Sap Oozing from Plum Tree Trunk

Sap oozing from the trunk of plum

Q. Last week I noticed sap bubbles 6 to 8 inches off the ground on the trunk of my year old Santa Rosa plum. I removed the bubbles and reapplied the whitewash. I checked again today and they are back. I've had plums before and the boars always win. I had hoped the Santa Rosa would do better. What can I do to save this tree?