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Leaf Scorch: On maple (Acer species) trees a number of problems cause symptoms that are generally classified as leaf scorch. Scorch symptoms are light brown or tan dead areas between leaf veins or around the leaf margins. Occasionally the leaf margins are yellow or chlorotic. Scorch symptoms tell us that one or more of the following factors are affecting the tree:
Anthracnose: This disease is caused by the fungus Gloeosporium apocryptum. Leaves and buds may turn brown and die, followed by twig and branch dieback. Infected trees may be deformed with crooked and angular branches or witches’brooms” (clusters of shoots growing from one area of a branch). This disease is most severe during wet weather.
Prevention and Treatment: The most effective control is to replant with resistant trees. Spraying three times at two-week intervals with a copper fungicide (Hi-Yield Copper Fungicide, or Ferti-lome Black Spot & Powdery Mildew Control) or mancozeb (Bonide Mancozeb Flowable, Southern Ag Dithane M-45) starting when the leaves begin to unfurl in spring will provide control. Read and follow all directions on the label.
Bacterial Leaf Scorch: This disease is caused by the bacterium Xylella fastidiosa. Symptoms often start out as a marginal chlorosis or yellowing of the leaves before they fade to a drab green or brown color. Presumably the symptoms develop because of water stress within the water conducting vessels. Diseased trees lose vigor, and branches or entire trees may eventually die. The symptoms are most noticeable in late summer to early fall, following extended periods of drought. The bacteria are transmitted by leafhoppers and vegetatively through grafts and cuttings.
Prevention and Treatment: In general, practices that encourage root development and root function are recommended. Incorporate organic soil amendments into the soil to improve aeration and drainage of clay soils or to improve the water holding capacity of sandy soils. Irrigate during periods of drought. The disease has been suppressed by oxytetracycline injections, but not cured. A certified arborist should be contacted if chemical control is needed.
Phyllosticta Leaf Spot: This disease, also known as purple eye, is caused by the fungus Phyllosticta minima. On the leaves, spots appear with pale yellow centers and purple borders. The spots are irregularly round and ¼ inch in diameter. Black fruiting bodies of the fungus develop in a circle in the centers of the spots. These fruiting bodies occur in greater numbers on the upper leaf surface. Severe infection can result in partial defoliation of the tree. Often the disease goes unnoticed until leaf accumulation occurs under the tree.
Prevention and Treatment: The fungus survives the winter in fallen leaves. In the spring spores are produced and dispersed to the new leaves of susceptible trees. Rake up all fallen leaves. Fertilization and watering may help to reduce the disease. ‘Autumn Flame’, ‘Tilford’ and ‘Gerling’ red maple varieties are relatively resistant to leaf spot. For chemical control use the same fungicides as listed for control of anthracnose.
Tar Spot: Tar spot is caused by the fungus Rhytisma acerinum. Spots arise in late spring or early summer after leaves attain full size. At first the infected tissue is light green or yellow. Then, during late summer, raised, shining black, tarlike dots develop within the yellow spots on the upper leaf surfaces. The lower surface of a leaf beneath a large tar spot turns brown, but the surface beneath speckled tar spots remains yellow. Leaves with multiple spots may wither and drop prematurely, but seldom so early or in such quantities as to threaten the health of the tree.
This disease is more common in the forest, but may be seen in some landscape situations. Tar spots are among the most showy and least damaging foliar diseases.
Prevention and Treatment: The fungus survives the winter in fallen leaves. Rake up and discard the leaves in fall. For chemical control use the fungicides recommended for control of anthracnose.
Aphids: Aphids are soft-bodied insects that range from 1/16 to 3/8 inch long. They may be green, yellowish, pink, gray or black. They feed by piercing plant tissue and sucking plant sap. They prefer feeding on new growth in such areas as shoots, buds and the undersides of leaves. As they feed on plant sap, they excrete honeydew (a sugary material). The sooty mold fungus feeds on the honeydew, resulting in unsightly, dark fungal growth.
Woolly alder aphid (Paraprociphilus tessellatus) is gray to black in color. It gets its name from the fluffy, white wax found on its abdomen. It requires alder and silver maple to complete its life cycle. Occasionally, it is found on red maple. Colonies of these pests are obvious because of their white, fuzzy appearance. They are usually seen on leaves, twigs or bark. Although infested leaves shrivel and drop early, the pests cause little permanent damage. As a result of the honeydew, sidewalks and cars become sticky.
Prevention and Treatment: Several natural enemies, such as ladybird beetles (ladybugs) and lacewings feed on aphids. As much as possible, these predators should be allowed to reduce aphid populations. Controlling this pest on a large tree using chemicals is expensive and often not practical. Since little permanent damage results from woolly alder aphids, tolerating some damage is a good choice. As a result of their phenomenal ability to reproduce, aphids are very difficult to control with insecticides. Leaving one aphid alive can result in the production of a new colony very quickly. In addition, the use of insecticides kills the beneficial insects that normally keep aphid populations under control. However, if natural predators do not reduce aphid populations sufficiently, the following foliar spray insecticides are recommended: esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), cyfluthrin (Bayer Advanced Garden Power Force Multi-Insect Killer Concentrate or Bayer Advanced Garden Rose & Flower Insect Killer Concentrate), and malathion (Ferti-lome Mal-A-Cide or Hi-Yield Malathion Insect Spray), (slight injury by malathion has been reported on maples). Treat when aphids appear and repeat at seven- to 10-day intervals, if needed. As an alternative, imidacloprid (Bayer Advanced Garden Tree & Shrub Insect Control Concentrate) can be applied as a drench around the root zone of aphid-infested plants and is systemically taken up by the root system for insect control. As with all pesticides, read and follow all label directions and precautions.
Scale: Many scale species¾ including Pulvinaria acericola, Pulvinaria innumerabilis and Melanaspis tenebricosa¾ are pests of maples. Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex and species. Some are flat and appear like scales stuck to a plant, while others appear like white cottony masses. They feed on sap by piercing the leaf, stem or branch with their mouthparts and sucking. Their feeding can weaken or kill branches. Heavily infested trees are stunted with small flowers and leaves. Leaves may yellow and drop early. Like aphids, they also excrete honeydew. The growth of the sooty mold fungus results in leaves that are dark. Adult scales are relatively protected from insecticides by their waxy covering. Their immature forms, called crawlers, are susceptible, however.
Prevention and Treatment: A combination of various natural enemies, including ladybird beetles (ladybugs) and parasitic wasps, usually keeps scales under control. In small trees with light infestations, scale can be scraped off or infested branches can be removed and destroyed. In a large tree, controlling scale chemically is not always practical. The size of the tree, the need for specialized equipment and the cost may prohibit this approach. If it is determined that chemical control is necessary, the recommended chemicals include the following: esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), cyfluthrin (Bayer Advanced Garden Power Force Multi-Insect Killer Concentrate, or Bayer Advanced Garden Rose & Flower Insect Killer Concentrate), and carbaryl (Sevin 50WP or Ferti-lome Carbaryl Spray). Apply materials when crawlers appear and repeat in 10 days. As with all pesticides, read and follow all label instructions and precautions.
Gall Makers: Maples often develop irregular growths or swellings known as galls on their leaves. Gall development is a reaction by the leaf tissue to feeding or egg laying by various mites (such as Vasates quadripedes and Vasates aceriscrumena) and insects (such as Acericecis ocellaris and Cecidomyia ocellaris). Galls vary greatly in appearance from wart-like bumps to spindle-shaped protrusions to felt-like patches on the leaf’s surface. Each insect or mite produces its own distinctive gall shape. Often the distinctive shape allows for identification of the pest. Galls typically develop in spring at about the time that leaves are expanding. Once the gall forms, the pest is protected inside the structure. When homeowners see these growths on the leaves of their maples, they often become quite concerned. It is important to remember that while unsightly, they do not cause permanent injury to a tree.
Prevention and Treatment: Since leaf galls do little, if any, long-term damage to the tree, control efforts are typically not needed or recommended. If a tree is small, the homeowner can handpick and destroy leaves before exit holes form to allow the release of the pest.
Asian Ambrosia Beetles: Japanese maples are among the more common hosts of the Asian ambrosia beetle (Xylosandrus crassiusculus), with other hosts including styrax, ornamental cherry (especially Yoshino), pecan, peach, plum, dogwood, persimmon, sweetgum, magnolia, fig, Chinese elm and azalea. This pest is attracted not only to damaged, stressed or transplanted trees, but to seemingly healthy trees as well. The beetle becomes active in early March (or earlier), and the female beetles bore into trunks or branch wood of thin-barked hardwood trees. Once a tree has been attacked, it becomes more attractive to further attack. Often these trees are less than four inches in diameter. Visible symptoms include wilted foliage, as well as the toothpick-like strands of boring dust (frass) that protrude from these small, pencil-lead size holes. The Asian ambrosia beetle does not feed upon the wood of the host, but instead carries with it an ambrosia fungus, which grows within the galleries made by the beetle. This fungus serves as a source of food, and may partially be responsible for the death of the host plant.
Prevention and Treatment: Heavily infested plants should be removed. If only a few braches are infested they may be cut out. The life cycle takes approximately 55 days until the emergence of the next generation of beetles, so prompt removal or burning of the wood is important. Protective sprays of other susceptible plants may reduce their spread. Permethrin (such as Green Light Borer Killer, Bonide Borer-Miner Killer, or Astro) may be used as a truck and scaffold limb spray. Thoroughly wet the bark. Multiple treatments may be needed during a season. Research indicates that spraying the infested trunks with permethrin may cause the beetles to leave the galleries they have already created. Since the beetles do not consume the host plant material, imidacloprid is ineffective.
Girdling Roots: If a tree shows symptoms of poor vigor such as small leaves, death of small limbs, top dieback or leaf scorch, the condition could be due to girdling roots. This problem occurs when a root entwines around another large root or the base of the tree and prevents or hinders water and nutrient movement. Often girdling roots occur below ground level, indicated by a lack of root flare at the base of the trunk.
Prevention and Treatment: The portion of the root that is girdling the tree should be removed. The open wound can be treated with wound paint prior to covering with soil. Fertilization of the tree after root removal will aid in recovery.
NOTE: Chemical control of diseases and insects on large trees is usually not feasible since adequate coverage of the foliage with a pesticide cannot be achieved.
Prepared by Marjan Kluepfel and J. McLeod Scott, HGIC Information Specialists, James H. Blake, Extension Plant Pathologist, and Clyde S. Gorsuch, Extension Entomologist, Clemson University. Revised by Joey Williamson, Horticulture Information Specialist, HGIC, Clemson University. (New 1/01. Revised 12/06.)
The Clemson University Cooperative Extension Service