Description

The black scale species which are a pest are Parasaissetia nigra (black scale/ hibiscus shield scale) and Saissetia oleae- (black coffee scale / olive scale / citrus black scale). Both these types of scale belong to the same family of soft scale, although the waxy shell can appear quite hard. They can be easily confused with each other as they both have oval-shaped black shells. S. oleae tends to be more convex in shape, not as shiny and has a raised ‘H’-shaped ridge crossways on its shell. The females remain under cover for their entire lives and are usually headless, legless and wingless. They live in colonies that can completely cover the stems of a plant.

Adult size: 3mm

Out and about

Found all year round in warmer areas and greenhouses, but most numerous in summer after the eggs laid in spring have hatched. Thought to have originated in Africa but now found all over the world mainly in tropical and subtropical areas including southern Europe, the Americas, Asia, Australia and New Zealand. They are a particular pest in Queensland and to a lesser degree in other states.

Reproduction and Life cycle

The female black scale can produce offspring without having to mate, either by eggs or live-born, under the hard shell of her body. She can produce as many as 2,000 eggs, spring through summer. If the female dies, the young (crawlers) will stay protected and emerge to find their own feeding spot. At this stage they are soft, not having begun to produce the waxy coating. The “crawlers”, which are pale in colour will make their way to the stems, moulting at about four weeks then, when mature, they will develop the black shells and lay eggs. At this stage they do not move around.Their life cycle is comprised of three instars. Males are rare. One or two generations will occur during the year depending on climatic conditions.

To deter

To control

Sprays are particularly effective on the young crawlers before they have developed their waxy coatings Spray with: - Soapy water - White oil - Neem oil - Tea of garlic, nettles, basil or wormwood, or a combination - Spray pyrethrum if infestation is bad, but this will also harm beneficial insects If ants are protecting them, sprinkle diatomaceous earth around the base of the plant. See the information on ants for other methods of dealing with them.

Plants to repel

Plants to attract

Predators

Lacewings / Lady beetles / Minute pirate bug Parasitoid wasps

Why they are a Pest

They feed on a wide range of plants, and can severely affect the growth of the plant, weakening it and distorting the new growth. Heavy infestations can severely affect the health of the plant. As with aphids, these scale secrete honey dew which attracts ants. The ants protect and “farm” the scale bugs, transporting them to other areas on the plant. S. oleae can be found on citrus, pistachio, pear, stone fruit, pomegranate, passionfruit, quince, fig and is a major pest in olives P.nigra- avocado, citrus, guava, ginger, hibiscus, lillypilly, mango The honeydew itself can grow sooty mould (a fungus), which will not kill the plant but does inhibit photosynthesis. It can be treated with a soap spray, white oil or neem spray.