What is killing my plum trees?

[fubar2]

Two Santa Rosa and one Matheny. What causes a black growth about three inches long and about three sixteenths out from the limb? It seems to be on the smaller limbs mostly. I noticed it last year on the Metheny. This year it looks as if the tree is dieng and with no fruit. Now I see it is spreading to the others. Anybody know what it is and what I can do about it? I've never posted pics before so if you can tell me without pics it would be great. Thanks in advance.

 

[ATH]

Is it black knot?

 

[fubar2]

I dug around on the net after I posted and I think it is. What is cheap and effective for getting rid of it?

 

[Urban Forester]

Black Knot is a fungus that is self-replicating. The black growths contain the spores that are released and spread through out the tree. Prune out the cankers (growths) Apply 3 applications of thiophanate-methyl, mixed at labeled rate at 2 week intervals from late April to late May (infection period).