Scale Insects

To the untrained eye, a tree or shrub may look unhealthy or unsightly for no apparent reason. Upon closer inspection however, the culprit may be present in plain sight.

Scales are tiny insects that feed on plant sap, and certain species of scale may injure plants. In large numbers, scales may cause significant damage to trees or shrubs if left untreated. Because of their miniscule size, these insects may go unnoticed until it may be too late to revive a landscape plant. Monitoring visits are important in this regard, as technicians will visit customer landscapes with the changing seasons in order to be on the lookout for cryptic threats such as these.

There are two main types of scales, armored scales and soft scales. Armored scales produce a waxy, hard coating overtop of their bodies acting like a shell, protecting the insect from the environment. Euonymus scale, pine needle scale and oystershell sales are a few examples of armored scale. Armored scales can have several generations a year and usually spend the winter as eggs, first instar nymphs (first growth stage), or as a mature female (depending on species and location). Eggs usually hatch late May or early June. Once scales hatch from their eggs they are called crawlers. Unlike the adult scales, the crawlers are mobile insects which travel to the leaves to feed during the summer and migrate to the twig before the leaves drop in the fall. Using a long mouthpart called a stylet, which is usually 6 to 8 times as long as the insect itself, the straw-like stylet is inserted into the plant tissue to feed on sap. Once the crawlers produce the waxy, armored coating, they lose their legs and become immobile. If a plant is heavily infested with scale, not enough sap is left for the plant to maintain proper vigor for growing and the plant will begin to decline.

Soft scales, appropriately named are soft compared to armored scale, they do not produce a shell-like coating, merely a waxy, penetrable coating. They are generally larger in size than armored scales. A few examples of soft scales are cottony maple scale, magnolia scale and lecanium scale. Soft scales usually have only one generation per year and generally spend the winter as second instar nymphs (second growth stage), and remain attached to twigs. They complete their development in the spring when the females lay eggs. Soft scale eggs hatch later in the year than armored scales, usually in late June or early July. When soft scales feed on plant sap, also with a stylet, they produce a sugary liquid called honeydew. The honeydew attracts ants and flies. If scales are in large in number, there can be so many wounds on the tree or shrub that sap can drip, creating sticky sidewalks and landscapes. A black fungus called sooty mold eventually
also sets in to feed on the honeydew.

Here at Integrity Tree Services, we have had many phone calls from Tree & Shrub Care customers regarding their trees or shrubs looking unhealthy. Occasionally, upon inspection the culprit for the plants’ decline is scale. The significance in the scale infestation depends on the species of scale, the size of the population, the species and value of the plant the scales are affecting as well as other environmental factors. Not all scales are harmful to landscape plants. Scales usually feed on plants that are already stressed, however, it is perfectly normal for a tree or shrub in the landscape to house some scale. Scales have many predators in the landscape such as parasitic wasps, ants, lacewings, ladybugs, beetles and mites; an abundance of predators may not warrant chemical action. Sometimes, if simply a branch is infested, just pruning the branch can be enough to prevent infestation.

If a landscape plant has significant value, is heavily infested with scale and if natural predators are not abundant in the landscape, chemical control can help fend off scales. If you’re suspicious that scales are a reason for the decline of you tree or shrub, please feel free to call us to set up a free estimate with one of our certified arborists. Call (616) 301-1300 extension 118 to schedule an appointment. We can help determine if scale is present, if it is harmful to your landscape and if chemical treatments could be beneficial to the health of your plant. As usual, the easiest method
to prevent infestation is prevention. Keeping your landscape plants healthy with proper irrigation and maintaining optimum, growing conditions can make your plants more resistant to insect infestation.