Why are my plums and apples going brown and furry on the tree?

The rot that spreads by touch through a cluster and overwinters in the mummified fruit left hanging — and why removing those mummies is the whole of the control.

Difficulty: beginner
Time: 40 min
Read: 4 min

Short answer

Brown rot. A brown patch spreads across the fruit with rings of buff-coloured pustules on it, and infected fruit shrivels into a hard black mummy that stays on the branch all winter, infecting next year's crop. Pick off and destroy every rotting and mummified fruit, thin so fruits do not touch, and control the wasps and birds whose wounds let it in.

Brown rot needs a way into the fruit: a wasp hole, a bird peck, a split from rain, codling moth damage, a scab crack. Once in, it spreads by contact, so a cluster of touching plums rots as a unit. The crucial part of its life cycle is the mummy — the shrivelled fruit that stays attached through winter and produces spores in spring, right where next year's fruit will be.

Step by step

Confirm it.A brown, firm patch spreading across the fruit, usually with concentric rings of small buff or cream pustules on the surface. The fruit does not go slimy — it goes brown, then hard, then black and shrivelled.
Remove every affected fruit from the tree.As soon as you see it. Take it off carefully so you do not spread spores, and bag it. Leaving one rotting plum in a cluster reliably rots the ones touching it.
Hunt out the mummies in winter.Walk the tree after leaf fall and pick off every shrivelled blackened fruit still hanging. This is the highest-value ten minutes in the whole fruit year, and it is the step everyone skips.
Clear fallen and rotting fruit from the ground.Weekly through the season. Fallen rotten fruit is both a spore source and a wasp magnet, and wasps make the wounds the rot enters through.
Thin so fruit does not touch.Contact spread is the main way it moves through a crop. Thinning at the normal spacing dramatically reduces losses in a wet year.
Reduce the wounds.Deal with codling moth, manage scab cracks, net against birds where practical, and pick fruit before it becomes wasp-damaged and overripe.
Prune for airflow.An open crown dries quickly after rain. Congested crowns hold humidity and brown rot thrives in them. Apples and pears in winter, stone fruit in summer.
Watch for blossom wilt on plums and cherries.The same fungus can infect through the blossom, causing whole spurs of flowers and leaves to wither and die back with the dead leaves clinging. Cut affected spurs out in summer, back into healthy wood.
Handle harvest carefully.Bruised fruit rots in store and one rotten apple genuinely does infect its neighbours. Pick with the stalk on, do not tip fruit into a bucket, and check stored fruit every fortnight.

Tips

Brown rot is worst in wet, warm summers and on tightly clustered fruit — plums, cherries and dessert apples suffer most.
Never compost mummified fruit in a cool heap. Bag it, bury it deeply, or hot-compost it.
The rot spreads far faster in store than on the tree. Any fruit with a bruise, a hole or a soft patch is for eating now, not keeping.
There is no useful garden fungicide programme against brown rot. Hygiene is genuinely the whole answer.

Common mistakes

Leaving mummified fruit hanging over winter — Each mummy produces spores in spring, at the exact height and place where the new crop will be. Removing them in winter is the single most effective control.
Knocking rotten fruit onto the ground and leaving it — It carries on producing spores, attracts wasps that wound more fruit, and gets forgotten. Bag it and take it away.
Storing fruit that has been dropped or bruised — Brown rot enters through bruises and spreads by contact in the box. One infected apple will take a whole tray with it.

If it doesn't work

Brown patches with rings of buff pustules on fruit

Cause: Brown rot — Fix: Remove and destroy all affected fruit, clear windfalls weekly, and take off every mummy in winter.

Shrivelled black fruit hanging on the tree in winter

Cause: Mummified fruit — next year's infection source — Fix: Pick every one off and destroy it. Do not leave any.

Whole spurs of blossom and leaves wither and die on a plum or cherry

Cause: Blossom wilt, the same fungus infecting through the flowers — Fix: Cut affected spurs back into healthy wood in summer and destroy the prunings.

Fruit rotting in store weeks after picking

Cause: Infection through bruises, spreading by contact — Fix: Sort at picking, store only unblemished stalked fruit not touching each other, and check every fortnight.

Rot appearing beside a wasp hole or bird peck

Cause: Secondary infection through a wound — Fix: Deal with the wasps and birds; the rot is following the damage rather than causing it.

Questions people ask

Can I eat fruit with brown rot?

No. Cut away the rot and the rest looks fine, but rot fungi can produce mycotoxins that spread beyond the visible damage in soft fruit. Discard visibly rotten fruit rather than trimming it.

How do I stop brown rot next year?

Remove every mummified fruit from the tree in winter, clear windfalls through the season, thin so fruit does not touch, and reduce the wasp and bird damage that lets the fungus in.

Why does it spread so fast in the fruit bowl or store?

It spreads by direct contact. Fruit touching each other in a box passes it along in days, which is why stored fruit is laid out in a single layer and checked regularly.

Is it the same disease that killed the blossom on my plum?

Very likely. Blossom wilt is caused by the same group of fungi, infecting through the flowers instead of the fruit, and it is controlled the same way.