How to Control and Prevent Scale Insects

Scale insects are common pests, but not difficult ones to tackle if you know how to control and prevent them. Learn all about scale insects and how to get rid of them in this complete guide by horticultural expert Lorin Nielsen.

Clusters of tiny, circular, light brown bumps densely cover the surface of a green stem, some appearing slightly raised, with small parts of the green plant still visible beneath.

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Perhaps one of the weirdest pests in the garden is scale insects. At first glance, they might not appear to be insects at all. And because there are so many types, identifying them can be difficult. 

Scale insects feed on varying parts of plants, shrubs, and trees. What they consume largely depends on the scale species in question. Just like aphids, thrips, and spider mites, scale insects have host plants particular to their type. 

Because they can do a lot of damage quickly, it’s important to control scale insects in your garden or indoors on your houseplants. Infested plants need assistance as soon as possible. 

Let’s talk about scale and how you can keep them from eating up your trees and shrubs.

What Are Scale Insects?

Several small, reddish-brown raised bumps dot the surface of a green, thorny stem, surrounded by sharp, thin spines pointing outward, with the smooth green surface partially visible.
Females in certain species can reproduce asexually and do not need males to reproduce.

Appearance differs by type, but scale insects are generally circular to oval and about 0.1 inches long. They feed on plant sap within plant stems, and leaf tissue.

Adult females are much more visible than tiny adult males, who are white to yellow with one pair of long antennae and one pair of wings. Females in certain species can reproduce asexually and do not need males to reproduce.

There are several species of scale. Because they do not resemble other insects, and because they have such variance in appearance, it is important to know the types of scale to look out for. 

Types of Scale Insects

A group of small, irregularly shaped white and brown bumps are scattered across the surface of a grayish-green branch, creating a textured appearance against the smoother background.
Here is a list of the most common scale insects you’ll find on indoor plants, herbaceous plants, and trees and shrubs.

Species-specific controls make proper identification important. So here is a list of the most common scale insects you’ll find on indoor plants, herbaceous plants, and trees and shrubs. You’ll notice from this list that they are grouped into soft scales, armored scales, and miscellaneous species of scale insects. 

Coccidae

Tiny brown and white bumps cluster together along the length of thin, woody twigs, set against a soft-focus background of deep blue and green tones, creating a subtle contrast.
These soft scales flatten themselves against tree branches to feed.

The Coccidae are a family of soft scales that secrete a waxy coating that can protect them against many forms of insecticide, although any oily insecticide will likely stay on long enough to have an effect. They also produce red dyes emitted from carminic acid extracted from females.

One of the best-known soft scales in this family is Coccus viridis, also known as the coffee scale or green scale. Coffee scale is a major agricultural pest in coffee crops, especially compared to other soft scales.

Other species of wax scales or soft scales include tree dwellers like the cottony maple scale (Pulvinaria innumerabilis), brown soft scale (Coccus hesperidum), or the calico scale (Eulecanium cerasorum). These soft scales flatten themselves against tree branches to feed, which is why many people mistake them for a fungus or bacterial infection – especially with brown scale that blends into the stems of woody plants.

Other soft scales in this genus and their hosts:

  • Black Scale (Saissetia oleae): Almond, apple, apricot, aspen, bay, citrus, cottonwood, coyote brush, fig, fuchsia, grape, holly, maple, oleander, olive, palm, peppertree, pistachio, plum, pomegranate, poplar, privet, prune, rose, and strawberry tree.
  • Citricola Scale (Coccus pseudomagnoliarum): Citrus and hackberry.
  • European fruit lecanium, aka brown apricot scale (Parthenolecanium corni): A few evergreen species and alder, cottonwood, coyote brush, elm, fruit and nut trees, poplar, and toyon.
  • Frosted Scale (Parthenolecanium pruinosum): Walnut.
  • Irregular Pine Scale (Toumeyella pinicola): Monterey pine. 
  • Kuno Scale (Eulecanium kunoense): Stonefruit, especially plum. 
  • Oak Lecanium (Parthenolecanium quercifex): Live oak.
  • Lobate Lac Scales (Paratachardina pseudolobata): Woody dicotyledonous plants, southern red cedar, palm, and a few herbaceous species.

Diaspididae

A large, vibrant yellow leaf with several small, raised orange spots spreads out against the background, its natural veins standing out in contrast to the bright color.
Needless to say, these scales have an armor-like coating that they use to protect themselves.

This genus is specific to armored scales. Over 2650 species of armored scales exist. Needless to say, these scales have an armor-like coating that they use to protect themselves from predators or insecticidal sprays.

One of the most stubborn examples of armored scales is the San Jose scale, Quadraspidiotus perniciosus. This agricultural pest is widespread throughout the United States. While it was documented in the late 1800s in San Jose, it originates from China. In 1914, the San Jose scale was the first documented scale pest to develop resistance to insecticides

Another major agricultural pest in the armored scales genus is the California Red Scale, Aonidiella aurantii. While its primary target is citrus trees, it also feeds on olives and other fruit and can be found on some vegetables such as pumpkin.

Other armored scales in this genus and their hosts:

  • Cycad Scale (Furchadaspis zamiae): Sago palm and bird of paradise.
  • Euonymus Scale (Unaspis euonymi): Wintercreeper, boxwood, bittersweet, English ivy, holly, privet, honeysuckle, cliff green, Japanese spurge.
  • Latania Scale (Hemiberlesia lataniae): Kiwi fruit.
  • Minute Cypress Scale (Carulaspis minima): Mediterranean cypress.
  • Oystershell Scale (Lepidosaphes ulmi): Poplars and willows. Have oyster shell-shaped bodies.
  • Tea Scale (Fiorinia theae): Chinese and Japanese hollies, bottlebrush, dogwood, euonymus, ferns, mango, Satsuma orange, orchids, tea plant, and yaupon.

Miscellaneous Species

Clusters of soft, cotton-like white masses cling to the surface of a green stem, with wispy strands extending from the growth, contrasting sharply against the smooth plant surface.
Some scale insects don’t fall under soft or armored types.

Some scale insects don’t fall under soft or armored types. Here are some miscellaneous ones to look out for. 

Margarodidae
A delicate, star-shaped white structure with thin, thread-like arms spreads across the surface of a dark green leaf, creating a stark contrast against the smooth, glossy surface.
Many of them appear to be cottony or soft.

Ground pearls are strange-looking large scale insects. Many of them appear to be cottony or soft. Others look almost berry-like in their shape and coloration, such as the Armenian cochineal scale.

They are larger than most other forms of scale, mostly because of their cottony exterior. You’ll often find this scale with some ants on it, harvesting the honeydew which the scales provide.

Eriococcidae
Several round, dark brown bumps line the surface of a green thorny stem, nestled between sharp, outward-pointing spines, with the green background creating a muted, organic tone.
These scales look more like lumps or bumps on twigs and branches and can be mistaken for buds on the branch.

One excellent example of the Eriococcidae is the wooly beech scale, Cryptococcus fagisuga. These scales look more like lumps or bumps on twigs and branches and can be mistaken for buds on the branch.

Sapsuckers and other related scales are at risk from birds and beneficial predators like ladybugs.

Pseudococcidae
A small, fuzzy white bump clings to the surface of a deep green leaf, surrounded by fine strands of white, blending subtly into the softly lit environment.
Unlike most scale, mealybugs have legs, but they seldom if ever move once they’ve located a good feeding spot.

While most people don’t realize that mealybugs are a form of scale, they are. Unlike most scale, mealybugs have legs, but they seldom if ever move once they’ve located a good feeding spot.

Mealybugs are common greenhouse scale pests. Widespread throughout agricultural areas, they also attack many commercial crops.

Other miscellaneous species not mentioned above:

  • Ehrhorn’s Oak Scale (Micrococcus ehrhorn): Evergreen oaks in Southern California.
  • Cottony Cushion Scale (Icerya purchasi): Laurel-leaved snail tree.
  • European Elm Scale (Eriococcus spurius): American and Chinese elms.
  • Incense-Cedar Scale or Monterey Cypress Scale (Xylococculus macrocarpae): Incense-cedar, some cypress species, and junipers.
  • Kuwana Oak Scale (Kuwania quercus): Blue oak.
  • Oak Pit Scale (Asterodiaspis spp.): Valley oak, blue oak, English oak.
  • Sycamore Scale (Stomacoccus platani): California sycamore and London plane.

Life Cycle

Clusters of tiny, round, brown growths are scattered along a bright green twig, nestled among small leaves, with the natural curve of the twig subtly visible beneath.
Soft scales move around hosts and under the cover of bark as winter nears.

A scale population’s life cycles begin when scale eggs hatch. After the eggs hatch, scales go through varying numbers of nymph stages, called instars. Newly hatched nymphs begin in the crawler stage and are orange or yellow in most species.

In this life stage, they move around the surface of a host plant or make their way to others via the wind, people, or birds. Then most species of scale crawlers feed on plant branches or leaf matter. They may not move from that spot until they become adults.

Soft scales move around hosts and under the cover of bark as winter nears. It’s here that immature scales overwinter and emerge again in spring. In this case, there is only one nymph stage in their life cycle. In the case of scale insects that feed in climates that are mild year-round, they’ll remain present on their hosts the entire time. Insect development takes place out in the open.

Armored scales overwinter on their hosts and go through one nymph stage, and one as primarily adult female scales. They have multiple generations in one year, too. Because they don’t have prominent enough appendages, they stay in one place their entire lives.

Soft scales only have one generation per year – except for the brown soft scale, which has multiple. These scales can move around, but very slowly due to their small legs. Some female scales can hold eggs underneath their shells, while others hold eggs underneath their waxy scale cover.  

Identifying Scale Insects

A close-up view of the underside of a grayish-brown oval insect, revealing fine, ridged striations and slightly segmented details along its surface, with a dark, blurred background.
If it looks like an insect body, you’ve got scale.

One way to identify scale damage lies in knowing how to identify scale insects. If you see little bumps congregating on the leaves of ornamental plants or fruit trees, try popping one off with a q-tip dipped in rubbing alcohol or clear liquor. Then inspect the underside of the bump. If it looks like an insect body, you’ve got scale.

Some scales have an oyster-shaped shell or a waxy covering. Cottony cushion scales have a cottony covering

Another way to identify scale damage is to look for damage to particular plants. Some species stunt overall plant growth. Other species cause damage that appears at first like stress from underwatering and then progresses to the point of yellowing leaves and premature leaf drop. Some plants die, while other plants retain their brown leaves that have died from scale infestation. If the particular species of scale insects produce honeydew, it could progress to a sooty mold stage. This and ant harvesting honeydew may be signs you have scale. 

You should look out for a scale infestation, especially when it’s warm. This is when most scale insects are active. This is also when the beginnings of sooty mold take place, as ants tend to fend off scale insects’ natural enemies.

Most scale populations aren’t severely detrimental to your plants, but they can be. This is why it’s so important to protect your plants, trees, and shrubs as soon as you see scale covering varying parts.  

Control

Several light brown bumps cling to the rough bark of a tree branch, surrounded by sparse leaves and set against a backdrop of soft-focus greenery in the distance.
Scale control is important, especially because the presence of honeydew that some species secrete can turn into sooty mold.

There are lots of different ways to go about managing and eliminating scale. Scale control is important, especially because the presence of honeydew that some species secrete can turn into sooty mold.

Cultural Control

A hand tightly grips blue pruning shears, snipping a branch covered with rough brown bark, surrounded by lush green foliage in the background, with sunlight filtering through.
Always remove any scale-damaged branches, twigs, or leaves as soon as they appear.

Start with a good base of conditions for healthy growth. Ensure your irrigation schedule is consistent. Give plants proper nutrition and care. Pruning trees and shrubs to promote air circulation will prevent black scale, cottony cushion scale, and citricola scale infestations.

Always remove any scale-damaged branches, twigs, or leaves as soon as they appear. Destroy the removed parts rather than put them in the compost pile.

Another way to culturally practice scale control is to replace plants that are susceptible to scale. Trees, shrubs, and sensitive plants prone to a soft scale infestation can be replaced by similar trees that aren’t susceptible to damage. Dealing with infested trees that are fully grown can be difficult, so it’s best to make that decision before scale numbers have come to a head.

Finally, hand-removal of individual scale insects is a possibility. A cotton swab dipped in rubbing alcohol is surprisingly effective. The rubbing alcohol makes the scale release from what it’s latched onto, and you can dispose of the pest. Note that this method is meant only for one or two insects, and isn’t effective on large outbreaks.

Biological Removal

A hand gently wipes the surface of a vibrant green leaf, removing dust and debris, while the leaf remains attached to a plant surrounded by thick green foliage in soft lighting.
Dust is a deterrent to these garden friends, so ensure your plants are free of dust.

When it comes to biological control agents, you have lots of options – natural predators being one. By encouraging natural enemies of scale into the garden, you control scale infestations.

While it is possible to purchase beneficial or predatory insects (parasitic wasps, certain beetles, bugs, lacewings, and mites), this control method is more effective when you do so in conjunction with plants that host these natural enemies.

Dust is a deterrent to these garden friends, so ensure your plants are free of dust. If you’re working with parasitic wasps that use adult scales as a breeding ground, adult scales will become puffy and darkened. Another sign they’re doing good work is the presence of the larvae visible under the scale shell. This is especially visible in armored scale, where wasp larvae leave a hole in the scale shell.

Controlling ants is a huge part of preventing an uptick in scale populations. Not only does it prevent the spread of sooty mold, but it also removes scale protectors. Prune to prevent bridges where ants can get to canopies where scale is prevalent.

Alternately, wrap your trees in a protective covering and place a sticky surface on top of the paper to trap ants. Ensure there isn’t damage to bark by checking under the wrap consistently. There are also sticky paint types that can be used to trap ants, either on a removable protective coating or directly on the bark.

Remove accumulated debris or reapply sticky surfaces as needed to ensure ants don’t make their way across dirt or leaves that adhere to the trap. Ant bait is another viable option, especially slow-working baits. While they take time, they are highly effective.

Insecticidal Removal

Before you spray, establish a healthy habitat for beneficial insects.

Using insecticides in scale control should be the last-ditch effort. Ensure first that you’ve given your plants a good foundation to promote plant vigor, and that cultural controls have been attempted. Before you spray, establish a healthy habitat for beneficial insects.

Organic Insecticides

A person wearing a gray shirt sprays the leaves of a vibrant green orange tree with a handheld sprayer, standing among thick foliage with a blue sky faintly visible above.
Spray the plant thoroughly at infestation sites, especially at leaf terminals and the undersides of leaves.

Then start with organic controls like horticultural oils, neem oil, canola oil, and botanically derived plant oils. Insecticidal soap is another effective option. These should be applied in the morning before the sun rises or at dusk. Spray the plant thoroughly at infestation sites, especially at leaf terminals and the undersides of leaves. Do not spray an infested plant in hot weather, and follow up with reapplications every 7 to 10 days until the scale is gone.  

Horticultural oil sprays can also be sprayed on plants in dormancy. This is incredibly useful when it comes to armored scale which overwinters on trees in certain plant groups. Heavy infestations on oak trees can be sprayed just before buds open, in late winter or early spring. This method is not as effective on oyster shell scale, because they don’t have generations in winter.

You can also spray horticultural oil and insecticidal soap on an infested plant in spring and summer when immature scale insects have just emerged. Spray broadleaf plants in late spring and summer. Spray twig terminals and the undersides of leaves to cover the insect underneath.

Systemic Insecticides

A person uses a sprayer to apply a mist of insecticide to a tree trunk, which is partially covered in rough white patches, with a lush green lawn and trees in the background.
Trunk applications will be faster than soil injections, and some systemic insecticides can only be applied by professionals.

Aside from horticultural oil, systemic insecticides are another form of chemical control. Because systemic insecticides call for localized application in the form of injections, they may be better for the environment than horticultural oil.

Trunk applications will be faster than soil injections, and some systemic insecticides can only be applied by professionals. So weigh your options when it comes to chemical controls. It may be much easier to use horticultural oils or plant-based organic pesticides on ornamental shrubs and plants than it is to hire an exterminator.

Furthermore, systemic chemical control can sometimes cause a spider mite outbreak because they are damaging to beneficial insects, whereas horticultural oils do minimal damage or none at all if they are applied correctly. 

Prevention

A tree trunk is tightly wrapped with white duct tape, the sticky side facing outward, in a neatly wound spiral pattern, with the lush green lawn and trees in the background.
Consider the tree wrap option to catch any ants that might head up the plant to consume scale honeydew.

Scale insects tend to attack plants that don’t have a good foundation for healthy growth. Another thing that causes scale is planting plants that host-specific scale insects. For instance, if you plant camellias and holly plants, you’re providing habitat for tea scale. Instead of growing those plants, consider growing similar plants that aren’t hosts. 

Another thing we’ve discussed is controlling ants in your garden. If you’re going to grow hosts, keep the populations of ants down in your yard first. After you plant a host, consider the tree wrap option to catch any ants that might head up the plant to consume scale honeydew. 

Provide adequate nutrients and irrigation. The basis of these two foundational aspects of plant care is soil. Healthy soil retains enough water to handle moisture fluctuations. Nutrients provide adequate biofeedback that ensures plants are absorbing the water they need at the root level.

Another important way to prevent scale is to develop a significant habitat for beneficial predators, like parasitic wasps that lay their eggs under the shell of armored scale. 

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