Monitoring for Scale

Indian wax scale cover
Photo: Max Bertone 2016, NC State

Updated: February 28, 2023

Key points

Scale insects have relatively sedentary lives. Their small size and often-inconspicuous colors make them hard to detect.
Plant damage is not always evident until populations become fairly high.
Their waxy covers stick to leaves or bark and dead scale don’t always fall off of a plant right away, making populations look larger than they really are.

For soft scale only

Look for honeydew and sooty mold. Honeydew is a sticky waste product and sooty mold is the dark fungus that grows on it. Sooty mold is often the first noticeable sign of a scale infestation. It can be quite extensive when scale is abundant. Aphids and other sap-sucking pests also produce honeydew, so the scale may not be the only source.
Look for ants. They are attracted to honeydew and will protect this food source from predators. Ongoing ant activity on plants suggests scale may be present if aphids are not found.

twice stabbed lady beetle on leaf with sooty mold — Sooty mold growing on a honeydew-covered leaf. The presence of the twice-stabbed ladybird beetle, a beneficial helping to manage the scale, suggests the pest is active.
Photo: Mengmeng Gu, Texas A&M AgriLife Extension Service, Bugwood.org

ants tending scale on a magnolia — Magnolia Scale tended by ants.
Photo: Sarah Vanek, Bugwood.org

For all scale

Look near plant damage. If you see yellowing blotches on leaves, check leaf undersides for scale, especially along the main veins or at the base of the leaf. If an entire plant is stunted, flowers poorly, has patchy dieback, or shows other signs of stress, check the bark on trunks or main stems for scale.
Look for crawlers. Their tiny size – smaller than a poppyseed or grain of salt – will be more visible with a magnifying land lens.

tiny Oyster Shell scale crawlers — Scale crawlers can be trapped on double-sided tape wrapped around a twig, though it can be challenging to distinguish them from dust, and the tape may get cluttered with debris. Magnification will be needed to verify crawlers are present.
Photo: Joe Boggs, OSU Extension

Know their life cycle. If you can identify the scale based on the host plant and scale appearance, investigate when to expect the crawler period. Many species have temperature benchmarks that herald this window of vulnerability.
Look for evidence of natural controls. By inspecting scale covers for holes (from parasitoid wasps), spot-checking mature scale for live individuals, and looking for predators (like lady beetles), you can determine if natural enemies are suppressing scale numbers well enough without intervention. Live scale will have a tender body and be easily squashed, leaving a wet residue; dead scale will be crumbly or dry, or so desiccated they won’t be very visible.

parasitized scale holes — Arrow points to parasitized scale cover

Plant Diversity

Landscapes with a variety of plants provide better habitats to support natural enemies.

Studies show that creating an ecosystem welcoming to birds, predatory and parasitic insects reduces pest problems eliminating or greatly reducing the need to use insecticides.

Learn more about creating a garden to attract beneficial insects.

Scale lookalikes

Juvenile stages of other pests that are fairly flat, oval, and tiny can resemble scale crawlers. Whitefly nymphs are the closest match in body type, plus they secrete honeydew, but in this case, there will be no older scale present nearby.

whitefly pupae can look like scale on the back of a holly leaf — Whitefly pupae look very similar to juvenile scale.
Photo: Joe Boggs, OSU Extension

If honeydew is your main sign of a pest problem, look for other sap-sucking insects, in addition, to scale - leafhoppers, aphids, or whitefly.

white planthopper nymphs can look like scale — Planthopper nymphs with waxy coatings can look like cottony scale
Photo: Joe Boggs, OSU Extension

Colonies of flat lichen on bark might resemble an outbreak of scale, especially since they can be clustered and numerous. Lichen is harmless to trees and may easily detach, but won’t have the even convex or oystershell shape of scale covers. They are often much larger than scale.

Adventitious or extra, small roots growing on a tomato stem — *Adventitious root buds on a tomato stem*

It only takes gentle prying to remove scale covers from plant surfaces. Some naturally-occurring bumps or spots on plants can resemble scale, but these will not easily detach. They include adventitious root buds and lenticels, which are pores in bark for gas exchange. Certain plant species have more obvious lenticels than others; one example is the bark of young cherry trees (Prunus).

Aphid mummies, parasitized by wasps, are scale-like in being hardened, wingless, rounded, and tan. However, they tend to be surrounded by healthy, live aphids, and are not as numerous as a scale infestation.

The larvae of some beneficial insect predators camouflage themselves to avoid being eaten and to better prowl their prey undetected - a “wolf in sheep’s clothing.” A few lady beetle species resemble mealybugs while they consume scale, and debris-carrying lacewings create a shell of lichen on their backs. The easiest way to confirm these are not scale is to nudge them - scale won’t crawl away.

lady beetle larvae that can be mistaken for scale — Some species of lady beetle larvae look very similar to mealybugs and scale

small black artillery fungus spores — Artillery fungus on white surface

Artillery fungi, which grow harmlessly on mulch, projectile-launch their spores as tiny sticky dark brown pellets which strongly adhere to any surface within about fifteen feet. Plants covered with these, especially on lower stems or foliage undersides, may look infested with scale, but this residue will actually be harder to remove than scale themselves.

(PDF) Artillery fungi