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K-State Turf and Landscape Blog

Impatiens downy mildew – it’s still “out there.” K-State’s Prairie Star program can help you diversify your shade beds

It is April, and everybody has spring fever. As you plan your ornamental beds for the year, consider using a diverse array of species. Specifically, I’m talking about avoiding a monoculture of impatiens.

You might remember a few years ago when a disease called impatiens downy mildew (IDM) hit the scene. Here in Kansas we did not see the vast losses that occurred in states farther east, but a few sites got hit. IDM has not received as much attention recently, but it is still out there. I’m not saying don’t use impatiens at all, I’m saying you should consider some diversity in the landscape. Don’t put all your eggs in one basket.

Filling every shady nook and cranny with impatiens now may seem easy, but that easy may turn into “disease-y”, and you might look back and wish you had included more diversity.

The standard, typical impatiens, Impatiens walleriana, is highly susceptible to downy mildew. If the weather is conducive to disease (moderate temps, wet, humid), a bed of I. walleriana can get wiped out quickly. The plants lose all their leaves, with only a stand of stems left behind. The pathogen can survive year-to-year as a survival structure called an oospore. So, if you know you had IDM history last year you should definitely avoid impatiens in the same bed this year.

The two photos below show dense, white sporulation on the undersides of leaves. The leaves drop, and entire plants can lose their leaves quickly.


Other related species, such as I. balsamina and certain hybrids, exhibit good tolerance, and those are options. Breeders are working to develop more resistance. Stay tuned!

What else can we use in shade, besides impatiens? K-State’s Prairie Star and Prairie Bloom program highlights species and varieties that thrive here. You can scan through to see which species flourish in shade, and click on photos to check out the blooms and other traits. Begonias are one option, but there are other shade-tolerant plants to explore. At the Prairie Star website you can opt to print a pdf version of the list to carry with you to the garden center for easy shopping. Here is a link to some of the new additions for 2017.

If you want to read some more details about impatiens downy mildew you can check out this article by Margery Daughtrey in the online version of Grower Talks.