Botryosphaeria canker of Douglas-fir

The causative agent of this disease is the fungus Botryosphaeria pseudotsugae, an ascomycete that acts as a pathogen primarily affecting the bark and cambium of woody hosts. It disrupts the vascular system, causing localized necrosis and the formation of perennial cankers on stems and branches.

The primary host for this fungus is the Douglas-fir (Pseudotsuga menziesii), although other conifers can also be affected depending on environmental conditions. It is of particular concern in forest nurseries and young plantations where high humidity and plant density provide an ideal environment for the pathogen to thrive.

Symptoms are typically manifested as sunken areas of dead bark, which eventually develop into distinct cankers. As the fungus progresses, the branches above the infection point often show wilting, chlorosis, and eventual necrosis. The presence of small, black, erupting fruiting bodies (pycnidia) on the affected bark confirms the diagnosis.

Environmental conditions such as high moisture levels and warm temperatures significantly enhance the spread of spores. The pathogen is opportunistic, often invading trees that are weakened by environmental stress, drought, frost, or mechanical damage, which provide accessible entry points for the fungal hyphae.

• Prune and dispose of infected branches to reduce the inoculum level in the area.
• Maintain tree vigor through proper site selection and balanced fertilization.
• Avoid mechanical injuries to the stems during maintenance operations.
• Apply fungicides preventively, especially during periods of high humidity.
• Ensure adequate spacing between trees to improve air circulation and canopy drying.

The damage caused by Botryosphaeria pseudotsugae includes reduced growth rates, branch dieback, and in extreme cases, the mortality of entire saplings. Effective management requires an integrated approach focusing on sanitation and the reduction of physiological stress in the host trees to minimize economic losses.