Myrtle rust

Myrtle rust, caused by the fungal pathogen often identified as Austropuccinia psidii (synonym Uredo rangelii), is a devastating plant disease. It belongs to the order Pucciniales and primarily affects species within the Myrtaceae family, posing a significant risk to biodiversity and agriculture worldwide.

The host range includes a wide array of plants such as eucalyptus, guava, syzygium, feijoa, and various native myrtle species. This pathogen is particularly aggressive toward young, actively growing tissue, which makes nurseries and forest plantations highly susceptible to rapid infection outbreaks.

The diagnostic symptoms include the appearance of small, yellow, circular lesions on young leaves, stems, and flower buds. Within a few days, these lesions develop into a characteristic bright yellow to orange powdery mass, which consists of masses of urediniospores that allow the fungus to spread rapidly.

The development and spread of the disease are highly dependent on high humidity and warm temperatures. Spores are easily dispersed by wind currents, splashing rain, and irrigation, as well as by human activity, including the movement of contaminated equipment, clothing, or infested plant materials across regions.

Effective management strategies require an integrated approach. Prevention is critical, involving strict quarantine measures and the monitoring of imported plant stocks. Control methods in affected areas include the systematic pruning and destruction of infected material, improved sanitation practices, and the application of fungicides such as triazoles or strobilurins to suppress sporulation.