Ace Landscaping Services Inc.

Tree and Shrub Problems - Scale Insects

Scale insects are often inconspicuous pests of many evergreen and deciduous plants. They can occur on leaves, twigs, branches or trunks. Their small size and general lack of mobility make them difficult to notice by the casual observer. Scales derive their name from the shell-like, protective covering they form over themselves. Scale insects are broken into two categories:

Soft Scales—generally secrete an attached, thin, waxy layer over themselves. The soft covering they secrete cannot be separated from the scale's body. Soft scales typically move between branches and leaves during their lifecycle. They also produce honeydew.

Armored (Hard) Scales—use shed skins and wax that is unattached to their body to form their hard, shell-like cover. These covers can be separated from the scale's body. Hard scales typically do not move to leaves during their lifecycle and also do not produce honeydew.

Immature scales, upon hatching from eggs, are soft-bodied, mobile and are termed "crawlers." These crawlers seek suitable sites in which to feed, secrete their protective shell, and mature to adulthood. The immobile, "shell stage" of scales are adult females; males are small, fly-like and infrequently seen.

Natural controls (parasitoids, predators, pathogens, environmental conditions) usually maintain scale populations below damaging levels. Also, maintaining healthy, vigorous plants through proper watering, fertilization and pruning (including removing scale-infested branches), will often increase a plant's ability to withstand pest pressure. However, under certain circumstances, scale populations can increase and become injurious. Once scales begin adversely affecting plant health, management measures should be taken.

Scale insects cause damage by removing vital plant fluids from their hosts using their sucking mouth parts. Leaf and needle stunting and yellowing, twig and branch dieback as well as plant death are possible depending on population levels. In some instances, scales weaken plants making them susceptible to damage from secondary pests such as borers or environmental extremes, which may ultimately kill the plant.

Scales can also create nuisance problems by producing a sticky, sweet substance called honeydew, which they secrete while feeding. The stickiness and associated black sooty mold that grows on the honeydew can be an annoyance if cars, patio furniture, decks, etc., are underneath scale-infested trees.