Aphids are small (usually 2-5 mm long) pear-shaped, soft-bodied insects and are one of our most common garden pests. They are commonly known as greenfly, or blackfly, but there are actually many different species which come in many different colours, e.g. green, black, yellow, white. They are small and slow-moving with two specialised cornicles projecting from their rear. They come in both winged and wingless forms. The winged form can fly weakly but may travel long distances on wind currents.
Aphids have sharp mouthparts which pierce plant tissue allowing them to feed off plant sap. They subsequently secrete a sugary honeydew over leaves. Some aphids can feed off several different plant species while others are limited to only one. They may attack all parts of the plant but the tender new growth is much more vulnerable.
Aphids have many generations each year and life cycles are very complex. They generally over-winter as eggs but in mild winters adults may survive. When temperatures increase in the spring the adults give birth to live young which are all female allowing populations to multiply rapidly. When lots of aphids are present on a plant the winged form may be produced which can then fly to new plants. Aphids are often 'farmed' by ants for their honeydew and ants may move them to previously unaffected parts of the plant.
Although aphids infestations may not damage plants in some cases they cause serious problems. They may reduce the overall vigour of a plant. Sooty moulds can grow on the honeydew and, although these do not directly harm the plant, they block sunlight from reaching the leaves. Also, the saliva of some aphids may be toxic and can cause distortion or discoloration of leaves. Most significantly some aphids may transmit viruses to plants, such as cucumber mosaic virus.
Here are some ideas for ways to reduce aphid attack.
• Mechanical removal of aphids with a strong stream water. This should be repeated once or twice a week and is effective for most infestations. You can use a normal garden hosepipe but may consider buying a specialised attachment which concentrates the jet of water
- AphidsNoMore (sell Aphid Eliminator)
• Smear bands of grease around trees or plants to prevent ants from moving aphids around
- Chase Organics
• Cover plants with horticultural fleece or enviromesh
- Chase Organics
• Prune affected parts of plants
• Plant species resistant to the viral diseases transmitted by aphids
• Avoid synthetic fertilizers. These supply too much nitrogen to the plant allowing lush soft growth which is more susceptible to attack.
• Wash with warm soapy solution (try a small amount on a few leaves to see if it damages them). Commercial sprays are
Suffolk Herbs Ltd.
• Use oil-based spray in the winter on fruit trees (these smother over-wintering eggs)
- Green Gardener (Winter Wash)
- Defenders (Eradicoat)
• Encourage insects, birds and bats which eat aphids. Certain plants are particularly effective at attracting beneficial insects e.g. marigolds, poached egg plant (Limnanthes douglasii), nettles.
• Introduce aphid-eating insects such as ladybirds (Adalia bipunctata), lacewing (Chrysoperlus), Aphidius (a parasitic wasp) or Aphidiletes aphidimyza (a predatory midge)
- Green Gardener
- Just Green
- Scarletts PlantCare
- Chase Organics
- English Woodlands Ltd
- Biological Crop Protection Ltd
Exclude ants when introducing biological controls
Least toxic chemical controls
• Spray a dilute solution of fatty acids or soft soap on affected leaves and rub the aphids off with your fingers. This will probably have to be repeated once or twice a week but as the plants age their tissue becomes tougher and less vulnerable to attack. These can be purchased from most local garden stores or online from
- Green Gardener
- Suffolk Herbs Ltd.
- Gone Gardening
- Chase Organics
• Treat with neem oil
- House of Mistry
- Handa Fine Chemicals
Traditional organic remedies
• Plant resistant varieties - certain varieties are resistant to the viral diseases transmitted by aphids.
• Avoid synthetic fertilisers - these supply too much nitrogen to the plant allowing lush soft growth which is more susceptible to attack.
• Companion planting - plant garlic cloves (just one or two) among rose bushes. An infusion of garlic crushed into water and sprayed on the aphids will also help remove them. Many herbs, such as hyssop, sage, dill, lavender and thyme discourage aphids if planted near to susceptible plants.
• Plant a trap crop e.g. blackfly love nasturtiums which can be pulled out when they are infested.
• Spray nettle spray – this is made from common stinging nettles and is reported to help control aphids.
Gather 224g (l/21b) young nettles and soak in a bucket of water for a week. Strain and use undiluted as a control for aphids on roses and celery leaf miner. Add the mushy nettles to the compost heap.
• Spray rhubarb spray - the oxalic acid in rhubarb leaves can help to control aphids, particularly on roses.
Cut 450g (1lb) rhubarb leaves, place in an old saucepan (the oxalic acid may damage one that you still use) with 1.1 litres (2pt) water and boil for half an hour, topping up as necessary. When cool, add 1 dessertspoon of soap flakes dissolved in 275ml (1/2pt) warm water. This acts as the wetting agent when added to the strained rhubarb liquid. Stir the mixture thoroughly and use undiluted as a spray. Rhubarb leaves are quite toxic so be careful to keep this away from children and pets.
Spray rhubarb soap - spray healthy plants as prevention and affected plants to help remove infestations.
Shred a couple of pounds of rhubarb leaves into a couple of pints of water and boil for half an hour (use an old pan you don't want any more). Strain the liquid, mix in two ounces of soft soap dissolved in another pint of water. Rhubarb leaves are quite toxic so be careful to keep this away from children and pets.
• Use elder spray - this is effective against aphids, small caterpillars and for mildew and blackspot on roses. The effective agent is hydro-cyanic acid, so use an old saucepan when preparing the spray
Gather 450g (1 lb) leaves and young stems of elder prefer-ably in spring when the sap is rising. Place in the saucepan and add 3.3 litres (6pt) water. Boil for half an hour, topping up as necessary. Strain through old tights and use the liquid cold and undiluted. It will keep for three months if bottled tightly while still hot.
• Sprays made from hot peppers, garlic or onions are also reported to be effective.