If you live anywhere along the east coast of Australia you might have noticed that the leaves of your frangipani look brown and rusty. There is a new disease attacking frangipanis in Australia called frangipani or plumeria rust (Coleosporium domingense syn C. plumeriae). It affects leaves and is only found on frangipani (Plumeria rubra).
Frangipani rustis a severe problem in Florida, and has been a problem in Queensland for the past 12 years. In recent years the disease has become more widespread in Australia. It has been noticed in Sydney for about 3 years and has been seen as far south as Nowra. It is likely to spread wherever frangipanis are grown.
What you’ll see:
Frangipani rust is most noticeable in late summer and early autumn. Small yellow pustules appear on the underside of leaves. They rupture and spread spores which pass the disease to other plants nearby. The upper sides of the leaves are brown and discoloured. Severe infections may cause the leaves to drop prematurely.
Simply tolerate the disease, or use a mixture of physical and chemical methods to reduce its spread and delay its recurrence.
Chemical: researchin the United States has shown that Plantvax, with the active ingredient oxycarboxin, controls frangipani rust and stops defoliation as well. However, oxycarboxin is not registered for this disease at present although it is registered for rust in ornamentals in Queensland and Western Australia. Plantvax is distributed by IHD Pty Ltd and is not readily available for home gardeners. For details of cost and availability contact the head office on (03) 8545 8777.
Researchers found that fungicides such as Mancozeb and sulfur which are available for home garden use to control rust and other fungal problems in ornamentals were not as effective as oxycarboxin. You could try using a general fungicide to slow the development of the disease (such as Yates Spray Insecticide and Pesticide, which contains sulfur and Mancozeb), and as a winter cleanup.
Physical: disposing of all fallen leaves in winter and spraying the tree and the area under the tree with a fungicide may slow the reappearance of frangipani rust next season. Frangipanis are normally deciduous, so they will soon lose their leaves and the problem will not reappear until humid periods of next year.
Biological: a foliar spray of friendly fungi (Verticillium lecanii) has also been an effective control in research carried out at the University of Florida. This product is not yet available in Australia.