What is currant blister aphid?

Currant blister aphid is one of a number of aphids that feed on currants. It is a sap-sucking insect that can be found on the lower leaf surface in early summer and causes leaf distortion.

Symptoms

• 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

Control

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

Check currants frequently from spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (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.

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
• 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

• 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. Vitax 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 detrimental to natural enemies and can mean that spring sprays are unnecessary 
• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) 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, RHS Bug and Mildew Control, 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)
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. On 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.
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener
 

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Pesticides for gardeners (pdf document)
 

Biology

• Currant blister aphids are pale yellow and live on the underside of the leaves where they feed by sucking sap
• They also secrete chemicals into the foliage and this causes puckering, distortion and discolouration
• Other species of aphid also occur on currants but they do not produce this characteristic blistering symptom
• 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
• The aphids return to currants in the autumn when overwintering eggs are laid