The Beech Blight Aphid

Beech blight aphids are small insects that feed on the sap of their host tree and, in large numbers, ruin its appearance. Female beech blight aphids can give birth to other females without needing to mate, which allows these insects to replicate quickly. The beech tree species most commonly affected by beech blight aphids is the American beech, which is hardy in U.S. Department of Agriculture zones 3 to 9.

Beech Tree Aphids

Beech blight aphids are small, soft-bodied insects. There are many aphid species in many colors, but the beech blight aphid has a light blue color. Wax filaments that stick out from the abdomen of these aphids make them appear woolly. Beech blight aphids usually gather by the thousands on the undersides of leaves or on small branches.

Like all aphids, the beech blight species has specialized mouthparts that allow them to extract sap from their host tree. Aphids excrete a sweet waste product called honeydew, which in turn becomes a breeding ground for sooty mold, a type of fungus. The honeydew is also attractive to other insects, such as ants.

Beech blight aphids usually gather on the undersides of leaves or on small branches. Beech blight aphids are also known as "boogie woogie" aphids, says the N.C. Cooperative Extension, because of their habit of swaying the bottom half of their bodies when disturbed by potential predators.

Beech Tree Insect Infestation

The leaves of a tree infested with beech blight aphids will often wilt or turn yellow because of the lack of sap, according to the University of Kentucky College of Agriculture, Food and Environment. Even early on in the infestation, when few aphids are present, you might see the leaves become puckered and distorted because of the saliva these insects inject into the tree's foliage.

Because ants like to feed on the honeydew that aphids produce, a population of ants climbing up the trunk of a tree is often an indicator that the tree is suffering from an aphid infestation. A beech blight infestation usually becomes impossible to ignore around July. At its height, in September or October, a beech blight aphid infestation is impossible to miss: These insects often form colonies so dense that the branches of the infested tree appear as though they are covered in wool or snow.

Controlling Beech Blight Aphids

According to the Carnegie Museum of Natural History, neither beech blight aphids nor the black sooty mold that grows on the honeydew that the aphids excrete causes serious harm to a beech tree; however, both can be an annoyance. You can often spray these pests off tree branches using the water stream from a garden hose. Insecticidal soaps, horticultural oil sprays and some pyrethroid insecticides are also viable options.

A systemic insecticide called imidacloprid is highly effective at eliminating beech blight aphids, according to the University of Massachusetts Amherst. However, you must exercise some patience when using this method: It can take several weeks for this chemical to make its way up to the branches and leaves where the aphids will consume it. This insecticide should be applied in the spring when the soil has reached a temperature of 50 degrees Fahrenheit or higher and is no longer waterlogged from rain or melting snow.