Scale Insects. Advice about control of Scale Insects on Garden Plants.  

Scale insects feed on plants in the garden, greenhouse, or the living room! There are various types of scale insects and they are difficult to control in a single application of insecticide. It normally takes several treatments of suitable pesticide - insecticide.

Scale insects are normally quite easy to recognise, in that they are literally like small raised scales - usually brown - living along the leaf 'veins' either on the top of the leaf or its underside.

They can either be 'crusty' or soft scales. They are also to be found upon stems once the infestation has taken hold. They do not move too much, and you will not find any legs! (Just think in terms of a miniature tortoise minus legs or head.) They are typically up to 3 or 4 mm long (1/8th in). The young are much smaller and sometimes light sandy brown in colour.

Scale insects are often first noticed, when investigating the fact that the leaves of your plant has a sticky substance over the surface - often leading to sooty mould - a black sooty covering of portions or all of the leaf surface. This sooty mould or sticky substance (honeydew) is secreted by most sap-sucking insect pests.

Scale insect on a Bay Leaf Tree.     © David Hughes

Scale insects are sap-sucking insects - more or less inserting a 'straw' into the plant, and happily sucking away in the same place for most of their lives. Female of some types of Scale Insects even lay their eggs under their shell as they feed. The young Scale insects then move off to find their own little plot further along the leaf, or perhaps venture out to once of the stems.

The protective coating of the scale, makes for difficult control by normal spraying of insecticides. A systemic insecticide is normally the best for total control, for it is difficult to locate each insect in order to spray it. A drench spray does not always kill all of the pests.

Malathion is a good spray to use for outdoor plants - also indoor plants providing that you take them outside to avoid the smell of the Malathion. The most effective time to use insecticides is during early summer, for it is then that the more susceptible young scale insects are more vulnerable to the insecticide. For indoor plants, you will find the young insects at most of the year.

Some scale insects have a fluffy white coating - not too dissimilar to Mealybugs - usually seen on larger shrubs or trees such as Beech. Under the fluff, you will find the unmistakable scale insect.