Black Stuff On Plum Stones

[johnk]

My Plum tree is fruiting now but the plum stones have some sort of black dirt coming from them inside what appears to be a nice plum. Some of them have a grub inas well but not all. Anyone know what's causing this?

[rowanwitch]

The black stuff is the grubs poo. Best to forget about plums this year, unless you are willing to cut open every one,
Next year you might want to spray for plum fruit moth