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Beware of downy mildew, from the Whistling Gardener

For years I have planted flats of impatiens in our garden. Last year however our impatiens seemed to drop dead overnight early in the fall and the cause was a disease called downy mildew.
The Whistling Gardener gives options for controlling Downy Mildew on Impatiens. Photo credit: Sunnyside Nursery.

This weekly column is being reproduced with the permission of Steve Smith, The Whistling Gardener, and owner of Sunnyside Nursery in Marysville.

For years the missus and I have planted a dozen or so flats of impatiens in our garden in cool shady areas (but also in full sun) and enjoyed months of nonstop blooms clear up to the first frost.

Last year however our impatiens seemed to drop dead overnight early in the fall several weeks before they should have and the cause was a disease called downy mildew. IDM (impatiens downy mildew) started out on the east coast and has become epidemic to the point the nurseries no longer sell them.

The disease causes the plants to turn a silver color, defoliate and melt away to nothing in a matter of a week or less and once you get it you can’t stop it. Considering that impatiens have been such a staple for northwest gardeners it is only fair to ask: “What are my options and are there ways to control the disease?” Here is what I know.

Diseases like downy mildew cannot be cured but they can be prevented if the gardener acts proactively. One must apply a fungicide before any signs of the disease appear which means spraying the plants at the time of planting and repeating applications on a regular interval throughout the growing season. Depending on the type of fungicide that interval could be one week or one month.

Monterey Agri-Fos is labeled for the homeowner to use for IDM and there are several other products that have downy mildew on the label too. Culturally speaking it is helpful to keep moisture to a minimum and it is always best to water in the morning so plants will dry out by evening.

Also, if you have had IDM then don’t plant impatiens in the same bed again. Finally, there are plant options for shady areas that don’t get IDM such as coleus, begonias, upright fuchsias and New Guinea impatiens (also know as Sunpatiens).

So while it is annoying that impatiens are no longer the easy-peasy no-brainer annual to plant in our shade gardens it is also exciting to explore the options for other colorful and interesting annuals that we can plant for summer-long color.

Look for them in the shade area of the nursery. And if you still want to take a chance on good old impatiens then be prepared to apply a fungicide several times during the season. Personally I wouldn’t hesitate to plant a few bunches here and there but I would avoid planting them en masse.

Looking to learn more about growing berries?

Come to our class on May 17, 2014, at 10 am here at the nursery where we will discuss all the ins and outs of successfully growing blue berries, raspberries, strawberries, black berries (yes, people actually grow blackberries) and a few other small fruits like grapes and kiwis.

Until next time go plant like a fool and remember, the best time to plant a tree is 25 years ago, the second best time is today.

Steve Smith is owner of Sunnyside Nursery in Marysville and can be reached online at info@sunnysidenursery.net.

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