Dothiorella canker

Dothiorella canker, caused by the fungus Dothiorella gregaria (also known as Botryosphaeria dothidea), is a destructive fungal disease affecting a wide variety of trees and shrubs. The pathogen primarily targets the bark and cambium layers, leading to the formation of cankers and subsequent dieback of branches. It is a persistent disease that can lead to the decline of entire woody plants if left unmanaged.

The host range for this pathogen is extensive, encompassing various fruit trees such as apple, pear, peach, and walnut, as well as many ornamental and forest trees like poplars and willows. Plants experiencing environmental stress—due to drought, nutrient deficiency, winter injury, or mechanical damage—are significantly more susceptible to infection by this opportunistic pathogen.

Symptoms of the disease initially appear as small, slightly sunken areas on the bark. As the infection progresses, these areas expand and may crack, exposing the underlying wood, which often becomes discolored or decayed. In some species, heavy exudation of sap or gumming occurs at the margin of the canker. Eventually, the affected branches exhibit wilting, yellowing of leaves, and ultimately dieback, starting from the point of infection.

The development and spread of Dothiorella gregaria are heavily influenced by humidity and temperature, with warm and moist conditions accelerating spore production. Spores are disseminated by wind, rain splashes, and movement of infected wood or tools. Entry into the host typically occurs through natural openings, pruning wounds, or sites of mechanical damage, such as sunscald or frost cracks.

Management of Dothiorella canker relies heavily on good sanitation and stress reduction. Pruning out infected branches is the most critical step, ensuring cuts are made into healthy wood well below the visible symptoms. All pruning tools should be sterilized between cuts. Furthermore, maintaining tree vigor through proper irrigation and fertilization, as well as protecting trunks from sunscald with white latex paint, significantly lowers the risk of infection.