Cytospora canker of poplar

Cytospora canker is a serious infectious disease caused by the ascomycete fungus Cytospora populina. The disease belongs to the category of bark necrosis and is one of the leading causes of premature decline and dieback in poplar, willow, and various other deciduous tree species. The pathogen enters the plant tissues through mechanical bark wounds, pruning cuts, or frost cracks.

Primary host plants susceptible to this disease include various species of poplar (especially Lombardy and Canadian poplar) and willow trees. In forestry nurseries and urban landscaping, the infection can cause widespread mortality among young saplings and weakened mature trees, significantly reducing the aesthetic value and biological viability of the plantings.

Initial symptoms of the disease appear as localized color changes in the bark, which becomes brownish or reddish, gradually dries out, and cracks. Infected bark areas are typically covered with numerous tiny bumps, known as pycnidia. Under humid conditions, these structures release orange or reddish tendrils of spores that are easily spread by wind, rain, and insects to healthy parts of the tree.

The development of Cytospora canker is promoted by factors that weaken tree immunity, such as drought, waterlogged soil, mechanical damage, or infestation by wood-boring insects. Active fungal spread typically occurs during periods with moderate temperatures and high humidity, which provide optimal conditions for spore germination and colonization of weakened plant tissues.

The economic and ecological impact of this disease is significant, as it disrupts water and nutrient transport, leading to the gradual dieback of branches and eventually the death of the entire tree. Effective management requires a combination of strict cultural practices: prompt removal and destruction of infected branches, protection of trunks against sunscald and frost damage, and regular sanitary thinning. Chemical control with fungicides is most effective when applied at the early stages of infection alongside measures to improve tree vigor.