Why Has My Blackcurrant Bush Stopped Fruiting Well?

A blackcurrant bush that was once productive but has gradually declined — fewer fruits each year, sparse trusses, or barely any crop despite healthy-looking growth — may be suffering from reversion disease. Also called big bud disease when the mite vector is present, reversion is a viral infection that progressively destroys the fruiting potential of affected plants. Unlike nutrient deficiencies or pruning problems, reversion cannot be treated. Understanding the symptoms and transmission helps you make the right decision about what to do with an affected bush.

What is reversion disease?

Reversion is caused by Blackcurrant reversion virus (BRV), which is transmitted from plant to plant by the blackcurrant gall mite (Cecidophyopsis ribis). Once a plant is infected with the virus, it cannot be cured. The infection spreads through the vascular system of the plant and permanently alters the way it grows and flowers. Crop yields decline year on year and affected bushes become a reservoir from which the virus is spread by mites to neighbouring healthy plants. It is entirely distinct from big bud itself — a plant can have big bud mite without reversion virus, though the presence of the mite greatly increases the risk of reversion following.

Recognising reversion symptoms

The most diagnostic symptom is a change in leaf shape — leaves on affected shoots become narrower and pointed, with fewer lobes than a normal blackcurrant leaf, and the veins become more pronounced. These changes are known as "nettlehead" because the altered leaves resemble nettle foliage. A second key symptom, visible in spring, is flower abnormality — the petals of affected flowers become bright magenta or purplish rather than the normal greenish-pink, and the flowers are often sterile, setting little or no fruit. The combination of nettlehead leaves and bright flowers on a declining bush is a reliable indicator of reversion infection.

Gradual decline versus other causes

Poor fruiting on a blackcurrant bush has several possible causes: inadequate pruning, frost damage to flowers, poor pollination, nitrogen shortage, and waterlogging can all reduce crops without any disease being present. Before concluding reversion is the cause, check that the bush has been pruned correctly each year, that its flowers were not killed by late frost, and that it receives a proper spring feed. Reversion is a diagnosis by symptom pattern rather than a quick test — look specifically for the leaf shape change and the abnormal flower colour before deciding the bush must be removed.

What to do with a confirmed case

There is no treatment for reversion virus. A bush confirmed to have the disease should be dug out and destroyed — do not compost it, as mites can survive in the removed material. Before replanting on the same site, inspect all surrounding bushes carefully for big bud mite (swollen, rounded buds in winter) and any leaf or flower abnormalities. Purchase certified virus-free stock from a reputable nursery for replanting, and choose varieties with improved mite resistance such as Ben Hope or Ben Gairn, which carry partial resistance to the gall mite vector and thus to reversion spread.

Preventing reversion through mite control

Since the gall mite is the primary vector of reversion, keeping mite populations low is the most effective prevention. Remove and burn any shoots carrying big buds (swollen, rounded buds in late winter) before mites emerge in spring. Avoid propagating from affected bushes — taking cuttings from an infected plant spreads the disease to new stock immediately. Inspect new plants carefully before introduction, and maintain a physical barrier between new and old stock where possible during the establishment period.