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How to Identify “Bent Banana Disease” / “Pocket Plum Disease” in Damsons

What is “Pocket Plum” / “Bent Banana Disease”?

There’s a fungal disease that infects damsons that’s known by various names, including:

  • “bent banana disease”
  • “plum pocket”
  • “bladder plums”

Its Latin name is Taphrina pruni (“taphre” is Greek for trench or ditch).

This disease is fatal to damson fruits and so can seriously reduce your damson yield. It can be summed up in two words: grotesque deformity.

In ten years of growing damsons I’ve come across the occasional pocket plum-blighted damson. But this year,  2014, has been the worst ever.

In my patch on the Herefordshire-Shropshire border, every damson tree in my orchard and in the hedges in my meadow was infected to some extent. I estimate I’ve lost maybe as much as a fifth of my crop. That’s a lot of damsons to lose.

Where to Learn More About Pocket Plum

The web is a rich source of information on this disease. So, if you’d like to learn about the epidemiology, aetiology, symptoms and treatment of pocket plum you could always check out these sites:

When I spotted the arrival of pocket plum this year I took some photos to record how the natural history of this disease evolves.

What Does Pocket Plum Look Like?

Most commonly, the signs of pocket plum are seen on the fruitlets.

The first sign of infection is small spots on the fruitlet.

Blisters of damson pocket plum disease
The first sign that something is amiss: the small, apparently innocuous spots of pocket plum on damson fruitlets.

Next, these spots develop into small white blisters.

Blister of pocket plum on damson fruitlets
Pocket plum blisters have appeared.

Now, the infamous deformity caused by pocket plum is also becoming apparent. Also, notice how neighbouring damsons are healthy and normal in size, shape and colour.

pocket plum disease and blisters
The small blister-like spots of pocket plum in association with deformity of the fruit.

Next, a white spore layer forms on the surface of the fruitlet. When you squeeze the flesh of the damson it feels unappetisingly spongy.

Photo showing the spore layer on a damson infected with pocket plum.
The white spore layer of pocket plum on an infected damson fruitlet.

One of the features of pocket plum disease is that it there is no stone inside the fruit: it’s just a cavity.

Another feature is that the diseased fruitlet grows at an alarming rate. It’s as if the division stage of the cell cycle is out of control. Elongation is the name of the game.

Photo of a damson severely elongated due to pocket plum disease.
A pocket plum-infected damson that is several times its normal size.

Next, the diseased fruitlet starts to turn brown. Folds and fissures also deepen.

Photo of deformity of pocket plum disease on a damson
Brown patches start to appear on the infected fruit.

Here you can see how much bigger the infected damson is compared with a typical healthy damson. Notice, too, how flat it is; inside is just a hollow with no nutritious fruit flesh.

Photo of a damson infected with pocket plum that is curved like a banana.
The infected damson curls into the shape of a small banana. Hence the name “bent banana disease”.

The brown plaques become more extensive.

Photo showing the dried, brown deformity of bent banana disease on a damson.
The diseased damson gradually turns brown and then grey and dries out.

Eventually, this diseased damson will fall off the tree.

What Should You do if Your Damson Tree Develops Pocket Plum?

A  summary of the sources mentioned earlier suggest three actions you should take if you spot pocket plum on your damsons:

1. Removed diseased fruits promptly and burn them.

2. Cut off any diseased twigs and burn them.

3. Check for diseased decaying matter under the tree and burn it.

You could spray with Bordeaux mixture in early Spring, but this is not deemed effective.

The key message is not to panic if you spot pocket plum on your damson tree.

Your tree won’t die and it will continue to produce fruit.

Have you ever spotted pocket plum on your damsons? If so, what effect did have on your crop and how did you deal with it?

Please leave a comment below.