Thompson & Morgan

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pests - scale insects

Scale Insects - Pests


Commonly asked question(s):

- How do I kill scale insects on cyclamen plants?
- What are the small white 'blobs' on the underside of some of the leaves of my cherry tree? and how do I get rid of them?
- Why are all the leaves on my bay tree turning pale brown with spots?


How do I kill scale insects on cyclamen plants?

Scale insect is particularly tricky to eliminate as the adults form hard waxy shells that act as a protective armour. Worse still, on indoor plants the environment allows them to continue reproducing all year round.

The key thing to remember with scale insects is that they are relatively immobile, so infestations are normally brought in when new plants are introduced. This can be avoided by giving all new plants a thorough inspection, regardless of how reputable the supplier is! Use a magnifying glass and check every part of the plant. Scale insect occurs on all parts, so check the stems as well as the leaves. It would also be best to quarantine any new plants on a different windowsill for a month to check that they are not carrying scale insects. The moment that you suspect a problem you must remove the plant to prevent scale insects from spreading.

To combat the current problem on your cyclamen, you will need to use different methods for the adults and the juveniles. Scrape the adults off of the plant with your thumb nail and wipe the foliage and stems gently with a cloth dipped in soapy water. Chemicals are most effective on the crawlers (juvenile forms) as they are more vulnerable before they develop a hard shell. You will need to make a repeat application two weeks later in order to catch any that you missed first time. Make sure you spray the underside of the leaves and the stems too. It is worth knowing that the dead adults do not drop off of the plant which makes it difficult to spot new infestations.



What are the small white 'blobs' on the underside of some of the leaves of my cherry tree? and how do I get rid of them?

It sounds as if you may have a type of scale insect (a sap-sucking insect) residing on the leaves of your cherry tree. The ‘blobs’ may be a cluster of eggs beneath white waxy fibres.

You should treat them as soon as possible as they will affect the general health of the plant. It’s best to spray the affected areas with a chemical control - there are many available. Look for the ingredients Deltamethrin or Thiacloprid on the container and check they are ok to use on fruit trees (if you are growing the tree for edible fruit). You can also buy winter washes which are applied when the tree is dormant to control over-wintering young nymphs.



Why are all the leaves on my bay tree turning pale brown with spots?

The little white blobs that look like mould are actually scale insects. These little insects suck sap from the plant and causing a pale mottling to the leaves which eventually turn yellow and drop off. Such infestations can weaken the plant, and may even cause severe die back.

When scale insects first hatch they are quite mobile and crawl around the plant sucking sap until their hard scaly shells form, when they become firmly fixed to one spot. Males, females and juveniles may be present at the same time and they are particularly prevalent from May to August.

The best way to control this is to target the young mobile insects using a systemic insecticide such as Provado Ultimate Bug Killer Concentrate or Scotts Bug Clear Ultra. A systemic insecticide is absorbed through the foliage and kills the scales as they feed. I would also cut any dead stems back to healthy growth to encourage the plant to rejuvenate.