There is no need to be afraid of Silver Leaf disease, which rarely affects Cherry and Plum trees in gardens, and even then typically on old trees.
The disease is a concern for orchard owners, who have their livelihoods on the line with long rows of the same variety, creating the ideal environment for disease to spread.
With that said, when you have a choice about when to prune your Cherries and Plums, you may as well play it safe and prune them in Spring-Summer.
If you have to prune them in Winter, then so be it. Covering the wound with pruning paint will reduce the risk even further.
What Happens with Silver Leaf?
The leaves of infected plants take on a silvery sheen.
- Infected branches have brown staining in the wood; you can see this in the grain when you cut an infected branch off the tree.
- The disease can start in a single branch, which will begin to die back.
- If not checked, it will kill the whole plant.
Which plants does Silver Leaf attack?
Silver Leaf attacks a range of fruit trees (most famously Victoria Plum) including plums, damson, cherry, peach, apricot, and very rarely pear and apple.
It can infect a few other trees such as Laburnum, and poplars, but it mainly attacks members of the family Prunus (which includes the cherry laurel, but those are regularly trimmed in Winter and I have never heard of one catching the disease).
How does Silver Leaf work?
Silver Leaf (Chondrostereum purpureum) is a fungus whose spores penetrate a tree’s defences through recent wounds such as snapped branches and pruning cuts.
The spores grow fungal threads, which penetrate living wood, killing it as they proceed.
The silver leaves are caused by a poison which the fungus releases that causes the outer cells on the leaf to separate, resulting in the silvery sheen from which the disease gets its name.
The silver leaves themselves are in no way infectious. Silver Leaf spores are produced in small, tiered, purple/brown structures with a white, rather woolly top that grow on dead wood on standing trees and on stumps and logs.
The spores are the cause of new infection, which generally break out between September and May.
‘Don’t Prune Us’ in Winter
Winter is the main pruning season for fruit trees, except those in the Prunus family, such as Prunus avium, sweet cherries, and Prunus domestica, plums.
So, in Winter, don’t PRUN-US if possible.
- It is much easier for silver leaf spores to enter a wound in a tree when the sap is not rising, from Autumn to Winter.
- Therefore, Prunus species are best pruned when they are in growth and rising sap will push spores out of the wound.
How do you control Silver Leaf?
Prevention is always better than cure, and there is no chemical cure for silver leaf.
Well planted trees, in good soil, which are staked so the tree does not rub the stake, protected against strimmer and lawnmower damage, and mulched with good organic matter every spring are far less likely to get silver leaf in the first place.
Keep orchards clear of dead wood, and remove or grind out the stumps of dead trees.
- If you can catch it early enough, and it has only infected a branch, then remove and burn the infected material.
- Cut the branch off below the visible infection.
- Check the cut and if you can see a brown stain in the wood, remove more of the branch until there is no stain.
- Then cut off another 6 inches, and paint the wound with a sealant such as Medo or Prune n Seal.
- Disinfect the saw blade with Dettol, Jeyes Fluid or meths between each cut.
If the stain has reached the main trunk, the tree will die, and it should be removed and destroyed as soon as possible to prevent it infecting other trees nearby.