hi there. I have recently bought a house with a large garden, woodland and orchard. There is a lot of work to be done as everything seems to have been neglected. However, my immediate concern is the apple trees - there are about 8 apple trees, all different, it seems. On most of the apples there is a black film over the surface. It rubs off ok when i wash them, and the apples taste great, but i wondered if this black film was indicative of some sort of disease on the trees? any suggestions would be appreciated. Thank you.