Powdery mildew

Powdery mildew is a widespread fungal disease caused by members of the subclass Erysiphomycetidae (order Erysiphales). These obligate parasites colonize the surface of plant tissues, forming a characteristic white, powdery mycelial layer. They extract nutrients directly from the host cells using specialized structures called haustoria.

This pathogen affects a vast range of plants, including cereals, vegetables, fruits, and ornamental species. Common hosts include grapes, cucumbers, apples, roses, and wheat. Because many species within the Erysiphales order are host-specific, the symptoms may vary slightly depending on the infected crop, but the general appearance remains consistent across species.

Symptoms typically start as small white or gray spots on leaves, stems, or buds, which rapidly expand to cover the entire plant surface. As the infection progresses, the leaves may curl, turn yellow, and wither. Later in the season, tiny black, pepper-like fruiting bodies called cleistothecia often appear within the white fungal mat.

The development of the disease is heavily influenced by environmental conditions, particularly high humidity, moderate temperatures, and lack of air circulation. Powdery mildew spores (conidia) are easily dispersed by wind, making it highly contagious within greenhouses or dense field plantings. Unlike many other fungi, it does not always require free water on the leaves to infect.

Economic damage caused by powdery mildew includes significant yield loss, stunted growth, and diminished aesthetic value of crops. Management strategies involve a combination of practices: planting resistant varieties, proper pruning to increase airflow, and removing infected debris. When chemical intervention is necessary, fungicides including sulfur-based products, triazoles, and strobilurins are commonly used.