Maple trees (Acer spp.) are desirable for their distinctive foliage and beautiful autumn colour. These trees range broadly in size and shape, from the small, delicate Japanese maple to giant trees that can grow to heights of over 100 feet. Often used in the home garden as shade trees, maples can suffer from insect pests that attack the wood and sap of the tree.
Types of Bugs
Maple trees can be bothered by boring insects and sap-sucking insects. Aphids, which are tiny green, black or even pink bugs, often cluster on the undersides of leaves or on new shoots and buds. These insects suck the sap of the tree. Scale is another sap-sucking insect. Depending on the species, they appear as small, white fuzzy bugs or as small, round flat brown bugs. Scales tend to cluster along slender branches. Asian Ambrosia beetles are wood-boring insects that commonly attack maple trees, especially Japanese maples. These bugs bore into the wood of the tree and while they don't consume the wood, they do carry a fungus that infects the tree. Other bugs found on maple trees include mites, flies and caterpillars.
Effects of Infestations
Sap-sucking insects destroy leaves and new shoots before they even have a chance to uncurl. Heavy infestations can even kill small branches of the tree. If leaves do emerge, they are often small and yellow and may drop early from the tree. In addition, sap-sucking insects excrete a sticky substance called honeydew, which attracts fungal spores. The spores stick to the substance and multiply, covering the leaves and branches with a black, grey or white fungus. Maple trees infested by wood-boring insects will begin to wilt all over and will have telltale holes and sawdust in the trunk or branches. Growth will be stunted and the tree may die. Mites and other insects that lay eggs in the wood of maple trees are often the cause of gall development. The leaf and wood tissue of the tree reacts to the feeding and egg-laying of these insects by causing a growth to appear. This growth is usually large and bumpy and is called a gall. Galls appear on the wood of the tree or on the leaves. While unsightly, they do not pose a threat to the life of the maple tree.
Management depends on the type of infestation. Heavily infested branches should be pruned off, especially in the case of wood borers. Maple trees affected by wood borers can also be sprayed with an insecticide containing permethrin. Apply the spray directly to the trunk and branches. Control aphids and other sap-sucking insects with insecticides containing esfenvalerate, cyfluthrin or carbaryl. Apply the insecticide when you notice the bugs crawling and repeat after 10 days. Follow the directions on the label for specific application instructions based on the size of your tree. Chemical treatment for galls is not recommended, according to Clemson University.
Many maples grow very large. If your tree is big, you may not be able to use the insecticide effectively. On the other hand, insect populations on large, healthy trees are not usually life-threatening to the tree. In such cases, the best choice might be to leave the tree alone. Small, unhealthy trees are the most vulnerable. For that reason, keeping your tree healthy is the best prevention for insect infestations, because even if the bugs invade your maple tree (and they probably will), your tree will easily be able to withstand them. To keep your tree healthy, plant it in a location with rich, well-draining soil and at least partial sun. Maples have thin bark (which is why wood boring insects often plague them), so take care to avoid damaging the bark when using gardening implements around the tree.