Why Are My Plum Tree Leaves Turning Silvery?

A silvery or leaden grey sheen on plum leaves — as if the leaf surface has been frosted or coated with a thin metallic film — is the signature symptom of silver leaf disease. It is caused by the fungus Chondrostereum purpureum and is one of the most serious disease problems of stone fruit trees in the UK and northern Europe. Recognising it early and acting promptly is the difference between losing a branch and losing the whole tree.

What causes the silvery appearance

The fungus colonises the wood beneath the bark and produces toxins that travel up into the leaf tissue. These toxins cause the upper and lower leaf surfaces to separate slightly, creating an air space between the layers. Light reflecting off this air space produces the characteristic silver-grey iridescence. The leaves themselves are not infected with the fungus — the fungal mycelium is in the wood — which is why removing individual leaves has no effect on the problem.

Confirming the diagnosis

Not all silvery-looking foliage is silver leaf — false silver leaf (caused by nutritional stress or poor growing conditions) can produce a similar appearance without stained wood. To confirm true silver leaf, cut a branch showing the silvery leaves cleanly across. Look at the freshly cut surface — in confirmed silver leaf cases, the central heartwood zone will show a brown, reddish-brown or purple-brown discolouration compared to the creamy white of healthy wood. Moisten the surface with water to make the stain more visible. If the wood is clean, you may be dealing with false silver leaf.

Pruning to remove infected wood

There is no fungicide treatment for established silver leaf infection. The only response is to prune back affected branches until you reach wood that shows no staining in cross-section. This point of clean wood should be at least 10–15 cm behind the last visible stain. Make all pruning cuts during summer — from late May to the end of August — when the fungal spores are at their lowest levels and cuts heal most rapidly. Apply pruning wound paint to large cuts as a physical barrier.

Preventing reinfection

Silver leaf enters through wounds, broken bark and pruning cuts. Never prune plums in autumn or winter. Keep tools clean and disinfect between trees with methylated spirit or a horticultural disinfectant. Remove dead wood promptly as it produces the fruiting bodies (purple bracket fungus) that release spores. Burn all infected prunings.