Probably bacterial or fungal. Take samples to Master Gardener clinic or local Cooperative Extension office.

I would say soil issues that are leading to moisture concerns - judging by appearance of the soil, I'd say too much water/inadequate drainage. The container also looks to be sized too small for the plant, as well, so it may well be root bound. There is something else going on as well.........can you post a closer photo of the white objects attached to the branch in the first photo? Not sure what they are at this distance but they look suspiciously like some sort of insect egg case.......

Wow, it is puzzling. It doesn't look like an ower-watering issue to me, but since we're not coming up with any more likely possibilities, then it is something to consider. This late in the year, it has likely stopped growing, even in Florida temperatures. Pothos tolerates drying out pretty well, so let the top couple of inches dry between waterings. How long have they been in that soil? Did they grow well all summer? If so, they might be a bit pot bound now, which can cause some dry spots in the soil, or some roots to become so restricted that they aren't able to draw enough water. It isn't the best time of year to re-pot, especially if something else is causing the problem, but you should at least check this. Can you pull the entire plant out of the pot with the soil and rootball intact? If so, a photo would help us. Check the root ball and medium for dry or mushy spots, for discolored or necrotic roots, for root parasites, crowding, etc. A few, small disrupted places in the root ball where you dig in to check the condition won't hurt it, even this time of year, and if it's very pot-bound, you can plop the entire thing into a larger pot of soil until the spring when you can do a better job or repotting, detangling, root-trimming, and so on. What parts of the plant are affected the most? Were the oldest/lowest leaves on each stem affected first/worst/most, or is the damage worse on the younger, more tender leaves? Are there any parts of the plants that aren't affected? When was it last fertilized, with what, and how often? (Do not fertilize it now- that's the worst thing one can do to a sick plant if the illness isn't due to fertilizer nutrient deficiency.) It might just be lighting, but the plant in the upper photo appears to have an overall yellowish pallor. That would support Tiffany's hypothesis of too much water. Also, I see a yellow leaf near the base of a stem in the second photo near that little sprig of Acacia or whatever it is that's taken root there. Some yellowing is normal, but check through the lower leaves for more yellowing. Too much water or nitrogen deficiency both tend to affect older/lower leaves first. Evenly yellowing lower leaves is more indicative of too much water or poor drainage, while yellowing that begins at the leaf margins is more often nitrogen deficiency. Other things can cause yellowing though, and that curious staining appearance isn't typical of either issue, so don't fertilize at this point. More photos wouldn't hurt: Entire plant Root ball free from the pot Close-ups of the "stains"

Your irises look great! What I see is a little leaf spot.. Not a lot and not enough to worry about. Just take your clippers and cut back the fans that have the spots if you want to. . Leaf spot lives in the soil.. Hot wet humid conditions is what brings it on.. It will not hurt your irises it will just make them ugly.. The outer leaves also usually brown and die back this time of year as well.. You can treat with a fungicide but its not necessary.