Powdery mildew (Leveillula taurica)

Leveillula taurica is a specialized fungal pathogen responsible for causing a unique form of powdery mildew. Unlike ectoparasitic powdery mildews, this fungus is an endoparasite, meaning its mycelium colonizes the internal tissues of the host plant, emerging through the stomata to produce spores, which makes its detection often delayed.

The host range of this pathogen is exceptionally broad, spanning over 700 species of dicotyledonous plants. It is particularly devastating to crops such as tomatoes, peppers, eggplants, onions, and various cucurbits, often causing significant economic losses in both open-field production and greenhouses.

The primary symptom is the appearance of chlorotic spots on the upper leaf surface, which eventually turn necrotic and brown. A characteristic white, powdery appearance (conidial spores) is typically observed on the underside of the leaves, though in cases of heavy infestation, it can cover both sides of the leaf, leading to premature leaf senescence and defoliation.

The development of this disease is favored by warm and arid climates, which distinguishes it from many other powdery mildew species that require high humidity. Optimum temperatures for spore germination range between 20°C and 25°C. Wind-blown conidia facilitate rapid dispersal across fields, especially during periods of fluctuating temperatures and occasional dew formation.

Effective management requires an integrated approach that includes strictly following crop rotation and removing infected plant debris. Chemical control strategies focus on the application of fungicides such as triazoles, strobilurins, or sulfur-based compounds. Early detection is critical, and monitoring the lower leaf surface is essential for timely intervention to prevent the epidemic spread of the pathogen.