Question
There are black growths on our plum trees. The growths can be almost described as warts. The trees still flower and bear fruit, but some of the fruit has scabs on it similar to apple scab. Is this something that is just cosmetic, or can it be harmful to the fruit? Is there something we should be doing to treat this?

Answer
Rosemary:
There is a common fungus disease that you can use your computer to see.  Look for pictures of BLACK KNOT.  This can be a fatal disease. Best to prune out these hard black/crusty swellings and dispose of the swellings.  There is a lot of information on the web from Cornell University about controlling it.

Regards
Steve