Hello. If during the growing season they have been infected with powdery mildew, you may want to consider carrying out treatments specific to the dormancy period (which can be carried out before the first leaves start growing). The treatments involve applying a sulphur-containing fungicide such as , or , and 10-14 days after the fungicide treatment, you can carry out a treatment with horticultural oil: , or . The treatments should be applied on dry bark, not covered by ice, snow or frost, on days with positive temperatures, preferably minimum 5-6°C. More information on these treatments can be found in the following article: Winter treatments with oils and copper-based products.
Regarding the aspect of the branches, it can be caused either by pruning or by a phytopathogenic disease (apple proliferation), but to determine exactly if it is apple proliferation (Phytoplasma mali), a laboratory analysis is necessary. There are no known curative treatments for this disease, but a number of preventive measures can be taken: use of healthy grafts and rootstocks, proper irrigation, balanced fertilization, disinfection of pruning tools, control of pests (especially leafhoppers), removal and burning of branches with unusual growth, etc.
Later, during the growing season, to promote growth and fruiting, you can consider using a specific fertilizer: , or .