Why Silver Leaf Is a Pruning Problem

Silver leaf is a fungal disease that strikes fear into the hearts of many fruit growers. It is caused by Chondrostereum purpureum, a fungus that releases spores during wet weather from autumn through to spring. These spores land on fresh pruning wounds and germinate, sending threads into the wood. Over time, the fungus produces a toxin that causes the leaves to take on a silvery sheen, and branches begin to die back. Plums and cherries are especially vulnerable because they are members of the Prunus family, whose wood is soft and quick to wound. Once silver leaf is established, there is no chemical cure. Prevention is everything, and that begins with when and how you prune.

The Right Time to Prune Plums and Cherries

The single most important rule is to prune plums and cherries in late spring or summer, ideally between June and August. At this time of year, the fungus is far less active, and the air is drier. Spores are still present, but they are not being blown around in the same numbers as during autumn and winter rains. By pruning in late June, July or early August, you give the tree time to seal its wounds before the wet weather returns. For plums, aim for late June to mid-August. For cherries, wait until July or August, after the fruit has been picked. Avoid pruning between September and May if you possibly can. If you must remove a broken or diseased branch in winter, be aware that you are taking a risk, and seal the cut if it is large.

• Plums: late June to mid-August
• Cherries: July to August, after fruiting
• Avoid: September to May, when spores are most active

Keep Cuts Small and Clean

Silver leaf spores need an open wound to enter. The larger the wound, the longer it takes to heal and the greater the chance of infection. So your goal is to make as few cuts as possible, and to keep every cut small. Use sharp secateurs or a pruning saw for branches up to about 5cm (2in) in diameter. Anything larger than that is a major wound and should be avoided unless absolutely necessary. If you must remove a thick limb, do it in summer and make a clean cut just outside the branch collar – the swollen ring where the branch meets the trunk. Do not leave a stub, and do not cut flush with the trunk. A clean, angled cut that sheds water is best. For branches you can reach with secateurs, cut just above an outward-facing bud or side shoot. This encourages the tree to heal quickly and directs new growth away from the centre.

Pruning Young Trees vs Mature Trees

Young plum and cherry trees need formative pruning to build a strong framework of branches. Do this in late spring, when the tree is growing strongly. Aim to remove crossing branches, weak shoots and any dead wood. Keep the centre open so air and light can circulate. Mature trees need far less pruning. Once a tree is established, only remove dead, diseased or damaged wood, and thin out congested branches every few years. Renovation pruning – where you cut back a lot of old wood – is best done gradually over two or three summers. Never try to rejuvenate an old plum or cherry in one go. Large cuts on old trees are a magnet for silver leaf. If you inherit an overgrown tree on an allotment, take your time. Remove one or two big branches per year, in July or August, and let the tree recover.

Aftercare and Tool Hygiene

Clean tools matter more than you might think. Fungal spores can hitch a ride on your secateurs or saw. Before you start, wipe blades with methylated spirits or a strong disinfectant. Do the same between trees, especially if you have been working on one with signs of disease. After pruning, do not paint wounds with traditional tar-based products – they can trap moisture and do more harm than good. Modern advice is to leave small cuts to heal naturally. For large cuts on plums and cherries, some growers use a wound sealant, but the best approach is still to avoid large cuts in the first place.

Collect all prunings and burn them, or take them to your council green waste site. Do not compost them at home, as the fungus can survive and spread. Finally, feed and mulch your trees in spring to keep them vigorous. A healthy tree is better able to resist infection.

What to Do If You Spot Silver Leaf

If you notice leaves with a silvery, metallic sheen on your plum or cherry, inspect the branches carefully. Silver leaf sometimes appears on leaves without the wood being infected, but if you cut into a branch and see a dark stain in the wood, the fungus is present. There is no cure for an infected branch. The only action is to remove it. Cut back to healthy wood, well below the stain, and do this in dry weather in summer. Sterilise your tools afterwards. If the infection has reached the trunk, the tree cannot be saved. Remove it completely and burn the wood. Do not replant a plum or cherry in the same spot for at least five years. Instead, choose a different fruit tree, such as an apple or pear, which are not affected by silver leaf. With careful timing and clean pruning, you can enjoy healthy plums and cherries for many years.