White rust on crucifers

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Last week we received some turnip leaves into the lab with white patches on the undersides. After examining the leaves more closely under the dissecting and compound microscopes, we saw that the white patches were actually “rust” pustules containing sporangia. The pathogen, Albugo candida, which causes this disease, white rust, is actually not a true rust as it is not a member of the kingdom Fungi. However, the organism does imitate the true rusts in the manifestation of its reproductive structures as well as in the fact that it is an obligate parasite, requiring a living host for survival. Species of Albugo are found worldwide causing disease on crucifers, spinach, sweet potato, and several others. The disease is more commonly seen in spring and fall when conditions are cool and wet. Important strategies for managing this disease include scouting for and removing diseased plants, keeping weed populations under control, and applying fungicides. Keep an eye out for white rust!

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