Hi I live in Santa Cruz ca, zone 9 and I have a plumeria that was doing fine but now all the leaves are drooping and are turning black on the edges. On the "claw" at the top there is a white residue forming. I'm wondering if this issue is because of the cold, a nutrient problem, an insect problem, leaf rust, or all of the above(or none of the above) I'm also wondering how to proceed.. I.e building a greenhouse, organic pesticides, etc. I also am attaching photos so hopefully they show up. let me know what you all think!:)
Thanks,
Morgan

I am not sure about the brown spots, but the tiny white spots ON the leaves (not the residue you mention) makes me thing it may have spidermites.
I used to have some Plumerias around here (cold Romania) but I had to give them up - always infested with spidermites in summer.
Same goes for Adeniums.

plus it's about the time for them to go dormant.
Also the brown edges could point to some fertilizer imbalance. In spring I would repot this plant in a new fresh well-draining mix.

Your plumie is feeling cold already, sleep time..I would move it indoors now. I have moved mine 2 weeks ago. Our NorCal weather is getting too cold for it already. You may want to spray insecticidal soap or neem oil to remove those white things..it could be powdery mildew or mealy bugs.