Curled leaf tips in June indicate the completion of the first generation. Angela Ryczkowski is a professional writer who has served as a greenhouse manager and certified wildland firefighter. Overwintering immature scales (nymphs) are less than ⅛-inch long, gray, and are usually found in twig forks. Small plants when heavily infested may be defoliated. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. Spinosad, a biorational insecticide (which has the least toxic classification), may also be used on young and older caterpillars. Flowers 5-merous, usually in terminal corymbs. Mulch with chopped oak leaves, leaf mold, or pine needles and water deeply during drought periods. Janet Flower Shop Network Plant Expert Reply: First we need to determine if you really have a fungus. Scale … 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. This borer prefers rhododendron, but occasionally attacks deciduous azalea and mountain laurel. In spring, adults emerge from the soil and fly to the tips of branches where they lay eggs in new developing leaf tissue. Damage occurs in late summer and fall. Adult lace bugs are flat, about 1/8 inch long, with transparent lace-like wings. They feed in the evening and night. This beetle prefers rhododendron, but will also attack azaleas and mountain laurel. Rhododendron Linnaeus Evergreen or deciduous shrubs with alternate, entire or ciliateserrulate, glabrous to tomentose, lepidote or strigose leaves. Photo: John Davidson, University of Maryland. Many diseases and other problems can be prevented by following the recommended cultural practices for proper planting and care. There is one generation a year and larvae overwinter in tunnels in branches. The largely immobile nature of scales and their protective covering makes chemical control challenging. Larvae also feed on roots and crowns of hosts. 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. A registered insecticide (e.g., Imidacloprid) may be applied by a certified pesticide applicator only (as per the Maryland Pollinator Protection Act.). The borer causes wilting of leaves and twig dieback. They vary in appearance depending on age, sex, and species. Photo: John Davidson, University of Maryland, Azalea Leafminer (late instar). The females appear totally white when they produce their white, waxy egg sacs. 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. Photo: John Davidson, University of Maryland, Rhododendron borer is the larvae (caterpillar) of a clear wing moth. Water the infested shrubs deeply and infrequently during extended dry spells. Small shrubs may be defoliated in heavy infestations. Management: Rake and destroy fallen leaves in the fall to remove overwintering pupae. 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. Buds with several to many imbricate scales. 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. The caterpillars feed in groups when young and disperse as they mature. Adult feeding damage is very similar to that of black vine weevil but notches on leaf margins tend to be smaller. Healthy plants that are not under water stress can better withstand and recover from scale feeding. Mature larvae are 1/2 inch long and yellowish brown. 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. Rhododendron and azalea varieties vary in their susceptibility to some of these pests. Video shows close ups of Azalea Bark scale and provides some plant inspection tips. Be sure to observe all cautionary statements on labels to protect pollinators. Two-banded Japanese weevil (actual size is 3/16 inch). See the package for specific instructions. REC, Western Maryland
Damage on new foliage will be evident in May and July. 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. Azalea leafminer overwinters as pupae in the leaf mines. The larvae are whitish and have no visible head. Scale – Scale insects commonly cause black fungus on rhododendron. Damage caused by the stem borer, which includes wilting terminals and dieback, is similar to the Rhododendron borer. 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. In less than ideal growing conditions (i.e., full sun, drought), plants may become stressed and more susceptible to pest problems. Adult Japanese weevils feed during the day and will drop from the plants when disturbed. Beneficial nematodes, available under several trade names, are a control option. Preferred host plants are azaleas, but they may also attack witch hazel, sumac, apple, red oak, and andromeda. Azalea lace bug adult and fecal spots. All types of fruit and ornamental trees, shrubs. Look for discoloration of foliage and signs of sooty mold to indicate the presence of the scales. 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. Mature larvae are about 1/2 inch long, white with brown heads. Management. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Alternate, white scale on rhododendron or ciliateserrulate, glabrous to tomentose, lepidote or strigose leaves a registered insecticide when damage in. Abiotic problems of azaleas and rhododendrons on azalea and mountain laurel if possible by caterpillars feeding between the and. 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