Silver leaf

What you are looking at

The leaves on one branch of a plum take on a dull metallic sheen, as though someone had breathed on them. The rest of the tree looks normal. Over the following season the silvering appears on more branches, the affected ones die back with their leaves browning from the edges, and the tree loses a limb at a time.

The silvering is an optical effect rather than a coating. A toxin produced by the fungus separates the upper skin of the leaf from the tissue beneath it, leaving a thin layer of air that reflects light. It cannot be wiped or washed off, which is worth trying because a sooty or dusty deposit can be.

One cut confirms it

Silvering on its own is not enough. Drought, starvation and root damage all produce what growers call false silver leaf, where the whole tree silvers at once rather than a branch at a time, and it corrects itself when the underlying problem is fixed.

The test is in the wood. Cut across a dead or dying branch more than about 2.5 cm thick and look at the cut face. Silver leaf leaves a distinct purple-brown stain running through the wood, often as an irregular ring or a patch rather than a neat circle. Clean pale wood under silvered leaves means the tree has something else wrong with it.

Brackets are the third sign and the latest one. Small overlapping fruiting bodies, woolly and buff on top and lilac to purple underneath, appear on dead wood once the branch has been dead for a while. They shed spores through autumn and winter.

Which is why plums are pruned in June

The spores land on fresh wounds in the bark and germinate there. Autumn and winter are when they are in the air, and they are also when a dormant tree seals a cut most slowly.

Prune a plum in December and you have made a large, slow-healing wound in the middle of the spore season. Prune the same tree in June and the wound is callousing within weeks while there is little to infect it. That is the whole of the reason for the rule, and it is not a piece of orchard folklore.

The same timing prevents bacterial canker, which enters the same trees through the same winter wounds. Two diseases, one habit.

What can be saved

A tree with the fungus confined to one limb can be saved. Cut that branch back in summer, following the stain in the wood, taking progressively shorter branches until the cut face is clean, and then a further 15 cm. Trees held this way for a decade are common.

A tree where the stain has reached the trunk will not recover. The fungus is in the framework, further branches will silver each year, and the tree becomes a spore source for every other plum nearby. Taking it out is the right call, and replanting with a pear, an apple on the far side of the garden, or something outside the cherry family altogether avoids repeating it.

What to do about it

Prune between June and August and never in autumn or winter.

Cut a silvered branch out in summer, following the stain into clean wood.

Burn or bin the wood rather than stacking it.

Leave the cut unpainted.

Clear dead wood, old stumps and log piles from around the fruit trees.

Keep the tree fed, mulched and watered so it can hold the line.

Take out a tree that has silvered all over.

What it gets mistaken for

False silver leaf silvers the whole tree at once from drought, starvation or root trouble, and the wood underneath is clean. It recovers when the tree is fed and watered.

Bacterial canker sinks and kills patches of bark and weeps amber gum, with the damage visible from outside.

Honey fungus works up from the roots, with white fungal sheets under the bark at ground level and black bootlaces in the surrounding soil.

Powdery mildew coats the leaf surface in a white bloom that rubs off between finger and thumb.

Aphid honeydew and the sooty mould that grows on it leave a sticky black or grey film that washes off with water. Silver leaf cannot be washed away.