Identification
A microscopic mite (eriophyid, about 0.2 mm), invisible to the naked eye, that colonises the inside of buds. Infested buds swell abnormally, take on a rounded shape and die off instead of opening — a symptom known as "big bud". The pest is a vector of blackcurrant reversion, a serious virus-like disease that deforms leaves and causes loss of cropping. It attacks mainly blackcurrant, less often redcurrant and gooseberry. The mite's body is elongate, worm-like and spindle-shaped, whitish, bearing only two pairs of legs at the front — a feature typical of the whole eriophyid family (Eriophyidae). A single infested bud may overwinter anywhere from several hundred to several tens of thousands of individuals, so a single "big bud" is a focus of mass invasion. Infestation is easiest to recognise in winter and early spring, when the bush is leafless: healthy leaf buds are narrow, pointed and pressed against the shoot, whereas colonised ones are round, distinctly swollen and open, resembling miniature cabbage heads. The mites feed hidden under the bud scales for most of the year. Migration coincides with bud burst and flowering (usually April–May): the individuals leave the dying old buds and move — passively on the wind and on the bodies of insects, and actively along the shoots — to young, forming buds, which they colonise for the rest of the season. Direct feeding distorts and weakens the buds, but the most dangerous effect is the transmission of reversion: its symptoms are simplified leaves (fewer lobes and shallower marginal serration), with sparser venation, lacking the characteristic aroma of blackcurrant, and deformed, often reddened flowers, leading to a gradual loss of the bush's cropping.
Treatment
Systematically picking off and destroying infested, swollen buds in early spring, and removing whole bushes where infestation is heavy. The foundation is planting healthy, certified stock and choosing less susceptible varieties; a spray of sulphur or acaricides is possible during mite migration (flowering), when they leave the old buds. Hand removal of "big buds" is done from winter to early spring, necessarily before the buds burst and the mites begin their migration — the collected material must be burned or carted away from the plantation, because the mites survive in the detached buds. The treatment pays off only with single, loosely scattered foci; where infestation is heavy and diffuse, grubbing out and replanting is more reliable. Prevention is key: take cuttings only from healthy mother bushes, use certified material free of the pest and of reversion, and choose resistant cultivars (carrying the gene for resistance to the gall mite) — with the caveat that resistance is sometimes overcome and does not exempt the grower from inspection. New bushes are best isolated from old, neglected plantings and from wild currants and gooseberries, which form a reservoir. Propagation material can additionally be disinfected by a warm-water bath (a quarantine method for nurseries). Chemical control has limited efficacy, because for most of the year the mites are inaccessible inside the buds — it acts only on the migrating individuals, so contact treatments (a sulphur product, an acaricide) must be precisely targeted at the migration window during flowering and usually repeated. Cuttings should not be taken from bushes showing symptoms of reversion, even if the buds themselves look healthy.
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Picking off and destroying infested buds | Hand removal of swollen "big buds" and burning or carting them away eliminates the focus of invasion before the mites migrate out. | Winter to early spring, before bud burst |
| Healthy certified stock and resistant cultivars | Establishing the plantation from bushes free of the pest and of reversion, and choosing cultivars with the resistance gene, limits the source of infestation. | When establishing the planting |
| Removing infested bushes and isolating from wild Ribes | Grubbing out heavily colonised bushes and keeping new plantings away from wild currants and gooseberries removes the mite reservoir. | Where infestation is heavy and diffuse |
| Warm-water bath for cuttings | Thermal disinfection of the propagation material destroys mites hidden in the buds; a quarantine method for nurseries, not for mature bushes. | Before propagation |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Contact treatment during migration (sulphur / acaricide) | A sulphur product or a contact acaricide acts only on mites migrating outside the buds; efficacy is limited and repetition necessary. | Bud burst and flowering (April–May) |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Atlas of plant pests
- Institute of Horticulture – National Research Institute
