We have a small Victoria plum tree. Last year it was laden with plums, however most of the plums had a kind of sap running out of them. I thought it was caused by a bug of some kind. However, someone told me that it was caused by the stones splitting. The plums were all edible, and on cutting open, sure enough, the stones were split. Now, once again the tree is heaving with fruit and once again, the sap is running out of them, so presumably the stones must be splitting again. They are not ripe yet. Please, can anyone tell me how to stop this happening? Thank you.