Introduced Pests Outreach Project
Pest Alert: Chrysanthemum white rust found in PA nursery

Pest Alert: Chrysanthemum white rust found in PA nursery (October 14, 2004)

Chrysanthemum white rust was confirmed on approximately 800 field grown chrysanthemums at a nursery in Chester County, Pennsylvania on September 17, 2004. As a result of a trace forward survey 22 plants with chrysanthemum white rust were found in Delaware.

Chrysanthemum white rust (Puccinia horiana) is a serious fungal disease of chrysanthemum. White rust can spread quickly in greenhouse and nursery environments causing severe crop losses. Chrysanthemum white rust was first discovered in Japan in 1895 and was confined to China and Japan until the 1960s. Today it is established in Europe, Africa, Australia, Central America, South America, and the Far East. 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. Last year CWR was reported in one location in Norfolk County, Massachusetts. The MA DAR worked with the nursery to eliminate the disease from their facilities and surveyed the surrounding area to insure the rust had not spread. CWR is a quarantine significant pest in the United States; therefore, occurrence of this disease leads to state and federal regulatory action.

Twelve species of chrysanthemum (Dendranthema spp.) are susceptible including pot mums, spray mums, and garden mums. Other hosts include Nippon daisy (Nipponicanthemum nipponicum) and High daisy, and Ajania pacifica. Resistant species include annual chrysanthemum (C. carinatum), crown chrysanthemum (C. coronarium), pyrethrum (Tanacetum coccineum), marguerite daisy (Argyanthemum frutescens), ox-eye daisy (Leucanthemum vulgare), shasta daisy (Leucanthemum X superbum), and corn marigold (C. segetum)

The symptoms of chrysanthemum white rust are very distinct. Light green to yellow spots up to 5mm in diameter appear on the upper surface of the leaf. These spots become brown and necrotic with age. Raised beige to pink pustules form on the underside of leaves beneath the spots. Pustules become white with age. Pustules are most common on young leaves and flower bracts but may form on any green tissue or the petals. Symptoms usually occur during cool, wet weather.

The pest alert is from the Massachusetts Introduced Pests Outreach Project, a collaborative project between the Massachusetts Department of Agricultural Resources and the UMass Extension Agriculture and Landscape Program aimed at preventing the establishment of new pathogens and pests in Massachusetts. Visit the project website ( for more information on Chrysanthemum White Rust and other emerging pests or to subscribe and unsubscribe for pest alerts.

Massachusetts Department of Agricultural Resources
Massachusetts Introduced Pests Outreach Project is a collaboration between the Massachusetts Dept. of Agricultural Resources and the UMass Extension Agriculture and Landscape Program. This website was made possible, in part, by a Cooperative Agreement from the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS). It may not necessarily express APHIS' views.