Diplodia shoot blight

The causal agent of this disease is the fungus Diplodia scrobiculata, which belongs to the family of Botryosphaeriaceae. It is a well-known pathogen that primarily affects conifers, acting as a facultative parasite that thrives on stressed or weakened host trees in various forest and nursery environments.

The disease affects a wide range of pine species, including Pinus sylvestris and Pinus nigra. The fungus typically invades the host through buds, cones, or wounds in the bark, eventually spreading to branches and stems where it disrupts the xylem and phloem transport, leading to localized tissue death.

Typical symptoms of infection include stunted, chlorotic needles and the death of current-year shoots, which often curl into a characteristic hook shape. The presence of tiny, black, pimple-like fruiting bodies (pycnidia) on the bark of infected twigs or on the scales of old pine cones is a diagnostic sign of the pathogen's presence.

The development of the disease is heavily influenced by meteorological conditions, particularly high humidity and temperatures ranging from moderate to warm. Spores are primarily disseminated by splash-dispersal during rainfall, which allows the fungus to spread efficiently throughout the canopy of a tree or between adjacent trees in a plantation.

The impact of Diplodia scrobiculata is significant, as it can cause extensive crown dieback and reduce the overall vitality of forest stands, often predisposing them to secondary infestations by bark beetles. Effective management requires a combination of pruning dead wood, improving tree vigor through proper fertilization, and applying copper-based fungicides when conditions favor fungal sporulation.