Why Are My Blackcurrant Leaves Curling?

Currant aphid

Currant aphid (Cryptomyzus ribis) is a pale yellow-green aphid that overwinters as eggs on blackcurrant stems and hatches in early spring as the buds open. The aphids feed on the underside of young leaves, causing the leaves to pucker, blister, and roll upward around the feeding colonies. The puckering is very characteristic: the affected areas of the leaf surface become reddish or yellowish-green, and the leaf rolls tightly upward, concealing the aphid colonies underneath. By midsummer, the aphid colonies migrate off the blackcurrant to their summer hosts (plants in the Galium family), and the blackcurrant's remaining leaves, while still somewhat puckered from earlier damage, continue to function normally.

What to do

• The critical control window is early spring, just as the buds open and before the leaves have curled around the aphid colonies. Inspect the underside of opening leaves from March and treat with insecticidal soap or pyrethrum at the first sign of aphid colonies, when the leaf is still flat enough for the spray to reach the insects.
• Once leaves have curled and enclosed the aphid colonies, contact insecticides cannot reach the insects. At this stage, remove and destroy the most heavily affected leaves, or accept that the damage is largely cosmetic and will not significantly affect the crop.
• Encouraging natural predators through the season (by avoiding broad-spectrum insecticides and growing nectar-rich plants nearby) provides useful long-term reduction in aphid populations.

Big bud mite and reversion virus

Big bud mite (Cecidophyopsis ribis) is a microscopic mite that lives inside the buds of blackcurrant plants. Infested buds swell abnormally in late winter and early spring to become round and bloated (normal healthy buds are pointed and narrow). On an infested plant, individual round buds are visible among the normal pointed buds from January onward. Infested buds fail to open properly in spring, or produce distorted, crinkled growth.

The greater danger of big bud mite is that it transmits blackcurrant reversion virus (BRV). Plants with reversion virus develop leaves that are progressively narrower and more strap-like with fewer lobes than normal, shoots that become stunted and congested, and fruit set that declines dramatically until the plant becomes effectively barren. Reversion virus is incurable and distinguishes big bud mite infestation from currant aphid: currant aphid damage is cosmetic and temporary, while mite-transmitted reversion virus is a death sentence for the fruiting potential of the plant.

What to do

• Inspect blackcurrant buds in January and February for round, swollen buds. Pick off individual affected buds and destroy them when the infestation is light. This cannot eliminate the mite but reduces the population significantly.
• If a plant shows both big bud symptoms and the distinctive narrow, distorted leaves of reversion virus, remove and destroy the entire plant immediately. Do not replant blackcurrants in the same spot for at least 2 years.
• Replace with mite-resistant varieties: 'Ben Hope', 'Ben Gairn', 'Ben Tirran', and 'Ebony' are all significantly more resistant to big bud mite and the associated reversion virus than older varieties.
• Always buy certified virus-free blackcurrant plants from reputable suppliers. Do not propagate cuttings from plants with any big bud symptoms, as the mite is easily transmitted on infected plant material.

Gall midge

Blackcurrant gall midge (Dasineura tetensi) is a small fly whose larvae feed inside the growing tips of blackcurrant shoots in spring and early summer. The affected growing tips fail to develop normally: the small leaves at the tip curl tightly together in a mass of distorted, crinkled tissue. Several generations occur each season, and heavily infested plants have multiple distorted growing tips throughout the summer.

What to do

• Pinch out and destroy distorted growing tips at the first sign of damage. This removes the larvae within the affected tissue. Repeat throughout the season as new infestations appear. On a well-established, vigorous blackcurrant bush, gall midge damage rarely affects the overall crop significantly.

Drought

Drought causes blackcurrant leaves to curl inward at the margins and develop a dull, greyish-green colour. Blackcurrants have relatively shallow roots and are more susceptible to drought than gooseberries or redcurrants. Drought during fruit development significantly reduces berry size and causes premature fruit drop.

What to do

• Apply a thick mulch (8 to 10 centimetres) of compost or bark chips around the base of blackcurrant bushes in spring to retain soil moisture. Water during dry spells, particularly from flowering through to harvest. Established blackcurrants on heavier soils are considerably more drought-tolerant than those on light, sandy ground.

Frequently asked questions

Why are my blackcurrant leaves curling?

Blackcurrant leaves curl most commonly because of currant aphid (Cryptomyzus ribis), big bud mite (Cecidophyopsis ribis) carrying reversion virus, or gall midge (Dasineura tetensi). Currant aphid causes characteristic puckering, blistering, and upward curling of the leaves from spring onward, with the aphids feeding on the underside of affected leaves inside the puckered tissue. Big bud mite causes the buds to swell abnormally in late winter and spring; mite-infested plants often also carry blackcurrant reversion virus (transmitted by the mites), which causes the leaves to become narrow and distorted with fewer lobes than normal, and severely reduces fruit yield. Gall midge larvae cause distortion and curling of the growing tips and young leaves.

What is big bud on blackcurrants?

Big bud is caused by the blackcurrant big bud mite (Cecidophyopsis ribis), a microscopic mite that lives inside the buds of blackcurrant plants. Infested buds swell abnormally in late winter and early spring to become rounded and bloated (normal buds are pointed and narrow): this is the 'big bud' symptom that gives the condition its name. Infested buds fail to open normally in spring or produce distorted, crinkled leaves. The big bud mite also transmits blackcurrant reversion virus (BRV), which is a severe, incurable disease. Blackcurrant reversion virus causes the leaves to become narrow and strap-like with fewer lobes than normal, the shoots to become congested with very short internodes, and the flowering and fruiting to reduce dramatically. There is no treatment for reversion virus: affected plants must be removed and destroyed.

How do I treat currant aphid on blackcurrants?

Currant aphid (Cryptomyzus ribis) overwinters on blackcurrant and moves to its summer host plants (hedge bedstraw and other species in the Galium genus) in summer, returning to blackcurrant in autumn. The most effective control window is spring, before the leaves have curled and enclosed the aphid colonies: once the leaves have curled tightly around the aphids, contact insecticides cannot reach them. In spring, inspect the undersides of opening leaves for the pale yellow-green aphid colonies and treat at this stage with insecticidal soap. Natural predators (ladybirds, hoverflies) provide useful control through the season. By midsummer, many colonies naturally migrate off the blackcurrant and the plant can outgrow the damage. Heavy puckering and curling later in the season is cosmetic rather than a threat to cropping.

Which blackcurrant varieties are resistant to big bud mite?

Several modern blackcurrant varieties have been bred with resistance to big bud mite (Cecidophyopsis ribis) and are strongly recommended for UK gardens where big bud is a persistent problem. The most widely available mite-resistant varieties include: 'Ben Hope', 'Ben Gairn', 'Ben Tirran', and 'Ben Connan', all from the Scottish Crop Research Institute's Ben breeding programme, which specifically bred for big bud resistance. 'Ben Hope' is particularly well regarded for combining strong mite resistance with heavy cropping and good disease resistance. 'Ebony' is a newer variety with both mite resistance and large berries. Mite-resistant varieties do not eliminate the risk of infestation entirely but are significantly less susceptible than older varieties and provide a more sustainable long-term solution than relying on chemical control of the mite.