My two year old damson plum tree has not yet borne any fruit. One of its middle branches has something that looks like barnacles on it. What could this be and how can I get rid of it?
It sounds like you may have scale. These are small insects that spend most of their lives under a protective covering or scale attached to the bark of branches. They suck away at the sap and weaken the plant. Scales are easily scraped off with a fingernail or dull knife blade. On a small tree like yours, that may be enough to control the infestation. It is difficult to control scales with any kind of spray because of the protective coating. Next spring, spray the tree with dormant oil before the buds break; the oil coats the over-wintering eggs and smothers them.
Here is a link from OMAFRA with photos to help you with identification:
If the ‘barnacle’ is not made up of small individual bumps, but is a large indented and bumpy area of bark that encircles the branch, it may be a canker, resulting from disease. In that case, you will want to cut off that branch completely. Do not put the branch in your compost; put it in the garbage or burn it. If this problem recurs, you will need to spray the tree with a copper-based fungicide at weekly intervals, beginning in August. Follow the package directions.