Plumeria Care – Plumeria Rust

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One of the most common worldwide threats to plumeria plants is a fungus disease known as plumeria rust, Coleosporium domingese. An airborne pathogen causes the plumeria rust to spread rapidly from one plumeria plant to another.

Plumeria rust was first recorded on Plumeria alba on the Caribbean West Indies island of Guadeloupe in 1902. It later spread to and throughout Central America. Today it is found in many countries where plumeria plants are grown. The one important piece of good news is that plumeria rust does not affect the plant’s growth and flowering.

Some plumerias are more resistant to rust than others, including Plumeria obtusa ‘Singapore’ and ‘Mele Pa Bowman’ which are very resistant to rust.

The majority of infections are caused by airborne urediniospores that stick to leaves under wet or humid conditions. Urediniospores are thin-walled spores. These spores look like a balloon pinched in the middle, or an un-separated eight. As these spores germinate, the nuclei undergo karyogami, reproduction in fungi, and thereafter meiosis, cell division. They penetrate the leaf surface infecting the cells of leaves.

The symptoms of the disease start on the undersides of leaves that begin to show numerous tiny, raised, yellow-orange, powdery rust pustules. These pustules may emerge sparsely on the upper surface of heavily infected leaves. Even though the spores can be rubbed or wiped off the leaves, it doesn’t eliminate the infection.

Yellow spots become visible on the upper leaf surface, opposite to the infected sites on the lower surface. As lesions age, enlarge, and coalesce, these yellow areas develop into sunken, angular and grayish to brown spots. When leaves are severely diseased, they may dry, curl, become distorted, and fall off. Premature defoliation can at times result in complete loss of leaves.

To control plumeria rust one needs to act promptly at the first indications of rust spots. In treating infected leaves it is important to treat both sides of the leaves with a fungicide. It is helpful to add a surfactant to the fungicide solution to prevent the solution from running off the leaves. It is important to remove any and all infected leaves. Remove all fallen leaves as well as the pathogen can continue to survive on these leaves and become a source of new infections.

Further preventive steps include regulating the airflow around plumeria plants. It is an invitation for diseases and insects if plumeria plants are planted too close together.

Copyright © Bob Walsh 2011

Plumeria during summer 2010, Chicago, USA

• 16 Jan, 2011
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