Those of you who grow impatiens in your shade gardens will shudder when you read this. We all love the look of these beauties and the colorful waves of soft pinks to white to fuchsia that we use to surround our shade trees or fill our landscape beds. Last year I helped a homeowner in our area fill his shade beds with impatiens. To his dismay the plants performed terribly and did not even last half the growing season. He emailed me an article about the dreaded powdery mildew attacking this beloved shade annual. After further research I found this fungus has been ravaging impatien beds for the past few years – unfortunately making its way to northern New York gardens in 2011.

After doing further research and contacting Cornell Cooperative Extension I would like to share what I have learned about this plant disease before people plan their 2013 gardens.

First off, it affects Impatiens walleriana – standard garden impatiens, including double impatiens and mini-impatiens – and the hybrids of I. walleriana.  That pretty much covers all the impatiens we choose in this area for shade beds, with the exception of the New Guinea varieties. The disease is rampant up and down the east coast: plants that seem healthy one week can be infected and gone the next week. Early disease symptoms appear similar to a nutritional deficiency or spider mite infestation. A slight stippling of the leaves; leaves may curl downward suggesting plant needs watering; sometimes you can see white colored spores on the underside of the foliage; and as the disease progresses the plants will appear stunted and drop the majority of their leaves and flowers – leaving you with unsightly stalks. The disease spreads quickly to other impatien plants/beds as it is spread by either water splash or spores that can be carried great distances by wind.  Its spread is weather dependent – thriving in humid cool conditions or periods when the leaves are wet for 4 hours or more.

Testing is still being done to determine if the fungus can overwinter in the soil of beds that were previously infected. Pesticides offer short-term protection, but would need to be reapplied during the growing season, maybe as often as once a week. Though many of us buy from local farmers markets, plants that were treated by the growers will not retain this protection for long. And who knows what you bring home on flats that are purchased from the big box stores.

The research I have done all suggest the same thing. Don’t plant the garden variety impatiens this year, or at the very least, inter-plant them with alternative bedding plants that are not susceptible to the disease:New Guinea impatiens, begonias, caladiums, coleus, lobelia, nicotania and torenia. All are shade lovers and will add color to your shade gardens. The New Guinea impatiens are very showy and will tolerate sun as well, but I have found the flats to be a little pricier than the bedding impatiens we have used in the past.