Botryosphaeria canker

Pathogen and Disease Type
The disease is caused by the fungus Botryosphaeria dothidea, a systemic pathogen that primarily infects the bark and vascular tissues of woody plants. It is considered an opportunistic pathogen, meaning it thrives when the host plant is stressed by environmental factors, pests, or poor maintenance practices.

Host Plants and Economic Impact
This pathogen affects a wide variety of deciduous trees, including many fruit and nut species. It is a major concern for the almond industry, as well as for pistachio, apple, and grape growers. The primary economic damage is caused by branch dieback, yield reduction, and in severe cases, the eventual death of the tree.

Symptoms and Signs
The most visible sign is the formation of cankers on branches and stems. These lesions are often sunken, discolored, and can exude gum (gummosis) in some species like almonds. Under the affected bark, the wood displays dark staining. In humid conditions, small black pycnidia erupt through the bark surface to release infectious spores.

Conditions for Development
Development is highly favored by hot, humid weather conditions. Spores are dispersed through wind and splashing water. Infections typically occur through wounds such as pruning cuts, cracks from sunscald, frost damage, or insect feeding sites, where the fungal spores gain direct entry into the host's vascular system.

Prevention and Protection Measures
Effective management relies on a combination of cultural and chemical strategies. Avoiding excessive stress through balanced irrigation and fertilization is crucial. It is essential to prune out and destroy infected branches during dry weather to prevent further spread. Applying copper-based fungicides to pruning wounds and protecting trees from mechanical injury are standard preventative practices.