A puzzling plant disease may dethrone one of the most popular and reliable flowerbed plants in North America, the garden impatiens.
A relatively benign condition known as impatiens downy mildew has recently turned ugly, for reasons under debate. For decades, U.S. gardeners rarely noticed downy mildew on their impatiens. But in the last two years, the disease has ravaged flower beds in some of the more humid parts of the country. After rain or fog followed by balmy nights, the disease can turn a lush flower border into a straggle of bare stalks that eventually collapse and die.
In recent years, aggressive impatiens downy mildew has flared up during disease-friendly weather in parts of Europe, South Africa and Australia. But the United States hadn’t seen more than a few scattered reports until widespread outbreaks began in 2011. By the end of 2012, pathologists had confirmed the disease in 33 states and Washington, D.C.
Since weather affects outbreaks, it’s hard to predict what 2013 will bring. But impatiens downy mildew was already active in Florida when the year began, says plant pathologist Colleen Warfield of Ball Horticultural Company, a Chicago-based company that breeds and distributes plants, including impatiens.
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