During summer in Florida, many of the beautiful frangipanis (Plumeria spp.) become symptomatic with a strange infection. Orange dots start to cover the bottom side of the leaves and yellow chlorotic spots or lesions can be seen on the top of the leaf. This is a disease caused by a fungus. Frangipanis are prone to infection by the fungus, Coleosporium plumeriae, commonly known as frangipani or plumeria rust. Fortunately, the disease only affects frangipanis. It starts as small yellow-orange pustules on the underside of the leaf and can quickly cover the entire underside of the leaf. The disease spreads by windborne spores, so it can quickly infect new leaves in the plant canopy. It causes premature leaf drop but does not affect the long-term health of the plant.
How does a Frangipani get Rust?
Frangipani rust tends to be more prevalent on plants in areas with little air circulation. The fungus becomes more abundant as moisture, heat, and humidity increase, so as summer progresses so does the disease. It is difficult to prevent or control the disease and there is no magic remedy. The best management strategies are proper sanitation, fungicides (to a limited extent), and selecting disease resistant varieties.
When the disease is present, immediately picked up and dispose of any fallen leaves in the trash and not in the compost. When the leaves are left in place or put in the compost, it increases the number of spores available to spread the disease. Highly infected leaves can be hand picked off the plant, but a soft touch is required. The slightest jostling of the plant can send spores airborne. Practice good sanitation by properly sanitizing pruning equipment between plants.
If considering fungicide applications, it’s important to know that nothing can be done for leaves that are already infected. Fungicide products that contain the active ingredient mancozeb with sulfur, chlorothalonil, or copper applied prior to disease arrival can help protect the leaves or slow infection of new leaves. Multiple repeat applications on the schedule recommended by the product label will be necessary to keep the disease at bay.
All frangipanis lose their leaves at the end of season, so it may be better to forgo the chemical applications and focus on keeping infected leaves picked up as they fall. Ultimately the disease only shortens the life of the leaf, but not the life of the plant.