UMass Extension Landscape Message August 10, 2012
"Impatiens Downy Mildew Update
Many growers are receiving requests for information from their home gardening and landscape customers about Impatiens downy mildew.
To help you answer questions from this audience a new fact sheet has been compiled, "Impatiens Downy Mildew in Home Gardens" Adobe PDF icon. This is a three page fact sheet (third page is colored photos) that can be printed and distributed to customers.
Just a reminder that once plants are showing symptoms advise customers to discard the plants, roots and all!
Remove and dispose of all infected Impatiens walleriana plants (standard impatiens, double impatiens) as well as all nearby impatiens plants. When discarding the plants, bag and remove the entire plant including the soil and any plant or soil debris; do not compost.
The white powdery spores on the leaf undersides do not overwinter, but are carried in wind and spread the disease. Also oospores (over-wintering spores) form inside infected stems and leaf petioles. Oospores survive in plant debris and are released into the soil as the stems decay. These resting spores are thick-walled, able to survive adverse conditions and can potentially survive in the soil for a period of years.
Advise landscape and home garden customers to remove infected plantings of impatiens. Some landscapers and gardeners are replacing impatiens with begonias as one option this season.
Tina Smith, UMass Extension, Greenhouse Crops and Floriculture Program"
I couldn't link to the PDF file, so you have to go to the Landscape Message for that.