Plum Tree with red/green branches turning black

I bought this Victoria plum back in October last year. It looked very similar to how it does now with green and red mottled branches. I didn't think much of it as all the others of this type were the same and so were the peaches in another nursery. I am now starting to worry slightly as the branches are turning black from the ends and the buds are very slow opening compared to the other trees in my garden. I thought this could be down to a weak root system as the roots weren't great when I got it back and planted it. I will be pruning it in June at the latest because I think the black is some kind of fungal infection but don't want to do it too early and risk silver leaf curl.

Any thoughts.....