Various scales attack azaleas and rhododendrons, but one of the most common is azalea bark scale (Eriococcus azaleae). Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Prune off portions of the shrub that are heavily infested with scales if the scales are largely concentrated on a limited number of branches. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. Damage caused by the stem borer, which includes wilting terminals and dieback, is similar to the Rhododendron borer. Rhododendron gall midge immatures spend the winter and early spring in the soil where they complete development and pupate. Immature scales, 0.0625-0.125 (1/16-1/8) inches long, overwinter on the stem, maturing quickly the next spring in late May. Prune the suspected branches and split them open longitudinally to see if larvae are present. Azalea leafminer overwinters as pupae in the leaf mines. Fully developed larvae drop to the ground where they will pupate. Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. There are as many of four generations of azalea lace bug during the growing season and into the fall. Thoroughly cover the infested plant, making sure you completely reach leaf undersides, twigs and other parts of the plant infested with scales. Azalea lace bug damage. Adults are present in June and July. Mature larvae are 1/2 inch long and yellowish brown. Leaves olive green, 20 x 8 cm. 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. Eggs hatch into tiny white maggots less than 1/16 inch in length. This scale is most obvious from May through June when white egg sacs may be found in twig forks. NPS Photo. 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. Mature larvae are 1/2 inch long and yellowish brown. Azaleas are visited by pollinators. There are no conventional insecticides that will kill stem borer larvae once they are inside the branches. Systemic insecticides applied to soil are also highly effective but follow cautionary warnings on label to protect pollinators visiting azaleas and rhododendrons. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. Adult feeding damage is very similar to that of black vine weevil but notches on leaf margins tend to be smaller. Apply either spray when caterpillars are numerous and young (less than 3/4 of an inch long). Numerous species of scale insects, typically classified as soft or armored, can attack a broad array of shrubs. Shrubs that are exposed to full sun and heavily infested may be killed. Prune off branches touching the ground or nearby structures to force ants up the main stem where they are trapped. Soil applied insecticides can harm ground beetles which are beneficial natural predators of a variety of pests. The caterpillars feed in groups when young and disperse as they mature. Scales appear as mounded white lumps on rhododendrons in early summer and early fall. In spring, adults emerge from the soil and fly to the tips of branches where they lay eggs in new developing leaf tissue. Stressed plants are more susceptible to lace bug feeding. Photo: John Davidson, University of Maryland. The larvae overwinter in branches the first year and in roots the second year. Heavy infestations of lace bug may cause leaves to turn yellow and then brown. The moths are 3/8 inch long and yellowish brown. If control is necessary, use a registered insecticide when damage begins in mid-June. The best control option for residents with only a few plants is to prune out (cut below active larvae) and destroy wilting branches in late summer or early spring before adults emerge. Insects, Diseases, and Other Plant Problems: Rhododendrons are susceptible to insect and disease problems. Masses of azalea (Rhododendron spp.) This weevil prefers azalea, rhododendron, privet, mountain laurel, forsythia, spirea, deutzia, lilac, and euonymus. 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. See the package for specific instructions. Photo: John Davidson, University of Maryland. A registered insecticide (e.g., Imidacloprid) may be applied by a certified pesticide applicator only (as per the Maryland Pollinator Protection Act.). The second generation mines begin in July. 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. To check for adults, place a tray under damaged shrubs and shake the plants. Females are approximately 1/8-inch long White felt-like sacs are secreted in May that enclose the body and eggs. This deformation will last as long as leaves remain on the plant. Rhododendron varieties with resistance to weevils are available and include species such as, A registered insecticide (e.g., Imidacloprid) may be applied by a certified pesticide applicator only (as per the, Rhododendron gall midge immatures spend the winter and early spring in the soil where they complete development and pupate. Azalea Bark Scale, Eriococcus azalea: This insect prefers azalea or rhododendron but can infest andromeda, maple, willow, poplar and other plants. Insecticidal soap may also be used. Interior leaves usually show most damage. Hand saws and pruning shears are helpful for smaller, less established branches, or when you are cutting less of the rhododendron. Damage occurs in late summer and fall. Description. If so, you have a fungus called powdery mildew. Soapy … © Copyright 2020 Hearst Communications, Inc. The azalea bark scale also feeds on ornamental cherry, poplar, willow and hawthorn trees. REC, Common Disease and Abiotic Problems of Azaleas and Rhododendrons. Damage on new foliage will be evident in May and July. Photo: Photo: M. Raupp, University of Maryland. 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. Weevils can be hand-picked and dropped into a container of soapy water for disposal. Look for nymphs and black fecal spots on lower leaf surfaces in early May to estimate potentially damaging populations. Photo: John Davidson, University of Maryland, Rhododendron borer is the larvae (caterpillar) of a clear wing moth. How to Treat Scale on Shrubs. This scale primarily attacks azalea and rhododendron, but also has been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. Females produce white, waxy egg masses in late June to early July. Damage occurs in late summer and fall. Most adult scales do not move, they look like brown or white “tortoise shells” on branches or foliage. Beneficial predators and parasites will usually provide adequate control of light bark scale infestations. Azalea Leafminer (early instar) inside of a leaf. This tiny fly attacks the new growth of rhododendrons. This borer prefers rhododendron, but occasionally attacks deciduous azalea and mountain laurel. 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. Mature larvae are about 1/2 inch long, white with brown heads. Mature larvae are about 1/2 inch long, white with brown heads. Video shows close ups of Azalea Bark scale and provides some plant inspection tips. Eggs, crawlers and adults under the wax are red. She holds a Bachelor of Arts in urban and regional studies. Photo: P.M. Shrewsbury, University of Maryland. Their feeding causes leaf margins to curl and the maggots complete their development within the curled leaf tissue. Make any pruning cuts slightly angled and next to a junction with another branch or main stem. Beneficial nematodes may be effective in controlling larvae in the soil. There are multiple generations of lace bug per 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. Photo: Bruce Watt, University of Maine, Bugwood.org. Boring larvae may cause branches to crack. They vary in appearance depending on age, sex, and species. Heavy larval populations may cause stunting, wilting, and may kill small shrubs and tree seedlings. They were first discovered by a Flemish botanist, Charles l’Ecluse. Studies in Connecticut indicate as many as three to five generations annually depending on climatic conditions. Photo: David Held, Auburn University, Bugwood.org. Decide what tool you need for your rhododendron size. Branches or entire plants may be defoliated. Curled leaf tips in June indicate the completion of the first generation. Spray the young lacebug nymphs off the leaves as they hatch. Apply a sticky, nondrying compound intended for trapping insects in a band around the main stem or stems of the shrub. Inspect plants for signs of early damage and remove curled leaves promptly. Heavy infestations cause wilting and eventual branch dieback. To control heavy infestations, spray dormant plants with a 4% rate of horticultural oil to kill developing nymphs on twigs. Heavy infestations over several seasons may kill plants. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. 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. The borer causes wilting of leaves and twig dieback. Management: Rake and destroy fallen leaves in the fall to remove overwintering pupae. Larvae also feed on roots and crowns of hosts. There is one generation per year in Michigan. 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. Be sure to observe all cautionary statements on labels to protect pollinators. Adult feeding damage begins on lower leaves in mid-June. The borer causes wilting of leaves and twig dieback. Photo: M. Raupp, University of Maryland. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. Beneficial insects often control this pest. Broadleaf evergreen, 6 ft (1.8 m) in 10 years, upright, vigorous, grows to a large plant. Sometimes, these growths may get covered with white spots. Examine the lower surfaces of leaves for the presence of nymphs, which are flat, yellowish green, and resemble scale insects. Heavy infestations over several seasons may kill plants. Plan to spray the shrub once the number of crawlers trapped begins to decline. Rhododendron Linnaeus Evergreen or deciduous shrubs with alternate, entire or ciliateserrulate, glabrous to tomentose, lepidote or strigose leaves. 5) appears as small white cottony masses on the bark. 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. Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Flowers 5-merous, usually in terminal corymbs. This borer, however, is a longhorned beetle. Eggs overwinter in leaves and may begin to hatch as early as late April. Watching the white mounds during hatching season will reveal the small crawlers moving along the plant searching for a spot to suck the sap. Damage is indicated by the presence of blotch mines in leaves of azalea beginning in May. The largely immobile nature of scales and their protective covering makes chemical control challenging. Bark scales are a type of soft scale and an infestation is indicated by clear sticky honeydew with attendant sooty mold (black fungus) on leaves or stems, yellowing of leaves, and twig dieback. 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. The larvae are “C-shaped”, legless, and white with brown heads. The females appear totally white when they produce their white, waxy egg sacs. Honeydew can … A few years ago, some developed azalea bark scale infestations. Studies in Connecticut indicate as many as three to five generations annually depending on climatic conditions. Photo: Jim Baker, North Carolina State University, Bugwood.org. Scale Download a PDF of this article Plants Affected. Follow instructions on label for timing and soil temperatures. Water the infested shrubs deeply and infrequently during extended dry spells. giganteum, reported to 30 m (100 ft) tall. The caterpillars feed in groups when young and disperse as they mature. Scales are so unusual looking that most people don’t recognize them as insects. Some cultivated varieties (Southgate series Rhododendrons) are more tolerant of high heat and humidity. This scale primarily attacks azalea and rhododendron, but also has been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. This is a pest that generally does not kill hosts, rather it causes aesthetic damage. Wrap several branches that are infested with scales tightly with narrow bands of double-sided sticky tape in late winter or early spring. Rhododendron borer is the larvae (caterpillar) of a clear wing moth. Beneficial nematodes are not effective on these borers. If hand removal is not feasible, spray shrubs with. Mulch with chopped oak leaves, leaf mold, or pine needles and water deeply during drought periods. Frass (sawdust-like material) indicating the presence of rhododendron borer. 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. 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). Gall midge larvae feed on the developing leaf tissue causing leaves to become distorted with puckered and curled margins. Rhododendron Stem Borer Damage. All types of fruit and ornamental trees, shrubs. The azalea bark scale, Eriococcus azaleas, is a prominent pest of rhododendron, azalea, and huckleberry (Vaccinium spp.). Photo: P.M. Shrewsbury, University of Maryland. Azalea leafminer overwinters as pupae in the leaf mines. In less than ideal growing conditions (i.e., full sun, drought), plants may become stressed and more susceptible to pest problems. Small plants when heavily infested may be defoliated. Dormant oil spray can be applied to kill overwintering nymphs prior to new plant growth. There is one generation a year and larvae overwinter in tunnels in branches. Central Maryland 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. Prune the suspected branches and split them open longitudinally to see if larvae are present. Eggs hatch into tiny white maggots less than 1/16 inch in length. Rhododendron varieties with resistance to weevils are available and include species such as Rhododendron cuneatum, R. dauricum, R. fastigiatum, and others.Black Vine Weevil (adult and larva). REC, Lower Eastern Shore Members of the genus Rhododendron support the following specialized bee: Andrena (Andrena) cornelli. Insecticidal soap may also be used. Immature lace bugs (nymphs) are black and covered with spines. Calyx 5-parted, often very small, persistent. Hosts include andromeda, azalea, rhododendron, hawthorn, poplar, willow, and most recently, blueberry in the Pacific Northwest. They were introduced to the European Alps and thus the name, Alpine Rose (Rhododendron histru… 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. The larvae bore down the center of twigs causing individual branches to wilt, and eventually die back to the ground. Azaleas can tolerate low populations of this bark scale without significant damage. Many diseases and other problems can be prevented by following the recommended cultural practices for proper planting and care. Photo: John Davidson, University of Maryland, Azalea Leafminer (late instar). 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. Rhododendron 'Charles Dickens'. There is one generation a year and all stages overwinter in the soil. Is the white substance powdery and can you wipe it off. Damage on new foliage will be evident in May and July. Adult moths are present in late June and August. Insect problems include aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips and whitefly. Adult Japanese weevils feed during the day and will drop from the plants when disturbed. blooms drifting above dense branches of lush green foliage illuminate countless spring gardens with weeks of color. The larvae are whitish and have no visible head. Scale … Management. (This was diagnosed from a photo I sent to your service a couple of years ago.) Cushion scale is a sap-sucking insect that feeds on the foliage of mainly evergreen trees and shrubs, especially camellia, rhododendron, Trachelospermum, Euonymus japonicus and holly. Heavy infestations cause wilting and eventual branch dieback. Their feeding causes leaf margins to curl and the maggots complete their development within the curled leaf tissue. 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. If there are no yellowing leaves, no treatment is necessary. There are no conventional insecticides that will kill borer larvae once they are inside the branches. 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. As with black vine weevil, soil drenches of entomopathogenic nematodes may reduce populations of grubs in the soil. There is one generation a year and larvae overwinter in tunnels in branches. Scale insects also secrete a sticky liquid called honeydew, which promotes the fungal disease black sooty mold. Numerous species of scale insects, typically classified as soft or armored, can attack a broad array of shrubs. Consider hand–removal by squishing the scales to prevent populations from increasing. Black fecal spots will be present on the lower sides of stippled leaves. Rhododendrons and azaleas are some of the most popular spring-flowering shrubs in the landscape, and healthy plants can give years of pleasure. 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