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Managing Myrtle Rust on Lilly Pilly: An Integrated Pest Management Approach

Myrtle rust, caused by the fungus Austropuccinia psidii, is a serious threat to lilly pilly plants and other susceptible species. Its impact on these plants can be devastating, leading to defoliation, stunted growth, and even plant death.

To effectively control this fungal disease, an integrated pest management (IPM) approach is crucial. This article will provide valuable insights into managing myrtle rust on lilly pilly through a comprehensive IPM strategy.

Myrtle rust can look like brown red orange yellow and or purple fungal symptoms on leaves
Myrtle rust is bad news

Managing Myrtle Rust on Lilly Pilly

Understanding Myrtle Rust

Myrtle rust is a fungal disease that originated in South America and has since spread to various parts of the world, including Australia and New Zealand. The scientific name of the fungus is Austropuccinia psidii. This pathogen primarily affects plants in the Myrtaceae family, which includes popular species like lilly pilly.

When myrtle rust infects lilly pilly plants, it causes distinctive rust-colored lesions on leaves, stems, and sometimes even fruits. These lesions release countless spores that can easily spread to other susceptible plants. Given the rapid spread and destructive nature of this disease, proactive management is essential to prevent its further dissemination.

Life Cycle of Myrtle Rust

Understanding the life cycle of myrtle rust is crucial for effectively targeting control measures. The life cycle consists of several stages, including germination of spores, penetration of host tissues, and production of new spores.

Spores of myrtle rust are produced in abundance within the rust-colored lesions present on infected plants. These spores are easily spread through wind, water, insects, or human activities such as gardening tools or clothing. When they come into contact with susceptible hosts, the spores germinate and penetrate the plant tissues. Inside the host, the fungus grows and reproduces, creating new lesions and releasing more spores into the environment.

By understanding the life cycle, gardeners and horticulture professionals can implement appropriate control measures at specific stages to minimize the impact of myrtle rust on lilly pilly plants.

Stay tuned for the next sections where we delve into the integrated pest management strategies for mitigating myrtle rust on lilly pilly. We will explore genetic controls, cultural controls, physical controls, biological controls, and chemical controls (as a last resort). These strategies will help experienced home gardeners, landscape architects, council decision-makers, and professional landscape experts effectively manage myrtle rust and protect their precious lilly pilly plants.

Integrated Pest Management (IPM) for Myrtle Rust

Integrated Pest Management (IPM) is a scientific approach to pest management that professional horticulturists use. It’s all about understanding how pests and diseases play into the circle of life, and using nature’s wisdom when designing, constructing and maintaining gardens. There are several control methods we can use.

Genetic Controls

When it comes to managing myrtle rust on lilly pilly plants, genetic controls play a crucial role in mitigating the severity of infection. By choosing lilly pilly 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 integrated pest management (IPM) as it allows plants to withstand or tolerate the presence of pathogens. In the case of myrtle rust, selecting resistant lilly pilly varieties can help prevent or minimize the development of rust-colored lesions and subsequent spore production.

Research conducted by Ozbreed has identified several lilly pilly varieties that exhibit high levels of resistance to myrtle rust. These resistant cultivars provide an excellent option for home gardeners, landscape architects, and professionals in the horticulture industry. By incorporating these resistant plants into landscapes and gardens, the risk of severe myrtle rust infections can be significantly reduced.

Sweeper Waterhousea and Sublime Acmena both showed no visible signs of infection and continued to thrive, even when other plants around them were severely suffering from the fungal disease.

It’s important 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 prioritising genetic controls and selecting resistant lilly pilly cultivars or species, experienced home gardeners, landscape architects, council decision-makers, and professional landscape experts can take a proactive approach to mitigate the effects of myrtle rust on lilly pilly plants.

If you’ve already got infected plants in the landscape, consider removing them and replacing them with a resistant variety. If you’re willing to fight a losing battle, and your infected lilly pilly is incredibly important to you, you can try a few other methods.

Cultural Controls

Cultural practices play a significant role in preventing and managing myrtle rust on lilly pilly plants. These practices focus on creating optimal growing conditions that promote plant health while reducing the risk of disease development.

  1. Proper Plant Spacing: Adequate plant spacing is essential to allow for proper air circulation and prevent overcrowding. Crowded plants can create a favorable environment for myrtle rust by limiting airflow and promoting high humidity levels. Follow the 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 lilly pilly plants. Dispose of the collected material properly and avoid composting infected plant material. By eliminating potential sources of spores, you can reduce the risk of reinfection.
  3. Water Management: Proper watering practices can help maintain healthy lilly pilly plants while minimizing the risk of myrtle rust. Avoid overwatering, as excessive moisture can create 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 that can help remove infected plant parts and improve airflow, reducing the risk of myrtle rust spread. But the proper sanitation of tools is a cultural control. When pruning lilly pilly 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, ensuring it is properly sealed to prevent spore release.
Myrtle rust on lilly pilly leaves
Keep an eye out for signs of myrtle rust.

Physical Controls

To limit the spread of myrtle rust, implementing physical controls is a good idea. These methods use mechanical methods to reduce the chances of spore transmission between infected and healthy plants.

Infected plant material, including leaves, stems, and fallen debris, can harbour myrtle rust spores. It is important to promptly remove and dispose of any infected plant material to minimise 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.

Avoid touching infected plants and then touching unaffected plants to reduce the chances of spreading the disease.

Biological Controls

Beneficial organisms play a vital role in IPM, but there aren’t any natural enemies that are helpful in the fight against this particular disease to the best of my knowledge.

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.

Commonly, copper oxychloride is used as a general all-purpose fungicide. It won’t just target the disease, but will wipe out a wide range of beneficial microorganisms including mycorrhizal fungi which are necessary for optimal plant health.

Adhering to label instructions is crucial for the safe and effective use of fungicides. There you’ll find important information on application rates, timings, safety precautions, and any restrictions that should be followed to minimise environmental impact and ensure human health and safety.

Implementing an Integrated Approach

To effectively manage myrtle rust on lilly pilly plants, it is important to implement an integrated approach that combines multiple control strategies. Here are key steps to consider:

  1. Monitoring and Early Detection: Regular monitoring is vital for the early detection of myrtle rust. Familiarize yourself with the symptoms and signs of infection, such as rust-colored lesions on leaves and stems. Regular inspections allow for timely intervention and prevent the spread of the disease.
  2. Developing an IPM Plan: Develop a tailored IPM plan that takes into account specific site conditions, level of infection, plant species, and available control methods. Consider factors such as plant spacing, sanitation practices, and the use of resistant cultivars to create a comprehensive plan.
  3. Collaboration and Knowledge Sharing: Collaboration between experienced home gardeners, landscape architects, council decision-makers, and experts is key to combatting myrtle rust effectively. Sharing knowledge, experiences, and best practices can help develop a collective understanding of the disease and its management.

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, an integrated pest management approach is crucial for managing myrtle rust on lilly pilly plants. By implementing physical, biological, and chemical controls as a last resort, alongside regular monitoring and collaboration, experienced gardeners and professionals can effectively mitigate the impact of myrtle rust and protect their lilly pilly plants.

This article provides general guidance on managing myrtle rust on lilly pilly plants. For specific recommendations and advice, it’s recommended to consult with local experts or horticulture professionals.

Remember to always adhere to local regulations and guidelines regarding the use of chemicals and biological controls.

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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