The graceful foliage and unique bark of birch trees make them a favorite garden tree. While there are numerous cultivars and species, almost all have the same susceptibility to certain pests. A healthy specimen should live 40 to 50 years. But because of the debilitating bronze birch borer, many die before they are 20 years old. Other pests may leave your tree weakened or with unattractive foliage. Protect your birch by watching for pests, giving it excellent growing conditions and properly using insecticides.
Bronze Birch Borer
The bronze birch borer (Agrilus anxius) can severely damage and kill birch trees. The insect will bore into the sapwood two-thirds of the way up, killing the tree's crown. Early symptoms include slightly raised and rust-colored tunnels. When the borer emerges, it leaves holes shaped like a capital D. Because trees stressed by drought or health problems are most susceptible, keep your tree healthy by fertilizing, controlling other pests and watering as needed. The river birch, heritage birch and red birch are the most resistant varieties. Systemic insecticides are available to battle the borer.
The birch leafminer (Fenusa pusilla) is a common pest found on birch trees. The leafminer, a small white worm, will eat out the middle of leaves, which then turn brown. Most damage will not exceed 40 percent of the tree, according to the University of Minnesota Extension. Heavy infestation of the leafminer can stress the tree and predispose it to attack by the bronze birch borer. The birch leafminer will appear on the tree in mid-spring after overwintering. Control the leafminer with a systemic insecticide.
Aphids are a common, but not serious, pest for birch trees. Symptoms of an aphid infestation include puckered marks on leaves, yellowing and twisted leaves, and leaves that appear to be dripping sap. This is "honeydew," which can lead to sooty mold. Severe aphid infestations can lead to leaf drop or dieback. Insecticides, or insecticidal soap for mild cases, can get rid of aphids.