I do impatiens, but not specifically SunPatiens. :-) And fewer to none of those lately given the wet and hot summers we've had; they die of a variety of nasty fungal diseases!

That does look fungal. I'd be tempted to graduate from Serenade and give something like Daconil a shot. It does look like the Serenade is holding it at bay, though, so if you do want to continue with it, I also don't object to continuing on. However, the SunPatiens in question are unlikely to be big producers of blooms either way.

And I'd recommend against repeating the SunPatiens Experience in that location next year, you're going to have the same issue.

Otherwise, your care is fine. Generally, feed on a normal schedule. Don't let them get dry (and this year, they haven't really gone dry). But if they get dry, they get wilty, and that'll let you know they went dry and you water them.

And just to make me happy, check for slugs. That's not the problem (slugs don't cause mottled flowers or dying tips of leaves), but they might be a minor secondary problem that are holding your plants back a little where the damage is more internal to the plant and not obvious from the photo.

Ok thanks Morph. I have some Azoxystrobin 22.9 % on hand could I use that? If so I wonder how much I should use and how often?

The impatiens are on Table 1, safe, for application for Azoxystrobin. Heritage uses it as its AI, and it's registered for a lot of diseases, so I'd go with their label.

You'll have to match strengths and whatnot, of course...

Great thanks......last question could I make a spray solution of DE for possibility of slugs.?

As it gets wet, DE stops working. So use that dry, or just apply Sluggo, Escar-Go, or the like. Or a small bathroom Dixie cup of beer or something sunk into the windowbox.

Seriously, I doubt you have a problem but they're famous for that. SunPatiens, however, usually don't have an issue due to their sunnier locales.