The term gummosis, gum-flow, is here used broadly to indicate a sign of disease or injury rather than any specific disease. Like other stone-fruits the peach is subject to a gumming from trunk and branches as the result of almost any kind of injury. The phenomenon has been observed since man began to give attention to stone-fruit trees, and the trouble occurs more or less all over the world. Gumming is not confined to stone - fruits, but is known also on citrus trees. Gumming of the former only is considered here.
Gummosis, or gumming, is usually evident in the spring, particularly after cold rains and when growth is active. Masses of gum, at first glassy or transparent and soft, then amber-colored and hard, exude from the twigs, branches and trunks. Examination will usually show the presence of a break in the bark through which the gum exuded. The gum becomes swollen and sticky in the presence of water. The casual observer will note gum only on the external portions; however, it is formed internally. Sometimes gum is developed internally and there is no evidence of it externally. Gumming often accompanies the blighting of blossoms or twigs, canker - wounds on limbs and trunks and wounds left by pruning operations.
The phenomenon of gum-flow, gummosis, is associated with a variety of conditions, and therefore it is difficult on finding gum-exudation to attribute it to any definite cause. Wounds are made inadvertently, and many factors are capable of making them; and wherever a stone-fruit tree is wounded, gum is very certain to exude. But wounds do not always exude gum; an exciting factor is often essential after the wound is made. Just why a tree should exude gum is a matter which has been discussed for years. It is now quite generally held that it is due to some enzyme produced by the host-protoplasm. Some authorities, however, believe that gummosis cannot be due to an enzyme. Others simply say that the gum exudes in response to some stimulus in an effort on the part of the tree to protect a wounded surface, and that the phenomenon represents a retrogressive change in the cell contents. The real causal factor, whatever it may be, passes up the ducts, enters adjoining cells, and comes in contact with living protoplasts which are stimulated to release an enzyme; this enzyme causes gelat-inization of the primary lamella. This gelatinized gum constitutes the exudate which is forced out through pits into the ducts and adjacent wood cells and fibers. Some of the various causal factors involved in gummosis of the peach follow: (1) frost; (2) fungi, such as Sclerotinia cinerea, Valsa leucostoma, Coryneum Beijerinckii, and others; (3) bacteria, such as Bacterium Pruni; (4) insects. Among the other factors which have been listed as possible causes of gummosis are: (1) lack of balance between the nutritive processes; (2) galls on the roots; (3) excessive rainfall; (4) severe pruning, particularly when the peach is pruned during the period of its greatest vegetative activity, that is, from April to August; (5) poor cultivation; (6) deep planting; (7) adverse soil conditions; (8) adverse atmospheric conditions; (9) hail; (10) over - bearing. It will be seen that gumming may be due to any one or several of the following classes of factors: (1) climate; (2) adverse soil and nutrition; (3) animal or plant parasites; (4) unfavorable cultural conditions.
The remedy involved will depend somewhat on the cause. In any case the local affected areas should be cut out wherever this procedure is feasible. In those cases where the exact cause is determined, the measures of control may be found in the discussions given under that heading for the individual diseases concerned (Frost cankers and gummosis, page 300; gum-flow due to Sclerotinia cinerea, page 275; to Valsa leucostoma var. cincta, page 302; to Coryneum Beijerinckii, page 313; to Bacterium Pruni, page 310). In general the phenomenon of gumming may be remedied by making conditions favorable to growth of the tree. It is always essential to learn the nature of the exciting factor. (See also Cherry Bacterial-Gum - mosis, page 181.)
Ontario Agr. Dept. Bul. 201: 38-40. 1912. Selby, A. D. Preliminary report upon diseases of the peach. 3. A twig disease with gum-flow. Ohio Agr. Exp. Sta. Bul. 92:199206. 1898. Taft, L. R. Spraying calendar for 1898. Gum disease of the peach.
Michigan Agr. Exp. Sta. Bul. 155: 304. 1898.