Plenty of corroboration on gardening websites. E.g.:

-> "Smaller cankers can be pared back to healthy bark with a sharp knife and the cut surfaces treated with a fungicidal wound paint such as Medo - containing cresylic acid - that's specially formulated for canker treatment."
http://www.which.net/gardeningwhich/advice/applepearcanker.h...

-> "canker is troublesome, paint large pruning cuts with a fungicidal wound paint and spray the bushes at pruning time with a copper fungicide."
http://www.homeandgardenlife.com/gardenexpert/diseases/roses...

-> "Affected larger branches can have affected wood scraped away with a sharp knife, removing all parings. Paint wounds with a fungicidal paint."
http://www.orchard-group.uklinux.net/glos/pests.html