There are two possibilities. One is the occurrence of pests and diseases, and the other is the fertilization. Open the leaf first to see if there are any insects, and if not, it is basically enough to make sure that the fertilizer is overdoing it.
If it is hypertrophy, pour flowers once a day with fresh water until the leaves are unfolded and fertilize water according to scientific methods. The base fertilizer of the plums is added every six months. The diluted fertilizer (composted in water) is applied seasonally. It is once every two months in spring and summer, once in autumn and not in winter.