How to get rid of scale insects
Follow our hints and tips for removing these destructive insects
There are about 25 different species of scale insects in the UK, ranging in colour from a darkish brown to pale cream and pale green. They are incredibly difficult to spot, especially on garden plants, and the first sign that you have an infestation is the leaves of your plants will be sticky, covered in a black sooty deposit or the leaves could have started going yellow and falling off. They resemble limpets, being small flat discs with a shell-like outer, hardly making a bump on the plant. They are usually on the underside of the leaves and on the stem. They infest a huge range of both garden and indoor plants.
Being sap suckers they will weaken the plant and if you have a heavy infestation they can seriously stunt the growth. As they ingest sap they exude sweet sticky honeydew which attracts sooty fungus, which can be another sign that you have an infestation, and is another problem to tackle. (Click here to read the blog explaining how to get rid of sooty fungus)
Garden scale insects only breed once a year with the eggs hatching in late June and July but indoors or in a heated greenhouse they will reproduce all year round so can quickly build up vast numbers. Some will lay their eggs underneath the protective shell and others cover the eggs in a tangle of white fibres, so this can also be something to watch out for.
They are incredibly difficult to remove due to their suction onto the plant and their protective shell. If you are using a spray make sure it is a cool, dull, windless day. Don’t spray when the plant is in full flower as you could also kill any pollinating insects.
- Scrape them off with your thumbnail.
- Scrub them off with an old toothbrush.
- Dip a cotton bud in rubbing alcohol and remove them.
- Outdoors the easiest solution is to feed the birds; small birds such as blue and coal tits, wrens and finches will pick them off.
- You can get a biological control but it is only effective in a greenhouse.
- Spray with a solution of mild washing-up liquid and tepid water. Make sure that you drench the plant and repeat every 4 – 7 days. Spray with a systemic chemical spray which gets into the sap or spray with a contact killer but with this method you have to make sure to spray each insect.
- There are now chemical sprays based on fatty acids, such as Solabiol Bug Free, which are safe to use on edible crops but will need repeated applications.
- In winter you can apply a winter oil wash to roses and deciduous fruit trees to kill any overwintering nymphs.
- If the infestation is particularly heavy and the plant can regenerate it may be necessary to prune out the insects. Remember to disinfect the pruners after use.