This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This disease, which appears to be confined to this country, often does an immense amount of harm to plants, whether grown under glass or in the open. Soon after infection the bark becomes dry, and minute radiating cracks appear, which gradually extend in all directions until eventually a large canker-like wound appears, which, in the case of the trunk or a stout branch, may extend for many inches. The fungus continues to live in the cankered patch until all the bark and sapwood are completely eaten away. The wood situated below a wound changes to an ashy-grey colour, a point which at once determines the cause of the injury. When young shoots are attacked they gradually die back from the tip, on account of the food supply being checked by the fungus. The fruit of the fungus appears only on dead portions of the plant, and appears on the surface of the dead bark under the form of numerous minute hair-like bodies, which consist of myriads of the minute spores of the fungus. The parasite can only gain access to the wood through wounds, which may be due to various causes, as pruning, broken twigs, the chafing of branches against each other, or even to the punctures of insects.
Branches, whether large or small, that are ringed by the fungus, should be removed, as it is on such branches, above the wound, that the fruit of the fungus is produced, thus furnishing a source of infection. When a wound is confined to one side of a branch the diseased portion should be cut away, care being taken to remove all the wood that is stained grey, as such wood contains the mycelium of the fungus, which would spread and break out higher up the branch. All cut surfaces should be protected with Stockholm tar; ordinary gas tar should not be used, as it injures the living bark with which it comes in contact. Care must be taken not to cut healthy parts of a plant with a knife that has been used for cutting away diseased portions, until it has been thoroughly cleaned.