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Plant NameTypeDescription 
Anthracnose and Bull's-eye rotAppleDiseaseApple anthracnose is a fungal disease that impacts apple production in regions with mild year-round temperatures, abundant winter rains, and cool-humid summers. Two disease problems result from this fungal group: anthracnose cankers on trees and a post-harvest fruit rot known as Bull’s-eye rot. Anthracnose canker typically affects twigs and small branches but can damage tree trunks and large limbs. Initial infection usually starts fall but can continue throughout winter and spring if weather is mild and moist. Young cankers appear as small reddish-brown areas and are most easily observed when bark is wet. Cankers elongate during spring reaching full size (1-10" long) by midsummer. Cream-colored fungal sporulation may be observed. The bark usually splits away around the canker edge. The dead tissue in the canker sloughs off leaving “fiddle-strings” of bark across the canker before eventually all bark tissue over the canker is gone. Spores mature in late summer/early fall and can spread by rain and wind to other parts of the tree or to nearby apple trees. The fungus survives each year in cankered limbs. These cankers also serve as the source of infection for the fruit rot phase of the disease. When it rains before and during fall harvest time, the fungus may enter fruit through natural openings, such as the gas-exchange pores known as lenticels, or through wounds. Damage first appears on the fruit skin as circular, flat, or slightly sunken spots that are brown with a pale center. After a 4-7 month period of fruit storage, fungal fruiting bodies may develop in the center, often in concentric rings giving the appearance of a bull’s eye. The decayed fruit tissue is somewhat mealy and firm, and does not separate easily from healthy tissue.
Bitter pitAppleDiseaseBitter pit of apples is a physiological problem which results from calcium deficiency in the fruit. Depressed spots appear on the fruit surface and the tissue beneath the spot becomes brown. The spots may be up to 1/4" in diameter and are most often seen near the blossom end of the apple. Later, the spots will become sunken and somewhat dry and corky in texture. Several cultural practices can increase the occurrence of bitter pit. Heavy pruning and large nitrogen applications result in vigorous shoot growth and increase bitter pit. Irregular watering, drought stress, and hot summer weather can also contribute to the problem, as will injuries to the trunk or roots which interfere with water and nutrient uptake. Certain apple varieties are more prone to this cultural problem.
BurrknotAppleDiseaseBurrknot of apples is a physiological problem which appears as a growth somewhat resembling crown gall. The roughened, warty-looking growth is comprised of root tissues. If buried with soil, burrknots may produce normal roots. Several apple varieties grown in western Washington are susceptible to this problem. High humidity, cool weather, and low light levels are environmental conditions which contribute to the problem. On some varieties grown in western Washington, the symptoms commonly occur on branches or may appear at or just above the soil line. In other areas, severe burrknot problems can cause trees to become stunted, girdled, or weakened at the site of the knot.
Crown and collar rotAppleDiseaseCrown rot of the rootstock and collar rot of the scion wood of apple trees is caused by a soilborne fungus. It can survive in infected tissues and plant debris, as well as in the soil. Symptoms typically appear in early fall, when one or more branches show signs of decline, including discolored (reddish-bronze to purple) foliage, smaller leaves and terminal growth, and a red discoloration of the bark. Infection occurs in the roots and moves within the roots to the crown. The bark is killed, and the cambium beneath the bark turns reddish-brown, instead of the normal white color. Crown or collar rots may completely girdle trees, resulting in death.
Crown gallAppleDiseaseCrown 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 or equipment. 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. Burrknot, a physiological problem of apple trees, can be mistaken for crown gall.
Cytospora cankerAppleDiseaseThe fungi which cause Cytospora canker attack through wounds on twigs and branches. The disease can spread to healthy tissues after the initial infection. Initial cankers are small, but enlarge quickly and may streak up and down the stems without girdling. The cankers may also girdle twigs, resulting in dieback above the infection site and causing "flags" of dead material to appear in the canopy. The leaves on the dead twigs turn color and droop, but often remain attached. The canker itself appears as a dark, sunken area of dead bark and wood. Pinhead-sized black fruiting structures of the fungi often erupt through the bark and produce reddish tendrils or droplets of spores in wet weather. Spores are easily spread by wind, rain, and insects. The cankers are often perennial, enlarging through several seasons.
Fire blightAppleDiseaseFire 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, appearing scorched. Cankers can develop on twigs and branches, sometimes girdling the limb and causing dieback. Bacterial ooze occurs on infected tissues during humid weather. Fire blight symptoms can sometimes be found around the graft union in apples. Water-soaked purplish cankers may occur near the base of the tree. Reddish-brown streaking beneath the bark in the cankered area may be observed. Some apple trees may collapse and die without showing any characteristic blight symptoms in the canopy. These deaths may be confused with other disease problems such as root rots. Fire blight is not a proven problem in western Washington.
Fruit russetingAppleDiseaseRusseting is the appearance of corky, roughened, brownish or grayish areas on apple fruits. There are several possible causes for fruit russeting, including cool wet weather, frost damage, spray damage, powdery mildew infections, and some viral infections. The pattern of the russeting may indicate the cause. Russeting caused by wet weather may be associated with corky lenticels and tan-colored markings, typically raindrop-shaped and concentrated near the stem end of the fruit. Frost russeting often occurs in a band around the fruit. Spray damage russeting is usually concentrated near the bottom of the fruit, where spray collects. Russeting associated with powdery mildew may be tan to gray with a net-like appearance.
Nectria canker (European canker)AppleDiseaseNectria (European) canker is a fungal disease affecting the twigs and branches of apple and pear. The fungus infects during rainy weather in the fall, attacking through leaf scars and wounds. Young cankers are sunken, dark, and water-soaked in appearance. White fungal fruiting bodies appear in the canker during the spring or fall/winter of the first season following infection. Twigs are often girdled and die back above the infected site. Older cankers are either irregularly elongate and covered with dead bark, or surrounded by roughened, irregular, cracked bark in concentric rings. Round, red fruiting bodies are produced on cankers during the second winter and spring. Fruit may also be infected, causing an eye rot at the blossom end or a rot on the side of the fruit which may resemble bull's-eye rot.
Nectria twig blight (Coral spot)AppleDiseaseNectria twig blight is caused by a fungus which invades plant tissues through wounds and natural openings in the bark. The infections typically occur on twigs and small branches. Cankers are initially small and sunken, gradually girdling the twigs after two or more seasons. Leaves above the canker wilt and die on girdled twigs. The cankered areas produce pinkish or coral-colored fruiting bodies of the fungus.
Perennial canker (Bull's-eye rot)AppleDiseasePerennial canker is a fungal disease. It is similar to anthracnose, but occurs primarily east of the Cascades in Washington. The characteristic symptom of perennial canker is a sunken canker surrounded by rings of dead wood. Cankers are often associated initially with wounds. The fungus does not survive in the wood, but reinfects around old cankers each year, especially when woolly apple aphids are present. Aphid feeding provides wounds which serve as re-entry sites for the fungus. Winter injury and other weakening factors also contribute to disease severity. The disease also causes a bull's-eye rot of stored fruit. Infected fruits develop spongy light brown spots with darker margins. There may be additional rings around the spot, giving it a "bull's-eye" appearance.
Phytophthora fruit rotAppleDiseasePhytophthora fruit rot is caused by a soilborne fungus which can also be found in and carried by irrigation water. Infection occurs when water contacts fruit on low-hanging limbs or when overhead watering is used. Firm tan spots approximately 1" or more in diameter develop on infected fruit. If the infection moves up into the wood, a dieback of one-year-old wood resembling fire blight can occur. This fungus can also infect pears. Phytophthora fruit rot occurs sporadically and is of minor importance.
Powdery mildewAppleDiseasePowdery mildew of apple is a fungal disease found on twigs, leaves, blossoms, and fruit. New growth is particularly susceptible, since the fungus overwinters in buds. The entire terminal may become covered with powdery mildew. Leaves typically develop a characteristic gray-white powdery growth, often on the underside. Infected young leaves may be curled and distorted. Infected foliage is brittle and may be killed. Dark brown fungal fruiting bodies may be seen by midsummer, when the white fungal mats turn brown. Affected fruits typically show a net-like pattern of russeting in the infected areas. Powdery mildew is favored by humid nights and warm days. Find "Recommended Fruit Trees for the Puget Sound" at
ScabAppleDiseaseApple scab is caused by a fungus which also causes scab on crabapple and hawthorn. The first infections occur during wet weather in the spring. Initially, the disease causes tiny, pale, chlorotic, water-soaked spots on the leaves. The spots enlarge and darken to a dark, velvety, olive-green then to black. Leaves may become distorted, puckered, and mottled. Leaves may drop, sometimes resulting in severe defoliation of susceptible trees. Scab can also affect fruit. Fruits infected early in development show olive-green to brown, roughened or corky spots which may develop deep cracks. These apples are often misshapen. Fruits infected at later stages develop small black "pinpoint" scab spots while in storage. The disease is favored by cool, wet conditions and overwinters in infected plant debris. Refer to PNW0582 Apple Scab for more information.
Virus diseasesAppleDiseaseVirus diseases of apples are rarely significant problems in home orchards. Symptoms are most commonly seen as bark disorders, leaf mottling, or misshapen fruit. One of the more common virus problems is apple mosaic. Apple mosaic virus is most commonly seen on older (heirloom) apple varieties. This disease causes creamy to yellow mottling, spotting, or vein yellowing visible mainly on the upper surface of leaves. Extremely sensitive varieties may lose leaves. Apple mosaic is transmitted by grafting or natural root grafts and spreads slowly.
AphidsAppleInsectThree aphids are important pests of apple. Green apple aphids feed throughout the growing season on terminals, causing twisted and deformed leaves and stunted shoots. They produce honeydew, a sweet, sticky material which may become covered with sooty mold. Rosy apple aphids are purplish to pink with a powdery gray coating. They feed on leaves and buds, causing curled leaves and distorted shoot growth. They may feed on fruit, causing fruit distortion. Colonies of these honeydew-producing aphids are often found in curled leaves. Woolly apple aphids are pink to purple with a dense, woolly coating of white wax. They feed on trunks, branches, and twigs, often at wound sites, causing bark to become swollen or galled in appearance. These aphids feed on apple roots during the winter and are associated with the spread of perennial canker.
Apple ermine mothAppleInsectThe apple ermine moth is an imported pest which feeds exclusively on apples. The adult moth has silver-white wings spotted with black. Larvae are gray, cream-colored, or greenish with dark spots along the sides. They may reach 3/4" long at maturity. Young larvae feed on developing leaves, mining out leaf tissues. They later move into the foliage and feed as tent caterpillars. Several leaves are tied together with webbing to make nests up to 3" across. Each nest contains several caterpillars. New nests are made as leaves in old ones are consumed. The caterpillars pupate in clusters within webbing, beginning around June. Adults emerge from late June onward, with females laying eggs into the fall. Egg masses are about 1/2" across and are found on the bark. They are initially yellow but age to red then gray in color.
Apple maggotAppleInsectThe apple maggot is potentially a serious pest of apples. Transportation of home-grown fruit from infested to non-infested areas is prohibited in Washington. The adult apple maggot is a small fly about 1/4-3/8" in length. It is black with a white mark on the back and has black markings on otherwise clear wings. The female lays eggs on apple fruits by puncturing the skin. The cream-colored larvae feed inside the fruit, creating irregular brown tunnels throughout the fruit. The tunnels are often infected by rot organisms which ruin the fruit. At maturity, the 3/8"-long maggots drop to the ground where they pupate and overwinter. Adult flies emerge in the summer. Early-maturing apple varieties are more severely affected. Apple maggots may also feed on crabapple and hawthorn. For more information, see WSU Extension Publication EB 1928, Protecting Backyard Apple Trees from Apple Maggot.
Apple-and-thorn skeletonizerAppleInsectThe 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 brown and papery and drop prematurely.
Brown marmorated stink bugAppleInsectThe 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 pear, 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 mothAppleInsectThe gray wings of adult codling moths are marked with dark brown bands near the wingtips. Wingspan is 1/2" to 3/4". 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 larvae are cream-colored to pinkish-white with brown heads and about 3/4" long. The 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 armywormsAppleInsectCutworms 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 spend the day just beneath the soil surface or under debris near the host. They usually feed at night, so it is advisable to search for them with a flashlight in the dark. Weeds are the primary food source for cutworms.
EarwigsAppleInsectEarwigs are reddish-brown insects about 3/4" or less in length. Both males and females have pincers at the rear end. Earwigs are largely beneficial, feeding on many pests such as aphids (including apple aphids), mites, and nematodes, as well as on algae, fungi, and decaying plant material. However, earwigs can also damage plants. They sometimes feed on flowers, shoot tips, leaves, or fruit. Damaged shoot tips may fail to develop properly, sometimes stunting growth. Damaged leaves exhibit small to large holes. Fruit damage consists of shallow, irregular areas chewed into the surface.
Fruittree leafrollerAppleInsectThe larvae of the fruittree leafroller feed on leaves, flower parts, and sometimes young fruit. They are pale to dark green with a shiny black head and are about 3/4" long at maturity. Typical symptoms of leafroller feeding include leaves that are rolled and tied in place with webbing and shallow surface damage on the fruit. The caterpillars are active when disturbed, wiggling vigorously or dropping to the ground on a thread. Larvae are usually mature by the end of May, and adults may be found any time from early June to mid-August. The adult moth is 1/2" to 3/4" long and mottled tan and brown. Other leafrollers may also be found on apple.
LeafhoppersAppleInsectLeafhoppers are typically found on the underside of leaves. Immature leafhoppers (nymphs) are usually less than 1/10" long and white to greenish or yellowish in color. Adults are white and about 1/8" long. Leafhoppers somewhat resemble aphids but are larger and more active. They feed by sucking plant juices, often causing damaged leaves to develop a white to yellow speckling or mottling. Severely damaged leaves may turn brown and shoots may curl and die back. Feeding leafhoppers produce honeydew, a sweet, sticky material which may attract ants or become covered with a dark growth of sooty mold. Honeydew may be present on leaves and fruit. Leafhoppers rarely cause serious damage to plants, although very heavy infestations may result in premature leaf drop and small fruit.
LeafrollersAppleInsectCharacteristic signs of leafroller feeding include leaves that are rolled and tied in place with webbing, often with frass in the webbing. Damaged leaves are often near shoot tips and may be skeletonized or chewed. Leafrolling caterpillars on apple are usually green with light to dark brown or black heads. The caterpillars may be up to 1" in length at maturity. The adult moth of the obliquebanded leafroller, a common pest on apple, is an orange-brown, bell-shaped moth about 1/2" long. The adult of the pandemis leafroller is a buff-colored moth with tan bands on the wings. Fruittree leafrollers may also be found on apple.
Lecanium scaleAppleInsectLecanium scales are shiny brown insects found on twigs. Adults are 1/8"-1/4" in diameter and roughly turtle-shaped. They may have light markings or appear somewhat waxy. Crawlers (immature scales) are flatter. Scales produce large amounts of honeydew, a sweet, sticky material which may attract ants or become covered with a growth of dark sooty mold. Branches with heavy scale infestations may be wilted, yellowish, or show other signs of stress. New growth may be stunted or lacking. Lecanium scale is a common pest in the landscape, infesting many plants including dogwood, maple, rhododendron, willow, and most fruit trees.
San Jose scaleAppleInsectSan 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 develop sunken spots surrounded by reddish areas. The scale overwinters as black immature scales on bark.
Spider mitesAppleInsectEuropean red mites and other spider mites can cause damage in apple trees. The European red mite is a tiny red mite. Other spider mites vary in color from yellow to green to black, depending on species and age. Spider mites typically feed on the underside of leaves, causing yellowish to brown speckling of the leaves. Mites are usually accompanied by webbing on and between leaves and twigs. European red mites produce less webbing than other species. Mite infestations are worse in hot, dry, dusty conditions. Heavy infestations can cause leaf drop. Apple rust mites may also be present and may cause russeting of 'Golden Delicious' fruit. The presence of rust mites is often considered advantageous, as they are a food source for predatory mites which help control spider mite populations.
Tent caterpillarsAppleInsectTwo species of tent caterpillar are common in Washington. The forest tent caterpillar is about 2" long at maturity and has a bluish body with black and white markings. This species makes silk mats on branches and trunks. The western tent caterpillar is the most common species in western Washington. It is dark with orange and black markings. Characteristic tents are made on the tips of branches. Young caterpillars typically feed in large groups in the protection of the nests. Older caterpillars feed in small groups or as individuals. Tent caterpillars are present in spring and early summer. They can partially or completely defoliate trees, causing some loss of vigor. Badly weakened trees may be killed, but damage is rarely this severe.
Tentiform leafminerAppleInsectThis small caterpillar larva mines the leaves of apple (primary host) and sometimes cherry, prune and pear. High populations in late summer can reduce fruit size in certain varieties. Parasites usually keep numbers down below damaging levels. Most years yield three complete generations and sometimes a partial fourth. They overwinter as pupae in fallen leaves.