Chrysanthemum White Rust

CRW infected leaves from Montgomery County, MD - December 2010 Photo: T. Faulkner

Chrysanthemum white rust (CWR) has recently been confirmed on plants in a homeowner landscape in Montgomery County, MD. The disease is caused by the fungus Puccinia horiana, a federally regulated, quarantine-significant plant pathogen. Chrysanthemum white rust originated in Asia, and is now established in Europe, Africa, Australia, Central America, and South America. The disease has been introduced several times to the U.S. through importation of infected plants, but eradication and quarantine efforts have so far successfully kept CWR from becoming established here. The infected plants in this latest case were chrysanthemum cultivars “Snowdon” and “Yellow Snowdon” inadvertently distributed through garden club plant sales in 2010. The Maryland Department of Agriculture and University of Maryland Extension have joined forces to track down these potentially infected chrysanthemums.

CWR symptoms begin as yellow to tan spots on the upper surface of infected leaves. These lesions will turn brown as they age. Corresponding areas on the underside of the leaf are raised, white to pink pustules, which contain the spores of the fungus. The pathogen infects only chrysanthemum.

The Maryland Department of Agriculture requests that plants infected with CWR be removed completely (including any fallen leaves), placed in two sealed plastic bags and discarded in a landfill. Do not compost infected plants, and avoid planting chrysanthemums in the area where infected plants were removed.

If you think you may have chrysanthemum white rust on your plants, or have additional questions, please contact us through the “Send a Question” page.

Prepared by Karen Rane, Ph.D.; Director, UMD Plant Diagnostic Laboratory

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