Why Are Some Buds on My Currant Bush Swollen and Round?

Normal, healthy currant buds in late winter are elongated, pointed, and lie close to the stem. If some of the buds on your blackcurrant appear dramatically different — round, puffed up, and the size of a small pea rather than a slim teardrop — they have been colonised by Big Bud Mite (Cecidophyopsis ribis), a microscopic eriophyid mite that lives and breeds inside the bud tissue. This is one of the most serious problems a blackcurrant grower can face, because the mite is also the primary vector of Reversion Virus, a disease for which there is no cure.

Identifying Big Bud Mite

The inspection window is late winter to very early spring, before buds begin to open. Walk along each stem systematically and compare the buds — healthy ones are smooth, pointed, and brown; infected ones are visibly swollen, round, and may be pale or greenish. A single stem can carry a mix of healthy and infected buds. In mild infestations only a few stems are affected; in advanced cases most buds on the plant are abnormal. The mites themselves are invisible to the naked eye — it is the distortion of the bud that reveals their presence.

Removing infected stems

If only a small number of stems show swollen buds, cut those stems out at ground level and burn or bin them immediately — do not compost infected material. Remove also any stems that look suspicious, even if not all buds are affected. After pruning, wash your hands and disinfect your pruning tools before touching other plants. Monitor the bush closely over the following two years and remove further infected material as it appears.

When to remove the whole bush

When the majority of buds across the entire bush are swollen, the infestation is too widespread to manage by selective pruning. The mite is almost certainly carrying Reversion Virus by this stage, and the bush will progressively lose its cropping ability regardless of how much mite control you apply. The right decision is to remove and destroy the whole plant. Do not replant currants in the same spot for at least two years. Source new plants from certified virus-free and mite-tested nursery stock.

Resistant varieties and prevention

Several modern blackcurrant varieties carry partial resistance to Big Bud Mite, including Ben Hope, Ben Gairn, and Titania. These are not fully immune but support significantly lower mite populations than susceptible varieties. Growing resistant varieties is the most practical preventive measure, particularly in areas where the mite is known to be prevalent. Avoid moving propagation material (cuttings) from an infected plant to healthy ones, and check bought-in plants carefully before introducing them to your garden.