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Plant NameTypeDescription 
Crown gallPearDiseaseCrown gall is caused by a soilborne bacterium. The bacteria infect through wounds on the crown and roots. Young galls are fleshy, white, enlarged masses on the roots or stems. Older galls are hardened and turn dark brown and woody or corky in appearance. They range in size from less than an inch to several inches across. The bacteria can be spread from infected to clean soil by water movement. Damage varies with location and size of galls. Small galls are essentially harmless. Large galls on the crown may weaken or girdle trees. The growths can also be an aesthetic concern.
European canker (Nectria canker)PearDiseaseNectria or European canker is a fungal disease affecting the twigs and branches of pear and apple. Young cankers occur at leaf nodes on twigs and are sunken, dark, and water-soaked in appearance. Twigs are often girdled and die back above the infected site. Older cankers are either irregularly elongate and covered with dead bark, or are surrounded by roughened, irregular, cracked bark in concentric rings, indicating the infection's yearly advance. In spring or fall of the first season following infection, cankers produce white fungal fruiting bodies. Round, red fruiting bodies are produced on older cankers during subsequent winters and springs. The fungus infects during rainy weather in the fall, attacking through leaf scars and wounds. An eye rot may occur on the flower end of fruit, causing brown, depressed spots with lighter centers on the fruit surface.
Fire blightPearDiseaseFire 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 "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. A 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.
Pacific Coast pear rustPearDiseasePacific Coast pear rust is a fungal disease affecting pears, hawthorn, apple, crabapple, serviceberry, quince, and mountain ash. The alternate host is the incense cedar (Calocedrus decurrens), which develops witches' brooms. Infected fruits of pear are deformed and drop prematurely. On the surface of the fruit, yellowish spots with cup-shaped pustules develop. Leaves and green shoots may also be infected. Symptoms are most obvious after flowering and before July. For more information on pear rust diseases see Pear: Pear trellis rust.
Pear trellis rustPearDiseasePear 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 pears appear on both upper and lower leaf surfaces. Bright yellow to orange spots up to about 1" in diameter appear on pear leaves, fruit, 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 on pear rust diseases, see Pear: Pacific coast pear rust and Juniper: Pear trellis rust.
Powdery mildewPearDiseasePowdery 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. Fruits may show patches of russeting 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 diebackPearDiseaseBlossom 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. Ornamental 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.
ScabPearDiseaseScab on pear is a fungal disease very similar to apple scab. The disease infects during wet weather in the spring and summer. Lesions appear on leaves, petioles, twigs, and fruit. The spots enlarge and darken, first to dark, velvety, olive-green then to black. Lesions on twigs are first blister-like, later appearing brown and velvety to corky. Infected leaves are often twisted or deformed. Fruit infected early in development shows olive-green to brown spots, which are later russetted and corky, and may have deep cracks. These fruit are often misshapen. Fruit infected at later stages develops small black "pinpoint" scab spots while in storage. The disease is most favored by cool, wet conditions and overwinters in infected fallen leaves and sometimes on twigs. Pear scab does not infect apple, nor are pears susceptible to apple scab.
Stony pitPearDiseaseStony pit is a virus disease of pears apparently spread by vegetative propagation (budding, grafting, rooting cuttings). Insects are not known to carry the virus. The disease primarily affects the fruit. Dark green areas appear on young fruit. The areas become pitted, with tissue in the pits becoming hardened and sometimes dying. Affected fruits may be mildly to severely deformed. Severity of the disease varies from fruit to fruit and from year to year. Young leaves of infected trees may show a faint mottling and bark may be "pimpled" or cracked. Severe symptoms have been seen on the cultivars 'Bosc', 'Comice', and 'Seckel'.
Virus diseasesPearDiseaseVirus diseases of pears in home orchards seldom cause significant problems. Symptoms of common viruses are seen on bark, leaves, and fruit. Some virus diseases may cause bark to appear roughened or blistered. Most common virus diseases of pears are transmitted by grafting or other mechanical means. For more information on stony pit virus, see Pear: Stony pit virus.
AphidsPearInsectThree 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. Green apple aphids are also occasionally found on Asian pears.
Apple-and-thorn skeletonizerPearInsectThe adult of the apple-and-thorn skeletonizer is a small dark-brown or reddish-brown moth. It overwinters as a pupa or an adult, with the females laying eggs in the spring. The caterpillars are yellow-green in color, have black spots and brown heads, and feed on the leaves of several plants including apple, crabapple, pear, cherry, and hawthorn. Caterpillars are about 1/2" long at maturity. Characteristic damage includes skeletonized leaves, or leaves that are rolled into a cone and tied with webbing. Damaged leaves are papery brown and drop prematurely.
Brown marmorated stink bugPearInsectThe brown marmorated stink bug (BMSB) is an introduced pest species from Asia that is spreading quickly across the United States. Nymphs and adults feed on a wide variety of plant hosts. BMSB prefers to feed on fruit, seeds, and seed pods, but will also feed on stems and leaves of some hosts. Both adults and nymphs have piercing-sucking mouthparts and inject digestive enzymes into plant tissues to aid in feeding. Sunken areas and deformities (catfacing) on the surface of the fruit are typical symptoms on damaged apples and pears. Damaged areas are discolored beneath the fruit’s skin and become hard and pithy or corky in texture. BMSB damage that occurs close to harvest time may not be apparent, but the damaged fruit will come out of storage with brown spots. Other known tree fruit/nut hosts of BMSB include apple, filbert, and stone fruits including apricot, cherry, peach, and plum. One or two generations of BMSB per year are expected in the Pacific Northwest. Adults overwinter in sheltered locations (including houses, where they can become a significant nuisance pest). In the spring, light green to white eggs are laid in groups of about 20 to 30 on the underside of leaves. Young stink bugs, or nymphs, are black with a red-and-black striped abdomen. Nymphs often feed in groups when young. Older nymphs are dark with white bands on body, legs, and antennae. They may feed in groups or singly. Adults are a little over 1/2 inch long, with a shield-shaped body. Body color on adults is mottled gray and brown, while the legs and antennae have alternating dark and light bands. The abdomen also has dark and light bands which are visible at the edge of the wings. NOTE: BMSB adults closely resemble other stink bugs found in WA and OR. For more information on BMSB identification, see FS079E, Pest Watch: Brown Marmorated Stink Bug, available at
Codling mothPearInsectThe 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 home-grown fruit trees can serve as alternate hosts 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.
Cutworms and armywormsPearInsectCutworms and armyworms are the larvae of noctuid moths. These common moths are typically medium-sized with fairly dull coloration. The gray to tan caterpillars are hairless, nocturnal, and generally spotted, striped, or otherwise marked. They may be 1/4" to 1" in length and tend to curl up when disturbed. Cutworms and armyworms feed by chewing leaves and buds, typically on lower portions of the tree. Symptoms of damage include ragged, irregularly chewed leaf margins and buds damaged prior to bloom. Fruit may also be damaged, with small to large holes chewed into the surface. While armyworms typically feed during the day, cutworms usually feed at night. It is advisable to search for them with a flashlight in the dark, as cutworms typically spend the day just beneath the soil surface or under debris near the host. Weeds are the primary hosts of cutworms.
Pear psyllaPearInsectThe brownish-gray adult pear psylla is about 1/10" long, with clear wings held rooflike over the body. The wings may have a smoky gray spot halfway along the inner margin. The red-eyed nymphs range in color from yellow to dark brown, depending on age. Pear psylla nymphs feed on leaves, preferring succulent new growth in the upper portions of the canopy. Damaged leaves may be blackened or burned in appearance. Psylla feeding produces large amounts of honeydew, a sweet, sticky material which causes russeting when it drips onto fruit. Honeydew may attract ants and often becomes covered with a growth of dark sooty mold. Psylla feeding can cause reduced vigor of trees, stunting, and fruit loss. The pear psylla spreads the organism which causes pear decline.
Pear slug (pear sawfly)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.
Pearleaf blister mitePearInsectPearleaf 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.
San Jose scalePearInsectSan Jose scale is an armored (hard) scale found on many deciduous trees and shrubs including apple, cherry, elm, maple, poplar, and willow. The scale insects are about 1/16" in diameter. The female is gray with a yellow spot in the center. The yellow crawlers are easily spread by wind, birds, or people. San Jose scale may be found on twigs, branches, leaves, and fruit. Heavily infested branches or entire trees may wilt and appear water-stressed. Severe infestations can cause twigs and branches to die back. Repeated infestations can kill trees. Infested fruit develops sunken spots surrounded by reddish areas. The scale overwinters as black immature scales on the bark.
Spider mitesPearInsectSeveral species of spider mites may be found on pear leaves, including the twospotted and McDaniel spider mites and the European red mite. They may be various colors including yellow, greenish, brown, or red. All species feed on the leaves, causing a whitish to yellow stippling. More severe damage results in leaves taking on a bronzed appearance. Infested pear leaves often develop small to large necrotic brown spots during hot weather. This is known as transpiration burn and is a common symptom of mite feeding on pears. Severe cases of transpiration burn can result in premature leaf drop. Most spider mites spin webbing which may be found on the lower leaf surfaces and between leaves and twigs. The European red mite typically produces smaller amounts of webbing than other species.