Aphids

What are Aphids?

Aphids are sap-feeding insects which attack the underside of young leaves, flower buds and shoot tips.  Some suck sap whilst others feed on foliage, stems and flowers.  There are many varieties including Black, green, white, pink, white, yellow and mottled ranging from 1 to 7mm long.  Many aphids that live on fruit and vegetables overwinter on a shrub or woody tree in Winter.

In spring, the hatched aphids feed on the young shoots and winged varieties move to non woody plants with new young growth for feeding.  Generally, egg laying forms of aphid develop at the end of their period of activity (autumn) but in some it can be Summer.  Most species overwinter as eggs although some can remain active, particulary on indoor plants or in mild winters.


Do they harm plants?

Yes.


What damage do they cause?

The plant foliage can be left with a sticky residue which is a sugary honeydew which aphids excrete.  On top of this honeydew, a black sooty mould often develops.  If you look beneath an infected branch or stem, you may find an accumulation of aphid skin casts.


Do they affect certain plants?

Aphids can cause plants to grow leaves which are distorted or curly compared to normal leaves. Plants can also be stunted in growth.  Some aphids also carry plant diseases from plant to plant.  In order to stop the spread of viruses transmitted by aphids, affected plants should be destroyed. Plants which are particularly affected include fruit and vegetables like strawberry, raspberry, tomatoes and plants of the cucumber/marrow family.  Also ornamental plants like daffodils, dahlias, lilies, pelargoniums, tulips and sweet peas.  What plants do aphids tend to affect?  In short, most garden ornamental plants can be affected as well as fruit and vegetables.


How do I get rid of them?

Non-chemical control

There are a number of ways to get rid of aphids from your garden.  The most environmentally friendly solution to getting rid aphids is to encouarage their natural enemies.  These include blue tits, ladybirds, various parasitic wasps and the larvae of hoverfly and lacewings.


Chemical control

Aphid numbers can grow quickly however and large infestation can appear before predator numbers increase quick enough to take effect.  Used during the growing season, insecticides give varing degrees of success.  Insecticides can be based on natural materials eg pyrethrum, rotenone, fatty acids, plant and fish oils and plant extracts.  These insecticides work in the form of a contact action and their effects are not long lasting so treatments must be thorough and repeated as and when necessary.

They can be used on fruit and vegatables up to 24hours before harvesting.  Insecticides can also be based on synthetic materials, these giving a generally higher level of control.  Bifenthrin is a contact insecticide but care needs to be taken when using it on edible plant material.  Imidacloprid is a systemic insecticide which works in a different way to the contact action.  After being sprayed on the plant leaf and stem, it is absorbed by the plant and ingested by the aphid when feeding. Care must be taken when using these insecticides on fruit and vegetables.

Overwintering aphid eggs on dormant fruit trees and bushes can be treated with a winter wash.   The easiest way to immediately get rid of infestations is to run plant stems and leaves between your fingers (providing you are not too squeamish!).  Washing with a shot of water washes them away, but does not kill them.

Always use chemicals as instructed on the label and wear any gloves etc. when necessary.