SILVER LEAF

This is the reason you don't prune plum trees and cherries at this time of year.  It is the fruiting body of the fungus that causes silver leaf disease, Chondrostereum purpureum.  Here it is growing on the stump of a damson tree that was felled three years ago in our garden.  

In summer plum and cherry trees produce a resin, which can seal small wounds to prevent fungal spores from entering.  That's the time to prune them - if you have to.

A few days later some toadstools appeared, feeding on the dead roots of the damson tree.

2 days later.

And another 10 days later.

These are the fruiting bodies of honey fungus and will soon turn black and slimy when frost happens.  Meanwhile the fungus will be sending out underground runners called rhizomorphs in search of other susceptible plants to attack.  

I should probably grub this stump out to remove the food source for this fungus.