How to Manage Pests
UC Pest Management Guidelines
The fungus infects leaves and floral parts, causing distinctive white, raised pustules to form underneath the plant epidermis. These blisterlike pustules sometimes result in twisted, deformed growth of the stem, leaves, or flowers. When mature, the epidermis covering the pustule will rupture, releasing powdery white sporangia (a type of spore) that can be carried by winds or splashing water onto neighboring host plants. Severely infected leaves can wither and die.
The white rust pathogen of crucifers infects only plants in this host group, including arugula, bok choy, broccoli raab (rappini), Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, Japanese or Mizuna-type mustards, radish, tah tsai, and turnip. However, economic damage is only found on the crucifer crops in which the leaves are marketed. If free moisture and cool temperatures are present, the sporangia germinate by producing several smaller motile spores (zoospores) that swim and enter susceptible young tissues. Because A. candida is dependent on cool, wet conditions, the disease is consistently more severe during winter and early spring months. In addition to sporangia, A. candida also produces a second type of spore, the oospore, that can resist drying conditions and enable the fungus to survive in a dormant state in soil or crop residue. The white rust pathogen exists in the form of distinct races.
White rust resistant cultivars do not appear to be available for the host plants grown in California. Reducing leaf moisture by avoiding sprinkler irrigation will not prevent white rust, but keeping leaves dry may reduce disease severity. For sensitive crops such as arugula and rappini, avoid planting in fields having a history of white rust problems; soilborne oospores may result in severe disease. Fungicides may be appropriate in some situations on leafy crucifer crops. The same fungicides that control downy mildews are also effective against white rust.
UC IPM Pest Management Guidelines: Cole Crops