What are Aphids?
Aphids are small pests that infest a large number of garden plants and suck the sap from them.
Colonies are particularly attracted to areas of new growth, and are generally found on the underside of new leaves, buds, stems, and flower.
This causes the shoots and leaves to become distorted, and although this is unlikely to kill the plant it can seriously weaken it.
Aphids may transmit viruses so controlling them is quite important.
Some species attack a wide range of plants, others are host specific e.g. greenfly on roses, and blackfly on broad beans and nasturtiums.
Most are around 1.5mm long, with soft bodies.
The symptoms are generally seen as a sticky black substance on the leaves of the plant/s.
The stickiness is aphid excrement (honey dew) and the blackness is a sooty mould.
Another symptom is distorted shoot and leaf growth.
Both young and adult aphids feed almost continuously.
How to Detect Aphids:
Blackfly are easy to see but the presence of other types is often first recognized by the damage they cause.
Look inside rolled up leaves for Cherry aphid, under cabbage leaves for mealy aphid and in the fluffy lumps on fruit bark for woolly aphid.
If lettuce turns yellow and wilts, suspect Root aphids, and if plants are sticky with honeydew, or black with sooty mould, look on the leaves above for pests.
How to Control Aphids:
Prevention is the first method of control.
Healthy plants are less likely to be attacked by aphids, so, pay attention to correct feeding.
Walk around the garden daily and pick off infested leaves.
Alternatively, rub off aphids between thumb and forefinger without damaging the plant.
Use insecticides as little as possible.
Avoid blanket spraying of the whole plant as this can kill beneficial insects such as the Ladybirds, Lacewings and Hoverflies that prey on aphids.
Sticky yellow cards are an environmentally friendly way of controlling greenhouse aphids.
The colour attracts them away from plants and the adhesive acts like fly-paper.
Feed birds in bad weather and they will repay you by eating aphids in summer.
A family of blue tits can eat over 100,000 aphids a year.
Keep weeds under control. Aphids often feed and live through the winter months on common weeds.
There are now only three types of man-made chemical insecticides that can be used by the amateur gardener for aphid control, they are:
1) Contact insecticides:
When applied as a spray or in dust form this only kills the aphids it touches.
The natural plant extract insecticides pyrethrum and derris, and horticultural soft soap, are examples of tried and tested contact insecticides.
Various types of Insecticide Sprayers
2) Tar oil wash:
Is used only on dormant, deciduous (leafless), shrubs and trees, and kills both hibernating aphids and their eggs, which are hidden in cracks in the bark.
3) Systemic insecticides:
Are taken up by the plant and kill aphids that suck the sap as well as those that are directly sprayed.
This type can even reach aphids hidden in curled or tightly packed leaves.
There are no glasshouse fumigants licensed in the UK for use by the amateur gardener during the growing season.
Chemical & Biological control:
Garden insecticides, both organic and artificial, are considered safe for plants, pets, people and the environment provided you follow the rules.
The law requires you to read and follow the instructions on the label.
Check that the insecticide used is recommended for aphids, and that it is safe for your plants before you start spraying.
When to apply chemical insecticides:
- Apply before damaging aphid populations build up.
- Examine plants frequently, especially during March to October.
- Protect beneficial insects by spraying in the evening and treating fruit trees only before and after flowering.
- Spray only where there are pests.
- All-over spraying is dangerous to wildlife, causes pollution and wastes money.
Encouraging Aphidius colemani, Aphidloletes aphidimyza, Lacewings and Ladybirds into your garden is a cheap and safe way to control many pests
Specific Plant Treatment:
Tar oil winter wash on dormant trees, and systemic insecticide after flowering.
Pinch out growing tips to deter blackfly and / or spray with contact insecticide.
Rub off small infestations, and / or pray under leaves with contact insecticide.
Use systemic insecticide to reach aphid rolled within leaves.
Lettuce Root aphids:
Drench soil with contact insecticide.
Spray with contact insecticide as soon aphids are seen or destroy plant to prevent spread.
Rub aphids off, or pinch out infested tips, and / or spray with systemic insecticide.
Soap insecticides are very effective,as are systemic insecticide on heavy attacks.
Tar oil winter wash on deciduous types, and / or systemic insecticide in severe cases.
Wipe off smooth-leaved plants. Place systemic insecticide sticks into compost.