White leaf spot of crucifers

White leaf spot of crucifers, caused by the fungus Neopseudocercosporella capsellae, is a significant fungal disease affecting various species within the Brassicaceae family. It is particularly recognized as a major threat to oilseed rape (canola) production globally, often leading to reduced yields and lower oil content in harvested seeds.

The host range is extensive, encompassing crops like oilseed rape, mustard, radish, and several cruciferous weeds. The pathogen attacks all aerial parts of the plant, including leaves, stems, and pods. Infections starting at the seedling stage are particularly dangerous as they can stunt plant growth early in the season.

Symptoms are characterized by circular to irregular spots that initially appear water-soaked. As the disease progresses, these spots turn white or light gray, sometimes surrounded by a distinct dark margin. Under high humidity, grayish fungal growth can be observed on the underside of the lesions. Severe infection leads to premature leaf drop and potential damage to stem tissues.

The development of this disease is highly dependent on environmental conditions, favoring cool and wet weather. The pathogen survives between growing seasons in crop residues or on self-sown host plants. Spores are dispersed primarily by wind and rain splash, which means that seasons with frequent rainfall are usually associated with higher infection rates.

Effective management requires a multi-faceted approach. Preventive measures include burying infected crop debris, maintaining a break of at least 3 years between cruciferous crops, and controlling weeds that act as alternate hosts. When disease pressure is high, the application of registered fungicides, such as those containing triazoles, is essential for maintaining crop health and productivity.