Pocket Plum is a minor disease that affects damsons.
What does it look like?
Developing fruit becomes elongated and hollow, with no stone inside, and does not swell or ripen. A white bloom of fungus appears on the surface, then the fruit shrivels and falls. Distorted fruit appears from midsummer. Plums, damsons and some ornamental Prunus can be affected. Damsons are a type of plum, so plum pocket and pocket plum are the same disease.
What causes it
Infection happens in cool, wet weather when the buds break in spring, and fruit is infected more often than leaves or shoots (US handbook).
Is this disease active now?
Infection happens at bud break in spring, but the distorted fruit does not appear until midsummer.
Symptoms
Infected fruit is worthless to eat and drops. Twigs bearing deformed fruit may thicken and grow deformed, and the fungus can also cause witches' brooms, which are dense clusters of live and dead twigs.
Life cycle
Airborne spores from the white bloom lodge in bark and buds and overwinterKeeping a plant alive and intact through the cold months, whether left outdoors, moved under cover, or stored dormant. Full definition → there, and the fungus also survives on old infected fruit clinging to the tree or lying on the ground. It invades shoots as buds break the following spring and later infects flowers and fruit. The fungus is little studied.
Why this matters in Scotland
No Scottish records or incidence figures were found for pocket plum, and the UK sources give no regional detail. It affects plums and damsons, and the infection window is cool, wet weather at bud break.
Controls: what works
Remove infected branches, witches' brooms and affected fruit thoroughly, before the white fungal bloom releases spores
Prune out infected twigs, limbs and witches' brooms, and pick infected fruit off the branches and up from around the base of the tree, before the white bloom releases spores. Bin or burn the material rather than composting it, so the spores are not kept in the garden. Spores are airborne, so this reduces rather than removes the risk where other Prunus, such as blackthorn or wild plums, grow nearby.
Myths about pocket plum
“You can still eat plums or damsons affected by pocket plum if you cut away the deformed part”
Pocket plum leaves nothing to salvage: the fruit does not swell or ripen, stays hollow with no stone, and is worthless to eat. The deformity runs through the whole fruit, so there is no sound part to cut around.
What to do: Pick off any fruit showing the elongated, hollow, stoneless shape as soon as you spot it, and bin or burn it rather than trying to salvage part of it.
1 source
- RHS: Pocket plumInfected fruits do not swell or ripen and are worthless to eat.
“Spraying a copper fungicide like Bordeaux mixture at bud burst prevents pocket plum”
There are no fungicides available to amateur gardeners for controlling pocket plum in the UK (RHS). Dormant-season Bordeaux and lime-sulphur sprays appear only in US commercial advice (Pacific Northwest handbook), and a US university extension fact sheet on plum pockets recommends no chemical control.
What to do: Rely on removing infected fruit, twigs and witches' brooms promptly and binning or burning them, since there is no home spray available.
3 sources
- RHS: Pocket plumThere are no fungicides available to amateur gardeners for the control of pocket plum
- Pacific Northwest Plant Disease Management Handbook: Plum pocketsSpray during the winter dormant season with Bordeaux or lime sulfur (commercial US advice); the disease seldom occurs and has not caused economic loss.
- Washington State University Hortsense: Plum pocketsChemical control: none recommended.
“Pocket plum only takes hold after a cool, wet spring right when the buds break”
Infection of leaves, shoots and fruit occurs in wet, cool weather when buds break in spring (a US extension handbook). No weather detail appears in the RHS entry.
Our read This rests on a single source, so treat it as likely rather than proven.
What to do: Watch for the disease especially after a wet, cold spring, and check developing fruit from midsummer, when the deformed pockets start to appear.
In Scotland: No Scottish records or weather-linked figures were found for pocket plum.
1 source
- Pacific Northwest Plant Disease Management Handbook: Plum pocketsInfection of leaves, shoots and fruit occurs in wet, cool weather when buds break in the spring.
“Some plum or damson varieties are resistant to pocket plum, so you can plant your way out of the problem”
Neither the RHS nor the Pacific Northwest Extension handbook names any plum, damson or ornamental Prunus variety as resistant or more susceptible to pocket plum. Both cover identification and cultural control, but neither has a variety-resistance section for this disease.
Our read Neither source makes the claim, so there is nothing to confirm.
What to do: Don't choose a variety on resistance claims for this disease specifically; rely on removing infected material and accept that any Prunus tree can be affected in the right weather.
2 sources
- RHS: Pocket plumThe page covers identification, biology and control but names no resistant varieties.
- Pacific Northwest Plant Disease Management Handbook: Plum pocketsThe page covers cultural control and life cycle but names no resistant varieties.
“Removing infected fruit and branches promptly reduces how much pocket plum comes back next year”
The fungus survives winter on old diseased fruit still clinging to the tree or lying on the ground, and its spores lodge in bark and buds, ready to infect new growth when buds break the following spring. Taking infected material away before it can shed spores cuts down the amount of fungus left on the tree, though it won't stop reinfection completely if other Prunus trees are nearby.
Our read Neither source gives a measured before-and-after reduction; the case rests on the overwintering mechanism, not a trial result.
What to do: Prune out infected twigs, witches' brooms and affected fruit before the white fungal bloom appears and releases spores, and put the removed material in the bin rather than the compost heap.
2 sources
- RHS: Pocket plumRemoving infected material will not completely eliminate the risk of new infections if other Prunus species are nearby, but it will reduce the threat.
- Pacific Northwest Plant Disease Management Handbook: Plum pocketsTaphrina pruni overwinters on old diseased fruits clinging to the tree or on the ground, and cultural control involves pruning out infected twigs, limbs and brooms.
Frequently asked questions
What should I do first if I find pocket plum in my garden?
The first thing to try: Remove infected branches, witches' brooms and affected fruit thoroughly, before the white fungal bloom releases spores.
Is there a spray that works?
No. There are no amateur chemical treatments available for pocket plum. The controls that work are cultural: the measures listed above.
When should I watch for pocket plum?
Infection happens at bud break in spring, but the distorted fruit does not appear until midsummer.
Sources
Show the 4 sources
- RHS1: definition, causal organism, affected crops, identification, symptoms, active-by-month timing, the one non-chemical control, and the no-fungicide-for-amateurs stance
- Pacific Northwest Extension18: independent confirmation this is Taphrina pruni (not the related American species Taphrina communis), the cool-wet-weather-at-bud-break infection trigger, overwintering mechanism, low economic/garden severity, and independent agreement on pruning as the cultural control
- woodlands.co.uk8: removing infected fruit from the branches and around the base of the tree, burning dead leaves, blackthorn and sloe as hosts
- hortsense.cahnrs.wsu.edu8: raking up and destroying fallen infected fruit; overwintering on twigs, bud scales and fruit; no chemical control recommended (US extension, plum pockets)