if powdery mildew... i really wouldnt bother treating this late in the year ... but i dont know where you are ...

you can ALWAYS deadhead flower seeds ... but once they fall over... i dont see why you cant cut them back hard .... but i have no experience with B's

my kiwi vines died.. lol ...

as a newb ot the garden.. understand.. that by august.. many things are getting tired.. spent ... its not really a time.. that i would start worry about some minor leaf issues.. on plants that will die to the fground.. or lose their leaves in a month or two ...

if PM ... there are ways to avoid such.. like not making the plants wet in the evening.. so they stay wet in dark warm nights.. when mildews thrive...

increasing air circulation thru removing plants ...

and some prevention in spring ...

but we need to confirm the PM ...

there is also a garden clinic forum... should you fail to get answers in this forum ...

we need a few more pix ... on the other issues... you do that.. by replying to your own post ...

ken

I had baptisia & was doing same thing - after some research I found out that too much water would do that. It was planted close to area with hosta and other plants that got watered more often, so got too much of it. After paying attention to watering, I did see some improvements; unfortunately not enough to be 100% sure because year later I moved.
It may be worth considering.

I always put bamboo stakes and string around when it almost finished flowering - they disappeared in that beautiful foliage of baptisia. I always kept the seedpods on, they are very ornamental. There were few seedling coming up in spring, but so few & so easily pulled out, it was hardly any work (I wish I saved some seedlings to bring to new place...but I have saved seeds & will see...)
Rina

My brother planted peonies here 40+ years ago & I've added quite a few myself over the years. I've never done anything to them since moving here in 2005. The foliage gets discolored late in the growing season sometimes but I've never treated it and the plants just keep coming back every year with zero help from me. Since they also bloom heavily, I figure they're healthy and don't need my help.

I put peony rings around my baptisia to prevent flopping. They're perennials that are just really worth having in my garden beds--I have four. Like peonies, they need zero attention from me other than the peony rings for support and I leave those year-round. I do nothing either to or for my baptisias. They have incredible taproots so never need watering. The foliage remains lovely right through the growing season and once the weather cools they naturally go dormant. Basically all I do is enjoy them.

According to Perennials for Every Purpose by Larry Hodgson, baptisias grow 3-4 ft. tall and 3-4 ft. wide. I've had mine for a number of years and that's been my experience with each of the four I have planted. I don't know where you're located but don't guess yours will exceed those measurements.

Peonies can suffer from something called botrytis blight. I Googled it and found a picture on the Missouri Botanical Garden website (see link). Judging by the photo, your plants don't have it.

Sorry: I don't grow kiwi vine so can't help with that.

An established perennial garden generally shouldn't require a great deal of maintenance unless it includes roses. Mine doesn't for that very reason--I purposely have no roses in my garden.

Here is a link that might be useful: Botrytis blight

The peonies undoubtedly have botrytis, a fungal disease common to peonies, though they don't get it every year. Just leave them alone until frost kills them. Then cut them back, but never put peony foliage in the compost; put it in plastic bags and send it out with the trash. Clean your pruners with a weak bleach solution and just go on with the garden clean up.