I believe some maybe lichen. Iam from Fiji and I have lost many of my fruiting trees and others like sandalwood too to this. My advice is using copper based fungicide like copper oxychloride and mancozeb for this. It may not be a guaranteed cure but I have noticed that my remaining plants have really improved. It usually has to be sprayed every 3 weeks. Better still it should be sprayed on healthy plants too to stop the onset. Iam no expert, what I have is just experience. I was recently advised by agricultural staff to use water blaster to remove them.

Heliconias are very easy to grow especially Heliconia rostrata. They are very large plants which like hummidity and copious amounts of water. Could it be that your pots are too small and you are getting fertilizer burn or that they are staying too wet in your pots and you have root rot. Here in S.Florida(your climate is similar unless you are high up in the mountains) I grow Heliconia in the ground-they are far to large for pot culture IMO. If you look at the undersides of the leaves you can see spider mites if they are there-tiny little dark redish specks and they cause the top surface of the leaves to have a silvery appearance. You can blast them off with the hose or if a heavy infestation spray the undersides of the leaves with an insecticidal soap- this is completely harmless, except to the spider mites. Either method you will have to repeat several times. Unless you have had a very dry summer I don't think it is likely to be spider mites-they are only usually a problem in dry weather.The only insect pest I have really noticed on Heliconia is the mealy bug. I have found these in the roots and in the axils of the leaves where they are attached to the stems, but the plants are so vigorous they they are not much of a problem. I would take your plants out of the pots,wash off the soil and check for mealy bugs in the roots and leaf axils etc and cut of any rotten or dead roots and any rotten rhyzome. I would then plant them in the garden in either full sun or semi-sun in a spot where there is plenty of room, rich loamy well-draining soil where they will get plenty of water(the more sun the more water) and fertilize a couple of times a year(not till after they get growing, in your spring)-although I find they are such rampant growers that I don't bother to fertilize. The only problem for you now, at this time of year, is that they really prefer to be dug up,divided etc in the spring and you are now going into winter. However if they look like they are not happy perhaps it is better to do something! After 1 year you should have some big lush growths so if you have had adequate humidity and given them plenty of water I would suspect root problems possibly caused by your growing method. Heliconia rostrata can take quite a bit of cold so unless you are up in the mountains you should not have a problem. Hope this helps and good luck.

There are many different kinds of rose cankers. Some are slow to spread; others are fast . When I have had a stem or cane go black, they have been the worst kind of canker and when I didn't react quickly, I lost the rose. That said, in my opinion your rose is very sick. If it were mine, I'd cut below the black half an inch and then I'd clean by cutting tools with bleach, leave the bleach for 30 seconds, dry the blade and then cut another half inch lower. IMO you really want to get rid of what may be (something some of us here called) creeping black crud. In your first photo, you have what appears to be a good healthy green cane maybe a half inch in diameter. BUT to the right there's a stem that is black. That black stem IMO has infected, and affected the cane below it that supports both stems. I think you need to lose that good looking cane because the support area is already dead on one side and will only get sicker. IMO you need to cut that support cane off until you get pith that is alive (Compare the colors as you cut down a stem- you will see a change. This is one of those situations where you can learn a lot about how roses respond to problems and what you can do to try to direct their growth.

I bought my Francis Meilland from a nursery clearance three years ago as a half-dying potted bareroot rose, and it bounced back pretty well. I put it in a pot for one year, and after two years being in the ground, no matter how hard I pruned it back, it grew to 7 feet tall. (I removed about 3 feet from each stem after the first flush.) It's not stingy for me at all, blooming regularly every 5-6 weeks. Maybe it just needs some time to mature. I only fertilized once in March and water my roses every three days in summer. We're not as hot as other states/countries, though. Photo taken 3 days ago.