Chrysanthemum White Rust
Thursday, 29 July 2010 15:31
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 (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 few years chrysanthemum white rust is occurring with more frequency in New England.
The federal management plan for CWR includes the following measures 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.
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.
Infected plants may show no symptoms until environmental conditions encourage symptom development. If the warm, dry weather pattern this season in southern New England continues, symptoms may be delayed. Preventative fungicide applications, being used by some growers, will suppress disease development.
For a list of treatment options see the floricast by Margery Daughtrey, Cornell University . Syngenta has a bulletin on chrysanthemum white rust that can also be downloaded.
Note: Growers finding CWR are required to report the finding to their State regulator agency. There are on-going discussions concerning Chrysanthemum White Rust regulations. As a result, APHIS has established a Stakeholder Registry for those interested in receiving updated information related to these discussions. When registering, check Chrysanthemum White Rust in Topics of Interest.
Paul Lopes, UMass Extension
With input from Margery Daughtrey, Cornell University
