Help! My mature plumeria tree has a yellowish brown spot on trunk right above soil. I put outside May thru September. It flowers as well! . The smaller tree also! The mature tree is at least 18 years old. It's my baby!

Can you post a photo please, so we have an idea what manner of growing it is in. And tell us what watering regimen did you do?

Feel that yellow spot. My Plumies get that too, but if it feels firm and dried out to my touch I am not worried, especially since it is summer time. I regard it like its battle scar from the previous cold season.

I would be worried if it is winter, the season would be colder, and rotting instances are higher. If it is awake at the time, I would have to observe watering intervals for the time being, so I do not aggravate the yellow spot. Or if it is dormant, then I really should not water, got to let the plant callus and heal that spot.

It is summer here. It is potted and brought into my home in winter.

That looks to be sunburn. Since it is only a small spot I wouldn't worry.