Introduced Pests Outreach Project

Chrysanthemum White Rust

Pathogen Alert: CWR detected in Massachusetts (September 26, 2008)

(Click on an image below to see the captioned full-size version)
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Scientific Name: Puccinia horiana
Common Names: Chrysanthemum white rust

Known Hosts:
12 species of chrysanthemum are suspectible including pot mums, spray mums, and garden mums (Dendranthema X grandiflorum = Chrysanthemum morifolium).
Other hosts include Nippon daisy (Nipponicanthemum nipponicum = C. nipponicum), High daisy, and C. pacificum = Ajania pacifica

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. (Figure 1)
Raised beige to pink pustules form on the underside of leaves beneath the spots. Pustules become whiter with age.
(Figures 2 and 3)
Pustules most common on young leaves and flower bracts but may form on any green tissue or the petals. (Figure 4)
Severely infected leaves wilt and will eventually dry up completely.
Similar Disease or Symptoms
Brown rust of chrysanthemum Chocolate brown pustules are found on both sides of the leaves. See this page for images

Fact sheets and references:
Printable Chrysanthemum white rust pathogen alert (pdf)

Fact Sheet on CWR from UMass Extension

Cooperative Agricultural Pest Survey Chrysanthemum White Rust page

USDA/APHIS Chrysanthemum White Rust Web page

Chrysanthemum White Rust: Systematic Botany and Mycology Lab of USDA Agricultural Research Service

last reviewed February 18, 2021

Massachusetts Department of Agricultural Resources
The Massachusetts Introduced Pests Outreach Project is maintained by staff at the Massachusetts Dept. of Agricultural Resources. 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 (USDA APHIS). It may not necessarily express APHIS' views.