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What is myrtle rust?
A disease caused by a fungus that impacts some plants in the Myrtaceae family. Typically, only new growth is affected. Myrtle rust is originally from South America. However, it has spread around the world either by human introduction or by wind. In 2017, myrtle rust arrived in New Zealand via wind from Australia.
What should I do if I think I’ve found it?
Unless you are going to remove the plant, please DO NOT touch the plant as spores can spread easily. Report the infection on iNaturalistNZ to help scientists and land managers track the spread of the disease. Good images will help experts confirm the disease is present.
If you find an infected non-native myrtle in your garden, you might consider removing the whole plant so that it does not act as a source of infection for native myrtles such as pōhutukawa. For tips on removal, see “How should I remove infected plants” below.
If you find an infected native myrtle in your garden and it is small you might consider spraying it with a garden fungicide. If it is a large plant this might be impractical. More information about fungicide use is below.
If you see infected myrtles in public parks and gardens you could report this to your local council.
If you see it on native myrtles in a national park and on other Department of Conservation lands, you might report it to the local Department of Conservation office. If you have been out tramping, clean your gear so you don’t spread spores to new areas.
Should I remove my infected myrtles?
There is no law requiring you to remove infected plants, or infected plant parts. However, you may choose to do so. This will help non-infected plants by reducing the numbers of spores in the environment. You are especially encouraged to remove non-native myrtles, such as the highly susceptible Australian lilly pilly (Syzygium australe). However, please do not remove threatened native myrtles, such as maire tawake (swamp maire.) If plants are small, you might consider spraying them with garden fungicide.
Refer to the NZ myrtle key app for help identifying species.
How should I remove infected plants/plant material?
The best approach is to remove plants when there are no (or very few) visible symptoms. This is likely to be during winter or during a drought, as the fungus needs warm, wet conditions to make spores. However every day a plant with myrtle rust remains in your garden is another day it is producing spores (when the climate is right). So if you can get rid of it now and it is not a windy day - go for it! If you are going to remove a plant when spores are present, you should make every effort to limit the release of living spores. That may include:
- Putting the plant material in heavy-duty plastic bags and taking it to the landfill (as normal waste to be buried, not green waste to be composted).
- Chipping larger plants into a trailer and covering it on its way to the landfill (as normal waste to be buried, not green waste to be composted).
- Burying the plant material on site. Covering with a secured tarpaulin or other sheeting, mulch or soil ideally to a 50 cm depth, is also helpful, if in a location where it won’t be disturbed for at least 2 weeks.
- Avoid burning plant material. The heat from burning causes updrafts that can carry spores high into the air.
DO NOT attempt removals on windy days. DO NOT put infected plants into green waste. PLEASE WASH all tools and equipment thoroughly after use. Wear outer layers that can be quickly removed, contained and disposed of or washed after use (e.g. overalls and gloves).
How should I clean my gardening and tramping gear so as not to spread the disease?
Always clean your gear after tramping, or gardening where myrtle rust is present on your plants, as the wind may have blown tiny spores onto your equipment and clothes. Brush off any visible dirt or dust from your gear, ideally in a contained space like a garage, laundry or bathroom, hose it down and give your clothes a good wash, ideally in hot water.
Should I still plant myrtles in my garden?
You can reduce the threat posed by myrtle rust by not growing susceptible exotic species such as S. australe (lilly pilly) or Agonis flexuosa (willow myrtle, agonis or peppermint tree). Auckland Council has produced Myrtle rust: Reducing impacts through plant selection.
Native myrtle species are still valuable for local biodiversity, but be aware that they may become infected with myrtle rust in future, especially seedlings.
If you live in a place that has not had myrtle rust detected to date, you can help protect the environment by not transporting myrtles there from an area that has infection. Source plants locally and ecosource where possible.
Can I use fungicide?
Fungicide sprays are an option for controlling myrtle rust but should be used sparingly and with caution. Use only commercially available products for home garden use, following manufacturers instructions. Limit use of individual fungicide products by alternating between products using different chemicals to avoid resistance development. Be mindful that fungicides may impact on beneficial fungi and some are environmentally toxic. Research is currently underway to enable recommendations for specific chemicals and application protocols in New Zealand.