Plumeria Rust Fungus, Frangipani Rust Fungus
Frangipani Rust usually affects Plumeria (including: P. acuminata, P. acutifolia, P. alba, P. clusioides, P. rubra, P. obtusa, and P. variegata) in late summer and early autumn in Florida especially during and after very rainy periods.
Description of Coleosporium Infection
Small orange pustules appear on the underside of leaves. They rupture and spread spores which pass the disease to other leaves on the plant and other Plumerias growing nearby. The upper sides of the leaves become discolored. The entire leaf turns brown then falls off. Severe infections may cause the leaves to drop prematurely and tend to defoliate the plant.
Apparently the fungus invades the epidermis of the leaf, feeds on leaf cells and spreads throughout the leaf by rupturing leaf cell walls. The orange pustules are fungal bodies that produce spores which are spread by wind and rain.
Control of Frangipani Rust
There are no fungicides listed for use by the home gardener for control of Coleosporium domingense.
Limited control may be achieved by removing infected leaves as soon as the orange pustules are apparent and disposing of those leaves in the trash.
A foliar spray of the friendly fungi Verticillium lecanii has been found an effective control in research carried out at the University of Florida. Unfortunately this friendly fungi is apparently not currently available commercially for purchase by the home gardener.
As Frangipanis are normally deciduous, they will lose their leaves anyway as the cooler months approach and the problem will not reappear until the wet season the following year. Coleosporium domingense does not affect Plumeria flowers.
Sources: BIOLOGICAL CONTROL OF FRANGIPANI RUST WITH VERTICILLIUM LECANN; FIRST REPORT OF PLUMERIA SPP. RUST CAUSED BY COLEOSPORIUM PLUMERIAE IN LOUISIANA AND MALAYSIA AND CATHERANTHUS ROSEUS, A NEW HOST OF THIS RUST