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Bugwatch: Scale

Scale insects are some of the most common garden pests around.

They attract other pests and suck the vigour from your plants, but they are easy to control and even easier to prevent.

Scale can vary dramatically in appearance, too. There are, after all, over 8000 described species of scale insects in existence. The most common of these are the very small sea-shell-like objects (1–2 mm) growing beneath wax covers, shiny pearl-like objects (about 5 mm), and creatures covered with mealy wax. With the exception of mealybugs, scale almost always appear to be permanently attached to the stems of affected plants, which can make them difficult to see.


Citrus Snow Scale. Photo - Mary Keim 


Scale insects damage plants by feeding on sap and secreting honeydew which causes sooty mould. This in turn can cause leaf drop and dieback. Ants feed on the honeydew and act as bodyguards for the scale, keeping away natural scale predators such as lady bugs and wasps. Eggs hatch into crawlers, which can be carried on the wind to other plants.

Remember, plants under stress are more susceptible to scale attack so spoil them with a dose of seaweed solution and a light feed in spring and autumn.

Healthy plants are naturally more pest-resistant.


Chemical control

Eco-oil won't be enough to control a large infestation. Start treating with Yates Scale Gun as per instructions on the package until they are gone. Continue spraying with Eco-oil every fortnight to prevent another infestation.


Organic control

Cut plants back by one third (after frosts have passed), throw tepid soapy water over them and blast it off with a hose 20 minutes later. Spray with a mixture of Eco-Neem and Eco-oil, and then spray every fortnight with Eco-oil, following the directions on the label. Control ants by banding the base of the plant with petroleum jelly.


Biological control

Encouraging beneficial insects is the third step in reducing the occurrence of scale infestation in your garden. Ladybugs and wasps prey on scale and can be introduced safely into home gardens. The Spotless Ladybeetle is one of the commercially available beneficial bugs that can be very effective at reducing scale. These bugs can be purchased mail-order from OCP and released into the garden anywhere in Australia other than WA.


About this article

Author: Mez Woodward and Dan Wheatley