What's Bugging You? Scale

Scale can be light brown, dark brown or white. In a warm, dry environment they will multiply quite rapidly.

Scale is a tiny sap sucking insect pest of indoor tropical plants and outdoor trees and shrubs.  Scale is not that easy to spot as the females produce a protective dome-like coating over themselves that may or may not be attached to their bodies.  This coating prevents many contact insecticides from killing the pest.  Their coating shapes differ but are usually round, oval or oyster shell like in shape.  Some even resemble flattened snail shells!  Scale can be light brown, dark brown or white.  In a warm, dry environment they will multiply quite rapidly.  Females will often reproduce without mating.  The males of some species become winged adults and look like tiny fungus gnats.  They are rarely seen and do not feed on the plants. 

Scale often appear in clusters on branches, twigs, in leaf joints and the underside of leaves. Like aphids, most species exude a sticky substance while feeding.  This is a tell-tale sign of scale and a large outbreak can cause large sticky areas on a heavily affected plant.   Ants are attracted and feed on the honeydew and are often mistaken for being the reason a plant is doing poorly. 

In our climate, scale will attack:

  1. Outdoor shrubs - Dogwoods, cotoneaster hedges, roses and lilacs.
  2. Trees - Willow, aspen, ash, apples and crabapples.
  3. Most indoor tropicals can be attacked; even cacti and succulents.

Plants with scale will begin to show slow growth, yellowing of leaves, wilting, and leaf drop. There are two groups of scale:

Hard Scale (Armored)

Hard scale create a body covering that is very hard and durable.  This coating is not attached to the insect’s body.  The insect feeds under this shell, laying eggs and producing baby crawlers who roam close to home and create their own hard coverings.  They do not secrete honeydew. 

Oystershell Scale 

Photo: Whitney Cranshaw, Colorado State Univ. Bugwood.org. Oystershell Scale- Insect Images

Oystershell Scale is a hard scale and attaches itself to the twigs and branches of aspen, cotoneaster, dogwood, maple, willow and lilac.  As their name implies, they are oyster shell shaped and light to dark brown.  A dusty wax covering sometimes appears on their hard protective shell.  They are hard to spot as a heavy Oyster Shell scale infestation will look like bark from a distance.  When checking your plants take a close look at the branches, twigs, and leaves.

The eggs overwinter with their mother under her shell.  The eggs will hatch in mid to late spring. Adult females mature in mid-summer and then in fall lay the over -wintering eggs. In cool climates, Oystershell Scale produces one generation per year.

Pine Needle Scale

Photo: Kansas Dept of Agriculture: Insect Images

This species of scale occur on pine and spruce.  In North America, male pine needle scales are few and far between.  The females are white and manufacture a hard white shell.  The females may live and produce eggs through the winter and early spring.  In mid spring the newly hatched crawlers will emerge from under their mother’s protection and travel to a permanent feeding spot on the needles.  Hard body coverings are created and the cycle begins again. 

San Jose Scale

Photo: Mourad Louadfel, Homemade, Bugwood.org. Insect Images. San Jose Scale on an Apple.

San Jose scale is prevalent throughout North America.  It primarily affects trees and shrubs in the rose family such as apples, crabapples, and cotoneaster.  This scale can also affect the skin of the fruit.  Males produce a small cover which is narrow and oval.  Female bodies are yellow and produce hard covers that look like snail shells with a tiny yellow bump in the middle of the “shell”.  In winter the nymphs will remain dormant until spring.  By the end of April they have reached adulthood. Males and females mate and the eggs are laid under the hard cover. The nymphs will reach adulthood in a month or so and then repeat the life cycle.  In North America two generations are produced in a season.

Soft Scale

Soft Scale produce a waxy coating that is part of the body.  They move short distances or stay stationary.  They can produce a large quantity of honeydew.   There are over 1000 species of soft scale that occur in North America. They are broadly oval in form and swell when eggs are developing under the cover.   

Brown Soft Scale

Brown Soft Scale is a common houseplant pest.  Females are light brown, oval and generally flattened in shape. Males are rare.  The adult females lay eggs under their protective coating and they hatch over a period of 1-3 weeks.  The baby ‘crawlers’ come out from under the covering and travel throughout the plant until they find a good feeding spot.  As they eat they will develop their own protective coatings and remain in place to start the cycle once more.  Brown Soft Scale are very prolific and will have several overlapping generations per year. 

Hemispherical Scale

Hemispherical scale is dark brown and has a round helmet shape.  Females will die after laying their eggs. The eggs will hatch under the female’s cover and then crawl out to find a permanent feeding spot on the affected plant.    

What Can I Do to Get Rid of Scale?

Check out our "How To" on treating scale! Read on for quick tips!

Make a habit of routinely doing checks for scale (and other insects) on your houseplants and outdoor trees and shrubs including evergreens.  This is the most important step you can do.

Prune off affected branches, twigs and/or leaves. Do not compost.  Dispose of affected plant material in the garbage.

Ladybugs and lacewings are natural predators of the crawler or young larval stage.   

If you suspect you have scale on an indoor plant, isolate that plant and carefully check any plants that were near to the affected plant. 

If numbers are low you can remove them by hand or with an alcohol soaked cotton swab, rubbing them off with the tip. 

Dormant oil applied on outdoor shrubs and trees in late winter or early spring before bud break are very effective in smothering overwintering pests including some species of scale.  Please read the labels carefully for specific time of application, temperature windows and trees, shrubs that cannot be sprayed.  Do not use on indoor houseplants. 

FYI – Mealybug is a form of scale!

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