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Plant NameTypeDescription 
Fire blightOrnamental PearDiseaseFire blight is a bacterial infection which typically attacks via wounds or blossoms. Initially, twigs and flowers appear water-soaked. Infected tissues quickly turn brown to black and die back, often bending over in a characteristic "shepherd's crook." Blighted tissues remain on the tree, giving it a scorched appearance. Dark, somewhat sunken cankers develop on twigs and branches, sometimes girdling the limb and causing dieback. Brownish bacterial ooze is common at the margins of cankers, especially during humid weather. Fruit may also be infected, showing sunken black spots up to 1" in diameter and 1/4" deep. The bacteria overwinter in infected tissues and can be transmitted by rain and pollinating insects. Fire blight is not a proven problem in western Washington. Pseudomonas blossom blast and dieback is caused by a different species of bacteria, but the symptoms may be similar.
Pear trellis rustOrnamental PearDiseasePear trellis rust is a fungal disease that attacks pear trees and junipers. It is commonly reported on pear leaves in western Washington. Like many rust diseases, pear trellis rust requires both hosts to complete its life cycle. Spores produced on juniper infect only pear trees and spores produced on pear only infect junipers. However, pear can occasionally be reinfected from overwintering diseased material on the tree. Symptoms on pear appear on both upper and lower leaf surfaces. Bright yellow to orange spots up to about 1" in diameter appear on pear leaves, twigs and branches in spring and summer. Diseased fruit may become mummified. Small fungal fruiting bodies develop in the center of the lesions on the upper leaf surface. Opposite these pimple-like fruiting bodies, additional fruiting structures (up to 1/4" high) develop on the leaf underside. These brown fruiting bodies first appear blister-like, then develop a distinctive acorn-like shape with a pointed tip. The sides of the structure are finely divided, creating a trellis-like appearance that gives the disease its name. These may appear as early as mid-June, but are more commonly found in late summer. Spores produced in the trellis structure infect species of junipers in the fall. Infected junipers do not show symptoms until the following spring or later. Symptoms on juniper can be very difficult to detect and may include spindle-shaped swellings on twigs which girdle and kill plant tissues. The fungal fruiting structures which develop on juniper consist of long cylindrical, gelatinous, reddish-brown "horns" that appear during wet weather on the swollen tissues. Infected tissues on junipers may continue to produce spores for several years. For more information, see Juniper: Pear trellis rust.
Powdery mildewOrnamental PearDiseasePowdery mildew is a fungal disease found on twigs, leaves, blossoms, and fruit. New growth is particularly susceptible. The entire terminal may become covered with powdery mildew. Leaves develop a characteristic gray-white powdery growth, usually on the underside. Severe infections may spread to the upper leaf surface, as well. Dark brown to black fruiting bodies of the fungus can be seen around midsummer, while the whitish mycelia turn brown at this time. Infected leaves are often curled and distorted, while other infected tissues may become brittle and die back. Fruit (if present) may show russet patches after infection. Unlike apple powdery mildew, pear powdery mildew has not been observed overwintering in buds. Powdery mildew development is favored by high humidity, warm days, and cool nights.
Pseudomonas blossom blast and diebackOrnamental PearDiseaseBlossom blast and dieback is caused by a bacterial infection. The infection causes buds to turn a papery brown and die. Leaves may be spotted. Flower petals and stems may also be affected, and fruit cluster bases can turn brown or black. Occasionally, fruiting spurs may be killed. Cankers may develop in twigs and branches. Symptoms of this disease, especially on flowers, may closely resemble fire blight. However, blast infections seldom extend more than 1"-2" into a spur. Bacterial ooze, which is common with fire blight, is not present with Pseudomonas blast. Fruiting pears and most Asian pear cultivars are also susceptible. Frost and cold injury promote infection, which is common in cold, wet springs. Warm, dry weather inhibits disease.
AphidsOrnamental PearInsectThree aphids are commonly found infesting pear. All three species produce honeydew, a sweet, sticky material which attracts ants and that may become covered with a growth of dark sooty mold. Honeydew also causes russeting of pear fruit. The green peach aphid is pale green in color, the melon or cotton aphid is yellowish to dark green, and the bean aphid is black. The green peach and melon aphids feed on succulent shoots throughout the tree, while the bean aphid is primarily found in clusters on shoot tips. Aphid feeding causes foliage and shoots to be stunted, curled and deformed.
Codling mothOrnamental PearInsectThe brownish-gray wings of adult codling moths are marked with dark bands and a dark brown spot near the tip. Wingspan is up to 3/4" across. Adult females lay eggs on leaves or fruit. The larvae burrow into fruits, usually through the blossom end, where they eat the core and seeds. The fruit appears dirty brown or rotted in the center when cut open. Mature caterpillars are pinkish-white with brown heads and about 3/4" long. The mature larvae tunnel out of the fruit and make cocoons under bark or in the ground beneath the tree. They overwinter in the cocoons and pupate in the spring. Adults typically emerge around May-June. There can be two generations per year. Codling moth is a serious problem in commercial apple and pear orchards. Because ornamental pear can serve as an alternate host for codling moth, homeowners in fruit-growing areas are encouraged to manage this pest to help control regional codling moth infestations. Control may be required by law in some regions--contact your local extension office if you have questions.
Pear slug (pear sawfly)Ornamental PearInsectThe pear sawfly is also known as the pear slug (or 'cherry slug' when on cherry) because of its resemblance to a small, dark slug. These insects are the larval stage of a glossy, black sawfly about 1/5" long. The larvae are covered with a dark green to black slime which gives them the slug-like appearance. The caterpillar-like larvae are yellow immediately after molting until the slime is produced. Larvae are also yellow-orange immediately before pupating. Pear slugs feed on upper leaf surfaces, skeletonizing leaves. Severe infestations can cause defoliation, weaken trees, and affect fruit development on fruiting varieties.
Pearleaf blister miteOrnamental PearInsectPearleaf blister mites are tiny, white to yellowish eriophyid mites that feed on leaves and fruit. Damage on leaves is caused by mites feeding inside the leaf tissues, resulting in the formation of pale green to reddish blistered areas on the leaf. Later in the summer these blistered areas will turn brown to black as the leaf tissue dies. Leaf blisters are typically 1/8" to 1/4" in diameter. Severe blister mite infestations can cause leaves to drop. Blister mite damage to fruit consists of russetted, somewhat sunken areas on the skin. These mites overwinter under bud scales, attacking emerging leaves in the spring. Severely infested buds can fail to develop in the spring.