Growers, Florists want CWR quarantine lifted

A recent story in GrowerTalks magazine describes efforts by both growers of chrysanthemums and florists to convince the USDA’s Animal and Plant Health Inspection Service (APHIS) to lift the quarantine on plants infected by Chrysanthemum White Rust (Puccinia horiana, "CWR"). The concerned groups, which include the Society of American Florists (SAF), the American Nursery and Landscapers Association (ANLA), and florists and growers and Connecticut and Massachusetts, point out that the cost of enforcing the quarantine on mums impacted by CWR is expensive for all parties involved and that the effectiveness of that quarantine is questionable. Since concern remains that a complete removal of the quarantine would lead to rampant spread of the pathogen and a big increase in control costs, a common ground may exist in the designation of CWR as a "Regulated Non-Quarantine Pest," which would require that CWR outbreaks be controlled if found on imports but would not impact the transfer of cuttings or plants between states unless a state enacted its own regulations.

Chrysanthemum White Rust detected in Massachusetts

Chrysanthemum white rust (Puccinia horiana, "CWR"), a serious fungal disease of chrysanthemums, has been discovered in Massachusetts. Infected plants were found at nurseries and at retail locations, with diagnoses confirmed by plant pathologists from USDA APHIS-PPQ. This pathogen can spread quickly in greenhouse and nursery environments, causing severe crop losses.

Over the last 25 years, localized introductions of chrysanthemum white rust have occurred within the United States or Canada and have subsequently been eradicated. Earlier this month, CWR was reported to have overwintered in an outdoor planting of mums at a residential property in Connecticut, and was also found at nurseries in Pennsylvania and Michigan. CWR is a pest of quarantine significance in the United States, requiring state and federal regulatory action. The Massachusetts Department of Agricultural Resources and USDA APHIS-PPQ are currently working together with nurseries to eradicate it from Massachusetts.

Chrysanthemum white rust attacks several species of chrysanthemums, including potted mums, spray mums, and garden mums. The symptoms of this disease are very distinct. Light green to yellow spots up to 5mm in diameter appear on the upper surface of the leaf. The spots become brown and necrotic with age. Raised beige to pink pustules form on the underside of leaves. These 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 are more likely to be observed during or following cool, wet weather.

For more information about chrysanthemum white rust, including lists of susceptible and resistant species and a detailed eradication protocol, see our fact sheet. If you think you have seen Chrysanthemum White Rust, please call the MDAR Plant Pest Hotline at 617-626-1779, or report it on our website.

To sign up for pest and pathogen alerts from the Massachusetts Introduced Pests Outreach Project, visit this page.

Fighting Chrysanthemum White Rust

The American Nursery & Landscape Association (ANLA) and the Society of American Florists (SAF) recently released an excellent Powerpoint presentation for growers and sellers concerned about Chrysanthemum White Rust (Puccinia horiana, "CWR"). CWR is a rust fungus that is able to infect twelve different chrysanthemum species, including pot mums, cut mums and garden mums. It can cause serious economic damage, and is currently considered a pathogen of quarantine significance in both the USA and Canada.

Over the past thirty years, there have been several outbreaks of CWR across North America, including in Massachusetts, but these local outbreaks have always been eradicated. The threat remains, however, and it is extremely important to detect this pathogen early in order to minimize economic losses.

If you grow or sell mums, please take a few moments to view the Powerpoint presentation to learn how to recognize the symptoms of Chrysanthemum White Rust infection. Early detection, and a rapid response if CWR is found, are two important steps in preventing the establishment of this pathogen.

Because this is a pathogen of quarantine significance, anyone who detects the presence of CWR is required to inform the USDA, state or county officials. If you think you see signs of Chrysanthemum White Rust, you can let the Massachusetts Department of Agricultural Resources know through our Pest Reporting form, or call our Pest Hotline (617-626-1779).

(Source: ANLA and SAF press release. Photo of CWR courtesy of the Central Science Laboratory, Harpenden Archive, Bugwood.org)

Update: Gladiolus Rust

The April Pest Alert for Gladiolus Rust (Uromyces transversalis) has been updated to reflect information about the recent discovery of this fungal pathogen on gladiolus plants in Minnesota (check out a map of the US distribution here, courtesy of the National Agricultural Pest Information System). Until this past April, the only US records for this species were in California and Florida. The Minnesota record represents the most northern US location where the rust fungus has been found, by far - more information will be posted when it become available.

Gladiolus rust remains a problem mainly for nurseries that grow gladiolus for sale as cut flowers. But if you grow gladiolus (or related tropical plants in the Iris family [Iridaceae], including Crocosmia, Tritonia and Watsonia species) or know someone who does, it is worth checking out the links at the bottom of the pest alert so you know what to look for in case you ever encounter this destructive pathogen.

Pest Alert: Gladiolus Rust

On March 10, 2008, the Florida Department of Agriculture and Consumer Services identified a suspected infection of gladiolus rust (Uromyces transversalis) on the leaves of gladiolus plants at a cut flower production farm in Hendry County, Florida.

Gladiolus rust primarily attacks hybrid cultivars of gladiolus grown for cut flower production, and if uncontrolled, can lead to total yield losses. This disease could have a significant impact if it becomes established or is transported into greenhouses or nurseries that grow gladiolus or related species. It is a plant disease of quarantine importance in the United States and Europe.

Read more about gladiolus rust in the full pest alert.