Late winter and early spring are the best times to spray for scale insects

Red scaleRed scaleScale insects infest many species of trees and shrubs and can do damage out of all proportion to their size. They often go unnoticed by gardeners until they start pruning in winter and spring, but luckily these are the best times to spray. Learn all about scale insects below.

Scales are tiny parasitic insects that adhere to plants and live off the plant's sap. They look like bumps and are often mistaken for a disease. There are some 7,000 species of scale insects, varying greatly in colour, shape and size. Scales often go unnoticed by the gardener, but they can do damage out of all proportion to their size. They can quickly infest leaves, twigs, branches and fruit, and are found all year round.

Magnolia Scale Picture courtesy Scott CamazineMagnolia Scale Picture courtesy Scott CamazineScale is more prevalent in shady or protected places of the garden like walled courtyard and patios, than in open areas. They can be hard or soft, and like aphids, mealy bug and Australian bug, scale insects secrete honeydew which attracts ants. Ants crawling up and down the plant are a sign of possible scale infestation.

An unsightly black sooty mould often grows on the honeydew. The ants 'farm' the scale for its honeydew, and in return protect the scale from predators. Get rid of the scale as well as the ants and the mould will disappear.

When scale insects are young they are mobile and crawl around, searching for a place to attach to the plant, after which they are immobile. Control measures are most effective during the crawler stage. When they mature; the adult females are static, while the males have tiny wings and are a bit more mobile.

Hard or armoured scales are distinguished from soft scale by a tough lid on top of their bodies that is separate from the body of the insect, hence the name armoured scale. With soft scale the covering is the hardened part of the upper body.

There are many soft scale species like brown scale, black scale, green scale, wax scale, ground scale, protea soft green scale, and heart-shaped scale. Ground scale is rare and infests the roots of various plants. 

Pernicious Scale on Bay TreePernicious Scale on Bay TreeHard or armoured scales include pernicious scale, red scale, grey scale, circular purple scale, oleander scale, protea white scale, silver tree scale, aloe white scale, aloe red scale, white peach and palm scales.

Scale insects infest many species of trees and shrubs like camellia, bougainvillea, hibiscus, citrus, avocado, palms, ferns, orchids, roses, ficus species and ivy, as well as proteas and aloes, to name but a few. 

To control them spray with any oil based formulation like canola oil or a mineral oil like Oleum which will suffocate the insects. Repeat applications may be required if infestations are severe. The scale will die but remains attached to the branches and can be gently rubbed off with a soft brush.

Click here to find out how to make your own DIY white oil for an organic insecticide

White wax scaleWhite wax scaleNever apply oil based formulations onto plants in the heat of the day or when the temperatures exceed 30°C. Winter and early spring are ideal times to spray roses, citrus, deciduous fruit trees and deciduous shrubs and trees. To control scale heavily infested branches and twigs can be pruned away to reduce numbers. 

Please remember that natural oil sprays can also kill beneficial insects; so only spray the infected plants when absolutely necessary. One or two applications should not do too much harm.

Scale insects have many natural predators such as ladybirds, predatory thrips and lacewings. Controlling ant nests in the garden is one of the best ways to encourage natural predators, and growing a year-round supply of flowers and herbs will maintain beneficial insect populations throughout the year, as they rely on nectar and pollen for food during part of their life cycle.