Truncatella twig blight

The disease is caused by the fungus Truncatella hartigii (synonym Pestalotia hartigii), which belongs to the group of mitosporic fungi. This pathogen causes specific tissue damage, manifesting primarily as necrotic lesions and dieback in both young seedlings and mature forest trees.

The primary hosts for this pathogen include various species of conifers and some deciduous trees. Significant damage is typically observed in forest nurseries, where the fungus affects young pine, spruce, and larch seedlings, as well as certain decorative shrubs that have been weakened by environmental stressors.

Symptoms of the infection include the formation of small brown spots on the bark or foliage, which eventually enlarge to girdle the shoots. A characteristic diagnostic feature is the emergence of small black fungal fruiting bodies (pycnidia) that rupture the plant epidermis, leading to the desiccation of infected tissues and terminal shoot dieback.

The development of the disease is closely linked to high humidity and poor air circulation in densely planted areas. The fungus spreads most aggressively during prolonged wet weather conditions and via mechanical injuries to the bark, which provide easy entry points for fungal spores into the host plant's internal tissues.

The economic impact of this disease is significant, resulting in reduced quality of planting stock, stunted growth, and high mortality rates in nurseries. Protection measures include strict adherence to agricultural hygiene, the use of disease-free seed stock, early roguing of infected specimens, and the application of copper-based fungicides during high-risk periods.