Well, usually a vigorous healthy tree can fight the diseases and heal those cankers, but it looks like there may be a question regarding the health of the tree. I have fruit
trees myself and mix a foliar spray containing Effective Microorganisms, molasses, a biological disease control called Serenade, raw unfiltered and cold processed neem oil, and a little natural
soap as an emulsifier. The microorganisms will attack a lot of disease pathogens aiding the tree. The neem oil will disrupt the life cycle of insects (like borers) that will find the cracks in the bark from the canker and lay eggs in the cambium tissue just beneath the bark. Wounds on tree bark are open doors to pests that can cause real problems and I know borers can be a real problem in north america, but I am unsure of what sort of pest pressure is experienced in europe. I not only spray the leaves of my trees but all the branches and trunk as well. Also, quality
compost and even sawdust &
wood chips can be scattered thickly on the surface of the soil beneath the tree and out past the
drip line to help slowly
feed the tree and improve the soil.