Septotinia leaf spot

The disease is caused by the fungus Septotinia populiperda, an ascomycete pathogen that specifically targets Populus species. This fungus is known for its ability to cause severe necrotic lesions on leaves, petioles, and young shoots, often leading to significant foliage damage within nursery and plantation environments.

Initial symptoms are characterized by small, dark-brown spots on the leaves, which eventually enlarge and become necrotic. As the infection progresses, the leaves curl and drop prematurely. On succulent shoots, the infection manifests as sunken lesions that can girdle the stem, causing the upper part of the branch to wither and die.

Environmental conditions play a critical role in the dissemination of the pathogen. Wet and humid weather, particularly during the spring and early summer, facilitates the discharge of ascospores from overwintering structures. These spores are wind-dispersed and land on host tissue, where they germinate and infect the plant through natural openings.

The impact of Septotinia populiperda is significant, particularly in intensive poplar plantations. By causing premature defoliation and shoot necrosis, the fungus reduces the tree's photosynthetic capacity, leading to stunted growth, reduced wood volume, and increased susceptibility to secondary stressors, including other pathogens and insect attacks.

• Sanitation practices, including the removal and destruction of infected leaf litter.
• Pruning and destruction of diseased twigs to minimize the primary inoculum source.
• Application of protective fungicides during the active growth period.
• Improving site hygiene and air circulation in nurseries to lower humidity levels.
• Use of resistant poplar clones to mitigate the risk of epidemic outbreaks.