It is coming towards the end of the period when it is safe to prune plants that are susceptible to silver leaf. There are number of fruit trees that are prone to this potentially fatal and untreatable fungal disease, most notably plum and cherry. The silver leaf fungus releases most of its infectious spores between September and May during damp or wet weather, so pruning in the summer during a dry spell is recommended. Furthermore, during the summer months the trees produce a gum in the plant tissues which helps prevent the spread of silver leaf fungal threads. Any spores that enter and germinate are unlikely to go on to cause silver leaf symptoms.
Silver leaf usually appears on one branch initially. The leaves develop a silvery sheen in the summer and shortly afterwards the branch dies off. If this is not cut out the disease will gradually infect the rest of the tree branch by branch. It is important that any infected prunings are burnt immediately to prevent spreading the infection to other plants and trees.
The spores of the silver leaf fungus are carried by the wind and can travel for many miles. If they land on damaged wood, such as pruning cuts, they can infect the branch. Once the spores have gained entry they produce a mass of filament-like threads which spread and eventually kill the tree. The fungus also produces a toxin which is transported by the sap through the tree.
If you have a tree that is showing symptoms of silver leaf it is important to make a proper diagnosis as there is a condition call false silver leaf. With this condition, the leaves take on the same silvery appearance, but false silver leaf affects the whole tree rather than one branch at a time. Feeding and mulching will usually cure the problem.
To determine if the tree is infected by silver leaf cut through an affected branch. If there is a dark brown irregular stain in the wood this is by far the most reliable indicator that the tree is infected with silver leaf.