What is Phytophthora Dieback?
Phytophthora (pronounced Fyt-of-thora) dieback is a plant disease caused by a microscopic organisms present in the soil. The scientific name of the pathogen is Phytophthora cinnamomi, but it is commonly known as Pc. It attacks the roots of plants causing them to rot.
Pc spores infesting the plant root systems
Where did Pc come from?
Scientists believe that Pc was introduced by the early settlers who brought live plants (and soil) to Australia. The first unexplained death of Jarrah trees was recorded in the early 1920s around Karragullen, 45 km south east of Perth. Later, deaths were observed in many other parts of the forest. However, it was not until 1965 that a research scientist based at Kelmscott identified that Pc was the cause of the deaths.
What plants are killed?
Although the disease was initially called jarrah dieback, it is known to kill hundreds of native plant species. It kills banksias, persoonias (Snotty Gobbles), she-oaks, grass trees, zamias, hibbertias (native Buttercups) and many, many more. Some plants are resistant, including Marri (Red Gum), Yarri (local Blackbutt), Acacias (Wattles), Grasses and Sedges.
Grasstree and Zamia
How is Pc spread?
Mostly by human activity. Pc spores are microscopic (less than one hundredth of a millimetre in diameter) so they can be spread in soil and water - easily and invisibly. The natural movement of soil rarely occurs. Usually humans are the key transporters. The amount of soil moved can be large (e.g. a trailer load of gravel from an old pit) or small (e.g. mud on your tyres/shoes which washes into your garden).
Sometimes infected plants are bought from nurseries. Query staff about where the plants come from, whether the nursery and its suppliers are aware of Phytophthora dieback and/or have had problems with it in the past. Ask if the nursery is using Phytophthora dieback control procedures and has been accredited by the Nursery Industry Accreditation Scheme, Australia (NIASA). Check NIASA's webpage for a list of accredited nurseries. Be sure to ask before you buy your plants.
Fighting Phytophthora Dieback
We now know what causes it, how it is spread and what to do to help protect our plants. So it's time to go on the offensive! Roleybushcare (alias the Roleystone Dieback Action Group) has started to combat the disease in local bush reserves and many local residents are acting to protect their own properties.
Industry, Government and the Community are responsible for preventing the spread of Pc from infected to non-infected areas of bushland. The aim of quarantine and hygiene measures is to eliminate the transfer of soils between sites by human activity. This can occur through low impact forest recreation including bushwalking and picnicking or more serious and unauthorised interaction such as mountain bike, motorcycle and 4WD use. The latter can spread Pc over a wide area in very short time.
Plan activities for the dry summer months wherever possible and avoid wet areas in the winter months. Observe all signs notifying prohibited access and road closures.
Recognising symptoms of Pc in the jarrah forest
Don't just look at the Jarrah trees! Jarrahs can look healthy but the site could be heavily infected with Pc.
Alternatively, the Jarrahs could look sick and dying but they may be uninfected with Pc. There are many other reasons for Jarrahs looking sick.
Instead, look at the Banksia and shrub layer for symptoms of disease. Banksias are usually the first to die, and they die quickly and completely, not one branch at a time. So if your Banksias are dying in this manner then you probably have dieback in your property.
If you don't have Banksias then look for other species of plants which are used to indicate the presence of dieback disease. Dead Grass Trees, Snottygobbles and Zamias are indicative of the disease.
However, Phytophthora experts tend to use other plant species but training is required to identify these species. One of these species is the slender grass tree (Xanthorrhoea gracilis - the small one which sprouts from ground level and has the thin flower spikes with the flowers at the end). Its death is usually a reliable indicator of dieback. This species is common in the jarrah forest.
Slender grass tree Xanthorrhoe a gracilis
How dieback attacks
If you have doubts or want to know what the plants look like, attend a Roleybushcare Group field day.
Preventing the spread of Pc
- Don't bring any soil to your block unless you know it is "dieback-free". Pc is microscopic and lives in soil so the potential to spread Pc in soil is high. Always ask the supplier of the soil (or gravel, fill etc.) if it is "dieback-free". This is equally as true for truckloads of gravel as it is for a single potted plant. Pc present in the soil in one pot has the potential to devastate your entire block.
- Don't let any mud from your vehicle get into your bush. This is especially true if you have been driving on forest tracks. If you decide to wash the mud off your car then beware! The muddy water could carry Pc and provide it with the wet conditions that enable it to flourish. When the soil is very wet Pc produces literally millions of spores; each spore (less than one hundredth of a millimetre in diameter) has the potential to kill mature jarrah trees.
- Don't soak your bush. Pc is favoured by wet soil. Jarrah and many other jarrah forest species become stressed under these wet conditions. Pc can be present in soil but have minimal effect on plants - these sites are usually well drained. Do prevent water draining into your block. Pc loves water and the microscopic spores spread whenever water runs off an infected site.
- Do schedule earthworks in the driest part of the year. This will minimise the risk of introducing infected mud on the tyres and body of the vehicles.
- Do treat your banksias with phosphite (potassium phosphite This chemical is known to protect plants from Pc. Banksias are the first to die and their roots are believed to provide Pc with a food base and protection from desiccation in summer. By injecting the Banksias you will increase their resistance to Pc and prevent Pc getting a "hold" in your block.
- Do treat your other susceptible plants with phosphite.
- Do abide by the Dos and Don'ts prescribed in this section. You may have Pc on your property but you should try to prevent introducing more
The use of Phosphite
Potassium Phosphite is a cheap, environmentally friendly chemical used to fight Pc. Phosphite* has been used for many years as a standard treatment to treat avocados for a disease caused by Pc. Research by CALM scientists has shown that it also increases the resistance of Banksias, Jarrahs and other species to attack by Pc. Five years after injection the trees still had an increased resistance to Pc.
Phosphite has many advantages over other fungicides:
- It has been shown to be effective for the treatment of native plants
- It has a very low toxicity to humans (similar to table salt)
- There is a very low pollution risk associated with its use because it is usually only injected into the plant and sprayed at a low concentration.
- It binds to Jarrah forest soils so it won't reach the water table
- It eventually forms phosphate in the soil. This is an essential plant nutrient
- There is a very low risk of Pc becoming resistant to phosphite
- It is cheap! Less than 50c to treat a medium sized Jarrah tree
- It is simple to use - it can be injected or sprayed.
Drilling the hole in the tree
Inserting the syringe
To find out how to treat your plants with phosphite we recommend that you attend one of the regular field days in Roleystone with Roleybushcare. You will receive instruction and get experience using the equipment. It will also give you the opportunity to ask questions about Phytophthora dieback and its treatment.
Equipment to spray and inject your plants is available for hire from local conservation groups. Instruction sheets are provided with the kits or you could attend a field day.
Contact Roleybushcare (Roleystone Dieback Action Group) for dates and further information.