Dothidea canker

The fungus survives the winter dormant phase within the bark and infected stems of the host plant. It maintains its viability through mycelial structures that remain active beneath the bark layer.

During the growing season, particularly under wet conditions, the fungus produces spores. These spores are dispersed via rain splashes and wind, facilitating the colonization of new branches.

Entry of the pathogen into the host occurs mainly through wounds, pruning cuts, or natural cracks in the bark. Once inside, the hyphae spread into the vascular tissue and cortex.

The biological cycle is highly dependent on humidity levels. Prolonged periods of moisture increase the infection rate, allowing the fungus to establish firm control over the host's vitality.

The most prominent sign of Dothidea canker is the appearance of small, raised pustules or bumpy structures on the bark. These are the fruiting bodies of the fungus, often appearing dark or black.

As the infection progresses, the bark in the affected areas becomes brittle and cracks. These lesions often expand, leading to the localized death of tissues around the infected branch segment.

Leaves on branches distal to the canker may show signs of yellowing or wilting. This occurs because the fungal growth obstructs the transport of water and nutrients from the root system.

Detailed examination reveals a discolored, sunken area of the bark where the fungus is concentrated. This site of necrosis eventually turns into a hardened, irregular canker.

In advanced stages, small, hard black spots (pycnidia) can be clearly seen clustered on the surface of the bark. These are indicative of high pathogen activity and spore production.

Dothidea canker causes significant aesthetic damage to elderberry bushes, making them look unkempt. This is particularly problematic for ornamental varieties used in landscaping and garden design.

The disease weakens the structural integrity of the branches. Affected stems become brittle and are prone to breaking under snow loads or during high winds, compromising the plant's form.

Chronic infection drains the plant's resources, leading to stunted growth and reduced vigor. This general decline makes the bush highly susceptible to secondary attacks by insects and other pathogens.

Without intervention, the cankers can girdle the branches, leading to total branch dieback. This requires drastic pruning, which ruins the natural shape of the elderberry shrub.

Economic losses are notable in nurseries, as infected stock must be discarded to prevent the spread of the fungus. Maintaining disease-free plants is crucial for successful cultivation.

Pruning is the primary method of management. All infected branches must be removed well below the site of infection and burned or disposed of far away to eliminate the pathogen source.

Cultural practices are essential for prevention. Ensuring adequate spacing between plants improves air circulation, which helps keep the bark dry and reduces the chances of spore germination.

Strict hygiene protocols for pruning equipment are necessary. Disinfecting blades between every cut prevents the accidental transfer of the pathogen from diseased branches to healthy ones.

Copper-based fungicide applications are recommended as a preventive measure. Spraying during the dormant season helps create a protective barrier on the bark, limiting the colonization of the fungus.

Maintaining overall plant health through balanced fertilization and correct watering practices is key. A healthy, stress-free elderberry shrub is significantly more resilient to Dothidea infections.