December 2018 Myrtle Rust update

December 19, 2018

In this update you will find:

  • Where has myrtle rust been found
  • Check your myrtle plants for myrtle rust this summer
  • Give your plants the best chance against myrtle rust
  • How to reduce the risk of spread in your area

Where myrtle rust has been found  

811 infected properties have been reported since May 2017.

National detections of myrtle rust to date: 

Northland - There are 34 sites/properties in Northland with confirmed infection. Most of these are in Kerikeri. Myrtle rust has not been found north of Kerikeri.

Taranaki - There are 281 sites/properties in Taranaki with confirmed infection. Most of these are in New Plymouth and Waitara.

Waikato - There are 96 sites/properties in the Waikato region with confirmed infection. Most of these are in Otorohanga and the Taupo district. 

Bay Of Plenty - There are 156 sites/properties in the Bay of Plenty with confirmed infection. Most of these are in Te Puke and Bethlehem.

Auckland - There are 141 sites/properties in the Auckland region with confirmed infection. Most of these are in Remuera.

Wellington - There are 44 sites/properties in the Wellington region with confirmed infection. Most of these are in Lower Hutt and Upper Hutt

Manawatu-Whanganui - There are 25 sites/properties in the Manawatu region with confirmed infection. Most of these are in Fielding.

Tasman - There are 20 sites/properties in the Tasman region with confirmed infection. Most of these are in Collingwood, Patons Rock and Pohara.

Gisborne - There are 3 sites/properties in the Gisborne district with confirmed infection. These sites are all at the Northern tip of the East Cape.

Marlborough - There are 6 sites/properties in the Marlborough district with confirmed infection.

Nelson - There are 5 sites/properties in Nelson with confirmed infection. 

Check your myrtle plants this summer

During the warmer summer weather the conditions become ideal for the spread of the fungal disease myrtle rust  and there is a risk it will appear in new areas where it hasn't been seen before. We encourage you to check your local myrtle plants this summer to help track the spread of myrtle rust.

The disease, which is mainly spread by wind, generally attacks shoots and buds and leaf surfaces of the myrtle plants. infected plants show typical symptoms including bright yellow powdery spots.

If you think you see symptoms remember to not touch or collect samples, but take pictures and report it to Biosecurity New Zealand’s Exotic Pest and Disease Hotline on: 0800 80 99 66.

All plants in the myrtaceae family are susceptible to myrtle rust. For a list of myrtle plants in New Zealand you can visit the New Zealand Plant Conservation Network.  

There is no confirmed way to stop myrtles from contracting the disease, but there are some ways that you can give myrtle plants in your garden the best chance against it. 

Caring for your myrtle plants

It's the new spring flush that is most susceptible to infection. To avoid stimulating new growth in warm weather it's recommended that you avoid heavy pruning during warm weather if possible. Instead, prune myrtles only in late autumn and early winter. When pruning, use good hygiene practice, sterilise and disinfect tools and equipment with pure alcohol or methylated spirits to avoid transferring spores.

Reduce soil compaction and injury to tree roots

Reduce or avoid applying any herbicides around trees, trunk or root plate areas. Read the product label, as care is needed with some grass care products which can contain selective herbicides that impact on garden plants and their growth patterns. Avoid lawn care or weed control products around the dripline of a tree. Tree roots do not like soil compaction and this can reduce tree health by stopping water absorbing into the soil, reducing oxygen in the soil as well as physically damaging the roots of trees which can allow the entry of diseases. Consider selecting low clumping or bulb type plant varieties if planting under established trees.

Use Mulch

The use of wood chip mulch could help improve the soil around trees as it helps plant establishment and growth. It helps keep water in the soil, keeps soil cooler, and produces a better habitat for soil microorganisms. Wood mulch may be available for free from arboriculture companies. Keep mulch away from the stem or trunk, but you can pile it up to 20cm deep. Replenish mulch as it breaks down (faster in some seasons than others). Homemade compost is also a good top-dressing for around trees and plants. 

Apply Fertiliser

Only use fertiliser on garden or plantation trees. Wild natural trees or stands of vegetation should not be fertilised. Natural products such as fish meal, blood and bone or sheep pellets will support soil microorganisms as well as the plants. Seaweed based fertilisers can also be used, and the use of products with humic acid, and trace minerals can help with soil health and root development. Products with phosphorous and potassium can help with root and shoot development. 

Help limit the spread of myrtle rust in your area

Here's a few handy tips that will help reduce the risk of spreading myrtle rust in your area. 

Arrive clean, leave clean

The forest you visit could be infected with myrtle rust without you knowing it. Before entering such areas for work or recreation, you should minimise the risk of spreading the rust by ensuring your equipment, clothing and tools arrives clean and leaves the area clean.

Buy healthy plants

Make sure myrtle plants bought for your garden are free from the symptoms of myrtle rust. Inspect the leaves and stems of plants before you buy them, and avoid purchasing plants that have signs of disease.

Monitor your plants

Regular monitoring of myrtle plants will alert you to signs of myrtle rust, particularly new, young growth, shoots and seedlings. Early detection in your garden will give you time to consider options for myrtle rust control on your property. If myrtle rust does establish on your property, note which plants become the most severely affected.