Gadenin日本語Get the appBig bud mite: the one you must not ignore
Blackcurrant gall mite is a microscopic mite that lives inside the buds. You cannot see the mite, but you can see what it does: through the dormant season affected buds swell into round, soft, papery balls two or three times the size of a healthy pointed bud. They are conspicuous once the leaves are off and impossible to miss on a bare stem in winter. In spring the swollen buds either fail to open at all or produce a stunted distorted shoot, so every one of them is a piece of next year's crop gone.
The mites leave the old buds as the new shoots extend in spring and crawl or blow to this season's developing buds, where the next generation shelters. That short window when they are outside the bud is the only time they are exposed, which is why the practical control is mechanical: pick off swollen buds through the winter and burn them, and cut out whole stems where the swollen buds are numerous.
The real damage is not the lost buds. It is what the mite carries.
Inspect every bush in the dormant season, before you prune, and count the swollen buds on each. Take the worst-affected stems out first as part of the normal renewal cut. A bush with only a handful of swollen buds is usually worth saving.
Reversion: no cure, dig it out
Reversion is a virus disease spread by gall mite, and it is the reason blackcurrant bushes have a finite life in gardens where the mite is present. An infected bush keeps growing strongly and looks healthy at a glance, but it produces steadily fewer flowers and barely any fruit, and after two or three years it crops almost nothing while occupying full-sized space.
The signs are in the leaves and flowers rather than the fruit. Leaves lose their normal shape: the main lobe becomes narrower, the deep notches along the edge get shallower, and the number of veins running to the leaf margin drops noticeably. The flower buds turn a bright pinkish color instead of the usual dull gray-green, and they are hairless where healthy ones are downy. Put a reverted shoot beside a healthy one and the difference is obvious; in isolation it is easy to talk yourself out of it.
There is no treatment. Pruning does not remove it, spraying does nothing, and feeding a reverted bush simply grows more infected wood. Dig the bush out with as much root as you can, burn or bin it, and do not propagate from it or from anything near it. Plant the replacement on a different part of the garden and keep new bushes away from any older ones that may be infected.
| Feature | Healthy bush | Reverted bush |
|---|---|---|
| Leaf shape | Broad main lobe, deeply notched edge | Narrow main lobe, shallow notches |
| Leaf veins to the margin | Five or more per side of the main lobe | Noticeably fewer |
| Flower buds | Dull gray-green and downy | Bright pink and hairless |
| Flowers per strig | Full string of flowers | Few flowers, short strigs |
| Crop | Steady year on year | Falls away over two or three years to almost nothing |
| Bush vigor | Strong | Often still strong, which is what fools people |
Do not take cuttings from a bush you have any doubt about. Reversion travels in the wood, and a row raised from a single suspect parent is infected before it ever fruits.
Mildew, leaf spot and rust
American gooseberry mildew attacks blackcurrants as well. It shows first as a white powdery bloom on the youngest shoot tips and the undersides of new leaves, then the growth distorts and the coating turns brown and felted. It thrives in still, humid air, which is why a crowded, unpruned stool in a sheltered corner gets it first. Cut affected shoot tips out as soon as you see them and burn them, open the bush up properly at the winter prune, and go easy on late nitrogen, which produces the soft growth mildew prefers.
Leaf spot causes small dark brown blotches that spread until the leaves yellow and drop, sometimes stripping a bush by late summer. Early leaf fall means the shoots do not ripen, and next year's crop suffers. It carries over on fallen leaves, so raking out and removing the leaf litter from inside the stool each autumn is genuinely effective.
Rust shows as bright orange pustules on the undersides of the leaves in late summer. On an otherwise healthy bush this late in the season it does little real harm; remove badly affected leaves and clear the fallen ones.
Insects on leaves and fruit
Currant blister aphid is the commonest sight in early summer: the leaves at the shoot tips pucker into raised red or yellow blisters and curl downwards. The aphids are on the underside. It looks alarming but rarely costs much crop, and the aphids leave for other plants by midsummer of their own accord. Squash the colonies on a few shoots, or tolerate them, and encourage the ladybirds and hoverfly larvae that clear them up.
Gooseberry sawfly is far more serious and also feeds on blackcurrants. The larvae are pale green caterpillars with black spots that start low down in the center of the bush and eat outwards. They can strip a bush to bare stems in under a week, and a stripped bush makes no shoots for next year. Check the inside of the bush from late spring onwards and pick larvae off by hand; there are usually two or three generations in a season.
Capsid bugs puncture the young leaves at the shoot tips, leaving ragged holes with brown edges as the leaves expand. The damage looks worse than it is. Winter moth caterpillars loop along the shoots in spring and eat the flowers, which does cost fruit; hand-picking is usually enough in a garden.
| Symptom | Likely cause | First action | When to give up on the bush |
|---|---|---|---|
| Round swollen buds in winter | Gall mite | Pick off and burn buds; remove worst stems | If most buds are affected year after year |
| Strong bush, narrow leaves, almost no fruit | Reversion virus | Compare leaves with a healthy bush | Immediately; dig it out and replant elsewhere |
| White powder on shoot tips | Mildew | Cut out tips, open the bush, stop late nitrogen | Rarely fatal; manage it |
| Bush stripped of leaves in early summer | Sawfly larvae | Search the center and hand-pick daily | Rarely fatal, but a stripped bush loses next year's wood |
| Red puckered blisters on young leaves | Blister aphid | Squash colonies or tolerate | Not a reason to remove a bush |
| Berries gone overnight as they color | Birds | Net before coloring starts | Not a plant problem |
| Split berries after rain | Dry spell then heavy water | Pick at once; water more evenly | Not a plant problem |
Keeping a record that catches the slow problems
The pests that eat leaves announce themselves. The one that ends a bush does not: reversion takes three years to show up as a yield you cannot ignore, and by then you have lost three crops. The defense is a written record, bush by bush, using the numbering from your planting sketch.
Each dormant season, note the number of swollen buds on each bush. Each summer, note the weight picked from each bush and whether the leaves looked normal beside their neighbors. A bush whose swollen bud count climbs and whose yield falls two years running has reversion, whatever the leaves seem to say, and taking it out early protects the rest of the row from the mites it is feeding.
Also record the date you first saw sawfly larvae, mildew on the tips and aphids on the shoots. Those first-sighting dates repeat closely from year to year, and knowing them means you inspect a week before the damage instead of a week after.