Of all the members of the Apocynaceae family, plumeria (ploo-MEER-ee-a) has one of the greatest success stories.
Native to the West Indies, South America, and the Caribbean, this plant has become a global treasure but is widely cultivated in other tropical and subtropical areas, especially in Asian countries and the Pacific Islands.
More recently, plumeria rust was found in Sri Lanka, Thailand, Taiwan, India, and Africa.
The host Plumeria spp. (common names frangipani, melia [Ha- waiian], temple tree), are members of the Apocynaceae (dogbane family).
It’s a sacred flower to Buddhist philosophy and Hindu religion, connected to marriage and death in numerous countries, and the national flower of Laos.
But perhaps even more impressive is that plumeria flowers have been essential in making leis in Hawaii and other Pacific countries for 150 years or more.
When flipped over, the underside of the leaves will have to correlate with powdery orange lesions. These lesions are actually spore-producing pustules.
They’re pretty resistant to common ailments, with root rot, mealybugs, spider mites, and whiteflies being a nuisance.
However, the plumeria tree has a few problems endemic to the genus: plumeria leaf borers (Lagocheirus undatus) and plumeria rust fungus.
You’ve possibly dealt with rust fungi before, but plumeria rust is a hardy disease that can be difficult to control.
The good news is you can fight it off if you catch it early on or use preventative measures.
What Is Plumeria Rust Fungus?
Rust on Plumeria is caused by a specific fungus called Coleosporium plumeriae. The plumeria rust pathogen is the fungus Coleospo- rium plumeriae Pat.
Plumeria rust was first recorded on Plumeria alba on the West Indies island of Guadeloupe in 1902 and later spread to Central America.
This airborne species only affects the leaves of plumeria plants, spreading via air and water.
Plumeria fungus looks like tiny orange-yellow to bright orange specks of rust on the undersides of your plumeria leaves, but this is only the tip of the iceberg.
The fungus bores into the leaf, causing small lesions and reemerging on the bottom as rust pustules.
Usually, when you notice symptoms on the upper leaf surface, the infected leaves are already heavily infected.
Rust Diseases: What Damage Does Plumeria Rust Cause?
A number of fungal hyperparasites of C. plumeriae have been reported, as well as an insect predator (a midge).
The good news is this plumeria disease isn’t lethal. The bad news is that it can quickly defoliate healthy plants, and the fungus on your plumeria won’t go away.
The fungus appears first on the underside of leaves and isn’t visible from the tops.
To reduce relative humidity and increase airflow in the plumeria canopy, prevent tall weeds from growing near plumeria trees: plant spacing and intercropping.
There are a number of reported fungal hyperparasites of C. plumeriae and an insect predator (a midge). The first report of plumeria rust disease was caused by Coleosporium plumeriae in Taiwan.
As the new infections worsen, faint yellow spots may appear on the leaf tops, eventually spreading, turning brown, and sinking.
Eventually, the lesions will become necrotic, and the leaf will fall off.
Plumeria rust spores can overwinter and will not simply go away on their own. Most plumeria cultivars grown in Hawai‘i are susceptible to the pathogen and have numerous powdery spore masses on the underside of leaves.
Even more frustrating is that Plumeria rubra and its cultivars are hit worst, with rubra x obtusa hybrids a close second.
Plumeria obtusa also has a high susceptibility but is more resistant than Plumeria rubra.
According to the University of Hawai’i report at Mānoa, Plumeria obtusa var sericifolia, Plumeria pudica, and Plumeria alba have some resistance to the disease.
The report also states that Plumeria stenopetala and Plumeria caracasana are extremely resistant, although other species were still being researched at the report’s release in 2009.
Fungal Plant Diseases: How To Control the Plumeria Leaf Disease?
There are three approaches for plumeria rust treatment:
- Maintenance
- Chemical solutions
- Natural solutions
- … all of which have proven effective
You should already be practicing these maintenance techniques, as they can help prevent a wide range of fungal diseases and other problems.
- Remove any fallen leaves, sealing away any infected or diseased leaves in an airtight bag.
- Avoid splashing when watering the plant.
- Carefully prune away leaves showing infection, use sterile shears and gloves, and avoid contact with healthy foliage.
Several different chemical options are available, most of which use specific active ingredients.
A general fungicide for plumeria – GreenLight “Fung-Away” has proven useful against mild or early cases of Frangipani rust.
A few active chemicals and examples of products containing them include:
- Azoxystrobin (Heritage)
- Bayleton (Bayer Bayleton 50, Strike 50)
- Bonide Copper Fungicide
- Mycobutanil (Eagle 20EW, Eagle 40WP)
In terms of natural solutions, the best method is using a neem soil soak.
We can’t stress enough the usefulness of neem oil, although it is banned in a few countries due to its mild toxicity to aquatic life.
To make a Neem soil soak, you’ll need to emulsify a gallon of distilled water using 1 teaspoon of Dawn dish liquid or pure castile soap, then add 2 tablespoons of 100% percent cold-pressed raw neem oil.
Pour the mixture over your plant’s roots (it’s 2 to 4 cups for a regular houseplant, so scale up according to the current size of your plumeria), being careful not to splash the plant itself.
The Azardchtin contained in raw neem will be absorbed by the plumeria’s roots, becoming a systemic pesticide.
Fungicides can then be used to spray the plumeria plants and the soil around them. Using Stoprust spore control spray, treat any remaining rust spores by spraying both sides of the affected leaves.
These materials were brought to the Plant Pathology laboratory in the Department of Botany, University of Hawaii, for examination.
Neem is usually used for infestations but can also fend off many microbial and fungal infections.
As a systemic pesticide, the neem will kill off any plumeria rust breaking through the leaf surface.
The neem’s effects can take a while to become apparent, so have some patience.
Soil soaks protect a plant for up to 23 days, so reapply every two to three weeks as a preventative.