White rust of crucifers

The causative agent of the disease known as white rust is the oomycete Albugo macrospora. Although it is commonly referred to as a fungus, this pathogen is technically a water mold that infects plant tissues, disrupting nutrient transport and causing significant structural damage to the host plant.

This pathogen primarily targets plants within the Brassicaceae family. Key crops susceptible to infection include various cabbage varieties, canola, mustard, radishes, and turnip. Additionally, many cruciferous weeds serve as alternate hosts, ensuring the survival of the pathogen in the field between growing seasons.

Symptoms are identified by the appearance of yellowish spots on the upper side of the leaf surface. On the underside, creamy white, raised pustules develop, which are packed with sporangia. Severe infections lead to systemic issues, such as the thickening and distortion of stems, flower stalks, and stunted growth of the plant.

Development and spread are triggered by cool, humid environmental conditions. The pathogen produces zoospores that move through water films on leaves, making overhead irrigation or rainy weather highly conducive to outbreaks. The disease is easily transmitted by splashing water and wind-blown dust particles.

The economic impact of white rust includes yield reduction and decreased crop quality due to tissue malformation. Management practices include long crop rotation cycles, deep plowing to bury infected debris, and the application of appropriate fungicides. Maintaining good field hygiene and utilizing resistant varieties are crucial for effective disease control.