Scale Insects

Scale insects are landscape pests that thrive in our warm, dry, California environment. Scale insects affect many different types of plants, trees, and shrubs causing damage to leaves and sometimes, destroying the tree or plant itself. There are thousands of scale insects that can be broken down into several families, three of which are a major problem in landscape: Diaspididae, armored scales; Coccidae, soft scales; and Pseudococcidae, mealybugs. All are members of the same order: Homoptera — just like aphids. Though, to most growers, they refer to scale insects and mealybugs separately as “scales” or “mealies.” Whatever type of scale insect you may have, you can be sure of one thing – significant yield reduction; reduction in fruits, reduction in flowers. Typically, female scales attach themselves to a branch or leaf and don’t move for most of their life. You may not even realize you have a scale infestation because, in the case of armored scales, they may just look like little brown bumps. Males have wings but no mouths and live just long enough (about 6 hours) to mate, and then die. Armored scales (Diaspididae) are the largest family of scale insects and are generally very small. They can be one of the most difficult of scale insects to detect. Armored scales seem to be more of a problem on citrus and other trees then on greenhouse plants. One very common and major citrus pest is the California red scale (Aonidiella aurantii). Those brown spots on the lime you just picked are actually armored red scales. The red scale insect can be hard to control because of the waxy, protective “scale” the female exudes over her body. Soft Scales (Coccidae) are producers of honeydew which they emit from their rears while sucking sap from leaves or stems of a plant or tree. This sticky sweet substance discolors leaves, attracts ants, and encourages the growth of black sooty mold, a fungus that interferes with photosynthesis. Scale-damaged plants look withered and dying. Their leaves turn yellow and drop. Heavily infested plants produce little or no new growth. Scale insects are invasive and will infest other plants or trees in your landscape. If scale insects are not controlled, they can cause major damage to the point of killing your tree or plant. Mealybugs (Pseudococcidae) are white, soft-bodied scale insects with fringe that looks like legs all around their body. The fluffy looking cotton the females cover themselves in is actually a powdery wax coating where they hide their eggs. Mealybugs are also plant feeders that excrete honeydew and are found on many outdoor plants, bushes, and shrubs. Privacy bushes play a big host to mealybugs; you can often see them on the underside and upper side of leaves, usually with honeydew-seeking ants in tow. Damage to plants includes the same sooty black mold caused by honeydew excretion, slow growth, and dropped leaves.

Scale Insect Damage

Damage to trees and plants: Female scales insert their long sucking mouthparts into tree branches, leaves, and/or fruit to extract the sap causing trees and plants to appear water deficient with yellowing leaves and fewer flowers and fruit. Most damage occurs in late summer and early fall when scale numbers are highest and there’s less moisture for trees and plants. Severe infestations may result in the death of the plant or tree. Armored scales don’t produce honeydew but soft scales excrete honeydew in large amounts. This sticky substance drips on plants and promotes the growth of black sooty mold. Mealybugs spread easily and unlike other soft scale insects, move quickly. As they move, they eat. Next thing you know your plant isn’t looking to well. This can stunt plant growth and cause new growth to be misshaped.

Pest Control for Scale Insects

Armored Scales: The waxy covering of armored scale species protects them from contact with pesticides. Therefore, timing is important in treating armored scales. These scale insects are best susceptible to treatment in the first stage known as the “crawler.” If a branch is heavily infested with armored females, trimming and removing the most affected parts along with timely pest control treatment provides the best results. Treating frequently in early summer and late in winter, soon after scale crawlers are active can provide good control of armored scale insects.

Natural Predators of Scales and Mealies are parasitic wasps, birds, ladybugs, lacewings, and spiders.

Soft Scales: Some soft scale insects like the brown scale are year-round landscape pests but they can be controlled easily enough. Soft scales can be treated with horticultural oils and remain susceptible to oils during most of their life, especially when they are young. Mealybugs can also be treated (smothered) with oils. Rubbing alcohol helps remove their waxy layer making mealies more susceptible to treatment. Hearts Pest Management treats for scale insects (including mealybugs) and provides free landscape inspections. Please call today to schedule a free inspection and take back your landscape from scale insects and other pests!