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 exceedingly common, yet ill - understood disease attacks Plums, Cherries, Peaches, &c; in fact all the Pruneae, or trees bearing stone fruit, suffer. Small drops or tears of gum first show on the trunk or branches, and gradually increase in size until quite large masses of gum accumulate on the surface of the diseased parts. As the disease progresses, the fruit also shows gumming, several large masses being often present on a plum.
The gum consists of the tissues which have become dissolved, owing to the presence of an enzyme, and is not readily soluble in water, after being exposed to the air.
Probably no other single plant disease has been investigated more frequently, or more thoroughly, than gumming, or "gummosis" as it is frequently called, yet the various results are so diametrically opposed that it may be concluded that the true cause is as yet unknown.
If we concede that the cause of the disease is unknown it cannot be expected that a cure can be given; yet, following the rule-of-thumb method of first trying one thing then another, the fact has been arrived at that the best-known remedy is common salt. This should be sprinkled on the ground as far as the roots extend in the soil, at intervals, from 3 to 4 lb. of salt being used in a year. [g. m.]