The first plant looks like it has a watering problem. Either it got too dry while you were gone and the edges of the leaves were damaged, or it is getting overwatered and the roots are rotting. I see you have it on an automatic system. Did you ever find it badly wilted? If so, this is when the damage occurred and new growth should be normal. If not, then try taking it out of the pot and look at the roots. Healthy roots should be white and firm (older roots can become woody and darker, but should still be firm). There should be some new growth. Rotting roots will be mushy and discolored with little new growth. If they are rotting, take it off of the automatic system and hand water only when the soil gets dry.

Those black spots on your Peonies will not be the same fungi that causes Black Spot on roses, Phlox, or most other plants. There are many different fungi that can cause black spotting of many plant leaves and the best means of control is to make the soil the plants grow in a good, healthy soil so the plants can grow strong and healthy and withstand the spores that cause these plant diseases. Contrary to conventional wisdom there is ample research out there that shows that composting diseased plant tissue can help ward off future diseases, if the soil is good and healthy.

I have seen mildew on peonies, it's the first time I see them on tree peonies. Air circulation is very important. I think I have that. We had a lot of rain in Toronto this year, late summer and fall. Even though Ontario suffered great drought. On a sunny day there was moisture hanging in the air. Plants didn't have a chance to dry. I'll see what next summer brings. I have 4 tree peonies and a yellow one, which I incidentally cut when I was removing peony foliage on Thursday. I didn't cut too much, little bit of top growth. Hope it grows back! Can't believe I did that.

Thank you all for those answers. I keep my citrus indoor but I've put them one or two week on my patio in the middle of summer. I don't know if it's sunburn because white spot continue to appears months after I've put my plants indoor and away from the sun. I think it's a chemical burn most likely. One time, and one time only (hopefully) I used a "water spray" for human face on my citrus to hydrate them. But the water contain sodium, sulfate, bicarbonate, chlorine, nitrate, silicon dioxide... :(