The symptoms vary slightly depending on the host infected. Cankers are often diffuse, usually not sunken, and hardly noticeable unless they have girdled the stem, causing the wilting of leaves and eventually the death of the twig. The discoloration of the outer bark ranges from yellow, to red-brown, to gray or black depending on host species affected. The infected sections of the bark cave in and grow black, wart-like fungal fruit bodies that give a characteristic toad-skin aspect to the tree. On peach, cherry and plum, these cankers ooze gum. The multiplication of cankers on trunk, branches and twigs can reduce the vitality of the tree, cause branch dieback and even the death of the trees.
The symptoms observed are actually caused by several pathogens of the genus Valsa and Leucostoma. Together, they are often referred to as Cytospora cankers. At the beginning of the vegetation period, the spores are released by the wart-like fungal fruit bodies on trunk and branches and spread by rain to the healthy tissues. They enter the bark tissue with the help of threadlike structures of the fungus. The pathogens are exclusively wound parasites and need dead tissue to infect. They enter the wood via leaf scars, damage caused by hail or frost, as well as via mechanical injuries caused by pruning or other field practices. The fungus is an opportunistic pathogen that normally trees weakened by environmental stresses, for example temperature or moisture extremes. These pathogens can infect apple and stone fruit trees, and many other trees such as aspen, poplar, elm, willow, birch, maple, sycamore, oak.
Once infection has occurred, the best treatment is to increase the vigor of the orchard thought the use of fortifiers and a good fertilization program. .
Always consider an integrated approach with preventive measures together with biological treatments if available. The best management for this disease is to avoid its inception by following a series of preventing measures. Pruning cuts can be painted with fungicidal wound dressings.