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Plant NameTypeDescription 
Bacterial blightFilbertDiseaseBacterial blight of filbert may attack buds, leaves, twigs, branches, and the trunk. Infected buds may be killed before leafing out. Leaves initially develop pale green, water-soaked spots, which later turn reddish-brown. Current-season shoots show dark green, water-soaked spots on the bark. These later turn reddish-brown and can girdle the stem, causing dieback above the lesion. Leaves often remain attached to dead shoots. One- and two-year-old twigs are also attacked. Infections may spread into main branches or trunks, where cankers may girdle and kill trees. The infected tissues may show a bacterial ooze in the spring, when most new infections occur. Bacterial blight is more severe on trees that have been damaged by frost, sunscald, or other problems.
Eastern filbert blightFilbertDiseaseEastern filbert blight is a fungal disease found on both cultivated and wild filberts. The disease typically infects via wounds caused by mechanical or insect damage. Buds damaged by the filbert bud mite may be particularly susceptible. Buds, twigs, and stems may be infected. The disease causes cankers, sometimes girdling and killing branches in summer to early fall. Cankers are typically somewhat sunken and may be surrounded by a ridge of callus tissue. The wood beneath the canker is stained dark brown. The bark of infected twigs may develop rows of bumps or pustules which split open to reveal white fungal fruiting bodies. The sticky white spores are released during wet weather through winter and early spring. The ornamental contorted hazelnut (Corylus avellana 'Contorta') may also be infected.
Powdery mildewFilbertDiseasePowdery mildew is a fungal disease found on leaves and succulent shoots of hazelnut. A characteristic powdery white growth occurs on the underside of leaves and sometimes also covers shoot tips. Young growth may be distorted, particularly later in the season. Small, dark fungal structures may be seen in the white mats. The disease often appears late in the growing season. It typically causes little damage. Powdery mildew development is favored by a combination of warm days, cool nights, and humid weather. The fungus can overwinter on the plant and on infected plant debris.
Apple mealybugFilbertInsectApple mealybugs are gray, flat, scale-like insects found on trees during winter and spring. They are typically found in cottony clusters on twigs and the underside of leaves, often on new growth. Mealybugs feed by sucking sap from the plant. Feeding may cause distortion of new growth. Mealybugs also produce honeydew, a sweet, sticky material which may attract ants or become covered with a growth of dark sooty mold. Apple mealybugs overwinter on twigs and branches of the host plants. They feed on many fruit trees and ornamentals.
Brown marmorated stink bugFilbertInsectThe 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. The type of injury to filberts depends on when BMSB feeding on the nut occurs. Damage by BMSB early in nut development may result in empty shells with no nuts inside. Damage later in the season causes corky areas to develop on the nut surface or in the nut meat. Other known tree fruit/nut hosts of BMSB include apple, pear, apricot, cherry, and peach. 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
Filbert aphidFilbertInsectFilbert aphids are small, yellowish-green, pear-shaped insects typically found on the leaves. Aphids are often found in colonies on the tender new growth. Heavy aphid feeding may result in stunting and distortion of leaves and shoots. Severe infestations may cause foliage to show signs of water stress. Filbert aphids produce honeydew, a sweet, sticky material which may attract honeydew-feeding ants or become covered with a growth of dark sooty mold.
Filbert bud miteFilbertInsectFilbert bud mites are tiny eriophyid mites which feed in the leaf and flower buds. The mites are yellowish and sausage-shaped and are difficult to see with the unaided eye. Mite feeding causes the buds to thicken and enlarge, resulting in a condition called "big bud". The swollen, infested buds fail to grow normally and do not produce fruit. The buds turn dark reddish-brown as they mature.
Filbert leafrollerFilbertInsectThe filbert leafroller is a greenish caterpillar with a light to dark brown head. The caterpillars are about 3/4" long at maturity. They feed inside webbed or rolled leaves, typically near the shoot tip. They may also feed on buds. The adult moth is 1/2" to 3/4" across and has light brown to buff wings with darker markings. The filbert leafroller is also called the European leafroller and will also feed on apple, cherry, pear, and hawthorn.
FilbertwormFilbertInsectThe filbertworm is the larval stage of a gray to reddish moth. The adult moth has copper- to gold-colored bands across the forewings and a wingspread of approximately 1/2". The female moth lays eggs on or near the developing nut. Emerging caterpillars bore into the nut through the base of the husk. The caterpillars feed inside the nut, blackening and destroying the kernel. Mature caterpillars are pinkish to white and 1/2"-3/4" long. They feed for three or four weeks before dropping to the ground to pupate.
Lecanium scaleFilbertInsectLecanium 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. Heavily infested branches may be wilted, yellowish, or show other signs of stress. New growth may be stunted or lacking. Twigs and small branches may be killed. Lecanium scale is a common pest in the landscape, infesting many plants including dogwood, maple, rhododendron, willow, and most fruit trees. Lecanium scales overwinter as immatures on the host.
Omnivorous leaftierFilbertInsectThe omnivorous leaftier is the caterpillar of a bell-shaped tortricid moth. The small larvae tend to be quite active when disturbed, often wiggling vigorously backwards or dropping from the plant on a silk thread. The caterpillars tie foliage together with webbing and feed inside the protective nest. The omnivorous leaftier also commonly feeds on foliage and flowers of cultivated flowers including asters, heather, chrysanthemum, and gladioli, as well as on strawberry fruit and legumes. Female moths typically lay eggs on bark or rough wood.
Tent caterpillarsFilbertInsectTwo 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.