APHIDS

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Aphids are slow-moving and defenceless insects found feeding on many garden plants and trees. They are also referred to as greenfly, black fly and plant lice. There are many different species of aphids, more than 500 in Great Britain. They range in size from 1-7mm long and are yellow, pink, white or mottled in appearance.  Some cover themselves in a fluffy wax secretion which gives them a woolly appearance.

Aphids feed on on foliage, stems and flowers and cluster around soft new vegetation, although some will suck sap from plant roots. This causes distortion of the plants and can transmit viruses from plant to plant and is a particular problem on strawberries, raspberries, tomatoes, cucumbers, dahlias, tulips and sweet peas. They excrete a sticky substance called honeydew, which adheres to the plant foliage and encourages the growth of sooty moulds. 

You can spot aphid infestations on your plants as they will gather in numbers around shoot tips, flower buds and the underside of younger leaves.  The plant will look stunted and leaves distorted, whilst the sticky honeydew will start to allow the growth of black sooty moulds on the plant. Empty aphid cast skins may gather on the upper surface of the leaves.Aphids are not fussy eaters and most plants are susceptible to attack including ornamentals, vegetables, glasshouse plants and house plants. They are at their most active spring to late summer, or all year round under glass.

Aphids live in wingless female colonies, and aphid wings only form when conditions become overcrowded or the host plant deteriorates.  Females give birth to live young, who are pregnant at the time of their birth.  During cold spells aphids overwinter as eggs.

Aphids can be controlled by biological means as they have many predators including ladybirds, parasitic wasps, hover fly larvae, lace fly larvae.  Aphids predators can be used successfully in glasshouses the effect is limited as it takes time for natural enemies to build up their numbers. Where possible you can squash aphids between your fingers.

Insecticides can effectively be used to control aphids.  Contact pesticides based on natural compounds have a short persistence and can be used on edible crops. Chemical contact pesticides have more persistence and give longer lasting control but have less effect on aphids within distorted leaves and more restrictions on spraying near harvest time. Systemic insecticides are absorbed into the plant tissues and will effect aphids hidden in curled leaves that contact insecticides will not reach.

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