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Plant NameTypeDescription 
Bacterial blightPoplarDiseaseBacterial blight of poplar causes leaf spots, which begin as small, dark, water-soaked spots. Twig dieback and branch or trunk cankers may also occur. Blighted shoots often turn black and appear scorched or burned as they die back. Infected tissues are less resistant to frost damage. Also, the bacteria often infect through wounds caused by frost injury. The bacteria are easily spread by rain, insects, and pruning tools. The disease is caused by the same bacterium that causes bacterial blight of lilac, euonymus, willow, and many other woody plants.
CankerPoplarDiseaseCanker of poplar is a fungal disease infecting twigs and branches of all sizes. The fungi enter twigs through wound sites and cause development of sunken, circular, brown cankers in the bark. Branch cankers are often associated with dead twigs and may grow down the branch and infect larger limbs. Bark beneath the cankered area turns black, and the wood is reddish-brown and appears water-soaked. Black, gray, or white fungal fruiting bodies may be present. Twig and branch dieback (with or without apparent cankers) is also associated with this disease. Weakened trees are more susceptible to infection. Injuries caused by heat, drought, frost, or other diseases can provide infection sites.
Leaf and shoot blightPoplarDiseaseLeaf and shoot blight is a fungal disease which affects poplars, aspens, and willows. The fungus infects succulent leaves and twigs. Mature plant tissues are resistant. Initial symptoms include the development of rapidly expanding dark brown or black spots on the leaves and shoots. Affected leaves and shoots are killed quickly, with the tissues turning dry and brittle. Killed shoots often tip over in a blackened "shepherd's crook". The fungi infecting poplars and aspens overwinter in infected shoots, but probably not in leaves. The disease can be spread by splashing water from the previous year's infected shoots to new growth.
Leaf blisterPoplarDiseaseLeaf blister is a fungal disease which infects the leaves of poplars. Leaves develop small to large yellow-green blisters or mounds on the upper surface. Severely infected leaves may be distorted. The undersides of the blisters develop a golden-yellow powdery or velvety coating or "bloom" which later turns brown. In early stages, the yellow bloom may be confused with rust. Rust, however, lacks the distinct, thickened, blistered areas common to leaf blister. Infection occurs following cool, wet weather in the spring. Infected leaves seldom drop. Although unsightly, leaf blister causes little real damage to trees.
Leaf rustPoplarDiseaseRusts of poplar are fungal diseases which usually require alternate hosts to complete their life cycle. They overwinter on the poplar leaves, then infect the alternate host in the spring (alternate hosts include pines, larch, and Douglas fir, depending on the rust species). Infection of new poplar leaves occurs around midsummer. Bright yellow or orange velvety rust pustules develop on either or both leaf surfaces (mainly on the underside). Severe infections cause leaves to develop large yellow areas. In fall, the rust pustules may also show dark brown areas, which are associated with dead gray to brown spots on the other side of the leaf. Heavy infections can result in considerable leaf loss. Rust fungi are favored by mild, wet weather.
Marssonina leaf spotPoplarDiseaseMarssonina leaf spot is a fungal disease which is favored by wet weather. Leaves develop spots or flecks which are initially bronze or brown with yellow edges. These spots enlarge and may involve almost the entire leaf. Later, the spots turn black and may have gray fungal fruiting bodies on the surface. Severe infections may result in premature leaf drop, which can reduce growth. Twigs may also be infected. The fungus overwinters in infected leaves on the ground. Trembling or quaking aspen (Populus tremuloides), Eastern cottonwood (P. deltoides), black cottonwood (P. trichocarpa), and balsam poplar (P. balsamifera) are typically infected.
CarpenterwormPoplarInsectCarpenterworms are the larvae of a mottled gray and black moth. The caterpillars are white to pinkish-red with a dark head and 1" to 3" long when mature. They bore in the trunk and main branches of poplar, elm, willow, locust, and other deciduous trees. Discolored or bleeding limbs, branch dieback, and lumpy or gnarled trunks are indications of carpenterworm infestation. Sawdust-like material (frass) and wood chips mixed with loose webbing on or around infested trees is typical. Adults emerge in early summer. Trees with severe carpenterworm infestations are susceptible to wind breakage and may need to be removed. Infestations may eventually kill trees.
Oystershell scalePoplarInsectOystershell scales are usually found on trunks, branches, and twigs. They occur infrequently on the leaves. Immature scales, or crawlers, are yellowish to white. They are typically present around June. Crawlers develop pinkish shells later in the summer. The hard-shelled mature scale is approximately 1/8" long, striped with grayish and brown bands, and elongated like an oyster or mussel shell. Infested plants may show off-color foliage, wilting, or other signs of stress. Heavy infestations can severely weaken trees. Scales can be spread from plant to plant by birds, people, wind, or other insects. Broadleaf trees, shrubs, herbaceous plants, and fruit trees are commonly infested.
Poplar petiole gall aphidsPoplarInsectAphids which cause galling of the leaf stem (petiole) are small, soft-bodied insects. The females lay eggs on tree bark in the fall. The eggs hatch in the spring, and the aphids move to and feed on the petioles, which react by enlarging and enclosing the insects. The hard, pale green, rounded galls form along the petiole or at the base of the leaf. Aphids inside the galls are grayish and waxy in appearance. The leaves are not damaged, but may be turned at right angles to the petiole. Aphids emerge from the galls in midsummer and fly to a summer host, where they feed on roots until fall. The aphids cause little damage to poplars, but may be serious pests on alternate hosts such as lettuce.
Poplar-and-willow borerPoplarInsectThe adult poplar-and-willow borer is a black and white weevil (a flightless beetle) about 3/8" long. The larvae are white, legless, and about 1/4" long at maturity. They feed by mining beneath the bark of trunk and branches. Feeding larvae expel large quantities of sawdust-like frass (excrement) through holes in the bark. Larval feeding may girdle branches, resulting in leaf wilt and eventual branch death. Severe infestations cause lumpy, swollen bark and bark scars with exposed wood. Old wood may produce large numbers of shoots. Willows are the preferred host, but the poplar-and-willow borer will also attack poplars.
Satin mothPoplarInsectThe caterpillars of the satin moth feed on leaves of poplars and willows. They may also occasionally attack oak and aspen. The adult moth is satiny and pure white, with a wingspan of 1 1/2" to 2". The caterpillars are voracious feeders, sometimes causing severe defoliation of trees. Mature caterpillars are approximately 2" long. They are black, with red and white patches and tufts of hairs along the sides.
Tent caterpillarsPoplarInsectTwo 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.