Plants can beautify a space; they purify the air, and they can even be grown for food. As such, one can’t argue that gardening is a rewarding activity. It doesn’t come as a surprise that several studies have proved that gardening can relieve stress and improve wellbeing. However, nothing can stress a gardener more than having to deal with pests.
If you don’t catch a pest infestation in time, you can lose years of hard work and numerous plants that you have come to love. Few pests can be more troublesome and more difficult to spot and deal with than scale insects. Nonetheless, what we truly fear most of the time is the unknown. So today, we are going to get as familiar as possible with these tiny pests, without actually having to deal with them. Learning about them will help you recognize them and it will make getting rid of them and preventing future encounters with them easy tasks.
What Are Scale Insects?
Scale insects belong to the Hemiptera order, which is an order of true bugs. Within this order, we can also find aphids, leafhoppers, or Cicadas. As you can see, it is a diverse insect order, with few similarities among different types of insects. Within this main order, scale insects are classified as part of the Sternorrhyncha suborder. This suborder includes several types of annoying plant pets. More specifically, scale insects belong to the Coccomorphia infraorder. The insects in this order exhibit extreme sexual dimorphism. This means that sexes of the same species can differ greatly in their appearance, their behaviour, and other traits as well. Scale female insects have soft bodies. They don’t have any limbs and their bodies are hidden by scales. The females create wax to protect themselves. The males can be confused with small flies, as they feature both wings and legs. The males have a very short lifespan. Some species are hermaphroditic.
Scale insects feed on plant tissue which makes them the nightmare of any gardener. They pierce the plant tissue and feed on the sap. While a single insect can’t harm the plant, an infestation can be very damaging. Plants need sap to transport nutrients from the root system to the leaves. Scale insects use the excess fluid to secrete honeydew. This is a sticky liquid with a high concentration of sugar. The honeydew can trigger other issues, as it can develop mould and is often eaten by other insects like ants. Unfortunately, the ants live in harmony with the scale insects, protecting them from predators, so a double infestation might make your job even more difficult.
Despite their small size and fragile appearance, these insects appeared over 50 million years ago, in the Triassic period. Back then, flowering plants hadn’t even appeared, so the diet of scale insects was a little different than it is today. Nonetheless, they managed to spread and survive long enough to occasionally meddle with our gardens. Most scale insect species are pests, but some can be used to control invading plants. Some species also produce valuable dyes like carmine or kermes. However, these are not the species that the common gardener will deal with. We usually deal with the pest scale insects, the ones that attack our beloved plants and give nothing in return.
Types of Scale Insects
As we already mentioned there are numerous species and behaviour and appearance can vary for each species. However, as an amateur gardener, you don’t need to know how to identify different species. You only need to make sure that you are dealing with scale insects so that you can employ the proper means of getting rid of them. The different species can be classified into two main types of insects:
Soft Scale Insects
The soft scale insects are usually found on indoor plants. For those of us that don’t have outdoor gardens, these are the pests that we are more likely to encounter. They have an oval shape and their size ranges between 0,3 and 0,6 cm.
Young insects are considerably smaller and lighter in shade. A single female can produce over 2000 eggs which take a couple of weeks to hatch. The younglings are called nymphs. Mature females are covered by a waxy scale. These females have small legs. Technically, they can move, but it requires a lot of effort, so they rarely do it. Most soft-scale insects are located on the undersides of the leaves.
Here are the most common soft scale insect species that you are most likely to deal with: Brow soft scales, cotton maple scale, European elm scale, Fletcher scale, Hemispherical scale, Lecanium scale, Magnolia scale or San Jose scale.
Armoured Scale Insects
As their name suggests, the bodies of these insects are covered in a hard, waxy armour. They are smaller than soft scales. Their size can range between 0,15 and 0,3 cm. They also have a flatter shape so they are more likely to pass unnoticed when checking the plants. They blend particularly well in the bark of trees. Most of them have a round shape like soft scales, but some species can have a more elongated shape. They also come in a wide range of colours. They lay eggs but some species also produce live nymphs.
The armoured scale insects prefer to lie on lower leaves or stems. They produce greater damage than soft-scale insects because they also inject the plant with toxins when they feed.
Here are the most common armoured scale insect species that you are most likely to deal with: Euonymus scale, Oystershell scales, or Pine needle scales.
How Do Scale Insects Spread?
Before adulthood, female insects pass through two or even three developmental stages known as instars. Males also pass through two stages. Young insects are called crawlers. They have functional legs which they use to find good feeding spots. Before they get the chance to settle down in a feeding spot, they can be blown away by winds or drafts onto other plants. This is how they establish colonies on other plants. Consequently, this is how one affected plant can create a large-scale infestation that can affect all your plants. There are also cases in which ants carry the young crawlers to dedicated feeding locations.
When young female crawlers shed their skin to encourage new growth, they also shed their legs. Once they do that, they remain in the same feeding spot for life. The males keep their legs and wings. They use their means of getting around to find females. In some rare insect families, the females can keep their legs for a limited time, until the next time when they shed extra skin.
Scale insects spread through sexual reproduction but also asexual reproduction and even parthenogenesis. Parthenogenesis represents the development of an embryo from an egg without fertilization. Asexual species are usually more common.
Once the young nymphs appear, they spread quickly from one plant to another. Outdoors they are carried by the wind. Indoors, they spread quickly when plants are crowded together. They can also use drafts to land on new feeding spots.
Early Signs of Scale Insect Infestation
You should always inspect your plants regularly as prevention is the best treatment. Aside from a visual inspection. Make sure to also feel the foliage, the stems, or the trunks of your plants. Here’s what you should look for:
- Honeydew – You should touch the foliage of your plants regularly to check for problems. If you notice a good amount of honeydew, there is a reason for concern. Honeydew is a sticky substance so it is easy to recognize. It tends to attract ants as well as bees, flies, or wasps.
- Black mould- This is actually called black sooty mould. It is a fungus that grows on honeydew, covering it with a black layer.
- Scales on plant tissue – Feeling up the plants is essential to detect pests and other problems. Scale insects feel like bumps. The undersides of the leaves are the most common place where you might find them. You can also find them on stems or tree trunks.
Symptoms of an Infestation
If you neglect the early appearance of a few scale insects, you might have an infestation on your hands sooner than you think. While we hope you never have to deal with this problem, here are a few signs that signal a serious infestation:
- Yellow leaves – When the plant runs low on sap, it is deprived of nutrients. Without a good amount of nutrients, the foliage quickly starts to wither.
- Distorted foliage – Curled or cupped leaves, as well as other malformations, are a sign of pets. Armoured scale insects can also cause yellow halos around feeding spots.
- Twig dieback – This is caused by lesions caused by pest damage. The lesions are more common in the places where the branches meet the trunk of the trees. The lesions are dark brown and diamond-shaped.
- Defoliation – Black spots are an early sign of defoliation. If the scale insects are not dealt with in due time, the black spots will eventually lead to leaf drops.
Easy Ways to Get Rid of Scale Insects
Based on the gravity of the infestation, several remedies can be efficient against these insects. Make sure to try these natural remedies before using chemical pest solutions.
1. Brush off the pests
This method works for lightly infested houseplants. You can brush off infested stems, trunks, and leathery leaves. This is a method that works well with plants that have large glossy leaves. Avoid brushing off thin leaves and use a soft bristle brush nonetheless. A toothbrush for sensitive teeth will be ideal. You can make the process more efficient by dipping the brush in soapy water.
2. Use a cotton swab
For more sensitive plants, you can use a cotton swab instead of a brush. Dip the brush in soapy water or a mild detergent solution to clean the affected areas. Alternatively, you can use 70% isopropyl alcohol. No matter what solution you use for cleaning the affected areas, make sure it doesn’t drip onto the soil. Whether you use a brush or a cotton swab, make sure to remove not only the insects but also the honeydew.
3. Spray rubbing alcohol on infected plants
Ideally, you should apply the alcohol directly to the affected plant tissue with a cotton swab. However, this can be quite time-consuming, especially when it comes to plants that have small leaves and dense foliage. If the infestation is not severe, you will have a higher chance to succeed with an alcohol spray.
4. Use horticultural oil
This is a petroleum-based oil that is very efficient against pests. You can apply it with a spray bottle. It works best if it is applied in late spring before the insects grow their protective scales. Mix 3 ounces of oil with one gallon of water. For the best results, use a hose-end sprayer.
5. Use neem oil
This is another oil that works great against pests. You can apply it even if you are not sure that you are dealing with scale insects as neem oil works against most plant pests. The trick with applying this oil is to mix it well. It doesn’t mix with water so you will have to add some soap to make the mixture more homogenous. Mix 2 teaspoons of soap, with 2 tablespoons of oil and a gallon of water.
6. Keep affected plants isolated
Depending on the severity of an infection, treatment may need to be applied several times, at least once a week. Until you make sure that a plant is pest-free, keep it isolated from your healthy plants
7. Dispose of infected plant parts
If treatment fails to work or if certain plant parts are too damaged, it is best to remove the infected parts altogether. Remove infected leaves, twigs, or even branches.
8. Know when to give up
Throwing away a beloved plant can be painful. However, it is important to recognize when it is time to count your losses and move on. Some plants can be beyond salvation, and it is better to throw away an infested plant than risk spreading the infection to your healthy plants.
9. Test chemical solution on small areas
As we already mentioned, we don’t recommend chemical solutions. First, you should know that they only work on crawlers. The waxy covers of adult insects protect them from harmful substances, so you must remove them mechanically. Secondly, chemical solutions can also damage the plant in the process. You can guess a plant’s sensitivity to synthetic pesticides. If you must use them, make sure to first test the solution on a small part of the plant. Avoid applying synthetic pesticides to the soil. This will only eliminate the pests temporarily.
How to Prevent Scale Insects
Inspect new plants
The best way to prevent an infestation is to make sure you don’t bring an infested plant among your healthy plants. As such, you should always inspect new plants before bringing them into your garden space. Usually, people inspect only the leaves, but you should inspect the whole plant. Some scale insects can overwinter in crevices in the bark of trees or shrubs. You can also find them in plant litter. As far as indoor plants are concerned, you must first inspect a new plant. After inspecting it, it is best to keep it isolated for a few weeks before mixing it with the rest of your plants.
When inspecting deciduous trees, you must first check the leaves, with a particular focus on the veins and the twigs. The underside of the branches is also preferred by many insects. This area is protected against adverse weather and different types of predators.
Isolate infested plants
Once you find scale insects on one plant, you need to inspect all the surrounding plants. The ones that prove to be infested must be moved to a secluded location until they are pest-free. Try to place them in another room, away from drafts which could be used for young crawlers to travel to new plants.
Keep your plants healthy
Healthy plants are less likely to be affected by pests and diseases. Make sure your plants get enough sunshine and water.
Attract beneficial insects
Beneficial insects like ladybugs and soldier beetles feed on plant pests so they can be real treasures in your garden. Provide them with food and shelter to keep them in your garden. They are attracted by pollen-rich blooms like marigolds, calendula, or sweet alyssum. Planting these plants in your garden is a great way to prevent not only scale insects but other equally annoying as well. To keep the beneficial insects around as much as possible, delay cutting back old stems until spring. They tend to overwinter in hollow stems. You can also create special hibernating spots for them out of bamboo sticks stuffed with straw.
Grow plants that are pest-resistant
There are many pest-resistant plants that will make gardening easier. Without worrying about pests such as scale insects, you’ll be able to focus more on the more enjoyable aspects of gardening. It is important to mention that some of the plants that are not attractive to pests might be toxic to pets and small children as well, so it is best to handle them with caution. That being said, let’s take a look at a few pest-resistant, yet very attractive ornamental plants:
Dracaena – If you love growing tropical plants indoors, you are surely familiar with Dracaena plants. These tall ornamental have attractive spear-shaped leaves that come in different shades of green, but can also be cream, white, burgundy, and striped. Dracaenas are easy to grow, they don’t need much attention to thrive, and as long as you water them regularly (whenever the soil is dry), they will reward you with their attractive leaves year-round. They are tropical plants, so they do enjoy humid environments, which means that they are perfect bathroom or kitchen plants. The leathery foliage of the Dracaena is not attractive to pests, but it is quite toxic to cats and dogs as well, so make sure you keep it in a place where your furry companions won’t reach. You can learn more about growing and caring for this ornamental from our Complete Guide to Dracaena.
Venus Fly Trap – This is a truly fascinating houseplant. As its name suggests, the venus fly trap plant will get its nutrients by trapping small insects. Despite being a carnivorous plant, Dionaea Muscipula is a friendly ornamental that is not dangerous to humans or pets. It makes a great desk plant, as it usually remains quite small and it is not picky about its growth environment. All it needs to thrive is a deep pot, regular potting soil, and plenty of light. You can learn more about this plant by reading our Complete Guide to Venus Fly Trap.
Sansevieria – This plant has so many qualities – it looks great, it is easy to grow, and it doesn’t need a lot of attention, so it comes as no surprise that it is pest-resistant as well. It is one of the most popular indoor ornamentals worldwide because it thrives in regular home environments. Its succulent stems can be braided together, so don’t be surprised if you find them like this in nurseries and shops. This plant doesn’t need much to grow healthy and happy on your desk or on a shelf. To have a thriving Sansevieria, make sure it gets a good amount of indirect light and some water when the soil feels dry to the touch. Read our Complete Guide to Sansevieria to learn more about this fascinating ornamental.
Cast-Iron Plant – Aspidistra Elatior, commonly known in the gardening world as the cast-iron plant is another great ornamental that you can grow indoors without worrying about pests. These plants are very popular thanks to their forgiving nature and attractive foliage. If you are a novice gardener and are looking for a pest-resistant plant that won’t mind occasional neglect, the cast-iron plant is a perfect option. Although toxic to humans and pets if ingested, cast-iron plants have plenty of benefits. They are great air-purifying plants, they don’t need much attention, and will thrive in most homes. Read our Complete Guide to Aspidistra Elatior to learn more.
Aglaonema – Commonly referred to as the ‘Chinese money plant’, Aglaonema is another friendly ornamental that doesn’t attract pests and diseases. Aglaonema comes in a wide range of colours and you can find specimens that are different shades of green, but also more special ones that are speckled or have streaks of pink, yellow, white, or red. These plants are highly poisonous to pets, but they are still popular ornamentals worldwide. Many fake plants are modelled after the Chinese money plant, so if you want to make sure that your pets are safe, you can always opt for a high-quality fake Chinese money plant. However, a fake plant won’t ever be as fun as a real one, so don’t forget to read our Complete Guide to Aglaonema to learn more about growing and propagating these ornamentals.
Other examples of pest-resistant ornamentals include bromeliads, coleus, culinary herbs, lavender, chrysanthemums, marigolds, petunias, etc.
Avoid growing plants that are prone to scale-insect infestations
If you want to avoid dealing with scale insects, it might help to know which of our garden buddies are more prone to develop this type of infestation. There are many indoor and outdoor ornamentals, herbaceous plants, trees, and shrubs, that fall victim to scale insects. For instance, Euonymus shrubs are frequently infested by scale insects. Fruit trees and magnolias are also quite sensitive to these annoying intruders. Oleanders, camellias, figs, ferns, and gardenias are commonly attacked by brown soft scales. Thuja, yew, Eastern red cedar, and pachysandra are more susceptible to the Fletcher scale.
In conclusion
There are many ornamentals that can be bothered by pests and it might be wise to avoid growing the ones that are extremely susceptible. However, avoiding pests completely isn’t always possible, so it’s quite important to focus on preventing and eliminating these pests. As you can see, scale insects are not so scary when you learn a little about them. They behave like most plant pests, and they can be removed without letting go of your plants. Your chances of success depend greatly on how early you detect the pests. As such, it is very important to keep your garden clean and to do regular pest inspections.
Have you ever dealt with scale insects? Let us know how you got rid of them in the comment section!
