Allantophomopsiella pseudotsugae

Pathogen and disease type. Allantophomopsiella pseudotsugae (syn. Phomopsis pseudotsugae) is a fungal pathogen responsible for stem and branch canker disease. It acts by invading the bark and cambium layers of the host, eventually disrupting the vascular system and causing tissue necrosis.

Host range. The primary host of this pathogen is the Douglas fir (Pseudotsuga menziesii). While it is most frequently observed in forest nurseries affecting young seedlings, it can also impact established trees if environmental conditions are favorable for fungal development or if the tree is under stress.

Symptoms and signs. Initial signs include the discoloration and browning of needles on specific branches, commonly known as dieback. Cankers or lesions appear on the stems and branches, often accompanied by resin flow (gummosis). In severe cases, the leading shoot may die, leading to stunted growth and permanent deformation of the tree.

Development and spread. The fungus thrives in humid, cool conditions with limited air circulation. Spores are primarily dispersed by splashing rain and wind currents. Entry into the host tissue usually occurs through natural openings, needle scars, or wounds caused by insect feeding, frost cracks, or mechanical damage during maintenance.

Damage and control measures. This disease poses a significant economic threat to nurseries, often leading to total loss of susceptible batches. Management strategies should prioritize sanitation, including the removal and destruction of infected branches. Cultural practices such as proper spacing and thinning help improve airflow. Chemical control involves the application of copper-based fungicides during the early bud-break stage to protect new growth.