White rust

White rust, caused by members of the Albuginaceae family, is a significant plant disease that affects a wide range of economically important crops. Although often colloquially grouped with rust fungi, these organisms are actually oomycetes, placing them in the same group as downy mildew and water molds.

The disease primarily targets members of the Brassicaceae family. Major crops such as broccoli, cauliflower, cabbage, canola, and mustard are highly susceptible. Besides cultivated crops, various wild weeds also serve as reservoirs for the pathogen, complicating management efforts in agricultural landscapes.

Symptoms initially manifest as small, chlorotic spots on the upper leaf surface. Soon after, white, chalky pustules appear on the underside of leaves, stems, and flower parts, breaking through the epidermis to release spores. Infected flower heads often become distorted and enlarged, a phenomenon that can drastically reduce seed yield.

The pathogen thrives in environments with high relative humidity and moderate temperatures. The zoospores are motile in water, meaning that rain splash or overhead irrigation is critical for moving spores between plants. Overwintering occurs through thick-walled oospores that can remain viable in crop debris or soil for several years.

Effective management requires a multi-faceted approach. Cultural practices such as crop rotation, removing infected plant debris, and controlling susceptible weed hosts are essential. When conditions favor severe outbreaks, the application of fungicides, particularly those targeting oomycetes, is necessary to protect yield and quality. Selecting resistant cultivars remains the most sustainable long-term strategy.