Waxy brown scale insects sucking sap on the underside of a leaf

Scale insects

BBC Gardeners' World Magazine

Published: Friday, 15 March 2019 at 3:00 pm

Tackle scale insects in your greenhouse and on your house and garden plants, with help from our expert guide.

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Tiny sap-sucking scale insects. They are 1-6mm long, and their whitish, grey-brown shells are covered by protective, waxy scales. The insects don't cause too much damage unless they are present in huge numbers, but some excrete an unsightly, sticky, sugary substance (called honeydew) which encourages the growth of a fungus called sooty mould. Early summer is the best time to tackle the problem, when the newly hatched insects are crawling around looking for a place to feed and settle.

Symptoms

Plants are infested with tiny, sap-feeding, scale-like insects packed around the stems and leaves.

Find it on

a wide range of plants, house plants, greenhouse plants

Organic

First try to remove them with your thumbnail. If there are too many, use an insecticidal soap spray. Alternatively, leave them for the birds to pick off. In a greenhouse, use the parasitic wasp, Metaphycus helvolus, bought by mail order as a biological control.

Chemical

Use a pesticide containing deltamethrin on ornamental crops - organic fatty acid sprays can be used on fruit bushes and trees.

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