Scale bugs are little insects that can infect cherry trees. They drill through the bark of the tree with their mouths, then drink the sap of the tree. In most cases, an infestation of scale bugs will not be noticed until it is substantial. While unsightly, in most cases, scale bugs cause few problems and can be easily controlled by biological methods.
Scale bugs that can attack cherry trees include black scale, calico scale, white peach scale, European fruit lecanium, Kuno scale and cottony maple scale. These are referred to as soft scales because they have soft bodies that are unprotected by a hard coat. Armored scale insects, including the San Jose scale, scurfy scale and greedy scale also attack fruit trees, including cherries.
Scale bugs often do not look like insects at all. They may appear as tiny discolored bumps or blisters on the surface of the plant. Many scale bugs can be found along the branches of the tree. They may be relatively inconspicuous, as with the black scale bug or the brown colored Kuno scale. Or they may be covered in a simple pattern of colors, as in the black and white spotted calico scale. In some scales, such as the peach scale, males are long and slender while females as more shell-like. The San Jose scale resembles small oyster shells that are stuck to each other and the plant.
Scale bugs feed by scraping away the surface of the bark of cherry trees. They then feed on the sap and other plant juices that exude from the wound. In some cases, as with the San Jose scale bug, the cherry fruit may also be affected, which can significantly diminish its value as a crop.
In most cases, scale bug infestations are more unsightly than threatening to the plant. Most scale insects produce little damage, unless the infestation is extremely severe. However, because some scale insects, such as the San Jose scale bug, can attack fruit, they can significantly diminish the value of cherries as a crop if left uncontrolled.
Biological controls are often the most effective way to treat scale bug infestations. These include the use of ladybugs, lacewings and parasitic wasps that feed on insects. Broad spectrum pesticides can also be used, but are often discouraged, because they also kill beneficial insects. During the dormant season, scale insects can be controlled with safer agricultural oils, which can be sprayed on cherry trees.