On our recent ‘Prunus Pruning Blitz’ in Hackney, London we noticed that some plum and damson trees are bearing quite deformed fruitlets. Some are split, some curled like little cashew nuts, mostly pale with no stone, and often combined with curled and shrivelled leaves. It turns out that this is most probably ‘Pocket Plum’ disease. It’s a fungal disease (Taphrina pruni) that is likely to send spores out quite soon, so if you recognise these symptoms on your own trees (see https://www.rhs.org.uk/advice/profile?pid=199 ) the best thing to do to prevent spread is to remove as much of the infected fruit as soon as possible (bagging it as you go around to prevent spore spread) and take them off-site for disposal.
As usual, don’t panic and do focus on overall tree health – making sure your trees are well mulched and watered. Now is also a good time of year to reduce congestion of branches – which can provide a favourable micro-climate for fungal pathogens.
It’s useful for us to keep track of how widespread this problem is, so do let us know if your trees are affected by commenting over on our Facebook page.