Cytospora canker

Cytospora canker, caused by the ascomycete fungus Cytospora nivea, is a severe stem and branch disease affecting several broad-leaved tree species. It is a classic example of a latent pathogen that transitions from a saprophyte on dead tissue to an aggressive parasite on weakened hosts.

This pathogen primarily targets poplars (Populus spp.) and aspens. It is frequently observed in shelterbelts, urban parkland, and forest nurseries where trees are subjected to environmental stress. The fungus colonizes the bark and cambium, effectively disrupting the vascular system of the infected tree.

Symptoms of the disease are characterized by the appearance of discolored, sunken areas on the bark. As the pathogen progresses, the bark dies and may crack or peel away from the wood. During humid weather conditions, characteristic pin-head sized fruiting bodies emerge, releasing spore masses that appear as whitish or yellowish tendrils on the surface of the bark.

The development of Cytospora nivea is heavily dependent on the physiological condition of the host. The fungus enters the plant through wounds, frost cracks, sunscald, or pruning cuts. Trees suffering from drought, poor nutrition, or transplant shock are significantly more vulnerable to infection, as the pathogen exploits the lack of bark resistance.

The impact of Cytospora canker is devastating, as girdled branches or stems die rapidly due to the loss of water and nutrient transport. Disease management relies on an integrated approach: proactive sanitation (removing infected branches), ensuring trees receive adequate irrigation, and protecting bark from mechanical or sun-induced injuries to prevent entry points for the fungal spores.