This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
On taking charge of the gardens here in the autumn of 1842, I found many of the Apple-trees in a very bad state from canker. Not knowing very well what to make of them, but, like many a young man on first entering a situation for himself, I concluded to do something that would be taken notice of; so during the winter I set to work and had many of the worst taken up. They were good-sized trees, that had been planted twenty years, more or less; however, I thought I would rather want the fruit they might produce than have the ground taken up by such unsightly objects. In order as far as possible to partly replace those dug up, I determined to make a beginning by planting a few healthy young trees wherever there was room for them, without coming too near to where the others had stood; and as concreting the bottoms of borders for fruit-trees was at that time in vogue, and having fully made up my mind that the subsoil (a ferruginous gravel) was the cause of all the mischief, I set to work in earnest, and had the site where every tree was to be planted thoroughly concreted.
After allowing the concrete time to dry, about 4 inches of broken stones was put over it, and on the stones some rough turf, so as to render the drainage as perfect as possible; then proceeded carefully to plant the trees, giving to each a cart-load of the best turfy loam I could procure, thinking that all had been done to insure success, and that in a few years I would have trees as free from canker as any in this part of the country. Judge of my disappointment when at the end of the third year I noticed my enemy beginning to show itself on some of the young shoots. I was now at a loss how to proceed, as it could not be from any bad effect of the subsoil; neither had pruning been neglected, as I do not happen to be one of those who think Apples more than any other sort of fruit-trees under cultivation ought to be left without pruning. A few years went on, and canker was not any better. At last (about twenty years ago) I determined to try what effect "heading-over" would have. Several of the oldest trees that were most cankered were subjected to that process, cutting away every branch 3 or 4 inches above where they had been grafted; they were all Dwarf Standards, with stems from 12 to 18 inches above the ground.
The season following they made excellent wood, which during the summer was well, thinned out, but not stopped. At the winter-pruning they were all shortened a little. For several years after, without showing the slightest symptoms of canker, they produced splendid crops of fruit. Owing to some alterations, they had to be taken up; but others that have since then undergone a similar operation, are perfectly healthy, and when the seasons are favourable produce excellent crops of fruit, although it is several years since they were cut over. In none of the cases have the roots been interfered with; neither do I attempt to say how "heading-over" happens to be efficacious in curing canker; I merely relate facts, and hope they may prove useful to some of the numerous readers of the ' Gardener,' from which, on many things, I have received much valuable information. I may also state that, on cutting over some of the largest trees, I had the surface of each wound thoroughly covered over with the following composition - two parts of bees-wax, and one each of tallow and rosin, melted slowly by the side of a fire, and laid on with a brush while warm. This, I think, prevents the wounds being injuriously affected by atmospheric changes.