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Plant NameTypeDescription 
Botrytis petal blightAzaleaDiseaseBotrytis petal blight is a fungal disease typically found in early spring. Symptoms of infection include brown, water-soaked spots on the leaves, and masses of gray-brown spores which form on infected tissues. Botrytis petal blight often occurs after the plant is injured or stressed.
Cylindrocladium blight & root rotAzaleaDiseaseThis fungal disease may infect plants through the roots or stems and cause diverse symptoms. Leaf spots, cankers on stems, root rot, and/or sudden general wilting may be observed on infected plants. Cylindrocladium can be transmitted in infected soil, through movement by wind and water, and by hand. The fungus grows best in conditions of high temperature and high humidity and is only a greenhouse problem.
Leaf and flower gallAzaleaDiseaseThe leaf and flower gall fungus attacks expanding leaf and flower buds. Initially, the affected plant part shows a thickening and gradually assumes a fleshy appearance. Leaves may thicken into fleshy, bladder-shaped galls. The galls are pale green to pink and may later be covered with a white material. Eventually the leaf galls lose their green or pink color and become brown and hard. Parts of leaves or entire leaves may be affected. The disease is favored by high humidity and wet leaves. Damage is primarily aesthetic.
Leaf spotAzaleaDiseaseLeaf spot or leaf scorch on azaleas is caused by a fungus. At first, dark red to brown spots appear on leaves in early summer. Later these spots turn lighter brown, while the leaf turns yellow around them. The fungus can survive the winter on dead leaves or on infected plants in a greenhouse.
Lime-induced chlorosisAzaleaDiseaseLime-induced chlorosis, or leaf yellowing, is caused by alkaline soil conditions. High alkalinity of soils can make iron or manganese unavailable to plants, causing leaf chlorosis. Pale to bright yellow leaves, particularly on the new growth, are common symptoms. Typically the chlorosis begins at the edges and progresses into the leaf, with only the veins remaining green in severe cases. Plants near new concrete may also suffer from lime-induced chlorosis.
Marginal leaf necrosisAzaleaDiseaseLeaf burn on azalea is a response to stress. Leaves turn brown, especially at the tips and along the edges. Water stress (too much or too little), root or stem damage, excess fertilization, frost damage, and exposure to drying winds are some of the possible causes of leaf burn.
Nematode (stunt)AzaleaDiseaseNematode problems are most common in nursery plantings. Nematodes are tiny, worm-like parasites found only in the soil that feed on the roots. The root damage causes an overall stunting of affected plants, and plants may also show signs of drought stress or iron deficiency. Leaves can die back or drop prematurely, or entire plant tops may be yellowed. Nematode stunt symptoms often appear in a circular pattern. Soil samples must be taken to confirm nematode infestation.
Ovulinia petal blightAzaleaDiseaseOvulinia petal blight affects the flowers only (not leaves or shoots) of azaleas and rhododendrons. Infected flowers first display small, water-soaked spots which enlarge quickly. The petals quickly become slimy and turn brown, sometimes within two or three days after fully opening. The infected blossoms remain on the plant and later provide a source of infection for next year's flowers. Flowers on lower branches are affected first. The disease overwinters in dead flower material or top layers of mulch, and is favored by high humidity.
Powdery mildewAzaleaDiseasePowdery mildew on azalea forms a characteristic fuzzy white growth on upper or lower leaf surfaces. Entire leaves can be covered. In late summer and fall, small black specks may be found in the white areas. Powdery mildew is more severe on shaded plants. It is favored by the high humidity found in crowded plantings and damp locations.
Root rot (Phytophthora)AzaleaDiseaseThe symptoms produced by Phytophthora root rot are often confused with those caused by environmental or cultural problems. Above ground, infected plants may show stunting, yellowish-green leaves, branch dieback, wilt, and even plant death. Dead leaves persist on the branches instead of dropping. Underground, the roots rot, progressing from the smallest to the largest. The fungus may also cause rot in the main stem. Phytophthora persists in the soil and can infect new plants placed in the same area. Diseased plant tissues and debris are other sources of infection.
Azalea bark scaleAzaleaInsectThe azalea bark scale is a soft scale resembling mealybugs. Red females cover themselves and their eggs with a white, waxy, protective coating. Cottony masses of the scales are often located on twigs and in the forks of the branches. Sticky honeydew is excreted by the pests, and may have black sooty mold growing on it.
Azalea lace bugAzaleaInsectAzalea lace bug (Stephanitis pyrioides) is a relatively new insect pest in the Pacific Northwest. Unlike rhododendron lace bug (S. rhododendri), azalea lace bug attacks both azaleas and rhododendrons and may cause significant damage on both. Both adults and nymphs feed on the underside of leaves. Symptoms of damage are stippling, bleaching, or a silvery or yellowish (chlorotic) appearance of the leaves. The underside of the leaf will appear dirty due to the presence of insects (eggs, nymphs, and adults) and brownish or tar-like fecal spots, particularly along the leaf veins. Heavily damaged leaves may drop from the plant. Adults are about 1/10 inch long with lacy, net-like, transparent wings. The azalea lace bug has smoky, brown markings on the wings, which distinguish it from the pale whitish-tan rhododendron lace bug. The young nymph is colorless to black and spiny depending on age. The first generation of nymphs emerges in spring after frost danger has passed. Several generations may occur in a year. Since these insects overwinter as eggs laid on the leaves, evergreen varieties are most susceptible. Plants in full sun or suffering from drought may suffer greater damage. Damaged leaves do not recover, so early detection is important. See also Rhododendron: Rhododendron lace bug.
Azalea leafminerAzaleaInsectThe azalea leafminer is a small yellowish caterpillar that grows to about 1/8 to 1/4" long. Young larvae mine leaves, leaving blisterlike blotches that later turn brown. Older larvae roll and skeletonize leaves. Damaged leaves may drop from the plant. Azalea leafminers are mainly an aesthetic problem, though occasionally they may destroy entire leaves.
Obliquebanded leafrollerAzaleaInsectObliquebanded leafrollers are usually found on the new growth. Their presence can be determined by rolled leaves held in place with webbing. The smooth green caterpillars, about 3/4" long, can be found feeding inside the rolled leaves. The adult is an orange-brown moth approximately 1/2" long and bell shaped from above when at rest.
Root weevilsAzaleaInsectCharacteristic damage includes notching of leaf edges by adults and minor to severe root and bark damage by larvae. Azaleas generally have less severe leaf notching than rhododendrons, but may be damaged or killed by root weevils feeding on lower stems and roots. Occasionally the trunk is girdled at or just below the soil surface. Adults are wingless and begin feeding around June to August, depending on the species.
Spider mitesAzaleaInsectSpider mites cause mild to severe stippling (little specks or dots) on leaves. Usually yellowish or bronzish, stippling can, in severe cases, cause leaves to turn brown and drop. Fine webbing is often present, especially on the underside of leaves. Mites may be found on the underside or both sides of leaves.