Impatiens disease: The flower disaster that didn't happen...at least for one year
As summer peaked in 2012, gardeners across much of the United States saw their normally reliable plantings of impatiens mysteriously wilt and die en masse. The culprit turned out to be a deadly and fast-spreading disease called downy mildew that suddenly flared, decimating America's No. 1 annual shade flower in 33 states. Growers and plant pathologists feared the worst. Since the disease organism travels readily on wind and rain and can persist in the soil, warnings went out that impatiens likely would be a poor risk for at least the near future. Growers cut back production, and some garden centers stopped selling them altogether.
Many plant breeders are already at work on developing additional lines of mildew-resistant impatiens. Another option is switching to other species of shade-tolerant annuals. These include begonia, coleus, wishbone flower (Torenia), browallia, caladium and ivy geranium. Downy mildew doesn't affect any of those. An alternative approach is to use a mix of choices -in other words, never putting all of your eggs in any one basket. In gardening, that's a "monoculture," and the risk is that if a bug or disease comes along that likes your singular choice, you lose the whole shebang.
Greenview with GreenSmart Impatiens Food is a slow-release product targeted specifically for impatiens. Some gardeners reported in 2013 that their bedding impatiens did better in pots and window boxes than in the ground. That could be because drainage is generally better in those settings, and containers can be grown with new, disease-free, soilless potting mix each season.
The pathogen that causes downy mildew is a water mold that's been known since the 1800s. It didn't begin devastating garden impatiens until about a dozen years ago when Europe was widely affected. The disease is still entrenched there. Downy mildew infected impatiens on a small scale in the United States starting in 2004 before suddenly flaring in 2012. The disease also infects native jewelweed, which is in the impatiens family. The usual first sign is stunted growth along with leaves that start to yellow, wilt and curl. A telltale sign is a whitish-gray coating on the leaf undersides. As the disease progresses – often within a matter of weeks – the plants go completely limp and die.