Plant scale insects come equipped with piercing/sucking mouthparts and are widespread around the world.
They appear as slightly raised bumps on the stems, twigs, branches, and foliage of all sorts of plant life.
They can be tough to see because in the adult stage they do not move around.
Instead, they hide carefully under camouflaged waxy constructions that blend right in with the host plant. This scale cover or waxy shell is what gives these insects their name.[toc]
The adult bugs secrete a waxy substance and construct a shell or shelter that protects them against predators, the environment, and most insect management methods.
In this article, we will look at the various types of scale insects and share information to help you recognize them and deal with them. But first below are some quick tips for treating scale on plants.
Read on to learn more.
What Does Scale Look Like On Plants?
To prevent and manage a scale insect infestation, you need some knowledge of the biology and life cycle of these little pests. It is important to understand and recognize the vulnerable life stages of the creatures.
There are several types of scale insects commonly referred to as armored scale and soft scale.
The scale coverings they create protect both varieties throughout most of the life cycle.
It’s important to understand that the scale is not an attached shell. It is a protective barrier ranging in texture from hard and slick to somewhat flexible to soft and cottony.
The common “body” color of plant scale is brown, but scales can also be black, dark red, white, yellow, pink, gray, green, or glassy and transparent.
The fluffy or wooly scale insects are Australian immigrants. They are a bit larger than the other types and are easy to see because of their fluffy, white scale structures.
Scale Insect Size, Appearance, And Behavior
Soft scale insects measure between a 1/8 and a 1/4 of an inch long. They are convex in shape. This variety of scale insect feeds on a plant’s phloem tissue. This is the vascular tissue of a plant responsible for conducting metabolic products, such as sugars down through the plant from the leaves.
Soft scale insects excrete the excess sap they get from the phloem to produce a sweet, sticky substance called honeydew. You’ll see this substance and the insects it attracts on the leaves and stems of a bush, plant or tree infested with these pests.
If you notice the leaves of your plant are stuck together, and the plant swarming with flies, wasps and/or ants, take a closer look.
You will probably see some sucking insect congregated on the branches. It may be soft scales, or you may find woolly aphids or regular aphids have infested your plant. These insects produce honeydew, too.
Armored scale insects don’t produce honeydew. They are a little smaller than the soft scale version, topping out at a 1/8 of an inch in length. These pests are usually elongated or oval in shape. They do not feed on the plant’s phloem. Instead, they eat individual plant cells.
Because of their small size and superior camouflage abilities, armored scale insects are a bit harder to see. Their hard shells often match the surface of the host plant.
They can escape notice until they become very well established and the plant begins to suffer.
The Biology Of Scale Insects
In addition to providing adult insects with a hiding place, the manufactured scale also provides a safe place for the female insect to lay eggs.
When the eggs hatch, crawlers (aka nymphs) are released. They move from beneath the scale and seek out locations of their own on the host plant and/or on neighboring plants.
Soft scale nymphs go through two growth stages (aka instars) before settling down to build their scale shelter and lay eggs.
The crawlers usually move out onto the host plant and feed on the foliage during the first growth stage.
During the second stage, the nymphs move back into the branches and twigs of the plants to finish growing and build their protective scales.
As crawlers, armored scales move to new plant tissues and settle right in to eat and to build their scale covering. They do not typically travel far, and their shelters are usually pitched very near the parent scale.
Once scale crawlers reach a suitable destination, they settle in and build a waxy shell to cover themselves.
With this accomplished, the armored scale variety shed their legs and are no longer mobile. They stay in the same place for the rest of their short lives.
Soft scale insects keep their legs and can move about, but do so very slowly.
When fully mature, female scale insects of both sorts mate with males, which have wings.
The males are very elusive, and you are unlikely ever to see one. After mating, the female insects lay eggs underneath their protective scales and then die.
Soft scale insects are capable of overwintering as either an adult or as nymphs.
Armored scale crawlers and adults do not do this.
Instead, the eggs overwinter beneath the protective shell left by the mother insect.
It is important to understand the difference in overwintering habits of these creatures, along with the timing of the nymph stages of both types.
This knowledge helps to determine how to best manage and eradicate the pests.
Stop The Crawlers Before They Spread!
It’s important to identify the type of scale insect you have and to catch it during the crawler stage to have the greatest efficiency with your extermination efforts.
You want to catch them right away after they emerge from the parent scale. In addition to moving about on their own, the tiny crawlers can blow onto neighboring plants by the wind.
They may also catch a ride on birds’ feet or as hitchhikers on other types of animals moving from tree-to-tree.
What Does Damage From Plant Scale Look Like?
If allowed to stay in place for more than one season, a scale infestation can spread very quickly.
It is possible for these pests to cover a plant before you notice their presence entirely. You may not see the damage done to the plant until the population level is nearly out of control.
When this happens, you will notice some signs of plant illness, along with the physical presence of the pests.
Typically, armored scale insects do more damage than soft scaled ones. This is due to the hard-scaled variety feeding on the tissues of plants and killing individual cells.
The death of the cells disrupts the plant’s ability to transport materials throughout its limbs, and entire branches die off.
When you notice branches dying on a plant, suspect armored scale insect infestation. Heavy infestation can result in plant death.
Leaf Discoloration and Loss:
Armored scales don’t feed only on individual cells in the stems and limbs of plants and trees. They may also feed on the foliage.
When this happens, leaves may turn yellow and purple.
It can be hard to tell if this damage is caused by hard scale insects because many other types of insects also produce this type of injury.
Clusters Of Scales:
Inspect the plant and its foliage carefully looking for the tiny, hard scales of armored scale insects. You will see both old, abandoned scales and the newer scales of active insects.
Both can be scraped off using a blunt blade or your fingernail. You’ll find the old scales scrape off easily, but the newer ones may be more difficult to remove.
Both types leave behind a white, waxy imprint.
Honeydew And Sooty Mold:
As mentioned, the presence of honeydew on a plant infested by soft scale insects should tip you off to their presence.
If you don’t catch it right away, you may also see sooty mold, which grows readily in the sweet substance. The mold does not damage plants, but it is unsightly.
Related Reading: Sooty Mold And Its Connection To Honeydew
Large Dead Zones:
When soft scale infestation is severe, you may notice individual limb damage before it reaches the foliage of a plant or tree.
In addition to limb death, soft scale insects also cause branch tip dieback and leaf deformation. These effects are visible across large sections of the tree canopy.
How Can You Control Scale Insects?
Organic scale insect control is the best and easiest method of managing these pests.
Ladybugs and parasitic wasps are beneficial insects and natural predators of scale insects. By maintaining a welcoming garden setting for them, you may never need to take steps to manage scale insects.
When biological control is not sufficient to deal with these scale pests, you will need to take steps to reduce the population.
Identification Your First Step
Your first step is identification. Once you identify the type of scale insect plaguing your plants, you can make plans to deal with the crawlers when they venture out.
It is best to deal with them immediately after hatching when they are actively seeking feeding sites. You want to catch them before they migrate and produce shelters of their own.
Monitor: Watch For Activity
Once you’ve identified the type of scale insects, begin watching for them just before you expect them to emerge from the parent scale. You may not be able to see them with the naked eye against the backdrop of the plant. Use a pocket magnifying glass like this for a closer look.
Verify The Crawlers Movement
Here are a few other tricks you can use to verify the presence of crawlers:
- Place pieces of double-sided tape on the branches of your plant, shrub or tree to trap a few crawlers when they emerge. Once you trap them, you’ll know it’s time to deal with them.
- Hold a white paper plate or sheet of white paper under a branch and shake it. If yellow or red specks the size of a pinhead or smaller appear on the white background, it is time to treat for crawlers.
- Check every few days during the active season of the crawler type on your plant to catch them and treat them as soon as they begin crawling. [source]
Scale Insect Control Tips Indoors and Outdoors
With proper timing, scale insects are not difficult to eradicate. Indoors or outdoors, keep these scale insect control tips in mind:
Always begin with non-toxic or mildly toxic options – Neem oil or Insecticidal soap.
Give your plants a thorough watering before treating for scale insects or releasing predatory insects.
Release predatory insects at dusk after giving your plants a “foliar watering.” This will encourage the insects to stay in place, quench their thirst after traveling and provide them with a place to sleep at sundown.
If you release predatory insects during the day, they are likely to fly away.
When using chemical solutions, remember to wear protective chemical clothing and gear. This includes long sleeves and pant legs, rubber gloves, a respirator or spray mask and eye protection.
Avoid using chemical pesticides indoors. Doing so could have a negative impact on your pets, family members and you.
Neem oil, is a pesticide extracted from the Indian neem tree. It works as an antifeedant on scale, clusters of mealybug, aphids and others. The is considered safe to plants, humans and wildlife.
Spray neem oil weekly at a rate of 2 tablespoons per gallon of water to control scale and loosen sooty mold. Apply when temperature will not exceed 80 degrees Fahrenheit. Buy Neem online from Amazon
Insecticidal soap has long been a pest control tool in the gardeners tool box.
A insecticidal soap solution only kills pests on contact; it has no residual action. Soap spray may damage plants, especially at higher concentrations or at temperatures above 32 °C (90 °F). [source]
For a 1 Quart Solution mix in 1 quart of water 1 tablespoon of soap. Shake well!
How To Treat Scale Insects On Houseplants
Scale insects, aphids, wooly aphids and spider mites may also invade your indoor plants. Just as with outdoor plants, vigilance and quick action help you keep them under control.
- Examine your houseplants for signs of scale insect infestation.
- Move infested plants away from other houseplants. Plants scale travels well and can infect other plants.
- Gently wipe and scrape scale off by hand using a soft cloth.
- Bath the affected plant with lukewarm water and a couple of drops of dish soap or insecticidal soap or Neem oil (our recommended choice).
- Spray the affected plant (in a shaded,well-ventilated area) using insecticidal soap or Neem oil (our recommended choice). Be sure to spray leaves and the undersides thoroughly.
- Introduce predator insects (IPM or integrated pest management) if your indoor plants are in a sunroom or other area separate from your living area.
- Ladybugs make a charming addition to your plant area. Ladybugs love eating scale and can help keep aphids, and spider mites under control.
- If your ladybug population becomes too great, open the window and let some of them fly away.
- Examine your plants regularly and keep the leaves clean to prevent re-infestation.
Houseplants often “attacked” by plant scale insects:
- Ficus elastica – Rubber plant
- Ficus benjamina – Weeping Fig
- Ficus Lyrata – Ficus pandurata
- Schefflera plant – Umbrella tree
- Crassula – Jade plant
How To Get Rid Of Scale Insect Pest On Outdoor Plants?
The waxy coverings of the adults protect them from almost any sort of pesticide or treatment. The nymphs are a different matter.
They are vulnerable to a wide variety of pesticides, and it is easy to eradicate them with low impact pest control methods.
Sprays: Insecticidal Soap, Horticultural Oil, Neem Oil
In the springtime spray plants with insecticidal soap or a thorough spray application of horticultural oil.
Because the crawlers are so vulnerable, with the right timing, you can have significant effects with fairly benign substances such as horticultural oil (Neem oil) and insecticidal soap.
These are excellent choices because they do not leave a lingering residue.
For this reason, you can use them to do away with the immature scale insects with little impact on natural enemies of these pests.
Manually Remove Old and New Plant Scales
When you time it correctly, you can use horticultural oils and/or insecticidal soaps to do away with the crawlers and eliminate most of the scales.
Well established scale and those hatching eggs for an extended period of time may require multiple applications along with some scrubbing and scraping to remove them.
Apply A Dormant Treatment Of Horticultural Oil Spray
You can also apply a horticultural oil spray treatment during the winter to address adults and nymphs overwintering under scales.
This dormant application of oil suffocates the plant scale bugs. Dormant oil treatment will not have any effect on eggs overwinter under scales.
Treat For Every Type Of Plant Scale Bug Present
Be aware that several different types of plant scale may co-exist on your plants. This means you must be aware of the life cycle of each type of scale.
Some produce several generations annually, so you’ll need to spray more than once to succeed in controlling all of them.
For heavy infestations, spray thoroughly with horticultural oil or insecticidal soap once every couple of weeks throughout the spring and summer of a given year.
When spraying make sure to thoroughly spray and cover the leaves, stems, trunks, and undersides of leaves with the spray solution.
This should get the scale infestation under control without doing too much damage to your existing natural predators.
Increase The Population Of Natural Predators
Be sure to get a good population of natural predators in place for the next growing season. Once you eradicate a scale insect infestation, cultivate a healthy natural predator population of:
… and other predatory insects keep all sorts of juice-sucking insects under control with no interference or effort from you.
Letting nature manage your scale insects is a smart, healthy, effective way to deal with them.
Outdoor plants often “attacked” by plant scale bugs:
- Azalea plants and shrubs
- Hydrangea bush, shrubs and trees
- Oleander tree and bush
- Gardenia plant – bush and tree
What About Plant Scale Insecticide Sprays?
Sometimes horticultural oils and insecticidal soaps do not give the needed control.
When horticultural oils and insecticidal soaps do not work, or you are dealing with a very severe infestation, you may wish to look into low impact insecticides available to licensed technicians. Among them are:
- Pyriproxyfen is an insect growth regular which mimics a natural hormone in insects disrupting their growth. It affects mostly young insects and eggs.
- Buprofezin is a growth regulator, banned in some countries, especially toxic to aquatic organisms, low toxicity to humans and other mammals.
These substances work by interfering with insect growth and are classified as IGRs (insect growth regulators). They do not affect adult scale insects, and they are relatively easy on the natural predator population.
In addition to these reasonably mild pesticides, other choices do have a residual effect. Even so, these should be applied when crawlers are most active for the greatest impact. These types of pesticides contain pyrethroids, such as:
- Lambda-cyhalothrin an organic man-made compound used as a pesticide, a pyrethroid that mimics the naturally occurring insecticide pyrethrum which come from the flowers of chrysanthemums.
- Permethrin a broad-spectrum chemical, it kills indiscriminately, can harm beneficial insects, including bees, and aquatic life, used in mosquito control programs.
- Bifenthrin an insecticide used to control of red imported fire ants, highly toxic restricted use pesticide,
They also contain carbaryl and acephate. These chemicals have a residual effect that lasts up to two weeks during dry weather. Any nymphs emerging from beneath their scales during that time will be killed. Keep in mind you must reapply the product if it rains.
Malathion has long been recommended for scale pest control. However, residues of foliar broad-spectrum insecticides sprays like Malathion can last for weeks in the landscape and garden. Malathion can be highly toxic to pollinators and natural predators.
Use Of Systemic Scale Bug Insecticide
Systemic insecticides work by moving through a plant via its conductive tissues. One such product is imidacloprid, which is most useful for management of soft scale insects.
Imidacloprid is sold under trade names Kohinor, Admire, Advantage, Gaucho, Merit, Confidor, Hachikusan, Premise, Prothor, and Winner. [source]
Imidacloprid also is used to control aphids, cane beetles, thrips, stink bugs, locusts, and a variety of other insects that damage crops.
The application is to the soil surrounding the affected plant. Professionals may apply imidacloprid by injecting it into the soil or directly into the trunk of an affected tree.
Another systemic insecticide is dinotefuran, which is applied in granule form to the soil surrounding the affected plant.
Dinotefuran is sold under trade names Safari, Zylam, Alpine.
Professionals sometimes mix a solution that can be:
- Sprayed on tree bark
- Used as a soil drench
- Injected into the soil
This chemical moves through the plant very quickly and thoroughly and is effective against both armored and soft scale insects.
Note: Dinotefuran is also used to control fleas, bed bugs, along with insect pests such as aphids, whiteflies, thrips, leafhopper pests, leafminer, sawfly, mole cricket, white grubs, lace bugs, billbugs, beetles, mealybugs, sawfly larvae, and cockroaches in leafy vegetables, in residential and commercial buildings, outdoor uses for professional turf management, turf farms, professional ornamental. [source]
Protect Your Pollinators And Natural Predator Insects!
The downside of systemic pesticides – they also kill beneficial insects.
Do not use systemic pesticides on plants attractive to bees, butterflies, ladybugs, parasitic wasps and other desirable garden dwellers.
Just as with other products, this type of pesticide must be applied when the crawlers are active.
However, apply after flowers finish blooming as this will reduce the likelihood of the pesticide negatively impacting pollinators and other positive garden fauna.
Furthermore, do not use systemic pesticides on shrubs or trees planted near flowering plants that attract bees, butterflies, and other pollinators as the substance may spread to these plants.
Always follow pesticide labels precisely. Be aware that these labels are legal documents.
Instructions on the label may change from time-to-time, and instructions found online may not match the directions on your pesticide container. Always read the pesticide label on the container in your possession and follow the instructions exactly.
When Should You Call A Professional?
When dealing with a major infestation on a tree, your best bet is to call on a professional to help you deal with scale infestation.
They have the experience needed to monitor scale insect activity and apply the right choice in product safely and effectively. Pest control professionals can save you a lot of time and the life of your tree.
A professional tree care company has access to chemicals and methods for scale insect management not available to the general public.
Quick, efficient treatment will prevent the spread of the insects.
Keep in mind, if your tree dies, you will have to remove it or have it removed, and this is not a cheap process. [source]
Smart Gardening And Plant Care Practices Discourage Scale Insects!
There are more than 3000 species of scale insects in North America.
No matter where you live or what type of plant you care for and grow, it may be attacked by scale insects at one time or another.
Following the above-recommended ways to get rid of scale insects you’ll be able to control the most common plant scales on your plants such as:
- Cottony cushion scale
- Amoured scale
- Common Brown scale
- Soft scale
- Euonymus scale
- Oystershell scale
- Many or types of cochineal scale
Remember, the key to preventing any pest infestation is to keep your plants, shrubs, and trees healthy.
Understand and meet the needs of your plants. Examine and groom them regularly. Water and feed correctly. When you do this, you can prevent scale insect infestation and, indeed, an outbreak of most types of plant pests.