Pest 1 - Black Scale (Order : Hemiptera)

Black Scale infestation observed on umbrella plant during clean up of nursery greenhouse for preparation of upcoming propagation practical. 

Host Plants : 

Black Scale affects a wide range of plants, mostly woody.

Fruit crops include citrus, but also apricots, passionfruit, olive, vines. Ornamentals include house plants.

Distribution on Plant : 

Twigs and stems preferred, although any part of plant may be infested. 

Damage : 

Black scales are sap suckers and can target various parts of the plant. The young scales secrete honeydew with resultant growth of sooty mould fungus. Plants develop a black look and photosynthesis is affected, causing general weakening, stunting if untreated, sometimes defoliation. Fruit covered with black sooty mould. 

Appearance of Pest : 

Adult females are larger than males, are dark brown to black in colour,  hemispherical or "bun-shaped" and measure 3mm x 2mm, with a raised "H" formation on the back, although I did not notice this at the time. Before laying eggs, females are softer, grey and mottled - the "rubber" stage.  Male scales are narrower, flat and often not seen.                                                                       Nymphs are light brown and 0.5mm long. 

Life Cycle : 

2,000 eggs can be laid at a time beneath the adult female looking like little heaps of sand. Body of female shrinks and falls off after eggs hatch. Juveniles remain beneath the parent scale for a couple of days before actively settling on the leaves. After about a month, young scale moults and migrates to stem, where it remains. Another month, the scale develops the "H" backing, female deposits eggs shortly after and eggs hatch in 2-3 weeks, usually around early summer and also in autumn. 

Spread is by crawling from plant to plant, by insects (eg. ants), birds, wind or from clothing. They prefer humid conditions, moderate temperatures. 

Control methods

 cultural : severely infested portions can be pruned out.

 biological :  introduction of parasitizing wasps (target adult scale insects), or predatory insects like variety of ladybirds, green lacewing larvae, scale-eating caterpillars. 

 chemical : spray when eggs are hatching with white oil (2oml per litre of water). Rub scales carefully off with hand or 10ml of white oil + 2ml of maldison per litre of water. 

In this example, the plant was pruned back quite heavily as it can tolerate this. Less affected areas could have been washed with soapy water as another method of control. 

Reference : Kerruish  F-157