Disease - a rusty problem
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.
To prevent rust use copper based fungicides these need to be sprayed prior to the rust pustules appearing on the base of the leaves. In late spring 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.
To reduce the occurrence of rust remove older lower leaves on a regular basis and dispose. Don’t add them to the compost or let them fall to the base of the tree.
Black tip (specific to Plumeria obtusa in cooler climates)
In early spring,at the first signs of new growth, a bacterial problem commonly known as “black tip” can appear. This causes die back of the new growth but creates more branches.
“Black tip” rarely kills the tree.
The cause of the “black tip” fungus is low spring temperatures combined with high humidity. By late spring when temperatures increase the “black tip” disappears.
To try and reduce its unsightly appearance seaweed extract liquid fertilisers can help. Begin foliar spraying at the first signs of new growth prior to the first signs of the “black tip” fungus and then spray once a week until early summer.