Ask the Expert - Impatiens Downy Mildew
Daedre McGrath, our Trial Garden Manager, answers questions about Impatiens Downy Mildew.
Is impatiens downy mildew still an issue? Can I plant impatiens in my garden again?
-Bill T. From Muskegon
Yes, unfortunately Impatiens downy mildew can still be a problem for some gardeners. Impatiens downy mildew (IDM) is the fungal pathogen Plasmopara obducens that specifically impacts Impatiens walleriana. After the initial outbreak starting in 2011, many gardeners were instructed to stop planting Impatiens walleriana until a solution was found. Once your garden is infected, the pathogen can overwinter in the soil and re-infect next year’s plants. If you continue to plant Impatiens walleriana after your soil is infected, you are providing a host for the pathogen, increasing the potential for re-infection, causing the production of more spores and re-inoculating the soil for years to come.
Although they are generally much more expensive, you can still get that “Impatiens look” by planting New Guinea Impatiens or any of the impatiens hybrids that are currently on the market, as they are not susceptible to the pathogen. However, good news is on the horizon! A couple plant breeding companies are working on introducing varieties of Impatiens walleriana that are highly resistant to IDM! We evaluated a handful of these new resistant varieties in our 2019 MSU Trial Garden and found them to hold up all summer without developing the disease (which we know is present in our soil). The Imara XDR series from Syngenta and Beacon series from PanAmerican Seed will both be available in 2020.
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