How to Prevent and Control Scale Insects

Have you spotted tiny insects with waxy shields or shells hanging around your plants? You might have an infestation of scale insects! And left to their own devices, they can decimate your veg patch or flowerbeds. 

Scale insects are tiny pests commonly found in gardens and on plants that suck that sap from your beloved greenery. In fact, you’re more likely to see the result of an infestation before you spot the little critters. 

This article is about preventing and controlling scale insects to ensure your garden thrives, eradicating these unwanted visitors and taking steps to help infected plants recover. 

Ready? Let’s go. 

What are scale insects?

These tiny little insects are found all around the world, sucking sap from plants wherever they can find a tasty morsel. Belonging to the Hemiptera family, scale insects carry protective waxy shields or shells over their bodies that protect them from enemies, weather, and pesticides. 

Most scale insects feed by piercing their long straw-like mouthparts into the fleshy stems of plants and leaves. This is how they reach the sap, draining the plant of its essential sugars and nutrients.

After a while, the scale insect infestation weakens the plant and, in some cases, kills it — especially if the infestation has grown in size.

Recognise and distinguish between scale insects

The most characteristic feature of a scale insect is its protective shell, which often looks dusty or woolly.

However:

Most scale insects are tiny — typically shorter than 5mm in length — so individual insects can be difficult to spot (especially if you’re not wearing your glasses!). 

Scale insects can be green, brown, grey, yellow, or even red.

Some features to look out for:

• A shell — this is the most distinguishing feature of a scale insect
• Body shape — scale insects often have a flat, oval shape without antennae. This helps differentiate them from Aphids, which are typically longer in the body, have antennae, and no shell.
• Movement — aphids are more active than scale insects, which rarely move in their adult form. Adolescent scale insects can move (they just choose not to very much – typical teenagers!)

How to identify a scale bug infestation

Take a close look at your plants — they may show the following signs of scale insect infestation:

• Sticky residue — scale lice, such as mealybugs, suck the plant’s sap and excrete a sticky, sugary residue on the plant’s leaves and stems, called honeydew. This attracts ants. 
• Deformed or yellowish leaves and fruits — scale insects steal nutrients from the plant, resulting in yellow, misshapen fruits and leaves that die prematurely. 
• Clusters of insects — it’s difficult to spot individual scale insects, but if you look closely underneath the leaves, you may find a colony of small, woolly insects. 
• Ants — as mentioned, ants are attracted to the honeydew excreted by the insects, forming a symbiotic relationship — literally nurturing and protecting the colony. So, if you notice a large number of ants near your plants, this could indicate a scale insect infestation. 

The life cycle of a scale insect

Depending on the species, the life cycle varies. However, most consist of the following stages:

• Egg — the adult scale insect lays its eggs and hides them underneath its protective shell. Then, it emerges as a nymph.
• Nymph/crawler — nymphs have legs and antennae and are sometimes called “crawlers” because they can walk. Scales are most vulnerable to pesticides at this stage before their shells are yet to harden. They continue to shed their skin until they develop their shell. 
• Adult — at this stage, most scale insects move very little, and their shell helps protect them against most pesticides. An adult female lays hundreds of eggs at a time, having produced them asexually, depending on the species. 

Transmission and the spread of scale insects

Scale bugs spread in a variety of ways:

Crawling and flying — some scale lice move by crawling, and some can fly short distances. However, flying for most scales is rare. 

• Wind: scales are tiny insects, so a strong gust of wind can carry them from one plant to another. 
• Ants: as mentioned, ants and scale insects, like mealybugs, enjoy a symbiotic relationship. The ants protect the bugs so that they can feed off their honeydew, so scale insects can hitch a lift on an ant, which contributes to the transmission of the problem. 
• Human activities: it’s essential that you’re careful around infected plants. For example, if your shirt or jeans rub past an infested plant, the bugs can stick to the cloth and transfer to other plants. 

Scale insects’ favourite plants

Scale insects can infect any plant, but they’re more often attracted to specific plants:

• Ornamental plants — roses, hibiscus, azaleas, geraniums, and fuchsias. 
• Vegetable plants — mainly tomatoes, peppers, aubergines, and potatoes.
• Fruit trees — apple, peach, citrus, and plum
• Ornamental trees — boxwood, forsythia, privet
• Houseplants — ficus, orchid  

Fighting scale insects

The most humane way to get rid of scale bugs is to remove them by hand — but this isn’t an ideal solution and is not always permanent. 

To remove them manually, wear disposable gloves and use a soft cloth to rub the bugs off the plants. 

Alternatively, you could use a powerful jet of water to wash the bugs away — but be careful not to damage the plant!

Perhaps the most effective method is encouraging natural enemies like ladybirds and parasitic wasps. Introduce lots of nectar-rich flowering plants that attract ladybirds into your garden.

Insecticides are particularly effective, easy to apply, and will not harm the plant. Always read the instructions, and treat chemical insecticides as a last resort. However, a range of natural alternatives, such as neem oil, will eradicate pests without harsh chemicals. 

Aftercare for infested plants

After infestation, give the plant some TLC to promote their recovery. 

Follow these tips once you’ve solved the problem:

Water and feeding — water according to the plant’s needs. Not all plants need lots of water, but — in general — don’t let the soil dry out. Keep the soil moist and apply a general-purpose fertiliser to help it bounce back. 

Pruning — cut back damaged plant parts, such as leaves and branches. This will help promote new growth. 

Prevent scale insects

Prevention is always better than cure. 

So, if you’re introducing new plants into your greenhouse, keep them in isolation initially to prevent an unseen infestation from spreading to your other plants. If, after a week, there’s no sign of bugs, it’s safe to introduce the plant.

Inspect your plants regularly — a fast response is always the best solution! Look for sticky residue, deformed leaves or fruit, or the presence of tiny little waxy-looking bugs. 

Keep your plants healthy and robust by watering, fertilising, and thinning, making them less susceptible to pests. Remove weeds as soon as they occur to minimise potential food sources for scale insects. 

And look out for ants — their presence is a sure sign of scale insects. 

Plants that deter scale insects

If you’re experiencing frequent infestations, introduce some of the following plants into your garden to deter the little critters:

• Herbs: rosemary, lavender, oregano, thyme — all natural deterrents due to their pungent smell. 
• Strong-smelling bulb plants: garlic, onions
• Ornamental plants: nasturtium, marigolds
• Ferns: many fern species deter scale insects. These attractive plants offer beautiful foliage and are excellent in borders.
• Trees: cypress, fir, pine

FAQs

Any questions?

I hope you’ve got all the tips you need to handle a scale insect infestation. But if you have any questions, don’t hesitate to get in touch. 

We love hearing from you and will do our best to reply as soon as we can. 

Alternatively, add a comment to the Comments section below or check out our comprehensive Help & Advice section. 

Thanks for reading!  

Louis Hooft

Founder & Lawn expert

Introducing Louis Hooft, the founder of MOOWY and your reliable expert. With a profound love for stunning lawns and extensive experience in garden maintenance, Louis is here to assist garden enthusiasts in achieving a greener and livelier outdoors than ever before. Count on Louis for invaluable tips, clever tricks, and top-notch products to make your garden flourish!