Silver leaf is a severe disease of Plums, but it can infect many of the Rosaceae family, including Apple, Apricot and Cherry trees, Rhododendron and Laburnum species.
The main symptom of Silver Leaf is the foliage developing a silvery tint. Although, this isn't true for Rhododendron and Laburnum plants, and is most notable in Plum.
Other notable symptoms are a darkened irregular stain which can only be seen when cutting through the branch and bracket fungi appearing on older branches.
Cold and drought can cause similar symptoms to Silver Leaf, and this is what's known as False Silver Leaf. The irregular darkening of the bark is a definitive way to identify silver leaf from the false form.