Blackfly (Black Bean Aphid)
Dense colonies of black bean aphid, often referred to a blackfly, can be found on some beans and other plants during spring and summer. There are many other species of aphid that are black.
Scientific name Aphis fabae species group
Plants affected A very wide range including broad, French and runner beans, nasturtium, dahlia, philadelphus, viburnum and euonymus
Main cause A black sap-sucking insect
What is black bean aphid?
There are several species of black aphid that can be found on garden plants, a very common blackfly is the group of species known as the black bean aphid, Aphis fabae agg. These is a sap-sucking insects can form dense colonies on the soft young growth of many plants.
There are many other black aphid species for example cherry trees are often host to a different species known as cherry blackfly. Aphids are sap-sucking true bugs. They range in size from 1 to 7mm (¼in or less) long. Some aphids are known as greenfly or blackfly, but there are species that are yellow, pink, white or mottled. There are more than 500 aphid species in Britain. Some feed on only one or two plant species, but others can be found on a wide range of plant hosts. Many have lifecycles that involve more than one host plant. Almost any plant can be a host to aphids, including ornamentals, vegetables, fruits, greenhouse plants and houseplants. More information on aphids.
Black bean aphid are up to 2mm long and are mainly black but may have some white flecks on the upper surface of their bodies. Dense aggregations can rapidly develop on soft shoot tips, flower stems and on the underside of the younger leaves. The aphids are often attended by ants, which collect the sugary honeydew that aphids excrete, the ants will also remove aphid predators such as ladybird larvae. Whitish cast skins of aphids often accumulate on host plants.
Large populations can weaken host plants and can result in stunted growth. On broad beans, pod formation can be poor if the plants become heavily affected. Flower formation on ornamental plants, such as dahlia, nasturtium and poppies, can be damaged when blackfly are feeding on the developing flowers. The winter-spring host plants, such as Philadelphus, Viburnum and common spindle (Euonymus europaeus), often develop curled foliage in response to the aphids feeding, this damage is minor and the plants usually recover.
What should I do?
Here are our top tips to your most common questions on managing aphids.
Should you remove aphids? Tolerate aphids where possible. It is usual to have some in a healthy, balanced garden. They are a vital food source for a wide range of wildlife in the garden
Do aphids kill plants? Very rarely. Some aphids cause some leaf and bud distortion, they can spread plant viruses and you might see some honeydew on which a harmless sooty mould can grow. This can be wiped off with a damp cloth.
Do I have to control aphids? You don’t have to kill or control them. They are part of the biodiversity of gardens and a vital food source for other wildlife in your garden. If you do decide to control aphids, these are the ways you can cause least harm to the environment and avoid pesticides
- Check plants frequently so you can act before the damage has developed
- Use finger and thumb to squash aphid colonies
- Encourage the natural enemies of aphids in your garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. In spring, aphid populations increase before the natural enemies are active in sufficient numbers – so if you wait a while, they’ll often give the control
- Some natural enemies of aphids can be purchased as biological control for use in greenhouses, including hoverfly larvae, lacewing larvae and several parasitoid wasps. More information about these can be found on the ‘aphid predators’ page
PesticidesThe RHS recommends that you don’t use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
Where you cannot tolerate blackfly, manage them using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.
Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) can give good control of aphids. These pesticides have a very short persistence and so may require reapplication to keep aphid numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
- Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, Growing Success Bug Stop, Rose Clear 3 in 1 Action SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These products contain some synthetic ingredients and so are not considered organic
- Further information about the use of pesticides available for management of aphids is available on the pesticides for gardeners leaflet
Pesticides for gardeners (pdf document)
The group of species known as Black bean aphid Aphis fabae agg. overwinter as eggs on shrubs such as common spindle (Euonymus europaeus), Viburnum and Philadelphus. Egg hatch occurs in spring as the winter host plant is coming into new leaf. Several generations of wingless aphids, which are all female and produce live young rather than eggs, develop on the spring foliage. By May, the foliage on the winter host plants has become older and tougher, which along with increasing day length induces a change in the aphids. A generation of female winged aphids develops that fly away in search of suitable summer host plants, such as beans, nasturtium, poppies and dahlia. At that time of year male aphids are not required for reproduction, so a single winged aphid arriving on a broad bean can quickly establish a new colony. Blackfly colonies on the winter-spring host plants die out during May-June.
At the end of summer, another winged generation of aphids is produced that migrates back to the winter host plants. At that time there are males and females that will mate before the females deposit eggs around buds and in crevices on the stems.
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