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Plant NameTypeDescription 
AnthracnoseMapleDiseaseMaple anthracnose is a fungal disease affecting leaves and sometimes twigs. Infected leaves develop discrete brown spots and/or blotches, often at leaf tips and often associated with the main or secondary veins. Japanese maples tend to develop reddish-brown to light tan blotches. Small brown fruiting bodies may be seen in the affected areas. Diseased leaves of all maples may drop prematurely, sometimes resulting in severe defoliation. The disease occasionally causes twig cankers, where the fungus can overwinter. Cankers may also girdle twigs, causing tip dieback. The disease is favored by warm, wet springs.
Bacterial leaf spot and diebackMapleDiseaseBacterial leaf spot and dieback is caused by the same bacterium which causes bacterial blight of lilacs and many other woody ornamentals. Symptoms include leaf spots, blackening of leaf veins, and tip dieback. Leaf spots are initially small and appear water-soaked. The spots often have a yellowish halo and can expand in size, killing leaves and young seedlings. One-year-old twigs may die back during the winter, or shoots may die back in the spring. The disease is most common on Japanese, Norway, and red maples.
FasciationMapleDiseaseFasciation is a plant deformity which results in abnormally flattened stems. It is the result of a mutation in the growing point of the stem and is not a disease. Instead of being round, affected stems are flat or ribbed in appearance, and may be bent or curved in odd patterns. The leaves produced on the flattened stems usually appear normal, but may be somewhat undersized. Usually only a portion of a plant displays fasciation. Although not contagious, fasciation may sometimes be spread by seeds or through propagation of affected plant parts.
Leaf scorchMapleDiseaseLeaf scorch on maple has many possible causes. Plants that are under stress, such as drought or heat stress, may not provide sufficient water to the leaf margins, causing the edges of the leaves to turn brown and dry. In some cases, scorch may spread to areas between veins or entire twigs may die back. Trees placed near heat-reflecting surfaces, such as buildings or pavement, often suffer from heat stress. Excessive salts from overuse of chemical fertilizers may cause leaf scorch. Scorch may also be a symptom of damage to the roots or stem.
Nectria cankerMapleDiseaseNectria is a fungal infection which often attacks via wounds and forms cankers on twigs, branches, and trunks. The cankers are often sunken areas that develop conspicuous yellow to orange-red fungal fruiting bodies in the dead bark. Nectria cankers may girdle twigs and kill them or become elongated and enlarge year after year. Older cankers may develop a characteristic target or bull's-eye shape. Infected branches are susceptible to breakage in wind storms and should be removed.
Phyllosticta leaf spotMapleDiseaseSymptoms of Phyllosticta leaf spot on many maple species include the development of small (approximately 1/5 inch), roughly circular, brown spots with dark reddish or purplish borders. Japanese maples develop yellowish or tan spots, which sometimes have transparent centers. A circular pattern of black fungal fruiting bodies may be seen in the dead areas on infected leaves. On some maples, the diseased center portions of the leaf spots may fall out, giving a shothole appearance to the leaves. Infection occurs on wet leaves by water-splashed spores. Wet weather in spring and early summer favors disease development. The fungus probably overwinters on fallen leaves or on buds and twigs of host trees. This disease is not considered a serious landscape problem.
Powdery mildewMapleDiseasePowdery mildew of maple is a fungal disease which affects many hardwoods including maple, hazel, birch, and alder. On maples, a characteristic white, fuzzy or powdery growth appears on the upper or lower surfaces of mature leaves. Sometimes small black structures may be observed in the white areas. Shoots which develop late in the season may be distorted as a result of the infection.
Tar spotsMapleDiseaseTar spots are caused by a fungal infection that commonly attacks bigleaf maples and occasionally other species. In late spring to early summer, leaves develop small areas that appear water-soaked. The areas develop small, raised, glossy black tar-like spots on the upper side of the leaf between veins. The spots may develop in circular patches and are surrounded by discolored, yellowish to brown leaf tissue. Severe infections may cause some leaf drop. When leaves turn color in the fall, infected areas may remain greenish, giving a characteristic "green island" effect. Although conspicuous, tar spot infections do relatively little harm to plants.
Verticillium wiltMapleDiseaseVerticillium wilt is caused by a soilborne fungus. It infects plants via the roots and then spreads throughout the plant. Symptoms on the aboveground portion on the plant include suddenly wilted yellow or brown foliage which hangs on the branches. Symptoms of infection are often on only one side of the tree or scattered throughout the canopy, but may not be noticed until warm weather or other periods of stress. Infected maples may display greenish to black streaks when cuts are made into the wood and often develop long cankers on trunk or limbs. Infected plants may be killed or may tolerate infection for several seasons.
AphidsMapleInsectVarious species of aphids can occur on maples. They are typically small, yellowish-green insects that feed on the leaves and produce large amounts of honeydew, a sweet, sticky material. The honeydew may attract ants which feed on it, or it may become covered with a growth of black sooty mold. Aphid feeding may cause minor to severe leaf loss (especially on silver and Norway maples). Leaves that are damaged during growth may be curled or distorted.
Cottony maple scaleMapleInsectThe cottony maple scale feeds on the leaves, twigs and branches of maples and sometimes other ornamentals including dogwood, lilac, poplar, and willow. The conspicuous adults of this large scale are about 1/5" long at maturity, found on twigs and branches, and dark and flattened in appearance. The greenish-yellow crawlers (immature scales) feed on upper and lower surfaces of leaves in the summer and move to twigs in the fall. The large, white, cottony egg sacs are found on twigs and small branches. Cottony maple scale overwinters in the immature stage.
Maple bladdergall miteMapleInsectThe maple bladdergall mite is a tiny mite that feeds on the underside of leaves. The mites overwinter in cracks and under bark scales and begin feeding in spring. Infested leaves initially develop small depressions which soon grow into brilliant red galls 1/8" to 1/4" in length. Later in the season, the galls may turn green or black. Mite activity typically stops by around July. Silver and red maples are particularly susceptible to bladdergall mites. Severe infestations may cause leaves to become somewhat distorted. Although an aesthetic concern, bladdergalls are seldom harmful to the trees.