Managing Dieback 

Managing Phytophthora Dieback in Gardens

Phytophthora dieback is a common disease in home gardens in the Perth metropolitan area and across the south-west of Western Australia. Common garden plants that are susceptible to the disease include roses, azaleas and fruit trees (e.g. avocado’s, citrus, apples, macadamia’s).

Once the disease has been introduced into your garden it can not be eradicated and can become a major headache for enthusiastic home gardeners. To prevent the disease from entering your own backyard there are number of simple steps you can take, including:

1. Do not plant plants in your garden collected from local bushland areas;
2. Do not re-pot your plants using unsterilised soil. Always use a high quality potting mix;
3. Do not use green (raw) mulch; and 
4. Buy your plants from accredited nurseries or those that use hygienic practices to prevent the spread of Phytophthora dieback.

Its highly recommended that plants and shrubs are purchased only from accredited nurseries that have strict hygiene processes in place. This is because the disease can be transmitted in nurseries by contaminated potting mix, plant material and water sources. Good nurseries sterilise their potting mix and irrigation water. In addition, they use hygienic practices such as raised benches and quarantine areas, as well as regularly testing for diseases. Unfortunately a large number of nurseries are not accredited. For a complete list of accredited nurseries (NIASA) and garden centres (AGCAS) in your area go to www.ngia.com.au.

Transplanting established plants from one garden to another can also spread the disease. Propagating from seed and cuttings is safer because no soil is transported. However, when you do need to re-pot your plants, always use a good quality potting mix.

Plants typically die from Phytophthora dieback at the end of summer when they are under the most stress. For this reason the disease can often be confused with symptoms of drought. The best way to identify Phytophthora dieback is by taking a soil or plant sample to a diagnostic laboratory in your area. Phytophthora dieback will affect a range of different susceptible plants, but will not impact resistant plant species.

If you discover that you already have dieback in your garden, there are a number of steps you can take to reduce the impact of the disease, for example:

1. Don’t move soil from the affected area around your garden;
2. Use a good quality composted mulch. Composted mulch is highly suppressive to Phytophthora dieback and can prevent healthy plants getting infected. The use of green (raw) mulch can introduce weeds and diseases like Phytophthora dieback;
3. Plant resistant species that are not killed by the disease;
4. When replanting into a dieback infested area consider a pre-planting technique such as solarisation or biofumigation; and 
5. Inject or spray your plants with phosphite.