I can't make a definitive diagnosis from an image, but I would say it is likely of a fungal nature. There are several possible problems, since these are common in fruit trees. Here are several factsheets that describe fuller identifying features that may help you narrow down the problem: http://www.ext.colostate.edu/pubs/garden/02907.html, http://www.extension.umn.edu/garden/yard-garden/fruit/apple-pest-management/black-rot/, and http://www.caf.wvu.edu/kearneysville/disease_descriptions/disease_images/viskeyatbt.html

Generally advice is to prune away the infected branches, disinfecting the pruning tool between every cut, being sure to cut back well into healthy wood. Destroy all plant materials by burning or burying. A program of preventative fungicide spraying may help reduce reinfection or spread. However, specific actions would depend on the correct diagnosis. I suggest you contact a local extension office or arborist so someone can look at the whole trees and orchard in order to give a better idea of what's going on.