infested trees may become dark with sooty molds during the summer. Sooty molds grow in the honeydew excreted by the scales. Once the ovisacs are deposited, the plants should not be sprayed until June to give the lady beetles a chance to depart for their summer sites. If the scales are sprayed too early, the lady beetles may be killed, but not the eggs, which are still protected by the waxy ovisac. Thus, spraying too early would do more harm than good. Carbamates and pyrethroids are extremely effective against the crawlers and young scales feeding on the leaves.
Description: The adult is a slender beetle measuring 10 to 15 millimeters long and 3 millimeters wide. The head is dark to almost black. A triangle of three black spots is visible on the top of the thorax. The wing covers are yellow tan, with a narrow black line on the inner edge and a broader, darker line on the lateral margin.
When fully grown, the larva is yellowish, legless, and about 19 millimeters long.
Biology: The dogwood twig borer is the larval stage of a small, long-horned beetle known as the elm twig girdler. It emerges from damaged dogwoods in late spring or early summer after the new vegetative growth has matured somewhat.
Wherever flowering dogwoods are grown, these borers are a threat. They have also been recorded on elm, viburnum, azalea, and many fruit trees.
These beetles fly to the new growth and chew a series of holes around the stem and then another series of holes 1/4- to 1/2-inch away. The female beetle then inserts an egg into the bark between these rows. Within a few weeks, this egg matures and a slender, white grub hatches and begins to feed within the stem. As the grub bores downward, the stem dies and wilts above the area girdled by the adult. The presence of boring dust is diagnostic of this pest. Sawdust-like material is ejected from a series of closely placed holes as the borer continues down the stem.
The grub overwinters in a cell excavated inside the twig. The following spring, the grub matures and molts into a pupal stage. A few weeks later, a new generation of beetles emerges from infested plants to continue the life cycle.
Infested branches often die or are so weakened that the branches break off easily.
Control: When wilting occurs in the spring, infested twigs can be pruned off several inches below the girdled portion and destroyed to prevent the beetle grubs from surviving to produce more beetles next year.
Plants can also be sprayed with a labeled insecticide in late spring to prevent the beetles from laying eggs.
Fortunately, the dogwood twig borer is a sporadic pest so that treatment is probably not needed every year. If a problem is discovered during one season and preventative treatment is taken the following spring, the population of dogwood twig borers will probably abate without the need for further annual treatments.
DOGWOOD CLUBGALL
MIDGE GALLS
Photo courtesy of Dr. Jim Baker, North Carolina State
University
Order: Diptera
Family: Cecidomyiidae
Scientific Name: Resseliella clavula
Description: The adult fly is about 1.5 millimeters long. The abdomen is bright orange. The wings are mottled with varying patches of black and yellow hairs. The male's antennae are about the same length as its body. Joints appear bead-like. The female's antennae are shorter and less conspicuous.
The larvae is an orange colored maggot.
Biology: Galls are more common on ornamental dogwoods than on those growing naturally in the woods.
Flowering dogwood is the only known host for this pest.
This midge causes club- or spindle-shaped galls at the tips of flowering dogwood twigs. Up to 120 galls per tree have been reported. Twigs may die above the swollen part, and trees are deformed when infestations are heavy. In the fall, maggots emerge from the galls by chewing small, round holes through the sides. They drop to the soil under the dogwood trees, where they overwinter. Pupation occurs the following spring. In late spring, adults emerge and lay their eggs among the minute terminal leaves. Usually the eggs are laid on the most vigorous twigs where the nodes are close together in the developing bud. Upon hatching, the maggots work their way into the interior of the leaf base or into petioles at the junction of the apical pair or two pairs of minute terminal leaves. They may gain entrance to the midrib through adjacent leaf tissue. Feeding causes the formation of an elongated gall, where the maggots live in a central cavity. From 1 to 39 maggots may be found per gall.
Control: Swollen twigs should be cut off and burned while the larvae are present. When galls are first noticed, the galls should be pruned out during that growing season and the trees should protected with a persistent pesticide- just as the new growth is emerging the next spring.
Description: Adult flies are grayish brown and about 5 millimeters long.
The larva are yellowish white and about 6 millimeters long when fully grown. Larva are pointed at the front, legless, and tough-skinned.
Biology: Seedcorn maggot flies do not harm dogwood trees, but they are frequently reported on dogwood and other ornamental plants throughout the entire United States and southern Canada.
The fungus-infected adult flies are found on dogwood in spring. The flies are particularly noticeable on bare twigs. These flies are infected by a fungus (Entomophthora), that causes flies to light on and cling to protruding twigs, wire fences, etc. Infected flies usually die in the afternoon as the abdomen swells with internal fungal strands. Early the next morning, when the humidity is high, the fungal spores are released into the air to infect other flies. The dead flies shrivel and eventually fall from the twigs.
Most of the life cycle is spent in the maggot stage in the soil of various field crops. Flies emerge in May to deposit their eggs on seed, on plantlets, or on soil with an abundance of decaying vegetable matter. Upon hatching, the maggots burrow into the seed, often destroying the germ. They develop into pupae inside brown puparia in the soil and emerge as adults 12 to 15 days later. As many as three to five generations occur each year. However, the fungus-infected adults are usually noticed only in the spring.
Control: On dogwoods and other ornamental shrubs, no control of the adults is necessary because infected adult flies indicate a natural mortality factor at work.
Description Dogwood sawflies begin life as tiny, almost transparent, pale green larvae. These tiny caterpillars skeletonize the leaves. They next molt into a snowy white caterpillar which is pale lemon yellow below. This snow white stage feeds on the edges of the leaves as do the caterpillars in the last stage.
Last-stage dogwood sawfly caterpillars are greenish-brown worms with black spots. They grow to within 1 inch in length of the dogwood sawfly caterpillar. Mature larvae wander about seeking soft or decaying wood in which to hibernate. They will sometimes bore into siding or wooden lawn furniture. (Woodpeckers sometimes damage siding as they drill in to feed on the dogwood sawfly caterpillars.) The winter is spent as a prepupa. The caterpillars pupate in the spring, and the adult sawflies emerge, mate, and lay eggs from May to July. There is one generation per year.
LEAFHOPPER
Photo courtesy of Dr. Jim Baker, North Carolina State University
Order: Homoptera Family: Cicadellidae
Scientific Name: Rose leafhopper: Edwardsiana rosae;
Redbanded
leafhopper: Graphocephala coccinea
At least two species of leafhoppers feed on the leaves of dogwoods: the rose leafhopper (a whitish to pale straw yellow leafhopper) and the redbanded leafhopper (a green leafhopper with red orange and turquoise stripes). As the leafhoppers feed, they inject saliva into the plant which evidently predigests the protoplasm. They then suck out the liquid contents of the cells leaving behind the dead, empty cells which show up conspicuously as small, white spots. Leafhoppers have not been shown to transmit diseases to dogwoods.
Leafhoppers are skittish and agile. When foliar samples are submitted, often no leafhoppers are found because they jump off when they are disturbed as the foliage is cut. However, the cast skins of the nymphs usually remain on the lower surface of the leaf like white, miniature versions of the "shells" cicadas leave on tree trunks during the summer.
Control: Some systemic insecticides seems to be more effective than other materials. Consult the current North Carolina Agricultural Chemicals Manual for recommendations.
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