Powdery mildew of brassicas

The causal agent of this disease is the fungus Erysiphe cruciferarum, which belongs to the Erysiphales order. This obligate parasite lives on the surface of plant tissues, forming a white mycelial network that feeds on the host plant by inserting haustoria into the epidermal cells.

The pathogen primarily affects members of the Brassicaceae family. Major agricultural crops susceptible to this disease include oilseed rape (canola), cabbage, mustard, radish, and turnip. Wild cruciferous weeds frequently act as alternative hosts, maintaining the pathogen's presence in the field environment throughout the season.

Symptoms are easily identified by the appearance of white, powdery spots on the upper and lower leaf surfaces, petioles, and stems. As the infection progresses, these spots expand, eventually covering the entire surface with a white fungal bloom. Severe cases lead to leaf yellowing, chlorosis, deformation, and premature leaf drop.

Development and spread of the disease are favored by dry weather accompanied by warm temperatures and high humidity (such as heavy dew at night). Conidia, the asexual spores, are easily dispersed by wind and splashing water. Dense canopies that restrict airflow create a microclimate ideal for rapid epidemic outbreaks.

The economic impact of powdery mildew is significant, particularly in oilseed rape and leafy greens. The infection reduces photosynthetic efficiency, which stunts growth and leads to lower seed yields, poorer seed quality, and reduced oil content. In vegetable production, it significantly decreases the marketability of the produce.

• Crop rotation to break the pathogen's infection cycle.
• Sanitation, including the removal of infected crop residues.
• Control of cruciferous weeds in and around fields.
• Timely application of systemic fungicides (e.g., triazoles or strobilurins).
• Selecting resistant varieties to minimize disease pressure.