Impatiens downy mildew was first found on plantings on the Eastside during the summer of 2013. The disease can travel through the air or water. It is also spread by people, animals and infected garden tools.
Symptoms: Leaf yellowing is followed by defoliation of the plant. This results in bare stems with only a few tiny yellow leaves remaining.
Varieties: Impatiens walleriana are susceptible to the disease. This includes common impatiens (“Busy Lizzies”), Fusion impatiens, Patchwork impatiens and Double impatiens.
New Guinea impatiens are highly resistant to the disease. This includes Divine impatiens and Sunpatiens. Other types of plants are NOT affected by this strain of downy mildew.
Sanitation: Planting “clean” impatiens and providing good air movement can help reduce the threat of contracting the disease in your garden.
Once the disease is found in a garden bed, the spores can overwinter and infect new impatiens plants in future years.
We grow all of our impatiens here in our greenhouses. Our cultural practices allow us to provide “clean” impatiens for your enjoyment. It is impossible to forecast whether impatiens will ever contract the disease in your garden.
Chemical Control: Pesticides can be applied to prevent the disease. Once the disease has matured on the plant, it may be too late to spray. Bonide’s “Fruit Tree and Plant Guard” can be used to prevent downy mildew on impatiens.
Alternative Plants: Our greenhouses are bursting with many other shade loving summer annuals. They include New Guinea impatiens, coleus, begonias, torenia, fuchsias, and browallia. If you grow impatiens in sunny areas we have a multitude of alternatives for your consideration.
More information and photos can be viewed on these informative web pages:
from WSU, written for the horticulture industry:
http://pnwhandbooks.org/plantdisease/impatiens-impatiens-walleriana-downy-mildew
from the University of Connecticut, written for home gardeners:
http://www.ladybug.uconn.edu/factsheets/documents/impatiens.html
As always our friendly, knowledgeable staff would be pleased to help and inspire you as you select beautiful, colorful summer annuals for your garden and containers.