Pseudomonas syringae, Pseudomonas morsprunorum
The disease occurs on branches, twigs, buds, leaves, and fruit. The most conspicuous symptoms are the cankers that exude gum during late spring and summer. Gumming is common on stone fruit trees, whether on trunks, limbs, twigs, or fruit when injuries occur. Thus, the name gummosis does not define a cause, only a response. Cankers on the twigs are darkened areas often at the base of buds. On limbs or trunks they are often darker than the normal bark, sunken in their centers, and they may extend for a considerable distance. Leaves and shoot growth beyond the canker may wilt and die during the growing season. Sour sap often occurs following winter injury to the trunks or limbs. The sour odor is due primarily to the fermentation of sugars by yeasts under the bark of injured areas. So this term, too, does not describe a cause. Gumming and sour sap, however, are symptoms of bacterial canker infection.