How do I get rid of scale insects?

Scale insects are related to the aphid, but they are a good deal harder to get rid of. These small, sticky creatures look like woolly white dots and have a shield that protects them well against many kinds of treatment. No need to worry, there are plenty of effective ways to tackle them. They are only about 4 millimetres across and often settle on the leaves of your houseplant. Once they have settled in, they bite down and suck out all the nutrients the plant badly needs. So it is important to act quickly to save your houseplant.

Preventing scale insects

There is no specific way to keep scale insects away entirely. What is essential, though, is to check your plants regularly for unwanted visitors and deal with them the moment you spot them. That stops them spreading further and putting your plant's health at risk.

Different types of scale insect

Scale insects fall into three different types:

1. Parthenolecanium Corni - the 'common' scale insect, found on many different ornamental crops and houseplants.
2. Loccus Hesperidum - also known as the flat scale insect. This one has a flatter shield and a different colour, such as yellow-green, yellow-brown or light grey with dark patches and speckles.
3. Saissetia Coffeae - the hemispherical scale insect, the same size as the other varieties but dark in colour. It has a preference for the coffee plant and carnations.

How scale insects spread

Scale insects never turn up alone; the most common varieties are brown or grey. They always have legs, apart from the fertilised females, which do not. A single scale insect can hatch as many as 3,000 eggs in a few weeks, all of them protected under her shield. Scale insects are often carried to new plants on clothing or on the wind.

Where scale insects sit on the plant

Scale insects do not like the limelight; they would rather hide. They often tuck themselves away in the plant and are easily overlooked as a result. That can be dangerous, because by the time you discover the infestation the plant may already be damaged beyond saving. They have no particular preference for one spot on the plant, but they turn up most often around the veins on the underside of the leaf.

The damage scale insects do to your plant

The scale insect settles on the plant and bites down to draw out all its nutrients. The plant discolours as a result, drops its leaves and barely grows any more. Scale insects bring a second problem with them: honeydew, an excess of sugars that feeds sooty mould. All of which underlines how important it is to act quickly once you notice scale insects on your plant.

Getting rid of scale insects

There are countless ways to tackle scale insects. You can treat them with methylated spirits, soft soap, garlic, cold coffee and plenty more. The simplest method is to stand the plant in water for about 15 minutes, which lets you remove the whole infestation in one go. Do check first that your plant can cope with it! Spraying with water alone will not help, because the scale insect's shield protects it. Another effective method is alcohol. Soak a cotton pad in alcohol (do not use a sugary drink) and rub it thoroughly into every spot where scale insects are sitting. After roughly a minute you can lift them all off easily. Be precise, because if you miss even one you risk a fresh infestation.

Avoid removing scale insects by hand, as this can spread the eggs and cause a new infestation. So work thoroughly and carefully when you are getting rid of these unwelcome insects.