Ornamental Plum Problems

Hi. At Jersey Shore. Planted 3 ornamental plums 5 years ago in southern exposure. 2 are thriving. Middle one has always been noticeably shorter and less full. This year I noticed lots of big black ants up and down the tree....looks like they layed eggs all over the place (black bumps?). I sprayed. The ant population was reduced substantially, but the little buggers are still there. Are they the problem with the stunted growth? The other 2 trees remain healthy and unaffected Thx!

 

If there are curled leaves the ants are farming aphids which are inside the curled leaves.

 

Thx R. The black bumps appear mostly on the branches, a few on the trunk. Leaves are healthy, although looking sparce.

 

Perhaps your bumps are brown soft scale insects. Plums are also subject to black knot fungus.