Understanding Myrtle Rust: Signs, Symptoms, and Treatments

Myrtle rust is a significant threat to New Zealand’s native myrtle species, including pōhutukawa, rātā, and mānuka. This fungal disease, caused by Austropuccinia psidii, poses a severe risk to our natural heritage and biodiversity. Understanding the signs, symptoms, and treatments for myrtle rust is crucial for preserving these iconic trees and shrubs.

 

Tree species commonly found in Auckland that are affected by myrtle rust, include

1. Pōhutukawa (Metrosideros excelsa)
2. Rātā (Metrosideros robusta)
3. Mānuka (Leptospermum scoparium)
4. Kānuka (Kunzea ericoides).
5. Ramarama (Lophomyrtus bullata)
6. Rōhutu (Lophomyrtus obcordata) 
7. Swamp Maire (Syzygium maire) 
8. Eucalyptus species (Eucalyptus spp.)
9. Feijoa (Acca sellowiana)
10. Lilly Pilly (Syzygium smithii)

Signs and Symptoms 

 Early detection of myrtle rust is vital for managing its spread. The disease affects new growth, including leaves, shoots, and flowers, leading to several noticeable symptoms:

1. Yellow Powdery Spores:

   One of the most apparent signs is the presence of bright yellow powdery spores on leaves, stems, and buds. These spores are the reproductive structures of the fungus and can spread easily through wind, water, and human activity.
   
   

2. Deformed Leaves and Shoots:

   As the infection progresses, affected leaves and shoots may become deformed and twisted. The new growth is particularly vulnerable, leading to stunted development and dieback.
   
   

3. Lesions and Browning:

   Infected areas may develop lesions that turn brown or grey as the tissue dies. This can result in significant defoliation and weakening of the plant.
   
   

4. Flower and Fruit Drop:

   Myrtle rust can cause premature dropping of flowers and fruits, impacting the reproductive success of the plants and reducing the availability of nectar for native birds and insects.
   
   

5. Tree Death:

   Severe infections can lead to the death of the plant, especially in young or highly susceptible species. Repeated infections weaken the plant over time, making it more vulnerable to other stresses.

 

Treatments and Management:

 Currently, there is no cure for myrtle rust, making prevention and management essential. Here are some key strategies to help protect and manage myrtle trees and shrubs:

1. Hygiene Practices:

   To prevent the spread of myrtle rust, it is essential to implement strict hygiene practices. Clean all equipment, clothing, and footwear before and after working with myrtle plants. Avoid moving infected plant material to new locations.
   
   

2. Early Detection and Reporting:

   Regularly inspect myrtle plants for signs of infection, especially during the growing season. Early detection is crucial. Report any suspected cases of myrtle rust to local biosecurity authorities immediately.
   
   

3. Chemical Control:

   Fungicides can help protect plants from myrtle rust, especially in nurseries and high-risk areas. However, chemical control should be used as part of an integrated management approach and with consideration for the environment.
   
   

4. Removing Infected Material:

   Prune and remove infected leaves, shoots, and branches to reduce the spread of the spores. Ensure that the removed material is disposed of safely, following local biosecurity guidelines.
   
   
   

5. Planting Resistant Species:

   Where possible, choose to plant species or cultivars that show resistance to myrtle rust. This can help reduce the overall impact of the disease on your garden or landscape.

 

Conclusion:

Myrtle rust is a significant threat to New Zealand’s natural heritage. By understanding the signs and symptoms of the disease and implementing effective management strategies, we can work together to protect these iconic plants. While there is no cure, proactive measures and community involvement can help slow the spread of myrtle rust, ensuring that future generations can continue to enjoy the beauty and ecological significance of myrtle species. Let's take action now to safeguard our myrtle trees and shrubs and preserve this vital part of our natural heritage.