How do I control scale insects?

How do I control scale insects on my houseplant?

The scale insect is an irritating pest you want to avoid, or get off your houseplant as quickly as you can. These small, hard-to-spot insects belong to the soft scale family, but they stand apart because their shield is not attached to their body. That makes them extra awkward to deal with.

Preventing scale insects

There are no guaranteed ways to keep scale insects away completely, but there are a few precautions you can take. Plants that stand in a draught or close to a radiator are more likely to be invaded by scale insects. So keep the humidity steady and spare your plant any extreme conditions. Strong, healthy plants are less appealing to scale insects, which is why looking after your plants properly matters.

Different types of scale insect

Within the scale insect family there are two main types:

1. Boisduval scale - often confused with the mealybug, this variety is elongated and has a yellow centre.
2. Oleander scale - this type is dirty white or yellowish in colour with a red centre, and they grow to about 2 millimetres.

How scale insects spread

Scale insects never turn up alone; they multiply quickly and often form large colonies on your plants. Males live only a few hours to at most two days, while the females can live for up to 120 days and sometimes lay a hundred eggs at a time. They can reproduce both sexually and asexually, which means a small outbreak soon grows into a serious threat to your plant.

Scale insects are spread by the wind, by other insects, or they can even be carried along by us on our clothing. They often sit on the underside of leaves or on the stem of the plant, which makes them hard to see in the early stages of an outbreak. Checking regularly is essential if you want to catch an infestation in time.

How much damage scale insects do

Scale insects feed on the sap of the plant, which leads to wilting, leaf loss and slower growth. If the pest is not tackled in time, the plant can even die from a shortage of nutrients.

Treating scale insects

Getting rid of scale insects completely is tricky, because they tend to build their protective shield around themselves and stay put. One effective method is to submerge the whole plant in water for 15 minutes. The scale insects drown and disappear in one go. Do check that your plant can cope with that!

Another method is to use alcohol. Soak a piece of cotton wool in alcohol (not a sweet drink) and rub it over the spots where the scale insects are sitting. After about a minute the scale insects come away easily. Be careful, though, because if you miss just one, a new outbreak can start.

Take care when removing scale insects by hand, because it can release eggs and cause a fresh outbreak. So work thoroughly when you clear these unwanted insects away.