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. 

Three aphid (greenfly/blackfly) species are often found on currants.  All three species overwinter on the stems as eggs that hatch in the spring. Only the currant-sowthistle aphid may affect cropping and these aphids can often be tolerated as part of garden biodiversity.  

• The currant-sowthistle aphid (Hypermyzus lactucae), Is 2-3mm in length and usually green.
  In late spring it can cause distorted leaves with yellowish mottling, this is the only currant aphid which may affect cropping
• Currant blister aphid (Cryptomyzus ribis)  Is 1.5-2.5mm long and yellow. It cause puckered, reddish or yellowish leaves at the shoot tips. Cropping usually remains unaffected
• Permanent currant aphid (Aphis schneideri) is dark green or black and reaches 2.3mm in length.
  It remains on currants throughout the summer. It causes pronounced stunting of the shoot tips with the leaves compressed together. This species does not normally affect the crop

Aphids form the basis of many food chains in the garden and it is not unusual to have some of these animals in a healthy balanced garden ecosystem.  Check currants frequently from spring onwards so action can be taken before a damaging population has developed. On established bushes aphids can usually be considered part of the biodiversity they support, natural enemies will normally reduce numbers during summer. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.

Non-pesticide control

• Where possible tolerate populations of aphids. Some damage from these aphids can be tolerated with no effects on quality or quantity of yield. Aphids form an important part of many food chains and can be part of a healthy garden ecosystem
• Use finger and thumb to squash aphid colonies where practical
• Encourage aphid predators in the garden, such as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs. Be aware that in spring aphid populations often build up before natural enemies are active in sufficient numbers and then give good control

Pesticide control

• There is no point in spraying after the foliage has become distorted
• On fruit trees and shrubs. Overwintering aphid eggs can be destroyed by using a plant oil winter wash (organic e.g. Growing Success Winter Tree Wash). This can be used when the buds are fully dormant in November-early February on a dry frost-free day. Plant oil winter washes are less likely to be detrimental to natural enemies and can mean that spring sprays are unnecessary 
• 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
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer).
• A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles

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Pesticides for gardeners (pdf document)

Currant-sowthistle aphid (Hypermyzus lactucae) is up to 2.7mm long and green, with pale legs. The eggs hatch in March or April. By May large colonies of aphids can develop on currants. Currant-sowthistle aphid colonies die out on currants during May and June and winged forms migrate to the summer host sowthistle (Sonchus spp.) where they form colonies during the summer months. In the autumn there is a return migration to currants where mating occurs and overwintering eggs are laid in the bud axils.

Currant blister aphid (Cryptomyzus ribis) are pale yellow and live on the underside of the leaves where they feed by sucking sap. Where they feed a puckering, distortion and reddish discolouration often develops. Wingless forms of the blister aphid are active on currants from bud burst until July. In midsummer, winged aphids develop and migrate to the wild flower known as hedge woundwort (Stachys sylvatica). Populations on currants come to an end at that time, although damaged foliage remains visible until leaf fall. Aphids return to currants in the autumn when overwintering eggs are laid.

Permanent currant aphid (Aphis schneideri) reaches 2.2mm in length and is black. Eggs hatch in spring and colonies soon develop on shot tips. As the common name suggests this aphid can be present on currants all year although winged forms are produced in the summer these migrate to other currants.