Aphids are sap-sucking true bugs. They range in size from 1 to 7 mm (¼ in 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. 

Currant blister aphid is one of a number of aphids that feed on currants. Is pale yellow and up to 2.5 mm in length. It can be found on the lower leaf surface in early summer and causes leaf distortion. 

• Leaves at the shoot tips appear puckered or blistered
• The distorted foliage takes on a reddish or yellowish green discolouration
• Pale yellow aphids can be found underneath the blistered areas in late spring-early summer
• This aphid is a food source for many aphid predators and colonies can be wiped out 

Currants affected by blister aphid still make growth and produce a good crop, so treatment is not necessary.

Aphids form the basis of many food chains and it is not unusual to have some of these animals in a healthy balanced garden ecosystem. On established bushes aphids can usually be considered part of the biodiversity they support, natural enemies will normally reduce numbers during summer.

• Some damage from these aphids can be tolerated with no effects on quality or quantity of yield.
• 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
• Check currants frequently from spring onwards so action can be taken before a damaging population has developed
• Use finger and thumb to squash aphid colonies where practical