Scales, Armored

Click on images to enlarge.

Florida Red Scale
Photo: Brian Bushe, CTAHR

Magnolia White Scale
Photo: Brian Bushe, CTAHR

Problem

Leaves of affected plants wilt, turn yellow, and fall off. There may be spots on leaves and twigs. Scales can infest the bark, fruit, twigs or leaves of shrubs and trees.

Description

Scales attack a wide variety of trees, shrubs and other perennials. Some scales do not cause much damage to plants, whereas others can cause devastating loss. It is important to accurately identify the species of scale because control is different for soft scales and armored scales. Using the wrong control method is not only a waste of time and money, it can actually make the problem much worse.

Immature scales and adult females have a round or oval shape. The adult females do not have wings, nor can you see a head or legs. The males are tiny and gnat-like and you are unlikely to ever see them because they only live for a few hours and do not feed.

Armored scales (Diaspididae) have a flattened, plate like armor that covers and protects the insect. This cover is not an integral part of the insect and can be removed from the body. They are less than 1/8 inch in diameter and often have a protuberance (like a nipple) in the middle of the armor. Females remain attached to the plant while feeding, and they have long, piercing mouthparts. Armored scales do not excrete honeydew.

Information

• Scales (University of California, IPM On-line)

Scale Look-Alikes

It can be confusing trying to correctly identify scale insects. There are other pests that look a lot like scale, for example coconut mealybug, parasitized whitefly nymphs, and redgum lerp psyllid (HDOA Pest Advisory: Red Gum lerp psyllid).

Coconut Mealybug
Photo: Brian Bushe, CTAHR

Parasitized whitefly nymphs
Photo: University of Florida, Entomology Department

Control

Armored scales are generally well controlled by natural predators such as, parasitic wasps, lady beetles, and lacewings. Do not use broad spectrum pesticides as these will kill the natural predators. You can encourage natural enemies of scale by planting blooming plants nearby and by trying to keep the dust off of affected plants.

If the infestation is too large, you can try using a horticultural (narrow-range) oil spray, making sure that you spray the undersides of the leaves as well as the top side and all infested branches. This is especially important when treating for armored scales since they are generally less susceptible to pesticides than soft scales.

Insecticidal soap or a soap and oil spray can be sprayed on the affected areas. Complete coverage of infested plants (such as the underside of leaves) is needed to obtain good control. You can also prune heavily infested branches if the entire plant is not affected. 

Provide optimal growing conditions for your plants so that they are vigorous and can fight off infestation. It also makes sense to select trees and shrubs that are well adapted to the environment. If you have plants in your yard that repeatedly are attacked by scale or other pests, consider removing them and planting something better adapted.

Chemical Control: See an extension agent or the UC Davis website above for more information on chemical control and use of horticultural oils. It is important to correctly identify the scale that is infesting your plants. One insecticide, for example, controls most soft scales but does not control armored scales or cottony cushion scale. This insecticide can actually increase cottony cushion scale populations on your plants because it is very toxic to the vedalia lady bird beetle, Rodolia cardinalis. This natural predator is poisoned by feeding on scales that have ingested the insecticide. When the natural predators in your yard die, the number of pests can skyrocket.

Kendal Lyon, Hawaii Island Master Gardeners