Colonies can usually be found on the undersides of leaves as well as on soft new shoot tips or buds. Black bean aphids cluster together and are noticeable because of their dark colouring. As they feed, they secrete a sticky, honeydew substance which drips onto lower foliage and often becomes covered in a sticky black mould.
- Black bean aphids affect a wide range of garden plants, trees shrubs and certain vegetables (mainly beans and peas).
About Black bean aphid
- The black bean aphid is more commonly known as ‘Black fly’.
- Adult aphids are up to 2mm long and elliptical in shape. They are black in colour, although they can also appear dark green or purple.
- Black bean aphid infestations are commonly managed by black garden ants which ‘farm’ the aphids and ‘milk’ the sticky honeydew that they produce. Ants will often carry young aphids onto new plants to establish new colonies.
- Large colonies can cover areas on the youngest sections of stems, and the undersides of leaves and sometimes on flowerbuds.
- During the warmer months aphids give birth to as many as five live young a day, so large colonies can develop very quickly.
- When the colonies become over-populated, they move to different locations by producing winged aphids.
- During the cooler months, aphids mate and produce eggs which overwinter.
- Aphids feed on plant sap and excrete plant sugars as honeydew.
- Honeydew often covers the leaves of a plant and then becomes infested with black sooty moulds. However, this is less common with black bean aphids where ants are collecting the honeydew.
Products containing the following chemical ingredients are all effective on Black bean aphid
- Natural fatty acids
- Surfactant based products
- Inspect plants regularly and deal with early symptoms immediately.
- Remove as many aphids as you can by hand or, if possible, cut off infested shoots and stems on susceptible shrubs.
- Spray the infested areas of a plant with a strong jet of water to keep aphid numbers down.
- Use nettings and fleeces to stop aphids spreading to susceptible plants.
- Encourage natural aphid predators such as ladybirds, Aphidoletes, hoverfly and lacewing larvae. These can be obtained from commercial suppliers and released on to affected plants outdoors.
- For greenhouse plants use parasitic wasps of aphids such as Aphidius matricariae and Aphidius ervi which can be purchased for release in a contained space.
- Regularly check plants for signs of aphid infestation and deal with them as soon as they appear.
- Encourage natural enemies.
- Avoid using broad spectrum insecticides which will kill beneficial insects as well as aphids.
- Encourage insectivorous birds by hanging feeders during the winter months and provide nesting boxes in the spring.
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