Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Downy Mildew on Impatiens Causes Gardeners to Lose Patience

Newspaper article Pittsburgh Post-Gazette (Pittsburgh, PA)

Downy Mildew on Impatiens Causes Gardeners to Lose Patience

Article excerpt

Q. I have been gardening for more than 20 years. My yard is quite shady, and I plant impatiens every year to provide color once the daylilies and astibles are finished blooming. I have never encountered a problem until this year. Every one of my impatiens has died. They started to bloom less, then the lower leaves would drop until there was nothing left but stems, then they would die, too. This has occurred regardless of where they are planted (beds, pots or raised planters), so I know it is not caused by the soil. My neighbor is having the same problem, as is our county courthouse whose impatiens are also dying. What is going on?

A. If it is any comfort, you are not alone in your disappointment with impatiens this year. Penn State Extension of Allegheny County has received numerous calls and emails from landscape professionals and home gardeners alike, wondering what is happening to the impatiens they rely on for season-long color in shady landscapes.

Downy mildew is a relatively new disease on impatiens, although it has long been a problem on cucurbit crops, roses and grapes. The strain of downy mildew that affects impatiens is not the same one that affects those crops, so they are not infecting each other. Despite the similarity in names, downy mildew has different symptoms than powdery mildew that many gardeners are familiar with on ornamentals such as lilacs, peonies and phlox.

The disease has been identified on impatiens in the United States since 2004, but the mild winter and extra-early spring had large greenhouse growers in the southern United States scrambling to control the disease on their crops much earlier than normal. Although commercial growers scout and treat crops preventatively, those fungicides only provide protection for so long. By the time impatiens are moved through retail outlets and planted in landscapes, little protection is left.

Downy mildew affects all types of standard impatiens (Impatiens walleriana), including doubles, minis and interspecific hybrids such as Fusion. It is not a problem on New Guinea impatiens (I. hawkeri). Traditionally, downy mildew does not overwinter well in colder climates. …

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