Aphids are very common sap-sucking insects that can cause a lack of plant vigour, distorted growth and often excrete a sticky substance (honeydew) on foliage which allows the growth of sooty moulds. Some aphids transmit plant viruses which can be a problem on strawberries, raspberries, tomatoes, cucumbers, dahlias, tulips, sweet peas and many other plants.

Common name Aphids, greenfly, blackfly, plant lice

Plants affected Most plants are susceptible

Symptoms Poor and distorted growth, sticky honeydew and sooty moulds

Active Spring to late summer on garden plants; all year round indoors

What are Aphids

Aphids are sap-sucking true-bugs. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. Some species, like woolly beech aphid and woolly aphid on apple, cover themselves with a fluffy white waxy secretion and can be confused with some scale insects, mealybug or whitefly. Most aphids feed on foliage, stems and flowers but some suck sap from roots.

There are more than 500 aphid species in Britain. Some species only attack one or two plant species, but others attack a wide range of plant hosts. Almost all plants can be affected, including ornamentals, vegetables, fruits, greenhouse plants and houseplants.

It thrives in warm conditions, which is why it is not usually a problem on outdoor plants. Glasshouse whitefly is active all year round on houseplants and in greenhouses.

Symptoms

You may see the following symptoms:

It is usually possible to see aphid infestations with the naked eye, and they tend to colonise shoot tips, flower buds and the underside of younger leaves

Aphids cause stunted growth with curled or distorted leaves. This can weaken the plant

Many aphids also excrete a sticky honeydew which allows the growth of black sooty moulds

White cast skins of aphids can accumulate on the upper surface of leaves