Gall mites
Eriophyidae
also called Big bud mite, Blister mite, Eriophyid mites
Microscopic mites that distort growth — swollen "big buds" on currants, felty or pouch galls elsewhere. Prune out and destroy affected shoots in winter.
How to know it
Invisible without a microscope — carrot-shaped, four-legged, a fifth of a millimeter long. You identify them entirely by the gall: a swollen round bud, a felty patch, a raised pouch or a rolled leaf margin, each species making its own signature shape on its own host.
What you'll see
- Blackcurrant buds swollen round and loose over winter instead of slim and pointed — "big bud".
- Raised red or green pimples and pouches on the upper leaves of plums, limes and maples.
- Felty, suede-like patches — white, pink or rusty — on the leaf undersides of vines, walnuts and beeches.
- Leaf margins tightly rolled or thickened, and shoot tips distorted into rosettes.
- On blackcurrants, buds fail to open and the bush gradually stops cropping as reversion virus follows.
Where it comes from
Mites live and breed inside the gall the plant builds in response to their feeding, protected from weather and most sprays. They disperse on wind, on insects and on birds in early summer as new buds and leaves emerge, and overwinter inside buds or bark crevices.
Present in most gardens at a low level. Damage looks alarming in a warm spring when growth and mite activity coincide, but on trees and shrubs it is very rarely more than cosmetic.
Dealing with it
- Leave leaf galls on trees and shrubs alone — they do not harm the plant and there is no useful treatment.
- Pick off big buds from blackcurrants in winter, before they burst and release the mites.
- Grub out and burn a blackcurrant bush that is heavily budded and showing reversion — it will not recover.
- Prune out distorted rosette shoots on ornamentals for tidiness.
- Do not spray: the mites sit inside plant tissue where nothing reaches them.
Keeping it out
- Buy certified virus-free blackcurrant stock, and choose resistant cultivars such as Ben Hope.
- Never take cuttings from a bush with big bud.
- Inspect blackcurrants each winter while pruning, when the swollen buds are obvious.
- Keep new fruit bushes well away from old, infested ones.
- Accept galls on trees — they are part of a healthy garden’s traffic, and the birds work them over.
What it goes for
Blackcurrants above all, plus plums, pears, limes, maples, walnuts, beeches, vines and hazels, each with its own species.
Trouble it brings with it
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com