Chrysanthemum White Rust
Karen Snover-Clift, Cornell University, Bugwood.org
Chrysanthemum white rust (CWR) is a serious fungal disease caused by Puccinia horiana P. Henn. It damages chrysanthemum plants and related species. CWR can spread rapidly in greenhouses and plant nurseries.
Importation of certain chrysanthemum species are prohibited from several countries, territories, and possessions due to possible transportation of the fungus. CWR originated in eastern Asia and is now established in the Far East, Europe, Africa, Australia, Central America, and South America. Disease outbreaks in Canada and the U.S. have been quelled each time, as CWR has a limited host range and spreads inefficiently.
During hot and dry conditions, infected plants may not be symptomatic. Signs of disease usually appear during cooler, wet weather. Here's what to look for:
- Spots
- Small white or yellow spots, up to 4 mm wide, may be found on the upper surface of the leaf. These slightly dimpled spots become brown over time.
- Pustules
- These are light brownish yellow to pink-colored but become white as they age. Pustules form on the underside of the leaf, beneath the small spots. They're most common on young leaves and flower bracts but can be found on any green tissue and flowers.
Best management practices include:
- Buying plants from reputable sources
- Using proper cultural techniques
- Scouting for disease symptoms
- Sanitation
- Applying fungicide (This will not eliminate the disease, but it can keep it from spreading. Make sure the fungicide is labeled for use against CWR in your State; follow all label directions.)
- Worker training and education
Options for managing CWR include:
- Removing infected plants (including roots)
- Placing diseased plant material in plastic bags to keep spores from spreading
- Disposing infected plants or plant material in municipal waste; do not compost
- Applying fungicide (This will not eliminate the disease, but it can keep it from spreading. Make sure the fungicide is labeled for use against CWR in your State; follow all label directions.)
- Maintaining strict sanitation in greenhouses and nurseries to prevent CWR introduction and spread
Report Plant Pests and Diseases
Have you seen this pest or signs of pest damage? Immediately report your findings.
Find your State plant regulatory official
Find your State plant health director
Controlling Chrysanthemum White Rust
- Title 7, Code of Federal Regulations, Part 319.37 and 319.74
- Federal Regulation: 7 CFR 319 Quarantine Notice