Cytospora canker of poplar

Cytospora canker, often referred to as brown necrosis, is a serious fungal disease caused by the pathogen Cytospora chrysosperma. This fungus predominantly attacks the bark and cambium layers of poplar trees, leading to the rapid destruction of conductive tissues. It is a widespread disease that poses a significant threat to both forest plantations and ornamental landscape plantings.

The disease primarily targets various species within the Populus genus. Young trees and saplings are particularly susceptible, though mature trees subjected to environmental stressors like prolonged drought, winter injury, or poor soil conditions are also frequently colonized by the fungus, often leading to decline and eventual tree mortality.

Symptoms are marked by the appearance of discolored, sunken areas of bark that turn brown or reddish-brown. As the infection progresses, the pathogen develops small, pimple-like structures known as pycnidia on the surface of the bark. During humid conditions, these structures extrude masses of gold-colored spores, which are key diagnostic indicators of the disease.

The development of the fungus is closely linked to tree stress levels. Pathogens enter the host through pruning wounds, frost cracks, or sites damaged by insects. Once established, the fungus grows beneath the bark, girdling branches or the main stem. The cycle of infection is most rapid during cool, moist periods when spores are easily disseminated by rainfall and wind to susceptible host tissues.

The impact of Cytospora canker is severe, as it causes permanent damage to the vascular system, preventing the tree from transporting water and nutrients. Effective management focuses on cultural practices rather than chemical treatments, as systemic control is difficult. Key measures include maintaining tree vigor through proper irrigation, preventing mechanical injuries to the bark, and performing timely sanitation pruning to reduce inoculum pressure within the stand.