Serious impatiens disease spreading fast
A serious fungus attacking impatiens is killing plantings over many states, north, south, midwest. It is called "impatiens downy mildew". There is no cure. You have to rip out all affected plants and put them in the trash, not compost. You can't plant impatiens in the same place next year.
It does not affect New Guinea impatiens. It does affect the wild jewelweed.
There is much more to it but Google "impatiens downy mildew" or read this link.
Here is a link that might be useful: Impatiens Downy Mildew