Impatiens is a shade-loving tender perennial (often grown as an annual) that blooms in a wide range of beautiful colors such as reds, purples, pinks, whites and oranges. While they are popular selections with long-lived, eye-catching blooms, they are becoming more and more susceptible to a widespread, rapidly killing disease known as downy mildew.
Downy mildew, Plasmopara obducens, is specific to Impatiens walleriana and is a type of “water-mold” or oomycete that thrives in damp, cool conditions. Even though downy mildew has been around for years, lately it has swiftly spread to decimate impatiens in a wide range of regions, from Florida to the Northeast and into Europe, growing in intensity since 2011.
The spores of downy mildew are very easy to spread, often disbursed when splashed with water or carried away in the wind—hence why the disease is so quick to take over. There are two types of spores: “short-lived”—which spread by the ways listed above and is found on the underside of leaves, and “resting spores”—which often take over the stems and can spread within the soil, establishing itself from growing season after growing season and infecting new plants.
At first the symptoms of downy mildew may be subtle. So if you have impatiens, it is important to check them often.
• The leaves will start stippling—curling at the ends, with color beginning to yellow.
• A down-like, white “mildew” is often present on the underside of the leaves.
• Eventually the damaged leaves will start to drop, leaving the stems bare.
• Lastly, the impatiens will slump over and die.
What to do:
Sadly, there isn’t much you can do if you have or want to grow impatiens. Some have tried fungicides with minor success, but because this disease flourishes in cool, moist climates and spreads simply by a splash of water touching its spores, it is no wonder that even fungicides will often fail. You can constantly check on your impatiens, removing possibly infected plants and growing them in a sanitized greenhouse or location; however, it is much easier to just discard of impatiens all together and settle for other charming alternatives instead. Try different varieties of shade-loving, flowering plants such as New Guinea impatiens (which aren't affected) and begonias. You can also try shade lovers that are grown for their colorful leaves, like caladium. For a list of more shade annuals click here.
Although impatiens are striking plants that often enhance borders and surround tree trunks with bursts of impressive color, with the prevalent downy mildew destroying any impatiens in its path, it is safer to settle for equally exquisite alternatives.
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