I'd never heard of "Sunpatiens" before so looked them up. So they're just a variety of Impatiens. From the publicity the company puts out they are miraculously easy to grow and look spectacular. They make a point of saying they are good with heat and humidity and are mildew resistant. If you have a good dry season then maybe only use them then.

My local go to nursery usually has a kick off day around the mid-late June timeframe, which is really the time when the temps are right where the annuals start to take off. Plugs planted early just kinda sit dormant...until the temps kick in. Heh, I am planning to look for packs come Memorial day timeframe just to see if they exist.... I can't recall how much they were per plant, but for sure I know they were not cheap....and then I had to DIG further to see why it was $$$, to discover it was a ~licensed~ plant as well, etc, etc. I've never really bothered with seeds, (not talking SP but just annuals in general) just short of vegs. But as years go by, and I grow wiser and thriftier, I often say to myself, why not start the annuals from seeds, as that is where a good majority of the spring/summer funding goes...

I first encountered and bought some SunPatiens a year ago in June 2017. It's reportedly a heat & sun tolerant variation on Impatiens (at first I suspected some would consider it the "Hostess Twinkie" of fine gardening). They didn't bloom profusely for me. But 4 of 6 plants survived the winter and got a head start in 2018. They get full sun from 12-5 or so. This year they started flowering in late April, then in July started pooping out. One of the survivors with more shelter from sun and wind kept blooming, although not abundantly. I'm patiently waiting to see any response to last week's big rains, milder temps and cloudy skies - nothing yet. This year's full blast summer started 2 months early (in May) so everything endured a double dose of mid-summer extremes. Forgive unsightly visual distractions in frame, some were temporary wind deflectors, and it was too late in year to prune live oak tree, etc. Below: Late April, just starting 2 weeks later, 8:30 am (below) 2 weeks later (end of May) in the shade 8:45 am (below) mid july, 11 am, the southernmost plant on right stopped producing as many flowers (below); the one on the left with more shade also gradually reduced # of new blooms, there were even less in August

The fungus would survive cold. Most would not survive proper (hot) composting but I am not sure if this one does or does not. Usually, it is the hot humid rainy conditions that trigger the infection. I got a bag of fresh potting mix recently and uppotted several plants without sterilizing the soil (it's presumabed to be sterile). No my petunias, penstemon, snapdragon, nasturtiums and stocks are going down one after the other and I am kicking myself for not nuking the potting mix (I microwave in batches for 8 to 10 minutes until the bag puffs up with steam. Temps are usually 200+ F. Let it cool before opening). The conundrum with using compost is that if one were to sterilize it, the good bacteria that it is supposed to add to the soil will be lost. If one doesn't then some of the pathogens that survive despite composting (those that are not killed by the process or survive in parts of the compost that never heated up during the process) will lurk around. Unfortunately, there are no good solutions. We'll draining media would be less prone to the issue. Otherwise just use sterile mix and start your own seed or cuttings because commercial plants may already have them lurking in their.... Another option is to grow only those plants that are largely resistant to these fungi. For example, I have never seen a Dipladenia or a purslane die like this, or a rose etc. Another is to just replace as and when you lose one. Unfortunately, if you replace with the same plant variety it will probably repeat the issue. Of course, at some point the growing season is over.