Eucalyptus leaf blotch

Pathogen and disease type. The disease is caused by the ascomycete fungus Teratosphaeria delegatensis. It is a specialized phytopathogen affecting various species of the Eucalyptus genus. Classified as a foliar fungal disease, it attacks the leaf tissue, disrupting physiological processes such as photosynthesis and weakening the overall health of the host tree.

Host plants and distribution. The primary hosts are eucalyptus species, with younger trees and seedlings in nurseries being particularly susceptible. The fungus is found primarily in temperate and subtropical regions where eucalyptus plantations are subject to high moisture levels. Its distribution is closely linked to environments where climate conditions facilitate the survival and reproduction of the pathogen.

Symptoms and signs. Early symptoms manifest as small chlorotic spots on the leaf blades, which eventually transition into necrotic lesions. In severe cases, significant premature defoliation occurs, leading to a reduction in canopy density. Under conditions of high humidity, the fruiting bodies of the fungus may become visible as small dark structures on the affected leaf surface.

Conditions for development. Development of Teratosphaeria delegatensis is favored by prolonged rainy periods, high atmospheric humidity, and moderate temperatures. These environmental factors create an optimal environment for spore germination. The fungus spreads mainly through the dispersal of spores by wind and rain splash, enabling rapid transmission across plantation stands.

Damage and control measures. The disease causes significant damage by reducing timber growth and affecting tree vigor. Management strategies include the use of resistant eucalyptus varieties, maintaining appropriate tree spacing to promote air circulation within the canopy, and sanitation practices such as removing infected debris. In nurseries, prophylactic fungicide applications are used to control the spread of the disease among young plants.