Plant problems

Why Are My Jostaberry Leaves Curling?

Q: Why are my jostaberry leaves curling?

Jostaberry (Ribes x nidigrolaria, a hybrid of blackcurrant and gooseberry) leaves curl most commonly in the UK because of aphid infestation, big bud mite (Cecidophyopsis ribis), powdery mildew, or leaf spot. The currant-lettuce aphid (Hyperomyzus lactucae) and blackcurrant aphid (Cryptomyzus ribis) colonise the undersides of jostaberry leaves in spring, causing the leaves to curl tightly upward and inward; the distortion is severe enough that badly affected leaves look like small green cups. Big bud mite (Cecidophyopsis ribis) is microscopic and lives inside the buds of currants and their relatives; infested buds swell to a distinctive rounded, bloated shape (big bud) rather than the pointed shape of healthy buds, and when they open, they produce distorted, curled, and stunted leaves. Big bud mite is also the vector of reversion virus, a serious, incurable disease of blackcurrant and related plants that causes reduced fruiting and leaf distortion. Powdery mildew causes white powdery coating and curling on young shoots. Leaf spot (Drepanopeziza ribis) causes brown spots and premature defoliation.

Q: How do I control aphids on jostaberry?

Aphids on jostaberry, including the currant-lettuce aphid (Hyperomyzus lactucae) and blackcurrant aphid (Cryptomyzus ribis), are most damaging in spring when they cause severe leaf curl on the young growth. The currant-lettuce aphid is notable because it spends winter as eggs on currant plants but migrates to sow thistle (Sonchus) in summer; removing sow thistles from the garden area reduces reinfestation in subsequent years. To control aphids on jostaberry: pinch off and destroy the most heavily infested shoot tips and curled leaves in spring. Apply insecticidal soap or neem oil to the shoot tips and the undersides of leaves, repeating every 7 to 10 days. Encourage natural predators by avoiding broad-spectrum insecticides; ladybird adults and larvae, lacewing larvae, and parasitoid wasps all feed on these aphid species. A winter wash of plant-based oil applied to dormant stems in December to January smothers overwintering aphid eggs. The leaf distortion caused by spring aphids persists through the season even after the aphids are gone; new growth produced after the infestation will be normal.

Q: What are the advantages of growing jostaberry over blackcurrant?

Jostaberry (Ribes x nidigrolaria) has several practical advantages over blackcurrant for UK gardeners. Most jostaberry plants are virtually spineless, unlike the sharp spines of gooseberry (one of its parents); this makes harvesting and pruning much more comfortable. Jostaberry is generally more vigorous and somewhat larger than blackcurrant, producing a big, upright shrub that can reach 2 metres. The berries are larger than blackcurrant and similar in flavour (a mixture of blackcurrant and gooseberry), ripening in July. Jostaberry is resistant to blackcurrant gall mite (big bud mite) and to American gooseberry mildew to a greater degree than most blackcurrant cultivars, which is a significant practical benefit. It is self-fertile, fully frost-hardy, and grows in most UK soils. The main disadvantage is yield: established blackcurrant cultivars such as 'Ben Lomond' or 'Ben Hope' typically produce higher yields of fruit than jostaberry; jostaberry also has a shorter picking season as all the berries ripen within a shorter window. Jostaberry is propagated easily from hardwood cuttings taken in autumn.

Jostaberry (Ribes x nidigrolaria) is a hybrid of blackcurrant and gooseberry, created by German breeders in the 1970s and now widely grown in UK gardens for its large, dark berries, vigorous growth, and near-spineless stems. It combines much of the flavour of blackcurrant with the size and ease of harvest of gooseberry. As a member of the Ribes family, it shares the pest problems of its parents, the most common of which in UK gardens is aphid-induced leaf curl in spring.

Aphids

Aphids are the most common cause of curling leaves on jostaberry in spring. The currant-lettuce aphid (Hyperomyzus lactucae) and blackcurrant aphid (Cryptomyzus ribis) both colonise the undersides of the young leaves, causing them to curl tightly upward and inward into small, cup-like rolls; badly affected leaves may almost disappear inside the curl. The distortion is caused by the aphids' feeding disrupting normal leaf cell expansion; the damage appears in April and May on the first flush of new growth. The currant-lettuce aphid overwinters as eggs on Ribes plants and migrates to sow thistle in summer, returning to lay overwintering eggs on Ribes in autumn.

What to do

Pinch off and destroy the most tightly curled leaves in spring. Apply insecticidal soap or neem oil to the shoot tips. Encourage natural predators. Remove sow thistles from the garden area to reduce reinfestation by the currant-lettuce aphid in subsequent years. Apply a winter oil wash to dormant stems in December or January to smother overwintering aphid eggs. New growth produced after the infestation clears will be normal.

Big bud mite

Big bud mite (Cecidophyopsis ribis) is a microscopic eriophyid mite that lives inside the buds of jostaberry and other Ribes species. Infested buds swell to a rounded, bloated shape in late winter or early spring, clearly distinguishable from the elongated, pointed shape of healthy buds. When these abnormal buds open in spring, they produce stunted, distorted, and curled foliage. Big bud mite is also the vector of reversion virus, a debilitating incurable disease; plants suspected of having reversion (reduced cropping, leaf distortion, abnormal flower structure with narrow, elongated buds) should be removed and replaced with certified virus-free stock. Jostaberry is generally considered more resistant to big bud mite than blackcurrant, but not immune.

What to do

In late winter, inspect buds carefully before growth begins; remove and destroy any swollen, rounded buds. If more than 10 to 15% of buds are affected, consider removing and replacing the plant with certified virus-free stock. Do not take cuttings from affected plants. Big bud mite has no effective chemical control for home gardeners. Buying certified virus-free planting stock is the most important preventive measure.

Powdery mildew

American gooseberry mildew (Podosphaera mors-uvae) can affect jostaberry, though it is generally less susceptible than pure gooseberry. The mildew appears as a white or greyish-white powdery coating on the young leaves and shoot tips, which curl and may die back as the infection progresses. In severe cases the infection spreads to the developing fruit. Mildew on jostaberry is favoured by warm, dry days and cool nights in spring and early summer, combined with a sheltered position where air circulation is poor.

What to do

Prune to an open, goblet shape to improve air circulation through the centre of the bush. Remove and destroy infected shoot tips as soon as mildew is spotted. Apply a sulphur-based or potassium bicarbonate fungicide spray at the first sign of infection and repeat every 10 to 14 days. Avoid high-nitrogen feeding in spring, which promotes the soft, susceptible growth that mildew colonises most readily.

Leaf spot

Currant leaf spot (Drepanopeziza ribis) causes small, brown circular spots on the upper surface of jostaberry leaves. In a wet summer, the spots multiply rapidly and merge; affected leaves yellow around the spots and drop prematurely. A severe early infection can defoliate a jostaberry bush by August, weakening it and reducing the following year's crop. Leaf spot overwinters on fallen leaves, so autumn hygiene is important for control.

What to do

Collect and destroy fallen leaves in autumn. Apply a copper-based fungicide spray in early spring as the leaves emerge, if leaf spot was a problem the previous year, and repeat every 14 days during wet conditions. Improve air circulation by pruning. Avoid overhead watering. Jostaberry is generally quite vigorous and can tolerate moderate leaf spot without significant crop loss.

Frequently asked questions

Why are my jostaberry leaves curling?

Jostaberry (Ribes x nidigrolaria) leaves curl most commonly in the UK because of aphid infestation, big bud mite (Cecidophyopsis ribis), powdery mildew, or leaf spot. The currant-lettuce aphid and blackcurrant aphid colonise the undersides of leaves in spring, causing them to curl tightly upward into cup-like rolls. Big bud mite causes distinctive swollen, rounded buds that open to produce distorted, curled, stunted foliage; it is also the vector of reversion virus. Powdery mildew causes a white powdery coating and curling on young shoots. Leaf spot causes brown spots and premature defoliation in wet summers.

What is big bud mite on jostaberry?

Big bud mite (Cecidophyopsis ribis) is a microscopic mite that lives inside the buds of blackcurrant, jostaberry, and related Ribes species. Infested buds swell to a rounded, bloated shape rather than the elongated, pointed shape of healthy buds. When these buds open in spring they produce stunted, distorted, curled leaves and reduced fruit. Big bud mite is the primary vector of blackcurrant reversion virus; plants infected with reversion cannot be cured and should be removed. Jostaberry is generally more resistant to big bud mite than blackcurrant but is not immune.

How do I control aphids on jostaberry?

Aphids on jostaberry are most damaging in spring when they cause severe leaf curl. Pinch off and destroy the most heavily curled leaves. Apply insecticidal soap or neem oil to shoot tips and leaf undersides, repeating every 7 to 10 days. Encourage natural predators by avoiding broad-spectrum insecticides. Remove sow thistles from the garden to reduce reinfestation by the currant-lettuce aphid. Apply a winter oil wash to dormant stems in December to January to smother overwintering aphid eggs.

What are the advantages of growing jostaberry over blackcurrant?

Jostaberry is nearly spineless (unlike gooseberry), vigorous, self-fertile, and more resistant to big bud mite and American gooseberry mildew than most blackcurrant cultivars. The berries are larger than blackcurrant with a similar flavour, ripening in July. The main disadvantages are slightly lower yield than top blackcurrant cultivars and a shorter picking season. Jostaberry propagates easily from hardwood cuttings taken in autumn.