This pathology is a serious disease caused by a fungus called phytophthora cactorum; this mushroom usually penetrates at ground level, in the rootstock shaft, more difficultly in the graft. It causes various types of symptoms, ranging from a generalized deterioration of the plant, to the chlorosis of the leaves and the withering of the fruits. Cancer species are produced in the stem, from which the fungus spreads throughout the plant. If left untreated, plants affected by this problem can die within a few years; more typically they have stunted growth, early fall of leaves and loss of fruit before ripening. It rarely happens that plants experience a sudden deterioration, which causes the total loss of leaves and fruits, within a few days.
Generally most of the rootstocks used today in the orchard are particularly resistant to the rot of the collar; however, rootstocks and some varieties of apples are present which are very susceptible to this disease. Furthermore, the climate can act as a trigger, as well as the planting soil: continuous rains throughout the summer, or heavy and poorly drained soil can favor an abnormal development of the fungus, and a lowering of the defenses by the plants. These fungi penetrate the stem from the ground, or carried by the wind; typically the infestation comes from other diseased plants, or from the pruning residues of these, left for a long time on the ground. Regular control of the health of the plant collar, and the removal from the orchard of remains, processing waste, dehiscent fruits or pruned branches, in synergy with good soil tillage and with correct irrigation, lead to a containment of the spread of the mushroom .