In the wild: Dock, fat-hen, nightshade, poppy, thistle
In the garden: Viburnum, dahlia, nasturtium and a number of ornamental garden plants
On Crops: Field & broad beans, dwarf French & runner beans, sugar beet, fodder beet, spinach
Throughout Europe and the UK
These are soft-bodied insects about 2mm long and are usually black, very dark brown or dark green in colour. Their legs are usually lighter in colour and the non-winged aphids can display small white patches on their backs. The winged adults are usually black. They are often found in dense clusters on tender new growth and are commonly farmed by ants.
Black bean aphids are usually visible on plants because of their contrasting colour and the presence of ants. Aphids feed by sucking plant juices, so infested growth is often yellowed and curled. In addition to the direct damage that aphid feeding does to plants, aphids can transmit several diseases.
Check plants often for early outbreaks. Either squash the aphid clusters or remove, contain and destroy the parts of the plants where they are present. Encourage beneficial insects including ladybirds, hoverflies, and lacewings, which are important aphid predators.
In small outbreaks, a high-pressure spray from the garden hose can help remove aphids from plants. Where aphid problems persist, as a last resort organic pyrethrum-based pesticides are available from garden centres. These need to be applied following the instructions on the label.
Ladybirds and their larvae are very effective predators of aphids and should be welcomed into your garden. Other predators such as hoverfly larvae and lacewings also provide effective natural ways of controlling aphids. Parasitic wasps will help to control aphid infestations by injecting aphids with their eggs. The eggs hatch into maggots that eat the aphids from the inside out. Eventually the wasp maggots kill the aphids, turning them into ‘mummies’ before emerging from the mummified bodies as adult wasps. Ants will often farm aphids and collect the sugary honeydew that aphids produce. The ants protect aphids from predators and will move them to new plants to establish new aphid colonies.