I am often asked "does my sick tree have Phytophthora"?
Phytophthora (dieback) is a type of fungus that infects plant roots and surrounding soil. Phytophthora cinnamomi is the nastiest type of this fungus in Western Australia, as it kills many plants. This is especially true for our native flora, where high susceptibility means many endangered plants and communities are threatened, but is also true for our garden plants including fruit trees - avocado and papaya being particularly susceptible. Phytophthora cinnamomi was introduced from south-east Asia and is considered (like the cane toad) one of the world's worst alien invasive species! Phytophthora cinnamomi spreads most easily by water-carried spores and in moist soil, and new infections will peak when soil is wet and there are puddles of standing water.
Symptoms of Phytophthora cinnamomi infection can often be confused with other diseases and deficiencies, so the best way
to prevent infection and spread is professional testing. Samples for testing can be collected professionally or by the block owner - here I am sampling from a sick Banksia. I am
looking just below soil level and under the bark for the characteristic cinnamon brown discolouration showing the disease front. Recently infected trees may have this disease front in the
root zone, so roots may need to be investigated. Soil is also sampled. Samples will then be taken to our labs for testing.
There are many advantages to a block owner in confirming Phytophthora cinnamomi presence: asick trees can be treated with phosphite, you can take action to prevent spread of the disease, and any new plantings can maximise use of Phytophthora-resistant varieties.