Plant Pests Scale Insects: Complete Guide to Identification and Management

Scale insects are one of the most common and destructive plant pests, affecting over 100 plant species worldwide.

These tiny, armored insects feed on plant sap, causing curled or distorted leaves, stunted growth, and reduced fruit production. They can also transmit plant viruses.

Scale insects have a complex life cycle, with multiple stages of development, including eggs, crawlers, and adults. The female scale insect can produce live young, called nymphs, or lay eggs that hatch into crawlers.

Some scale insects can produce a sticky substance called honeydew, which attracts other insects, like ants and bees, and promotes the growth of sooty mold. This can lead to a decline in plant health and productivity.

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Mealybugs are a type of scale insect that have no hardened covering, and are distinctive for their flocculent (wool-like) bodies.

They feed on the phloem of plants, which can cause problems for the plant's growth and health.

Mealybugs produce honeydew, a sweet, sticky substance that can attract ants and cause sooty mold to form on the plant's leaves.

Ants often tend to mealybugs and even move them to new plants in search of more honeydew.

Only a few mealybug species exist outdoors in Alabama, and they produce just one generation per year.

However, mealybugs that live on house plants or infest ornamentals in greenhouses can produce multiple generations per year.

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Mealybugs have no hardened covering and are distinctive for their flocculent (wool-like) bodies.

Mealybugs feed on the phloem and produce honeydew that can cause sooty mold.

Some mealybug species can produce multiple generations per year, especially when they infest house plants or ornamentals in greenhouses.

Sugar-loving ants tend to protect mealybugs from enemies and may even move them to new plants for the benefit of their honeydew.

Mealybugs have a white cottony/waxy body with no hardened covering, and they can have waxy extensions (filaments) around the edges and backside.

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They have sucking mouthparts made up of threadlike stylets that act like a straw, enabling them to draw out liquids from the plant’s vascular tissue or cells.

Mealybugs produce sugary liquid excrement called honeydew, which can lead to the growth of sooty mold fungi.

Honeydew drops from the plant and accumulates on anything located below the infested tree or shrub.

It's worth noting that honeydew is not exclusive to mealybugs, as many other insects, such as aphids and whiteflies, also produce it.

Mealybugs and scale insects are grouped together by entomologists because they have similar habits and life cycles.

Scale insects and mealybugs are plant parasites, with a few species able to kill the host plant on which they feed.

Scale insects can be tricky to spot, but there are some telltale signs to look out for. Scale often blend with plant bark or branches, making them hard to see.

To identify scale, look for clusters of tiny shell-like bumps on leaves, stems, or bark. These clusters are a dead giveaway that you have a scale problem.

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Scale insects can be found on foliage, particularly along leaf veins, on the leaf underside, or on leaf petioles. They can also be hidden underneath leaf sheaths or in crevices between emerging leaves.

Check your plants carefully, especially on the underside of leaves and in crevices, as scale insects often hide in these areas.

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The scale can infest a staggering array of plants, with 400 genera in 133 families.

Some of the most popular flowering houseplants that can be affected include orchids, bromeliads, and Oleander (Nerium oleander).

Flowering houseplants like cyclamen (Cyclamen), Chinese hibiscus (Hibiscus rosa-sinensis), and jasmine (Jasminum) are also at risk.

Foliage houseplants, such as ferns and palms, can also be infested.

Other foliage houseplants that may be affected include pothos (Epipremnum), peace lily (Spathiphyllum), and fig (Ficus).

Edible tropicals like citrus (Citrus) and rosemary (Rosmarinus officinalis) can also be infested.

The list of susceptible plants is long and varied, but being aware of the common hosts can help you take action to prevent infestations.

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Here are some examples of common hosts in different categories:

Scale bugs on plants can be difficult to spot because they are small and variable looking. Their unusual appearance can be easily mistaken for scabs, diseases, or other problems.

To start, look for clusters of tiny shell-like bumps on leaves, stems, or bark. These clusters are a telltale sign of scale insects.

You can also check the following areas for scale:

Scales most often appear as small, brown, and rounded lumps on your plant's stems, around the leaf joints, and the undersides of leaves. They don't resemble typical bugs and look more like odd-looking growths on the plants.

Mealybugs are highly reproductive, with some species able to produce up to 300 eggs at a time.

To control mealybugs, it's essential to understand their life cycle. They have three stages: egg, nymph, and adult.

Regularly inspecting your plants can help catch mealybug infestations early. Look for white, cottony patches on the stems and leaves.

Isolate infested plants to prevent the mealybugs from spreading to other plants. This will also help prevent the mealybugs from escaping and colonizing new areas.

Systemic insecticides can be effective in controlling mealybugs, but they must be applied carefully to avoid harming other beneficial insects.

Prune infested areas to prevent the mealybugs from spreading. Dispose of any heavily infested plants to prevent the mealybugs from re-infesting your garden.

Use neem oil or insecticidal soap to control mealybugs. These products work by suffocating the mealybugs and preventing them from reproducing.

Monitor your plants closely after treatment to ensure the mealybugs are under control. Repeat treatments as necessary to prevent re-infestation.

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Before investing in pesticides, it's essential to check the viability of scale insects on a plant. You'd be surprised how many dead scales are stuck to the tree or shrub, wasting your time and money.

Assessing whether a scale insect is alive can be tricky, but using a small sewing needle and a hand lens to flip over the waxy coating can help. Living scale insects will look full and rounded under the waxy coating.

Count at least 25 insects and multiply the number of live ones by 4 to estimate the total percentage of live scales. If the number of dead scales is high, you can rely on a dormant oil or insect growth regulator spray to reduce populations further over time.

Natural predators like parasitic wasps, soldier beetles, lacewings, and ladybugs can offer effective pest control. These beneficial insects can be purchased at local garden centers or by mail order.

Insecticidal soap is another organic control method that can be used to kill scale insects. It's most effective in the crawler stage, before the scale develop their protective coating.

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Chemical control methods can be an effective way to manage scale insects on plants, but it's essential to use them judiciously. Before applying any chemical control methods, it's crucial to assess the viability of the scale insects on the plant.

To do this, use a small sewing needle and a hand lens to flip over the waxy coating of the scale insect. Living scale insects will look full and rounded under the waxy coating, while dead ones will bleed when uncovered.

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If you've determined that the scale insects are alive, you can use a variety of chemical control methods to manage the infestation. These include contact active insecticides, insecticidal soaps, azadirachtin products, oils, and insect growth regulators.

One effective chemical control method is to use horticultural oil at a 1% dilution rate. This must be applied thoroughly, coating all bark or leaf surfaces (upper and lower). Repeat applications will be needed if the window of crawler activity is long.

Here are some key considerations for using chemical control methods:

Some pesticides are restricted-use, meaning that only certified applicators may obtain and apply them. In such cases, it's best to hire a professional pesticide applicator.

Systemic insecticides can be absorbed by the plant and then ingested by the scale as they feed. These should be applied at the first sign of crawler activity and may control scale throughout the rest of the season.

Here's a summary of the most effective chemical control methods for different life stages of scale insects:

Remember to always follow product label instructions and take necessary precautions to protect natural enemies.

Healthy plants are more resistant to pests and diseases. Keep them well watered during summer to prevent stress from heat and drought. Regular watering helps prevent stress, which can make plants more vulnerable to pests like scale insects.

Early detection is key to managing plant problems. Check plants regularly, especially during gardening chores like weeding, watering, and fertilizing. Focus on varieties that are most susceptible and examine all parts of the plant, including stem joints and the undersides of leaves where scale insects like to hide.

A black sticky coating on leaves and branches, along with the presence of ants, can indicate the growth of sooty mold, a fungal disease that impedes photosynthesis and harms plant health. Sooty mold often appears on the top side of leaves, causing yellowing or unattractive foliage.

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Healthy plants are more resistant to pests and diseases, making them a joy to care for. To keep your plants thriving, make sure to keep them well watered during summer to prevent stress from heat and drought.

Regular checks on your plants are essential for early detection of problems. This means inspecting your plants while doing gardening chores like weeding, watering, and fertilizing.

Sooty mold is a common issue that can be identified by a black sticky coating on leaves and branches, as well as the presence of ants. It's a sign that your plant is struggling with photosynthesis.

Healthy plants are less susceptible to pests and diseases, making them easier to manage. By keeping your plants healthy, you'll spend less time dealing with problems and more time enjoying the fruits of your labor.

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Regularly inspect your plants, especially those most susceptible to pests, when doing routine gardening chores like weeding, watering, and fertilizing.

Focus on examining all parts of the plant, including stem joints and the undersides of leaves, where scale like to hide.

Note the presence of black sooty mold, a sign of a fungal disease that can impede photosynthesis.

Sooty mold grows on the top side of leaves, causing a black sticky coating and attracting ants.

If you believe your plant is infected, quarantine it to prevent spreading to other plants.

Keep the infested plant isolated for at least three weeks to ensure you've gotten rid of the scales for sure.

If you have a small infestation, it's still recommended to remove the affected parts to be safe.

Use gardening shears to clip off any infested branches, twigs, and leaves.

Dispose of these clippings to prevent the scales from spreading – don't put them in your compost bin.

Some armored scales can be difficult to treat, so be prepared to scrape them off with your fingernails if necessary.

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