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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 it's 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 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 insect pests.
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.
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