Phosphite (Phosphonate) fungicide treatment
Phosphite salts can be used as a biodegradable fungicide to protect plants against Phytophthora dieback.
It is usually applied as potassium phosphite, derived from phosphorous acid neutralized with potassium hydroxide. Calcium and magnesium phosphite may also be used. Phosphite works by boosting the plant's own natural defences and thereby allowing susceptible plants to survive within Phytophthora dieback infested sites. It is important to note that there is no treatment that will eradicate Phytophthora dieback, including phosphite.
However, an integrated approach can successfully control the spread and impact of the disease. An integrated approach may combine strategic phosphite treatment, fumigants, controlling access, correcting drainage problems, removal of host plants and implementing excellent hygiene protocols.
Phosphite controls many species of Phytophthora, including Phytophthora cinnamomi. Phosphite is not toxic to people or animals and its toxicity has been compared to table salt. There is a very low pollution risk associated with phosphite. When phosphite is sprayed on to the foliage of plants, it is applied at a very low rate, so any phosphite that reaches the soil is bound to the soil and does not reach the water table.
Phosphite needs to enter a plant's water transport system in order for it to be effective. This can be done by injecting phosphite into trees, or spraying the leaves of understorey plants. Phosphite not only protects a plant from Phytophthora dieback infection, it can also help a plant to recover if it is already infected.