Phytophthora

Jonathan Garner dishes the dirt on soil-borne identities.

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Are some of your plants looking unwell? Are any completely dying back? Maybe just certain branches? Are the branches and trunks discoloured, splitting or oozing sap? Is healthy fruit rotting on the plant?

Sounds like you might have a soil-borne disease.

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As the name suggests, soil-borne diseases are plant illnesses caused by fungi, bacteria, water molds and, occasionally, virus. They live in the soil and infect plants through their roots, shoots or the base of stems and trunks. Most are cunning and quite difficult to manage. In many cases they are impossible to eradicate. Some rely on spreading by hitching a ride with soil pests like microscopic eelworms (nematodes), but most diseases are spread over distances by our dirty work boots, tools, machinery or anything else that can relocate soil from one place to another. Once they're in a new garden, they travel easily through water and adore wet, oxygen-starved soil.

We don't have enough time to tackle all of them, so let's focus on the most destructive plant disease in Australia.

Phytophthora

It's a mouthful to say and easily misspelt. Most of us have heard of it but what's it all about?

The name, when translated from Greek, means 'Plant Destroyer' and that says it all.

It's a diverse genus of around 200 species worldwide and around 60 have been detected in Australia. All species are introduced, which means virtually none of our native plants have resistance to the aggressive nature of the disease.

As this is an introduced organism, our native ecologies have little or nothing to control the disease (think feral cats and cane toads). These diseases are relevant to our workplace, many of the popular native plants such as Banksias, Grevilleas and expensive Xanthorea (Grass trees) have little resistance. In fact, most ornamental plants are susceptible to at least one of the many species of the Plant Destroyer.