Why Are My Redcurrant Leaves Curling?

Currant blister aphid

Currant blister aphid (Cryptomyzus ribis) is the same species that affects blackcurrant, but on redcurrant its damage produces reddish blisters rather than the greenish-yellow puckering typical on blackcurrant. The aphids overwinter as eggs on the currant stems and hatch in early spring as the buds open. Feeding on the underside of the young leaves, they inject a growth-disrupting chemical that causes the leaf tissue above them to swell, pucker, and develop vivid reddish-pink or yellowish blisters on the upper leaf surface. The aphids are concealed inside these blistered areas on the leaf underside and cannot be treated once the leaf has closed around them.

By June or July, most aphid colonies naturally migrate off the redcurrant to their summer hosts (Galium species) and the blistering damage stops. The plant continues to produce fruit normally. The impact on cropping is minimal unless the infestation is exceptionally severe in the spring.

What to do

• The only effective control window is early spring, before the leaves have blistered and enclosed the aphid colonies. From March, inspect the underside of opening leaves for the pale green aphid colonies and treat with insecticidal soap at this stage, before the leaves have curled.
• Once the blisters have formed, the aphids inside are protected from contact sprays. At this stage, either remove and destroy the most severely affected leaves, or accept the cosmetic damage and wait for the aphids to migrate naturally by midsummer.
• The blistered leaves persist on the plant for the rest of the season but do not spread to new growth after the aphids leave.

Gall midge

Redcurrant gall midge (Dasineura tetensi) affects redcurrants as well as blackcurrants. The larvae feed inside the growing tips, causing the young leaves at the shoot tip to curl together into a mass of crinkled, distorted tissue. Multiple generations occur each season.

What to do

• Pinch out and destroy distorted growing tips as they appear. Repeat through the season. The damage is rarely severe enough to affect cropping significantly on an established redcurrant bush.

Leaf spot

Currant leaf spot (Pseudopeziza ribis) produces small, dark brown spots on the leaves from early summer onward. In severe cases, affected leaves turn yellow and fall prematurely, weakening the plant. Leaf spot does not cause the same blistered curling as aphid damage but can cause some leaf margin curling and distortion around heavy spotting. It is most common in wet summers and in poorly ventilated bushes.

What to do

• Collect and destroy all fallen leaves in autumn: the leaf spot fungus overwinters in fallen leaf debris and re-infects new growth in spring. Improve airflow by open pruning. In severe cases, a copper-based fungicide applied at bud burst reduces initial infection levels.

Drought

Drought causes redcurrant leaves to curl at the margins, become dull green, and drop prematurely. Redcurrants are more drought-tolerant than blackcurrants but still perform best in consistently moist soil, particularly during fruit development when water stress reduces berry size.

What to do

• Apply a mulch of compost or bark chips around the base of the bush in spring. Water during extended dry periods, particularly from fruit set through to harvest.

Frequently asked questions

Why are my redcurrant leaves curling?

Redcurrant leaves curl most commonly because of currant blister aphid (Cryptomyzus ribis), which causes the characteristic red or yellow blistering and upward curling of the leaves that many redcurrant growers see each spring. The aphids feed on the underside of the leaves within these blistered, curled areas. Other causes include gall midge (Dasineura tetensi), which causes the young shoot tips to curl; leaf spot (Pseudopeziza ribis), which causes dark spots and eventual leaf drop without the distinctive blistering; and drought, which causes the leaf margins to curl and yellow in dry summers. The red blistering associated with currant blister aphid is the most visually distinctive symptom and is rarely caused by anything other than this specific aphid.

What causes red blisters on redcurrant leaves?

Red blisters on redcurrant leaves are almost always caused by currant blister aphid (Cryptomyzus ribis). This aphid overwinters as eggs on currant stems and hatches in spring as the buds open. The young aphids feed on the underside of the leaves, injecting saliva that causes the leaf tissue to swell, pucker, and develop reddish or yellowish blisters on the upper surface. The aphids are concealed inside these blistered areas on the leaf underside. On redcurrants, the blisters are typically red-tinged, which makes the damage more visually alarming than the same aphid causes on blackcurrant (where the blisters tend to be yellowish-green). Despite the dramatic appearance of severe infestations, currant blister aphid rarely causes serious long-term damage to the crop: the aphids migrate off the plant by midsummer and the plant continues to produce fruit normally.

Is it safe to eat redcurrants from aphid-infested bushes?

Yes. Currant blister aphid affects the leaves of the redcurrant but does not damage the fruit. The berries on aphid-infested bushes are entirely safe to eat and are not affected in flavour or quality by the aphid infestation on the foliage. The aphids migrate off the plant by midsummer, usually well before the redcurrant fruit ripens in July. Inspect the fruit as you pick and rinse before use: the aphids may occasionally be found on the underside of leaves near the fruit strings but are not found on the berries themselves.

How do I prune redcurrants?

Redcurrants fruit on short spurs on older wood and on the base of the previous year's shoots. The aim of pruning is to build a framework of permanent branches and to maintain a regular supply of young, productive side shoots while keeping the bush open and well-ventilated. Redcurrants are most commonly grown as open-centred bushes on a short leg (30 to 40 centimetres of clear stem). Winter pruning (December to February): shorten all new side shoots (laterals) to 1 to 2 buds from the main branches to form fruiting spurs; remove any crossing, weak, or damaged branches; and cut out one or two of the oldest main branches each year to encourage renewal. Summer pruning (June): pinch all new side shoots back to 5 leaves; this improves light penetration into the bush and reduces aphid and disease problems by removing the most susceptible young tissue.