Updated: Jan 15, 2022
Rust (Coleosporium plumeriae)
A recent fungal problem (within the last 15 years) is the occurrence of rust.
The rust (Coleosporium plumeriae) fungus is the small orange pustules that appear on the back of the leaves in late summer.
Rust is an unsightly problem but will not kill the tree but can lead to premature defoliation.
Once rust pustules appear under the leaves those leaves need to be removed and can't be treated.
To prevent rust, treatment must be made prior to the rust appearing on the plant. We recommend using a systemic fungicide formulated for flowering ornamentals - this can either be sprayed onto the foilage to runoff or mixed into a slurry and watered directly into the roots. Best to follow the directions provided with the fungicide. In early summer, or at the first sign of a few rust pustules, start spraying the leaves and continue this on a fortnightly basis through to Autumn. This will inhibit the rust pustules from blooming and keep the plant clean from rust. If watering in with a slurry do this on a monthly basis.
Organically you can treat rust with a horticultural plant based oil which will reduce the rust but some rust will still appear and leaves will need to removed on a regular basis.