Azaleas are visited by pollinators. This will interrupt the life cycle and reduce subsequent populations. Antonelli, et al. The larvae are whitish and have no visible head. Prune off branches touching the ground or nearby structures to force ants up the main stem where they are trapped. Black Vine Weevil (adult). This scale is most obvious from May through June when white egg sacs may be found in twig forks. Black fecal spots will be present on the lower sides of stippled leaves. The larvae are “C-shaped”, legless, and white with brown heads. Common problems of rhododendron bushes can be avoided by providing the best growing environment possible and maintaining a consistent pruning, mulching and fertilizing program. Curled leaf tips in June indicate the completion of the first generation. They vary in appearance depending on age, sex, and species. If only a few caterpillars are present, pick them off by hand. Damage caused by the stem borer, which includes wilting terminals and dieback, is similar to the Rhododendron borer. There are no conventional insecticides that will kill stem borer larvae once they are inside the branches. 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. If so, you have a fungus called powdery mildew. Spray the young lacebug nymphs off the leaves as they hatch. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. blooms drifting above dense branches of lush green foliage illuminate countless spring gardens with weeks of color. Mature larvae are about 1/4 inch long, “C-shaped”, legless, and white with brown heads. Rhododendrons and azaleas, in general, grow best in landscape conditions that mimic natural mountain habitats: acidic soil (pH between 4.5 - 5.5), good drainage, ample soil moisture and organic matter, understory areas with light shade, cool soil temperature, and protection from strong winds. Curled leaf tips in June indicate the completion of the first generation. As larvae mature they curl the tips of the leaves with silk and feed inside the curl. Plant azaleas in partial sun (morning sun and afternoon shade). They feed in the evening and night. Thoroughly cover the infested plant, making sure you completely reach leaf undersides, twigs and other parts of the plant infested with scales. Honeydew can … Make any pruning cuts slightly angled and next to a junction with another branch or main stem. Soil applied insecticides can harm ground beetles which are beneficial natural predators of a variety of pests. Janet Flower Shop Network Plant Expert Reply: First we need to determine if you really have a fungus. NPS Photo. Photo: John Davidson, University of Maryland. 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. See the package for specific instructions. A currently registered systemic insecticide may be necessary where coverage of the undersides of leaves is difficult. 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. Follow instructions on label for timing and soil temperatures. Decide what tool you need for your rhododendron size. Adult weevils are about 3/8 inch long and black with faint yellowish flecks. She holds a Bachelor of Arts in urban and regional studies. Photo: Photo: M. Raupp, University of Maryland. Armored scales measure less than 1/8 inch across and have a flattened cover over their bodies. Weevils can be hand-picked and dropped into a container of soapy water for disposal. Damage usually begins in early May on old leaves and later appears on new growth. Rhododendron is a genus of shrubs and small to (rarely) large trees, the smallest species growing to 10–100 cm (4–40 in) tall, and the largest, R. protistum var. If necessary a 2% summer rate of horticultural oil may be applied in July after all of the eggs have hatched. In spring, adults emerge from the soil and fly to the tips of branches where they lay eggs in new developing leaf tissue. Mature larvae are about 1/2 inch long, white with brown heads. Ask the Expert: what would get the white fungus off azaleas , leaf the azalea has white on them , on the leafs is it a fungus , what can spray on them will mild soapy water work. REC, Western Maryland All stages occur on the undersides of leaves. 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. Examine the lower surfaces of leaves for the presence of nymphs, which are flat, yellowish green, and resemble scale insects. Commonly seen in azaleas, leaf gall is a springtime disease, that may affect other rhododendron species. Branches or entire plants may be defoliated. This is a pest that generally does not kill hosts, rather it causes aesthetic damage. Black fecal spots will be present on the lower sides of stippled leaves. A registered insecticide (e.g., Imidacloprid) may be applied by a certified pesticide applicator only (as per the Maryland Pollinator Protection Act.). Gall Midge damage. Azalea caterpillar. Mulch with chopped oak leaves, leaf mold, or pine needles and water deeply during drought periods. Hand saws and pruning shears are helpful for smaller, less established branches, or when you are cutting less of the rhododendron. Inspect plants for signs of early damage and remove curled leaves promptly. Adult moths are present in late June and August. If hand removal is not feasible, spray shrubs with. Female scales are dark red, but remain hidden under the white mass. Apply a sticky, nondrying compound intended for trapping insects in a band around the main stem or stems of the shrub. Beneficial nematodes may be effective in controlling larvae in the soil. Scale … The azalea bark scale also feeds on ornamental cherry, poplar, willow and hawthorn trees. Management. Azalea leafminer overwinters as pupae in the leaf mines. Frass (sawdust-like material) indicating the presence of rhododendron borer. Check these sticky tape bands regularly and replace them with fresh tape once per week. A few years ago, some developed azalea bark scale infestations. There is one generation a year and larvae overwinter in tunnels in branches. REC, Lower Eastern Shore Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. Follow instructions on label for timing and soil temperatures. This borer prefers rhododendron, but occasionally attacks deciduous azalea and mountain laurel. 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. Photo: Jim Baker, North Carolina State University, Bugwood.org. Management: Look for caterpillars when chewing damage occurs. Older and more established rhododendrons may need a chainsaw to cut through the large woody branches, especially toward the middle of the plant. Immature lace bugs (nymphs) are black and covered with spines. giganteum, reported to 30 m (100 ft) tall. Heavy infestations cause wilting and eventual branch dieback. Females are approximately 1/8-inch long White felt-like sacs are secreted in May that enclose the body and eggs. Management: Rake and destroy fallen leaves in the fall to remove overwintering pupae. White Rhododendron, with a bumblebee. Mature larvae are about 1/2 inch long, white with brown heads. Photo: P.M. Shrewsbury, University of Maryland. This scale primarily attacks azalea and rhododendron, but also has been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. As with black vine weevil, soil drenches of entomopathogenic nematodes may reduce populations of grubs in the soil. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. REC, Common Disease and Abiotic Problems of Azaleas and Rhododendrons. Mature larvae are 1/2 inch long and yellowish brown. There is one generation a year and larvae overwinter in tunnels in branches. 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 beetles feed for two to three weeks before laying eggs. Large populations cause leaves to brown and drop prematurely. Damage occurs in late summer and fall. Scales are so unusual looking that most people don’t recognize them as insects. Sooty mold will also accumulate on the leaf surfaces and bark, much like it does during aphid feeding. All types of fruit and ornamental trees, shrubs. Females produce white, waxy egg masses in late June to early July. Immature scales, 0.0625-0.125 (1/16-1/8) inches long, overwinter on the stem, maturing quickly the next spring in late May. Scales are unusual insects. Pull mulch back prior to application. Branches or entire plants may be defoliated. Large populations cause leaves to brown and drop prematurely. These pests generally appear on plants as immobile bumps with no recognizable body parts. 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. Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. Eggs hatch into tiny white maggots less than 1/16 inch in length. 'Patty Bee': Has scaly foliage, like an azalea, that turns maroon in winter. Originally written by Mary K. Malinoski, University of Maryland Extension Specialist. Central Maryland It has been reported in the Eastern US, as well as Belgium and Russia. Most adult scales do not move, they look like brown or white “tortoise shells” on branches or foliage. Fully developed larvae drop to the ground where they will pupate. Larvae also feed on roots and crowns of hosts. If there are no yellowing leaves, no treatment is necessary. Properly timing any sprays for when the scales are in their active crawler stage is important. Photo: Jim Baker, North Carolina State University, Bugwood.org. Some scales can also cause bark to crack and leave blemishes on fruit where they feed. 5) appears as small white cottony masses on the bark. More on Mildew by Fred Minch Pests Of Rhododendrons by Arthur L. Antonelli Heavy larval populations may cause stunting, wilting, and may kill small shrubs and tree seedlings. Mines are initially formed near the midrib and caused by caterpillars feeding between the upper and lower leaf surface. This beetle prefers rhododendron, but will also attack azaleas and mountain laurel. Be sure to observe all cautionary statements on labels to protect pollinators. If control is necessary, use a registered insecticide when damage begins in mid-June. 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. Rhododendron gall midge immatures spend the winter and early spring in the soil where they complete development and pupate. Photo: Bruce Watt, University of Maine, Bugwood.org. Black vine weevil feeding damage (leaf notching) to rhododendron. Wrap several branches that are infested with scales tightly with narrow bands of double-sided sticky tape in late winter or early spring. 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. 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. Beneficial nematodes are not effective on these borers. There is one generation per year in Michigan. Leaves olive green, 20 x 8 cm. Whitefly adults and nymphs feed on the underside of the foliage. They were introduced to the European Alps and thus the name, Alpine Rose (Rhododendron histru… Adult feeding damage appears in late April and early May as adults become active and notch leaf margins on azalea and rhododendron. They may be injected into the active borer tunnels. Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Examine egg sacs for holes which indicates control by parasitoids, and look for predators such as ladybird beetles. Photo: M. Raupp, University of Maryland. The most common pests of rhododendrons and azaleas in Maryland are lace bugs, azalea bark scale, rhododendron borer, and weevils. Calyx 5-parted, often very small, persistent. The larvae bore down the center of twigs causing individual branches to wilt, and eventually die back to the ground. The adult female azalea bark scale is dark red with a long sucking mouthpart. In this case, the leaves, buds, or stems, develop swollen growths with distorted shapes. Signs of beneficials insects may be active lady beetle adults or larvae, lacewing larvae, or parasitoids indicated by small circular holes on the immature whiteflies. 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. 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. There are two generations each year in Maryland. 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. Azaleas can tolerate low populations of this bark scale without significant damage. Rhododendron Stem Borer Damage. Check inner branch forks in May and June for the white egg sacs and for reddish crawlers in late June into July. Look for nymphs and black fecal spots on lower leaf surfaces in early May to estimate potentially damaging populations. The caterpillars feed in groups when young and disperse as they mature. Severe scale feeding causes stress and affected plants appear thin and unthrifty. 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. Systemic insecticides applied to soil are also highly effective but follow cautionary warnings on label to protect pollinators visiting azaleas and rhododendrons. Sometimes, these growths may get covered with white spots. Is the white substance powdery and can you wipe it off. The caterpillars feed in groups when young and disperse as they mature. The largely immobile nature of scales and their protective covering makes chemical control challenging. Control. Studies in Connecticut indicate as many as three to five generations annually depending on climatic conditions. Adult beetles feed on the underside of leaves on the midvein, causing the leaves to curl. Adult lace bugs are flat, about 1/8 inch long, with transparent lace-like wings. Lacebugs perfer sunny areas so plant in more shaded areas if possible. Heavy infestations over several seasons may kill plants. Consider hand–removal by squishing the scales to prevent populations from increasing. Beneficial insects often control this pest. 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. 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. Small shrubs may be defoliated in heavy infestations. There is one generation a year and all stages overwinter in the soil. The underside will show a brownish residue. Azalea whitefly damage. Diligent, yearly removal of infested leaves may dramatically reduce damage in a few years. 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. Scale insects also secrete a sticky liquid called honeydew, which promotes the fungal disease black sooty mold. Continue changing the double-sided tape and observing crawler numbers. The borer causes wilting of leaves and twig dieback. 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. White Rhododendron Rhododendron albiflorum. Photo: University of Maryland Extension, Rhododendron Borer (adult). The second generation mines begin in July. 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. How to Treat Scale on Shrubs. Prune the suspected branches and split them open longitudinally to see if larvae are present. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. 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. Shrubs that are exposed to full sun and heavily infested may be killed. Hosts include andromeda, azalea, rhododendron, hawthorn, poplar, willow, and most recently, blueberry in the Pacific Northwest. Back then, they were known to classical writers only and were referred to as Chamaerhododendron which meant low-growing rose tree.Rhododendrons were first introduced in Britain in 1656. Rhododendron Linnaeus Evergreen or deciduous shrubs with alternate, entire or ciliateserrulate, glabrous to tomentose, lepidote or strigose leaves. 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. White flowers grow on top of the previous year's growth and tucked underneath the leaves from the current year. Photo: John Davidson, University of Maryland. The second generation mines begin in July. The adult moths, about ¼” long, resemble wasps, have mostly clear wings, and black bodies with 3 gold bands on the abdomen. The moths are 3/8 inch long and yellowish brown. The larvae overwinter in branches the first year and in roots the second year. The larvae live in the soil and feed on roots and may also girdle the plant at the root crown, causing the plant to wilt and die. Interior leaves usually show most damage. Revised and edited by Dr. Michael J. Raupp and Dr. Paula M. Shrewsbury, University of Maryland, April 2020. Azalea lace bug damage. Photo: John Davidson, University of Maryland, Rhododendron borer is the larvae (caterpillar) of a clear wing moth. Their feeding causes leaf margins to curl and the maggots complete their development within the curled leaf tissue. 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. Photo: Dow Gardens, Bugwood.org. Heavy infestations of lace bug may cause leaves to turn yellow and then brown. Insect problems include aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips and whitefly. The azalea bark scale, Eriococcus azaleas, is a prominent pest of rhododendron, azalea, and huckleberry (Vaccinium spp.). Photo: P.M. Shrewsbury, University of Maryland. Two-banded Japanese weevil (actual size is 3/16 inch). Susceptible cultivars include those of. Azalea lace bug adult and fecal spots. The adult moths, about ¼” long, resemble wasps, have mostly clear wings, and black bodies with 3 gold bands on the abdomen. Eggs overwinter in leaves and may begin to hatch as early as late April. To control heavy infestations, spray dormant plants with a 4% rate of horticultural oil to kill developing nymphs on twigs. Adult Japanese weevils feed during the day and will drop from the plants when disturbed. Azalea, rhododendron, and andromeda each have their unique species of lace bug. These infested leaves will eventually turn yellowish and appear wilted. 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. They were first discovered by a Flemish botanist, Charles l’Ecluse. Photo: David Held, Auburn University, Bugwood.org. Alternatively, place bait stations or stakes with a slow-acting active ingredient near the base of the shrub where you observe ant trails. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Prune the suspected branches and split them open longitudinally to see if larvae are present. Plan to spray the shrub once the number of crawlers trapped begins to decline. Rhododendron and azalea varieties vary in their susceptibility to some of these pests. This borer, however, is a longhorned beetle. Mines are initially formed near the midrib and caused by caterpillars feeding between the upper and lower leaf surface. 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. Damage on new foliage will be evident in May and July. Maryland are lace bugs ( nymphs ) are less than 1/16 inch in length overwinter on the stem, quickly. Mounds during hatching season will reveal the small crawlers moving along the plant cottony masses on the lower of. Mildew by Fred Minch pests of rhododendrons by Arthur L. Antonelli Decide what tool you need your... 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