Each year, some of my impatiens just wilt and die. I lose entire pots of them. I plant them in sandy soil so as not to get too wet. They're mostly in shade, but some do get a little morning sun. They can be beautiful one day & the next day, they look like what we call in Texas "sheeee-it". It just dawned on me recently, maybe they're susceptible to verticilium and/or fusarium wilt. Can anybody tell me? I tried to google impatiens & wilt and got all sorts of stuff, but nothing about the wilt we commonly have here. I know it can get my petunias & vinca, but impatiens?
Could be that it is just too hot for them. I know up here in Vermont they only do well until the heat tops 70 degrees and then it is too much for them. They don't tend to last too long after that. It is the heat and not necessarily the direct sun that can also cause them to wilt and not do well.
My impatiens are in full sun and are doing really well. As Gardenmama says it could simply be to much heat. Try watering them either early in the moring or once it's dusk (from underneath) so that their roots can remain a bit cooler. I hope you find the cause of the problem as they are lovely plants and will bloom right through until the first frosts as a rule.
I've been having a similar problem the past 2 years WTxDaddy. Last year they looked terrible and I assumed that it was from the wet summer we had. This year they have only been in the ground for a few weeks and some are already turning to mush. I was wondering if they had some sort of wilt but there is little info out there. I'll be watching this thread.
I've been doing a bit of research and found out a little about something called "Impatiens Necrotic Spot Virus". http://www.ppath.cas.psu.edu/extension/plant_disease/tswv.html