Australian Bug, Cottony cushion scale, Fluted Scale, Citrus Fluted Scale, Mealy Scale, White Scale, Australiese wolluis (Afr.)
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Icerya purchasi is a cosmopolitan pest originating from Australia. Females are easily recognised by the white, fluffy egg sacs. Each sac can contain up to 1000 eggs! Fluted Scale insects can lay eggs without the need to mate with males, making them self-fertilising hermaphrodites. New nymphs are mobile and will migrate from midribs of leaves to stems as they mature. These Scale bugs are a significant pest of Citrus. They thrive in warm conditions, although they can sometimes be seen on evergreen trees during spring and summer in temperate climates.
These bugs secrete honeydew which can attract sooty moulds.
Adults: Adult females are approximately 0.5 cm in size, oval and convex. The egg sac gradually grows from the body of the female and reaches a length between 0.5- 1.0 cm. Nymphs: Range between 0.5 mm to 0.4cm. They're reddish-brown with black legs and antennae. Eggs: Tiny, orange and oval. They're laid in white, fluted wax egg sacs.
Die-back or stunted growth. Premature leaf fall. Premature fruit fall. Clear, sticky secretions (honeydew) on leaves. Growth of sooty moulds.
It's thought that older, more established plants can tolerate lighter infestations. Regularly tending to plants and practising good housekeeping in the garden will give plants a better chance at survival. Monitor your plants regularly, making sure to check the branches, stems and midribs of leaves for fluffy white insects and honeydew. Badly infested branches can be pruned and removed and disposed of sensibly. Lighter infestations may be rubbed or picked off with hands or gloves. Alcohol-soaked cotton and neem-based leaf shine may be rubbed over the surfaces of the areas infested, if small! Horticultural oils, such as neem, may be used as the next alternative. If ants are also present at the site, they may be providing some protection to the scale. Ants can be controlled using a product such as Tanglefoot Pest Barrier. Capturing natural enemies and releasing them on the affected area may improve infestations. These include insects like ladybirds, hoverflies, lacewing and earwigs. Likewise, by letting parts of the garden 'grow wild', paired with an abundance of indigenous plants can attract the latter into your garden. Organic sprays, such as fatty acids and pyrethrums are less persistent than other pesticides, so they may require several applications. Always read instructions and make sure the edible crop is listed on the bottle for eating.
Scale can be difficult to treat with pesticides because of the waxy shell that protects them. When tackling scale, it's best to apply sprays during the earlier nymphal stages, when these insects are at their smallest and most vulnerable. For this species of scale, nymphs start to emerge at the beginning of spring in warmer climates, although they can survive all year when grown under glass. There are chemical alternatives available for home use, and they vary in the degree of persistence and strength. The chemicals deltamethrin and cypermethrin are just a couple of active compounds that are thought to be effective against scale. These can be long-lasting once sprayed, so do take care to follow manufacturers instructions before applying it to plants. Plants that are in flower should never be sprayed.