The photomicrograph below illustrates a stained thin section of cabbage stem infected with white rust, a destructive disease of crucifers, which is caused by the fungus Albugo candida. Also known as staghead, white rust is a disease that infects cruciferous plants -- such as cabbage, broccoli, and kale -- wherever they occur in the world.

A. candida belongs to the phylum Oomycetes (the phylum that also includes the downy mildews and water molds). These molds produce both fertilized and asexual spores. The asexual spores (zoospores) have two whip-like flagella that enable them to move about. Infections from these spores appear as pustules or blisters. The fertilized spores (oospores) grow inside the plant tissues and cause abnormal growths, called stagheads.

As a plant disease, white rust is not generally a serious problem by itself. However, infections of downy mildew often occur in association with white rust when conditions are damp and cool, which can cause serious crop damage.