Chrysanthemum white rust infects 12 species of chrysanthemum, including garden mums, pot mums, and Nippon daisies. Infected plants may not show any symptoms during hot or dry conditions but when the weather turns cool and wet, symptoms develop. Symptoms of CWR on infected plants are quite distinctive and include raised pink or white, waxy pustules on the underside of the leaf. Chlorotic spots develop on the upper leaf surface that may become sunken and necrotic. Severely infected leaves dry up and persist on the stems. Severe outbreaks of CWR may result in total crop loss.
Chrysanthemum white rust (CWR) is a quarantine significant pest in the United States ; therefore, occurrence of this disease leads to state and federal regulatory action. In the last 25 years localized introductions of chrysanthemum white rust have occurred within the United States or Canada and have subsequently been eradicated or are being eradicated. The federal management plan for CWR includes destroying symptomatic plants, fungicide treatments on remaining asymptomatic plants, surveys of the surrounding area, and trace backs of infected stock. The full management plan can be viewed on the web on the USDA, APHIS website.