Dead branch tips on plum tree
Thank you for your question. This looks like brown rot blossom blight. Sadly, it is too late to treat this year (https://cybercemetery.unt.edu/archive/allcollections/20090116082433/http://extension.oregonstate.edu/catalog/pdf/ec/ec631.pdf) You can take your photos and some samples into the CC Extension office (https://extension.oregonstate.edu/clackamas) be sure. They are closed 5/8. Good luck!