I have planted impatiens for many many years with little problems. This year, after growing and looking beautiful they suddenly go rubbery and wild and die. Looks a lot like when they get frost in the fall. Any ideas what is causing this?? I water and fertilize regularly and all the other varieties of annuals are all doing wonderfully.
Unfortunately, your plants have succumbed to a disease called impatiens downy mildew, which is caused by a fungus-like microorganism called Plasmopara obducens. This is happening through no fault of your own. The disease was discovered in nursery-grown plants last fall and although the greenhouse industry has tried their best to nip it in the bud, it seems that some plants carrying the disease are still being unknowingly sold. There’s really nothing you can do to save your plants, so dig them up and put them out with your garden waste for city pick-up, if available in your neighbourhood. Do not compost them or the disease will spread to next year’s plants.
Because the disease only affects a certain type of impatiens called Impatiens walleriana (this is the most commonly sold type of impatiens), to be safe, you may want to grow any of the sunshine or New Guinea impatiens next year. Although the name suggest they like sun, sunshine impatiens will also grow quite well in the shade and are not susceptible to Plasmopara obducens.
And here’s more information about sunshine impatiens.