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
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 insect on a Bay Leaf Tree. © David Hughes
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
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
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.
By David Hughes -