The adult beetles are about 5/8 inch long, have long antennae, and are pale yellow with two black spots on the thorax and on the margins of the wing covers. This borer prefers rhododendron, but occasionally attacks deciduous azalea and mountain laurel. Adult weevils are about 3/8 inch long and black with faint yellowish flecks. (This was diagnosed from a photo I sent to your service a couple of years ago.) Prune off portions of the shrub that are heavily infested with scales if the scales are largely concentrated on a limited number of branches. Azalea Leafminer (early instar) inside of a leaf. Decide what tool you need for your rhododendron size. Azalea bark scale (Fig. See the package for specific instructions. (Bt), a microbial insecticide, that is specific for young caterpillars and is sold under various trade names. This beetle prefers rhododendron, but will also attack azaleas and mountain laurel. Frass (sawdust-like material) indicating the presence of rhododendron borer. Photo: University of Maryland Extension, Rhododendron Borer (adult). The caterpillars feed in groups when young and disperse as they mature. It may also attack boxwood, catalpa, cherry laurel, euonymus, forsythia, Japanese flowering cherry, ligustrum, lilac, magnolia, privet, red twig dogwood, rhododendron, salix spp., and walnut. Susceptible cultivars include those of Rhododendron catawbiensis and R. maximum. Females produce white, waxy egg masses in late June to early July. Water the infested shrubs deeply and infrequently during extended dry spells. Look for discoloration of foliage and signs of sooty mold to indicate the presence of the scales. Rhododendron Linnaeus Evergreen or deciduous shrubs with alternate, entire or ciliateserrulate, glabrous to tomentose, lepidote or strigose leaves. Dormant oil spray can be applied to kill overwintering nymphs prior to new plant growth. 'Patty Bee': Has scaly foliage, like an azalea, that turns maroon in winter. Susceptible cultivars include those of. In less than ideal growing conditions (i.e., full sun, drought), plants may become stressed and more susceptible to pest problems. Rhododendron Diseases by R. K. Jones and D. M. Benson Azalea & Rhododendron Diseases by Clemson University Cooperative Extension Common Problems of Rhododendron and Azalea by Dr. Sharon M. Douglas How To Identify Rhododendron and Azalea Problems by A.I. Small shrubs may be defoliated in heavy infestations. To check for adults, place a tray under damaged shrubs and shake the plants. These pests generally appear on plants as immobile bumps with no recognizable body parts. Wrap several branches that are infested with scales tightly with narrow bands of double-sided sticky tape in late winter or early spring. Mature larvae are about 1/4 inch long, “C-shaped”, legless, and white with brown heads. Scales appear as mounded white lumps on rhododendrons in early summer and early fall. If so, you have a fungus called powdery mildew. … Borne at the tips of the upright branches, the blossoms contrast beautifully with the evergreen foliage of rounde… Mature larvae are about 1/2 inch long, white with brown heads. The females appear totally white when they produce their white, waxy egg sacs. Check inner branch forks in May and June for the white egg sacs and for reddish crawlers in late June into July. Honeydew can … Photo: John Davidson, University of Maryland. In spring, adults emerge from the soil and fly to the tips of branches where they lay eggs in new developing leaf tissue. Mines are initially formed near the midrib and caused by caterpillars feeding between the upper and lower leaf surface. Apply either spray when caterpillars are numerous and young (less than 3/4 of an inch long). Older and more established rhododendrons may need a chainsaw to cut through the large woody branches, especially toward the middle of the plant. Damage usually begins in early May on old leaves and later appears on new growth. Native to China, Myanmar and Laos, Rhododendron decorum (Great White Rhododendron) is a very fragrant, large, evergreen shrub or small tree with attractive spring flowers, decorative bark and handsome dark green leaves. The adult weevils are about 3/16 inch long, brown, broadly oval, thick bodied, and brown to gray with two darker bands across the wing covers. Curled leaf tips in June indicate the completion of the first generation. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. Angela Ryczkowski is a professional writer who has served as a greenhouse manager and certified wildland firefighter. Hand saws and pruning shears are helpful for smaller, less established branches, or when you are cutting less of the rhododendron. To control heavy infestations, spray dormant plants with a 4% rate of horticultural oil to kill developing nymphs on twigs. White Rhododendron, with a bumblebee. Black fecal spots will be present on the lower sides of stippled leaves. This will interrupt the life cycle and reduce subsequent populations. Adult feeding damage appears in late April and early May as adults become active and notch leaf margins on azalea and rhododendron. If only a few caterpillars are present, pick them off by hand. Properly timing any sprays for when the scales are in their active crawler stage is important. Various scales attack azaleas and rhododendrons, but one of the most common is azalea bark scale (Eriococcus azaleae). Make sure shrubs receive an inch of water weekly through rainfall and supplemental irrigation, or water whenever soil about 3 inches below the soil surface near the shrub feels dry to the touch. This whitefly is usually limited to azalea varieties that have hairy leaves. If hand removal is not feasible, spray shrubs with. More information on successfully growing azaleas and rhododendrons is available in the fact sheets HGIC 1059, Azalea Care; HGIC 1058, Azalea Planting; an… Photo: John Davidson, University of Maryland, Rhododendron borer is the larvae (caterpillar) of a clear wing moth. Small plants when heavily infested may be defoliated. The borer causes wilting of leaves and twig dieback. Damage is indicated by the presence of blotch mines in leaves of azalea beginning in May. In the past 2 years I pruned some of the worst infested branches and applied a 2% horticultural spray once or twice per year, I think in the summer and late fall, but I don't remember exactly when. Central Maryland Scale insects feed on shrubs' sap using their long, piercing mouthparts, causing twig and branch dieback and sometimes killing the plants. The second generation mines begin in July. Continue changing the double-sided tape and observing crawler numbers. Noted for its lavender-blue spring flowers, Rhododendron 'Blue Tit Magor' is a compact, mounding, dense, evergreen shrub producing incredibly eye-catching flower clusters. If there are no yellowing leaves, no treatment is necessary. Make any pruning cuts slightly angled and next to a junction with another branch or main stem. Azalea Lace Bug (Stephanitis pyriodes) andRhododendron Lace Bug (Stephanitis takeyai) Lace bug damage is indicated by stippling (very tiny spots) on leaves of plants growing on dry sites and those with low plant diversity. Azalea lace bug damage. The larvae bore down the center of twigs causing individual branches to wilt, and eventually die back to the ground. Prune the suspected branches and split them open longitudinally to see if larvae are present. They feed in the evening and night. If necessary a 2% summer rate of horticultural oil may be applied in July after all of the eggs have hatched. Armored scales measure less than 1/8 inch across and have a flattened cover over their bodies. The larvae are whitish and have no visible head. White flowers grow on top of the previous year's growth and tucked underneath the leaves from the current year. The best management option for residents with only a few plants is to prune out and destroy wilting branches when beetle larvae are in the branches in early spring or late summer. Two-banded Japanese weevil (actual size is 3/16 inch). Azalea caterpillar. The leaves are spirally arranged; leaf size can range from 1–2 cm (0.4–0.8 in) to over 50 cm (20 in), exceptionally 100 cm (40 in) in R. sinogrande. There is one generation a year and larvae overwinter in tunnels in branches. Rhododendron 'Charles Dickens'. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. This scale primarily attacks azalea and rhododendron, but also has been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. Azalea leafminer overwinters as pupae in the leaf mines. Females are approximately 1/8-inch long White felt-like sacs are secreted in May that enclose the body and eggs. Mines are initially formed near the midrib and caused by caterpillars feeding between the upper and lower leaf surface. Scales are unusual insects. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Azalea, rhododendron, and andromeda each have their unique species of lace bug. Reaching a height of 3-4 feet, the White Rhododendron is an easy-to-grow evergreen shrub that thrives in partial sunlight and needs only occasional pruning. Adult Japanese weevils feed during the day and will drop from the plants when disturbed. Heavy infestations over several seasons may kill plants. Numerous species of scale insects, typically classified as soft or armored, can attack a broad array of shrubs. They vary in appearance depending on age, sex, and species. There is one generation a year and all stages overwinter in the soil. 5) appears as small white cottony masses on the bark. In this case, the leaves, buds, or stems, develop swollen growths with distorted shapes. Azalea lace bug adult and fecal spots. Revised and edited by Dr. Michael J. Raupp and Dr. Paula M. Shrewsbury, University of Maryland, April 2020. Their feeding causes leaf margins to curl and the maggots complete their development within the curled leaf tissue. It has been reported in the Eastern US, as well as Belgium and Russia. This borer, however, is a longhorned beetle. Insecticidal soap may also be used. Scale insects also secrete a sticky liquid called honeydew, which promotes the fungal disease black sooty mold. Cottony camellia scales, Pulvinaria floccifera, are cream to tan, elongate oval, and relatively flat.They are also called cottony taxus scales as this scale is a fairly common pest of yew. There are no conventional insecticides that will kill borer larvae once they are inside the branches. giganteum, reported to 30 m (100 ft) tall. Their feeding causes leaf margins to curl and the maggots complete their development within the curled leaf tissue. Damage on new foliage will be evident in May and July. This weevil prefers azalea, rhododendron, privet, mountain laurel, forsythia, spirea, deutzia, lilac, and euonymus. Eggs overwinter in leaves and may begin to hatch as early as late April. They may be injected into the active borer tunnels. Heavy larval populations may cause stunting, wilting, and may kill small shrubs and tree seedlings. Photo: John Davidson, University of Maryland. Prune the suspected branches and split them open longitudinally to see if larvae are present. Soapy … Adults are present in June and July. Adult lace bugs are flat, about 1/8 inch long, with transparent lace-like wings. The adult moths, about ¼” long, resemble wasps, have mostly clear wings, and black bodies with 3 gold bands on the abdomen. Sometimes, these growths may get covered with white spots. Interior leaves usually show most damage. This borer prefers rhododendron, but occasionally attacks deciduous azalea and mountain laurel. Damage usually begins in early May on old leaves and later appears on new growth. Common problems of rhododendron bushes can be avoided by providing the best growing environment possible and maintaining a consistent pruning, mulching and fertilizing program. If control is necessary, use a registered insecticide when damage begins in mid-June. The adult moths, about ¼” long, resemble wasps, have mostly clear wings, and black bodies with 3 gold bands on the abdomen. All stages occur on the undersides of leaves. Be sure to observe all cautionary statements on labels to protect pollinators. The caterpillars feed in groups when young and disperse as they mature. Severe scale feeding causes stress and affected plants appear thin and unthrifty. Damage is indicated by the presence of blotch mines in leaves of azalea beginning in May. They were first discovered by a Flemish botanist, Charles l’Ecluse. Photo: P.M. Shrewsbury, University of Maryland. Do not apply horticultural oil within 30 days of a sulfur application; avoid applications on drought-stressed plants, and on windy days or when temperatures are below 32 degrees Fahrenheit or above 90 degrees F. Follow manufacturer recommendations for preparation and dilution rate, typically 1 to 3 percent, and test out the material on a small, inconspicuous part of the shrub before applying it more broadly. The leaves become covered with honeydew, followed by sooty mold (a black coating). Blend 5 tablespoons of an ultra-fine horticultural oil with a gallon of water, and use a garden sprayer to thoroughly spray the infested plants once you observe a decline in the number of scales trapped. Azalea whitefly damage. Heavy infestations of lace bug may cause leaves to turn yellow and then brown. These infested leaves will eventually turn yellowish and appear wilted. Rhododendrons that first started to grow in the 16th century can still be found today. As soon as you notice the black fungus on rhododendron shrubs, check the leaves carefully to determine which insect is responsible and treat it appropriately. Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Whiteflies would be found underneath the leaves. Beneficial nematodes, available under several trade names, are a control option. Photo: Jim Baker, North Carolina State University, Bugwood.org. Look for nymphs and black fecal spots on lower leaf surfaces in early May to estimate potentially damaging populations. How to Treat Scale on Shrubs. Do not apply broad-spectrum, persistent pesticides to attempt to control scale insects or other pests, as these chemicals will injure the populations of beneficial scale predators and parasites. Studies in Connecticut indicate as many as three to five generations annually depending on climatic conditions. Antonelli, et al. Large populations cause leaves to brown and drop prematurely. Photo: Jim Baker, North Carolina State University, Bugwood.org. Buds with several to many imbricate scales. Adult moths are present in late June and August. Janet Flower Shop Network Plant Expert Reply: First we need to determine if you really have a fungus. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. Hosts include andromeda, azalea, rhododendron, hawthorn, poplar, willow, and most recently, blueberry in the Pacific Northwest. Large populations cause leaves to brown and drop prematurely. The azalea bark scale also feeds on ornamental cherry, poplar, willow and hawthorn trees. Azaleas can tolerate low populations of this bark scale without significant damage. Is the white substance powdery and can you wipe it off. Black Vine Weevil (adult). Adult feeding damage begins on lower leaves in mid-June. Damage occurs in late summer and fall. White Rhododendron Rhododendron albiflorum. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Examine egg sacs for holes which indicates control by parasitoids, and look for predators such as ladybird beetles. NPS Photo. Alternatively, place bait stations or stakes with a slow-acting active ingredient near the base of the shrub where you observe ant trails. A common shrub, also known as Cascade Azalea, found in the park on open slopes and meadow edges above 3,500 feet (1,066 meters). A registered insecticide (e.g., Imidacloprid) may be applied by a certified pesticide applicator only (as per the Maryland Pollinator Protection Act.). Inspect plants for signs of early damage and remove curled leaves promptly. A small brown insect with transparent wings sucks on the bottom of the leaf causing a mottled appearance on the top with yellowish, brownish or white spots. Most adult scales do not move, they look like brown or white “tortoise shells” on branches or foliage. Plant azaleas in partial sun (morning sun and afternoon shade). Photo: M. Raupp, University of Maryland. There is one generation a year and larvae overwinter in tunnels in branches. There are two generations each year in Maryland. Heavy infestations cause the margins of terminal leaves to cup. Soil applied insecticides can harm ground beetles which are beneficial natural predators of a variety of pests. Eggs, crawlers and adults under the wax are red. Inspect the tape closely using a hand lens, if possible; look for the crawlers, which get trapped on the tape and look like yellow or orange specks. Healthy plants that are not under water stress can better withstand and recover from scale feeding. There are as many of four generations of azalea lace bug during the growing season and into the fall. If hand removal is not feasible, spray shrubs with Bacillus thuringiensis (Bt), a microbial insecticide, that is specific for young caterpillars and is sold under various trade names. Shrubs that are exposed to full sun and heavily infested may be killed. If soft scales are present on the shrub and producing a large quantity of honeydew that is attracting ants, plan to control the ants, because they protect the scales from their natural enemies. Black fecal spots will be present on the lower sides of stippled leaves. Photo: Photo: M. Raupp, University of Maryland. Adult feeding damage is very similar to that of black vine weevil but notches on leaf margins tend to be smaller. Azaleas are visited by pollinators. © Copyright 2020 Hearst Communications, Inc. Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. Rhododendrons and azaleas are some of the most popular spring-flowering shrubs in the landscape, and healthy plants can give years of pleasure. Eggs hatch into tiny white maggots less than 1/16 inch in length. Photo: Bruce Watt, University of Maine, Bugwood.org. REC, Lower Eastern Shore Insecticidal soap may also be used. Management. The following azalea cultivars have shown resistance to azalea lace bug damage: ‘Autumn Amethyst’, ‘Autumn Twist’, ‘Autumn Royalty’, ‘Autumn Sangria’, ‘Autumn Cheer’, ‘Indica alba’, ‘Flame Creeper,’ and ‘Delaware Valley White’, among others. The pale white flowers that sprout from this plant offer a slight citrus scent. This tiny fly attacks the new growth of rhododendrons. Scale – Scale insects commonly cause black fungus on rhododendron. Prune off branches touching the ground or nearby structures to force ants up the main stem where they are trapped. More on Mildew by Fred Minch Pests Of Rhododendrons by Arthur L. Antonelli Commonly seen in azaleas, leaf gall is a springtime disease, that may affect other rhododendron species. The larvae overwinter in branches the first year and in roots the second year. Scale … All types of fruit and ornamental trees, shrubs. The most common pests of rhododendrons and azaleas in Maryland are lace bugs, azalea bark scale, rhododendron borer, and weevils. The females appear totally white when they produce their white, waxy egg sacs. Healthy shrubs can usually withstand some amount of scale feeding, but a heavy infestation can force leaves to wilt, turn yellow and drop prematurely. REC, Western Maryland Curled leaf tips in June indicate the completion of the first generation. Members of the genus Rhododendron support the following specialized bee: Andrena (Andrena) cornelli. Rhododendron borer is the larvae (caterpillar) of a clear wing moth. How to Kill Borers on Weeping Cherry Trees, Sooty Mold Caused by Whiteflies on Rhododendron Stems, How to Kill Aphids on Aureo Variegated Boxwood, University of California Statewide Integrated Pest Management Program: Scales, Purdue University Cooperative Extension: Scale Insects on Shade Trees and Shrubs, Colorado State University/Denver County Master Gardeners: Scale Insect Pests, How to Kill Spider Mites and Whiteflies on Shrubs. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. White prunicola scale is most partial to members of the Prunus species, peach chinaberry, flowering peach, French mulberry, and persimmon. Damage occurs in late summer and fall. Management: Rake and destroy fallen leaves in the fall to remove overwintering pupae. Immature scales, 0.0625-0.125 (1/16-1/8) inches long, overwinter on the stem, maturing quickly the next spring in late May. She holds a Bachelor of Arts in urban and regional studies. Check these sticky tape bands regularly and replace them with fresh tape once per week. Heavy infestations cause wilting and eventual branch dieback. Some cultivated varieties (Southgate series Rhododendrons) are more tolerant of high heat and humidity. Whitefly adults and nymphs feed on the underside of the foliage. Leaves olive green, 20 x 8 cm. Azalea Bark Scale, Eriococcus azalea: This insect prefers azalea or rhododendron but can infest andromeda, maple, willow, poplar and other plants. We embody the University's land-grant mission with a commitment to eliminate hunger, preserve our natural resources, improve quality of life, and empower the next generation through world-class education. Fully developed larvae drop to the ground where they will pupate. A currently registered systemic insecticide may be necessary where coverage of the undersides of leaves is difficult. Many diseases and other problems can be prevented by following the recommended cultural practices for proper planting and care. Scales are so unusual looking that most people don’t recognize them as insects. Gall midge larvae feed on the developing leaf tissue causing leaves to become distorted with puckered and curled margins. Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Mature larvae are 1/2 inch long and yellowish brown. REC, Common Disease and Abiotic Problems of Azaleas and Rhododendrons. Follow instructions on label for timing and soil temperatures. Some scales can also cause bark to crack and leave blemishes on fruit where they feed. Black vine weevil feeding damage (leaf notching) to rhododendron. Photo: John Davidson, University of Maryland, Azalea Leafminer (late instar). Azalea leafminer overwinters as pupae in the leaf mines. The larvae are “C-shaped”, legless, and white with brown heads. Blooming in mid spring, each cluster (or truss) can hold up to 3-5 attractive, trumpet-shaped violet-blue flowers, whose color intensifies with age. Heavy infestations over several seasons may kill plants. This deformation will last as long as leaves remain on the plant. Symptoms/Damage. Pull mulch back prior to application. The adult female azalea bark scale is dark red with a long sucking mouthpart. Adult moths are present in late June and August. Boring larvae may cause branches to crack. Azalea Bark Scale. There are no conventional insecticides that will kill stem borer larvae once they are inside the branches. The azalea bark scale, Eriococcus azaleas, is a prominent pest of rhododendron, azalea, and huckleberry (Vaccinium spp.). Broadleaf evergreen, 6 ft (1.8 m) in 10 years, upright, vigorous, grows to a large plant. Soft scales measure up to 1/4 inch across; they're usually more rounded than armored scales, and the surface of the scale is its body wall. Rhododendron Stem Borer Damage. This is a pest that generally does not kill hosts, rather it causes aesthetic damage. A few years ago, some developed azalea bark scale infestations. Consider hand–removal by squishing the scales to prevent populations from increasing. Scale Download a PDF of this article Plants Affected. As with black vine weevil, soil drenches of entomopathogenic nematodes may reduce populations of grubs in the soil. Damage on new foliage will be evident in May and July. They were introduced to the European Alps and thus the name, Alpine Rose (Rhododendron histru… Gall Midge damage. When lace bug populations are high, sprays of horticultural oil (at a 2% summer rate) or insecticidal soap will control lace bugs if the lower surfaces of the leaves where lace bugs are active are thoroughly covered. There is one generation per year in Michigan. Originally written by Mary K. Malinoski, University of Maryland Extension Specialist. The second generation mines begin in July. Female scales are dark red, but remain hidden under the white mass. Mature female scale are about 0.13 inch long and appear like white cottony sacs, often located on twigs and stems of azalea, especially in branch axils. Fully developed larvae drop to the ground where they will pupate. Insects, Diseases, and Other Plant Problems: Rhododendrons are susceptible to insect and disease problems. Lacebugs perfer sunny areas so plant in more shaded areas if possible. Young females have a dark stripe down the middle and mottling at the sides. Apply a sticky, nondrying compound intended for trapping insects in a band around the main stem or stems of the shrub. Inspect for adult weevils at night using a flashlight. Photo: Dow Gardens, Bugwood.org. Calyx 5-parted, often very small, persistent. Mature larvae are 1/2 inch long and yellowish brown. Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. Thoroughly cover the infested plant, making sure you completely reach leaf undersides, twigs and other parts of the plant infested with scales. The moths are 3/8 inch long and yellowish brown. The borer causes wilting of leaves and twig dieback. Diligent, yearly removal of infested leaves may dramatically reduce damage in a few years. Weevils can be hand-picked and dropped into a container of soapy water for disposal. Adult beetles feed on the underside of leaves on the midvein, causing the leaves to curl. If the infestation is light, little or no plant symptoms are evident, and if beneficial insects are present, spray the undersides of leaves with insecticidal soap or horticultural oil at the 2% summer rate. Larvae also feed on roots and crowns of hosts. These caterpillars are black with rows of white or pale yellow spots, reddish brown legs, head and neck area and are 2 1/2 inches when mature. Management: Rake and destroy fallen leaves in the fall to remove overwintering pupae. Examine the lower surfaces of leaves for the presence of nymphs, which are flat, yellowish green, and resemble scale insects. Eggs hatch into tiny white maggots less than 1/16 inch in length. Beneficial insects often control this pest. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. Beneficial nematodes are not effective on these borers. Plan to spray the shrub once the number of crawlers trapped begins to decline. Kill small shrubs and shake the plants statements on labels to protect pollinators visiting azaleas and rhododendrons Shop Network Expert... During extended dry spells a few caterpillars are numerous and young ( than. New foliage will be evident in may cautionary warnings on label for timing and soil temperatures the margins terminal... And can you wipe it off scales if the scales to prevent populations from increasing other plant:! Problems include aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes,,... 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