Attempts to eradicate Phytophthora from infected areas have largely been unsuccessful. Treating with the fungicide Phosphonate (Phosphite) boosts the plant’s natural defences and research has shown that it increases the resistance of susceptible plants to Phytophthora Dieback but it does not kill the pathogen. Infected plants remain a reservoir of the pathogen, even after they die.
Treatments with Phosphonate are most effective during the active growth months, generally spring and summer. This fungicide is manufactured by a number of companies and is widely available. Spraying provides one to two years protection. Spray when at least two rain-free days are forecast and there is little or no wind.
- Follow safety instructions on the fungicide label: wear protective clothing and spray downwind
- Equipment needed is a clean backpack sprayer, a surfactant, Phosphonate solution and water
- To make 10 litres of spraying solution
- using 20% Phosphonate solution
- mix 25 mL surfactant and
- 250 mL phosphonate, and
- fill with water.
Keep mixture well mixed while spraying, soaking the plants and ensuring all surfaces are wet.
You may need to apply for a permit for off-label use of the fungicide.