I live in southern California. A month ago, the leaves began curling. I believed it was an insect issue and sprayed them twice with Bayer 3 in1 insecticide. Now, the leaves are black and yellow. Please see attachments. I have also sprayed them a sulphur based fungacide. I am worried because it seems like this issue has spread to all of my plumerias. Thank you for any advice you can give me,
Certified GKH Gardening Expert
It could be plumeria rust. Look on the underside of the leaf for rust looking spots. check below for approved fungicides. Be sure to pick up fallen leaves and destroy.