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A Simple Guide to Getting Rid of Scale Insects on Plants

ukhouseplants
Published on February 2nd 2021
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A vase of flowers on a table

What is a Scale insect and why are they bad for our plants?

Although a lesser common pest, Scale can still wreak a long-winded battle with your houseplants. An infestation can arise from an already-affected plant or a specimen that's recently been purchased from a store. There is a big difference between the female and male appearances, with the latter looking more like a winged gnat. A houseplant owner is most likely to see the Instars (the juvenile stage between the egg and adult) and the mother resting on the foliage, which looks similar to an orange or white armoured shell.
A close up of a green plant
Most indoor Scales will live for up to three months, laying several hundred eggs in their lifetime!
Most infestations will take six weeks to arise when the newly hatched eggs begin to mature, making it seem like it's come from nowhere.
Continue scrolling to learn more about how to eradicate Scale from your beloved houseplants.
A close up of some soft scale insects Coccidae attached to the back of a leaf

Soft Scale

Coccidae

How to identify a Scale infestation

Unlike Mealybugs and Spider Mites, this pest won’t produce a web to protect her eggs and instead will leave sticky patches from their excretions. In some cases, these areas will become black and remain sticky, caused by a fungus called ‘Sooty Mould’. Although harmless to the plant, a thin film of fungi will reduce the leaf’s ability to photosynthesise, thus weakening the specimen over time.
A close up of a plant
Sticky patches of honeydew can lead to formation of sooty mould
A close up of a cactus
Sooty mould prevents plant from effectively photosynthesizing
The individual Scale is small, circular and usually stays local to the hatching ground for many months. Depending on the species, its appearance may be brown, orange or even white, measuring around 0.4cm (one-sixth of an inch). The critters will remain stuck onto the plant’s leaves, stems or petioles, meaning that most plant areas can be affected above the soil line.

Most common plants infested by Scale insects:

Scale, with most infestations arising from the older leaves or semi-wooded stems, can affect many houseplants. The list below are the most common specimens to be susceptible to an attack:

How to get rid of Scale

Patience and consistency is the best method when eradicating Scale. The following step-by-step guide discusses how you can eliminate an infestation using simple steps, along with a few organic and chemical-based pesticides that we recommend.
1. Firstly, scan the plant from head to toe. Take a few minutes to check both sides of the leaves, along its petioles (which connect the leaf to the stem) and the stems itself. Scale can be either brown or white and will stick out like a sore-thumb when inspected closely.
A close up of a green plant
Scale tend to hide in hard to reach places on plants
2. With your fingernails, gently remove the bugs. Smaller Instars may bury itself in tight nooks within the plant, so it’s important to scan the WHOLE plant from the soil line upwards. Use a warm damp cloth to wipe away areas that have the sticky substance or Sooty Mould.
3. Take the plant outside and gently hose the entire plant - its stem, leaves and any potential hiding spot. This is a critical part of addressing an infestation, so be sure to put aside several minutes for this step.
4. Situate the plant in a warm, bright room away from other specimens to dry-off. If the temperature is above 15℃ (59℉) at night, keep it outside to recover naturally.
5. You can administer a pesticide once the foliage thoroughly dries from being hosed down. Although there is a choice between two options (organic or chemical-based sprays), we would recommend using an organic product first.
6. Keep the affected plant away from others in a quarantined room until the symptoms have subsided for at least six weeks. In some cases, dormant eggs may hatch several months after deeming the specimen pest-free, so it’s always important to keep an eye out for a potential relapse. Keep other, non-affected specimens safe by distancing the pest ridden plant at least a metre away from each other.
N. B. - Although you should perform the wiping and hosing-down process BEFORE each pesticide application, you can wipe/wash the foliage at any given time to keep the infestation under control.
Remember to respect the pesticide’s recommendations though, as frequent applications could result in burnt foliage.
Organic Pesticides
Diatomaceous Earth (D.E. or DE) is grounded diatom mantels (basically exoskeletons) that can be highly abrasive to many arthropods, including Scale.
Although the white powder may be soft to the human touch, the sharp tooth-like edges off each grain will begin to cut its way into the pests' eco-skeleton, causing significant discomfort and weakened health. After a period of several days, the infestation will decrease as the mature mothers won't be able sufficiently to lay her eggs.
Usually, DE is applied as a thin layer across the foliage of outdoor plants, which will work until there is a rainstorm; however, you'll have to change the method of application to eradicate indoor pests.
Instead of using powder to combat your infestation, mix the DE with water to create a more efficient solution to access the plant's cubbyholes and hard-to-reach areas. Add one tablespoon of DE to 500ml of water (0.11 imperial pints) and mix well. Finely mist both sides of the leaves and its stems so that the plant is covered in a thin film, which will begin its work within twenty-four hours once dry.
Its eggs may be immune to the pesticide, so it's important to perform another fine spray seven days later to attack to the recently-hatched Instar. As you have followed the first four steps mentioned in the previous section, you shouldn't see any signs of an infestation for several weeks. We'd recommend waiting six weeks before deeming the specimen pest-free, as relapses of later-hatching critters could occur. If pests do return, follow the four steps mentioned above, along with the misting of its foliage with this solution. If the infestation is large, you may wish instead to opt for a chemical-based pesticide to destroy the infestation more effectively. DE is considered safe to both pets and humans and has no links to the development of illness or cancers.
Neem Oil is used across the world, and for a good reason. Not only is it accessible in many stores, but it'll also get to work after the first application. Dilute the liquid, (to the manufacturer's recommended strength) with water and/or dish soap and spray thoroughly onto the foliage and its cubbyholes. Any flowers must be removed instead of misted, due to the heightened chance of another infestation lurking in the background.
Chemical Pesticides
We'd recommend using 'Bayer Garden Provado Ultimate Fruit and Vegetable Bug Killer Concentrate', as it worked rapidly after one application. It's a concentrated product, meaning that you'll have to dilute it with the appropriate amount of water. Spray both sides of the leaves, along with any cubbyholes that could house the infestation. Keep the plant away from other specimens once there are no signs of an outbreak for over a month.
If you're looking for something with even more strength, try an Isopropyl Rubbing Alcohol, which can be bought from many online stores. This pesticide will work immediately, killing the bugs within a few hours of contact. Follow the manufacturer's recommendations and repeat hosing the plant down and pesticide application steps fortnightly until the infestation has elapsed. Keep it well away from others until the plant is deemed safe.