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Myrtle Rust Treatment: An Integrated Pest Management Approach

Myrtle rust is a persistent fungal disease that poses a significant threat to certain plants, particularly those in the Myrtaceae family. This includes eucalypts, callistemons, lilly pillies, melaleucas, and many more native Australian plants.

To effectively control this destructive pathogen, it’s a good idea to adopt an Integrated Pest Management (IPM) approach. This article will provide valuable insights into understanding myrtle rust and outline various control measures using genetic, cultural, physical, biological, and chemical methods.

By implementing an integrated approach and promoting collaboration among stakeholders, we can effectively manage myrtle rust and protect susceptible plants.

Myrtle rust can look like brown red orange yellow and or purple fungal symptoms on leaves
Myrtle rust can look like brown, red, orange, yellow and/or purple fungal symptoms on leaves.

Understanding Myrtle Rust

What is Myrtle Rust?

Myrtle rust, scientifically known as Austropuccinia psidii, originated in South America and has since spread to various parts of the world. It primarily affects plants belonging to the Myrtaceae family, including popular species like eucalyptus, lilly pilly, and bottlebrush.

Proactive management is essential to prevent its rapid spread and minimize the damage caused by this invasive fungus.

Life Cycle of Myrtle Rust

Understanding the life cycle of myrtle rust is crucial for implementing effective control measures. This fungus undergoes several stages, starting with spore germination, followed by infection, colonization, sporulation, and dispersal. Spores are easily carried by wind, insects, animals, or even human activities, making it imperative to break the cycle and limit its spread.

Integrated Pest Management (IPM) for Myrtle Rust

Integrated Pest Management is a scientific and holistic approach to pest and disease management used by professional horticulturists. It uses the wisdom of nature to help us in our fight against unwanted problems like myrtle rust in our gardens. There are several approaches we can use in harmony with each other.

Genetic Controls

In managing myrtle rust on susceptible plants, genetic controls play a crucial role in mitigating the severity of infection. By selecting cultivars or species that possess genetic resistance to myrtle rust, gardeners can significantly reduce the impact of this fungal disease.

Genetic resistance is an essential aspect of IPM as it allows plants to withstand or tolerate the presence of pathogens. Ozbreed have conducted extensive research on myrtle rust-resistant varieties available in the market. These resistant cultivars provide an excellent option for home gardeners, landscape architects, and professionals in the horticulture industry.

Some of the most resistant Myrtaceae members showed no signs of infection, even though they were surrounded by infected plants. Some examples were Sweeper Waterhousea, Sublime Acmena, Luscious Tristaniopsis, Green John Callistemon, and Slim Callistemon.

It’s important to note that genetic resistance is not an absolute guarantee against myrtle rust. While resistant cultivars are less susceptible to the disease, they may still exhibit some symptoms under severe infection pressure. However, their overall resistance reduces the severity of the disease and its impact on these resistant plants.

By prioritizing genetic controls and selecting resistant lilly pilly cultivars or species, experienced gardeners and professionals can proactively mitigate the effects of myrtle rust on susceptible plants. If infected plants are already present in the landscape, consider removing them and replacing them with resistant varieties.

Cultural Controls

Cultural practices also play a significant role in preventing and managing myrtle rust on susceptible plants. These practices focus on creating optimal growing conditions while reducing the risk of disease development.

  1. Proper Plant Spacing: Adequate plant spacing is crucial to allow for proper air circulation and prevent overcrowding, which can create a favourable environment for myrtle rust. Follow recommended spacing guidelines for lilly pilly plants to ensure optimal growing conditions and reduce the risk of disease development.
  2. Sanitation Practices: Good sanitation practices are critical to prevent the spread of myrtle rust within and among plants. Regularly remove fallen leaves, plant debris, and pruning waste from the area surrounding plants. Disposing of infected plant material properly and avoiding composting can help eliminate potential sources of spores and reduce the risk of reinfection.
  3. Water Management: Proper watering practices can maintain healthy plants while minimising the risk of myrtle rust. Avoid overwatering, as excessive moisture creates a favourable environment for fungal growth. Water the plants at the base to keep the foliage dry and reduce the chances of spore germination. Additionally, ensure proper drainage to prevent waterlogged soils, which can promote disease development.
  4. Pruning Techniques: Pruning is a physical control method that can help remove infected plant parts and improve airflow, reducing the risk of myrtle rust spread. However, proper sanitation when pruning is a cultural control. When pruning infected and susceptible plants, make clean cuts using sterilised tools (using alcohol or a flame) to prevent the transfer of fungal spores. Promptly remove and dispose of any pruned material, properly sealing it to prevent spore release.

Physical Controls

Implementing physical controls can also limit the spread of myrtle rust. These methods use mechanical means to reduce the chances of spore transmission between infected and healthy plants.

Promptly removing and disposing of infected plant material, including leaves, stems, and fallen debris, helps minimize the chances of spore release and reinfection. Proper disposal methods, such as bagging and sealing the material before disposal, should be followed to prevent further spread.

Additionally, avoiding touching infected plants and then touching unaffected plants can reduce the chances of spreading the disease. While biological controls have shown promise in managing various pests and diseases, I’m unaware of any effective biological controls that are effective against myrtle rust.

Biological Controls

While biological controls have shown promise in managing various pests and diseases, I’m unaware of any effective biological controls that are effective against myrtle rust.

Chemical Controls (Last Resort)

Chemical controls should only be considered as a last resort when other integrated pest management strategies have proven insufficient. Fungicides can be used to manage myrtle rust, but their application should be done with caution due to potential negative impacts on the environment and non-target organisms.

Copper oxychloride is commonly used as a general all-purpose fungicide, but it can also harm beneficial microorganisms necessary for optimal plant health. Adhering to label instructions is crucial for the safe and effective use of fungicides. This includes following application rates, timings, safety precautions, and any restrictions to minimise environmental impact and ensure human health and safety.

By implementing a combination of genetic controls, cultural practices, physical controls, and chemical controls as a last resort, gardeners, professionals, and enthusiasts can effectively manage myrtle rust on susceptible plants.

Myrtle rust on lilly pilly leaves
Keep an eye out for signs of myrtle rust.

Implementing an Integrated Approach

Monitoring and Early Detection

Regular monitoring is vital for early detection of myrtle rust. Recognizing symptoms and signs of infection, such as rusty-colored lesions on leaves, is crucial. By closely monitoring plants, gardeners and experts can promptly take action and minimize the spread of the disease.

Developing an IPM Plan

To effectively manage myrtle rust, it is important to develop a tailored IPM plan that considers site conditions and specific plant species. This plan should outline preventive measures, monitoring strategies, and appropriate control methods based on the severity of the infestation.

Collaboration and Knowledge Sharing

Successful myrtle rust management requires collaboration between home gardeners, landscape architects, council decision-makers, and professional landscape experts. By sharing knowledge, experiences, and best practices, we can collectively combat the threat posed by myrtle rust. Participating in community initiatives or online forums can facilitate information exchange and foster a united front against this destructive pathogen.

Daniel’s Wrap

In conclusion, adopting an integrated pest management approach is crucial for effectively treating myrtle rust on susceptible plants. By understanding the nature of this fungal disease and implementing a combination of genetic, cultural, physical, biological, and chemical control methods, we can minimize its impact and protect our cherished plant species.

It is essential for experienced home gardeners, landscape architects, council decision-makers, and professional landscape experts to work together, sharing knowledge and experiences, to combat the spread of myrtle rust. Let us take proactive measures and seek professional advice when necessary to safeguard our plants and preserve the beauty of our gardens.

Daniel is a writer and content creator for Ozbreed, one of Australia's leading native and exotic plant breeders.

Daniel has worked in various capacities within the horticulture industry. His roles have ranged from team leader at several companies, to creator of the Plants Grow Here podcast and Hort People job board, as well as his position on the National Council for the Australian Institute of Horticulture (AIH).

He's passionate about explaining how to care for different types of plants to ensure home gardeners and professional horticulturists alike can get the most out of the plant babies.

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