Invasives & News dgregg on 26 Sep 2008 11:12 am
Chrysanthemum white rust (Puccinia horiana; “CWR”)
Here’s some hot news from our neighbor to the north (and east). The Massachusetts Introduced Pest Outreach Project reports that “Chrysanthemum white rust (Puccinia horiana, “CWR”), a serious fungal disease of chrysanthemums, has been discovered in Massachusetts. Infected plants were discovered 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 MA 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 at http://massnrc.org/pests/
The Mass. Introduced Pest Outreach Project is a nifty little program and you can learn more about it or sign up to receive you own email copy of their announcements by visiting their web site: http://www.massnrc.org/pests/
