Contributors: J.R. Baker, Extension Entomology Specialist; D.M. Benson, Plant Pathology, Professor; L.F. Grand, Plant Pathology, Professor; R.K. Jones, Extension Plant Pathology Specialist; M.A. Powell, Extension Horticulture Specialist; D.L. Stephan, Extension Entomology Specialist; J. Scott, North Carolina Department of Agriculture; H. Singletary, North Carolina Department of Agriculture

Azalea Insects

The principal insects that attack azaleas in the Southeast are azalea bark scales, azalea leafminers, lace bugs, whiteflies, peony scales, thrips, leaf-eating caterpillars, and beetles. To this list of insects can be added several species of mites. Though they are not insects, they may occasionally be troublesome. Following is information about azalea pests and their symptoms.

Azalea bark scale. Infested azaleas usually appear chlorotic; the bushes are often covered with a black fungus; and white cottony or matted waxy, thread-like masses may be found in crotches and on twigs.

Azalea caterpillar. The plant is defoliated or has "chewed-up" younger leaves. The length of the caterpillar varies from about 10 millimeters (reddish to brownish black with white and yellow stripes) to about 51 millimeters (black with white or yellow stripes and red head).

Azalea lace bug. The upper surfaces of the leaves are discolored in spots (mottled); the undersurfaces are often dotted with "fly specks" (excrement). Also on the undersurfaces of leaves are adult insects (3 mm long with brown and black markings on lacelike wings) and nymphs (small, dark, and spiny).

Azalea leafminer (leafroller). Brown blisters appear on leaf tips, and margins of leaves are often curled up. The small, yellow caterpillar causing the blisters is not visible because it feeds between the two leaf surfaces.

AZALEA BARK SCALE
Photo courtesy of Dr. Jim Baker, North Carolina State University


Azalea Bark Scale

Order: Hemiptera
Family: Eriococcidae
Scientific Name: Eriococcus azaleae Comstock

Description The adult female azalea bark scale is dark red with short legs and antennae and long, sucking mouthparts. The insect is hidden from view by the egg sac, a covering of felted or matted waxy threads . The sac is about 3 millimeters long and 1 1/2 millimeters thick.

The egg is laid within the egg sac, occupying the void left by the female's shrinking body.

The tiny nymph hatches from the egg and ventures out of the egg sac. It soon penetrates the bark with its long, sucking mouthparts and begins to feed. The nymph is inconspicuous and practically free of any waxy covering.

Biology
Distribution. The azalea bark scale occurs in the eastern United States; it has also been reported in Belgium, Germany, and Russia.
Host Plants. The azalea bark scale has been found on four azalea species, rhododendron, "flowering cherry," and huckleberry.
Damage. Since its discovery in 1881, the azalea bark scale has become recognized as a prominent pest of azaleas. Infested plants usually appear chlorotic and unthrifty. The bushes are often covered with sooty mold, a black fungus that grows in the honeydew excreted by the azalea bark scales as they feed. Eventually twigs may die back.
Life History. As the female azalea bark scale matures, it secretes white, waxy threads, which become felted or matted into a thick covering over its entire body. This covering is called the egg sac, where eggs are laid after mating. As the female lays eggs, its body shrivels gradually until the egg sac is almost completely filled with eggs. Eggs are laid in late April. They hatch in about 3 weeks. This new generation matures during the summer and produces eggs in September. Mature females tend to feed in crotches and on twigs. Adult males, two-winged and tiny, tend to feed on the leaves. Azalea bark scales overwinter as nymphs feeding on the bark.

Control Adult females and eggs are protected by the egg sac from virtually any pesticide. The key to control is treatment in late spring and late fall when the nymphs are present. The current North Carolina Agricultural Chemicals Manual should be consulted for specific chemical controls.

AZALEA CATERPILLAR
Photo courtesy of Dr. Jim Baker, North Carolina State University


Azalea Caterpillar

Order: Lepidoptera
Family: Notodontidae
Scientific name: Datana major Grote and Robinson

Description
Adult. The light-brown moth has a wingspan of 45 millimeters.
Larva. The partly grown larva (caterpillar) is approximately 10 millimeters long and reddish to brownish black with white and yellow stripes. The mature caterpillar is about 50 millimeters long and black with eight near-white, longitudinal, broken stripes; the head and legs are mahogany red.

Biology
Distribution. Azalea caterpillars are serious pests of azaleas in the Southeast: Virginia, the Carolinas, Florida, Alabama, Mississippi, and Louisiana.
Host Plants. An important pest of azaleas, azalea caterpillars have also been reported on blueberry in Delaware, on red oak in Maryland, and occasionally on Andromeda and apple in Atlantic states.
Damage. The caterpillars often defoliate much of the plant before they are detected.
Life History. The azalea caterpillar is gregarious, feeding in groups; all members raise head and posterior in unison when disturbed. Comparatively little is known about the biology of this insect. Apparently there is only one generation per year. Eggs are deposited by the female moth in masses of 50 to 100 on the underside of the leaf. The first-instar caterpillars feed in a cluster side by side unless disturbed. Most of the damage occurs in August and September.

Control Because the caterpillar is harmless to humans, it can be removed by hand. For specific chemical controls, see the current North Carolina Agricultural Chemicals Manual for recommendations.

AZALEA LACE BUG
Photo courtesy of Dr. Jim Baker, North Carolina State University


Azalea Lace Bug

Order: Hemiptera
Family: Tingidae
Scientific Name: Stephanitis pyrioides (Scott)

Description
Adult. The small adult, 3 millimeters long and 1.5 millimeters wide, has lacy wings with brown and black markings, and light-brown legs and antenna.
Egg. The smooth, white egg, which measures approximately 0.4 millimeters by 0.8 millimeters, is flask shaped with the neck to one side. It is usually deposited in the tissue of a young leaf along the midrib or a large vein. Each egg is inserted in the tissue with its neck slightly above the leaf surface. Up to 90 eggs have been found in a single leaf. Most of them are placed irregularly along the midrib.
Nymph. Commonly found on the underside of a leaf, the nymph is almost colorless at birth but soon turns black and spiny. It molts six times and ranges in size from 0.4 millimeters to 1.8 millimeters before becoming an adult. After the fourth molt, wing pads show distinctly.

Biology
Distribution. In the United States, the azalea lace bug occurs from New York and Massachusetts southward into Florida and Alabama.
Host Plants. The evergreen azalea varieties are preferred by azalea lace bugs, although the deciduous varieties may be attacked. Mountain laurel is also subject to infestation.
Damage. Injury is caused by the nymphs and adults as they extract sap from the undersurfaces of the leaves. The damage shows as spotted discoloration of the upper surfaces of the leaves. In severe infestations, the leaves become almost white, many of them drying completely and dropping off. The undersides of the leaves are also disfigured by the excrement and cast skins of the insects.
Life History. Since its introduction from Japan in the early 1900's, the azalea lace bug has been recognized as an important pest of azaleas. Female lace bugs lay groups of eggs on the undersides of the leaves, most often along the midribs. This egg-laying takes place over an average period of 2 weeks. These eggs require an average of 2 weeks for hatching.

Colorless at first, the spiny nymphs hatch from the eggs, gradually darken, and go through five growth stages before becoming adults. Because of the extended oviposition period, it is quite possible to find all stages together on the undersides of the leaves at the same time. Usually two or more generations are produced in a year. The insect overwinters in the egg stage. In the South these overwintered eggs start hatching in late February, building up to a dense population during March, April, and May. A second brood comes along in July, August, and September. During early August eggs are laid. By the middle and last week in September, many adults of this brood are present, the overwintering eggs are deposited at this time and during the first part of October.

Control Repeated applications of some insecticides may be needed to control lace bugs effectively. The first application should be made as soon as nymphs appear in the spring and be followed with a second application 7 to 10 days later, if needed. Applications should be repeated as needed at monthly intervals. Thorough coverage is essential when applying sprays if good control is to be expected. The undersides of the leaves must be covered. The current North Carolina Agricultural Chemical Manual can provide recommendations for chemical controls.

AZALEA LEAFMINER DAMAGE
Photo courtesy of Dr. Jim Baker, North Carolina State University


Azalea Leafminer

Order: Lepidoptera
Family: Gracillariidae
Scientific Name: Caloptilia azaleella (Brants)

Description
Adult. The adult azalea leafminer is a small, yellow moth with purplish markings on the wings. The wingspan is about 10 to 13 mm. Larva. The leaf-mining larva is yellowish and about 13 mm long. It has three pairs of prolegs found on abdominal segments three, four, and five. The proleg hooks (crochets) are singly arranged in a U-shaped pattern (penellipse) with series of crochets within the pen.

Biology
Distribution. The azalea leafminer is found in most states where azaleas are grown.
Host Plants. Azaleas are the only known hosts for this insect.
Damage. This leafminer larva has little effect on plants grown outdoors, but it may do considerable damage to cuttings in the greenhouse. Mining within the leaf, the young larva causes the formation of brown blisters on the leaf surfaces. As the larva matures, it emerges and rolls the edge of a leaf around itself for protection while feeding on the leaf surface. Seriously injured leaves usually turn yellow and drop, thereby causing an unsightly plant.
Life History. Eggs are deposited singly on the undersides of leaves along the midribs, usually one to five per leaf. The young (larvae) hatch in about 4 days, mine into the leaves, and feed inside them. At this stage, the leaves appear to have blisters. If a leaf is held up to the light, the larva can be seen inside. When about one-third grown, the larva emerges, moves to the tip of a new leaf, and rolls it up for protection while feeding and growing. When nearly grown, the larva rolls up the margin of a leaf and spins a cocoon inside. The moth emerges from the cocoon, mates, and deposits eggs for another generation.
Under greenhouse conditions, the larvae may be found at any time during the year. The insect overwinters outdoors as a larva or pupa. Adults appear and females begin to lay eggs about the time plants bloom in the spring.

Control Because the larva protects itself by mining into and rolling the leaf, this insect is not easy to control. Several insecticide-spray mixtures have yielded satisfactory control when applied at the first sign either of the adult moth or of foliar injury by the larva. One or two applications, 1 to 2 weeks apart, are usually sufficient. The current North Carolina Agricultural Chemicals Manual should be consulted for current recommendations on chemical control.

AZALEA STEM BORER
Photo courtesy of Dr. David Alverson, Clemson University


Azalea Stem Borer

Order: Coleoptera
Family: Cerambycidae
Scientific Name: Oberea myops Haldeman

Description. Azalea stem borers are slender, long-horned beetles about 1/2 inch long, with yellowish brown heads and thoraxes. The wing covers are yellowish gray with dark outer margins, and there are two black spots on the thorax. The eggs, which have been described as "yellow," occur under the bark. The grub, found inside the stem, is slender, yellow, and legless.

Biology. The azalea stem borer is found throughout the eastern United States wherever azaleas and related plants grow. Azalea stem borers infest azalea, rhododendron, blueberry and mountain laurel.

Infested twigs wilt and die as the larvae bore downward inside. Later in the season, infested stems often break off at the base, leaving the plant lopsided and unattractive. Small plants may break off completely.

Adult azalea stem borers emerge from mid-May through June. Eggs are inserted under the bark between two rows of holes chewed through the bark about 1/2 an inch apart. The larva hatches and bores down the twig into the stem and eventually all the way to the crown of the plant. The stem is greatly weakened at the base. The larvae then bore down into the roots where they spend the winter. Coarse sawdust-like frass is expelled through holes in the bark of the stem and at the base of the plant. Infested twigs wilt as the larva bores downward inside. The larvae pupate the following spring.

Control. Cutting off and burning infested stems as soon as they are noticed in the growing season is recommended for control. If shrubs have been reinfested year after year, it is probably necessary to protect the plants with an insecticide. Pesticides should give adequate control if applied in spring after the new growth has emerged and hardened off somewhat in mid-May and again in early June. The current North Carolina Agricultural Chemicals Manual should be consulted for current chemical recommendations.

OVIPOSITION DAMAGE BY AZALEA STEM BORER (left)
Photo courtesy of Dr. Jim Baker, North Carolina State University


AZALEA STEM BORER LARVAE DAMAGE (right)
Photo courtesy of Dr. Jim Baker, North Carolina State University

Return to Azaleas


Send comments, questions to WebManager at

webmail@ncsipm1.cropsci.ncsu.edu

Last Modified: 07/10/96