Rust is a type of fungus of the order Pucciniales that attacks a wide variety of plants and trees. The name refers to the uredospores, which is the main dispersal phase of the fungi which are often seen as a yellow or rust coloured powder on leaves and stems. Millions of these spores are produced on the host plant, which are then spread to germinate on other host plants through wind dispersion or by being carried from place to place by animals or humans.
The fungus is a parasitic life form, requiring a living host to complete its life cycle. While rust tends not to kill host plants straight away, it can severely weaken them and cause death at a later stage. For this reason, rust which affects cash crops such as cereal or coffee can have a devastating effect.
Many thousands of varieties of this microscopic fungus exist Throughout the world, each often referred to by the name of plant it infects. The rust family members often have extensive life cycles and many may produce up to five different spore types during this time -
- Pycniospores (Spermatia)
Each of these refers to a different stage of development and varieties of the rust fungus can be classified according to how many of these spore types they produce during their life cycle.
One of the more recent examples of the dangers of rust contagion in Australia has come from the fungi Myrtle Rust. First detected in the Central Coast region of NSW in 2010, the rust has spread to Queensland and Victoria since that time and is considered a serious threat to iconic Australian native species such as the lilly pilly, bottlebrush and tea tree. Because of its ease of reproduction (dispersal by wind and through movements by people and animals), authorities have considered that it is now impossible to eliminate the fungus. Nursery associations and government departments have now set out a series of strategies and protocols to try to contain the threat.
Another example of a recently-arrived rust fungus in the country has been that which affects the Frangipani tree. Frangipani rust, a disease caused by the fungus Coleosporium plumeriae Syn. C. domingense, has now obtained a firm hold in in Australia with the Queensland Government’s Department of Primary Industries confirming the disease has been present in the state since 1993.
Frangipani rust causes unsightly damage to the tree, with yellow pustules appearing on the underside of leaves which release clouds of powder-like spores which go on to spread the fungus. While unlikely to kill the tree, the disease may severely weaken it, causing leaves to fall to the ground.
This form of the disease affects the Frangipani or Plumeria species, including P. acuminata, P. acutifolia, P. alba, P. clusioides, P. rubra, P. obtusa, and P. variegata. Preventing rust is very difficult. While some fungicides and the application of sulphur powder may prevent germination, this form of treatment may be problematic on a larger scale and difficult to carry out safely in the garden. Preventative measures such as monitoring known host plants — and then dealing quickly with any infection — is recommended as a way to stop contagion.
Prevention and Eradication
For the gardener this would involve ensuring that the plant or tree is bought from a nursery which carries out essential hygiene practices designed to reduce the spread of the fungus. Continual monitoring of the host plant should be carried out and any infected leaves or branches (including those that have fallen on the ground) should be removed and disposed of in a safe manner. This may include bagging the infected material before disposing of it, or burning it to destroy the spores.
Overwatering of the plants should be avoided, particularly in humid conditions, as this will help the spread of the spores. Care should also be taken to avoid water remain on the plant for long periods of time.
- Queensland Government Department of Primary Industry
- Frangipani Society
- Cornell University
- Backyard Nature
This informative article was written from our own research and development, by our horticulturalists and industry professionals here at eplants.