Thursday, July 14, 2011

Myrtle Rust Reaches Toowoomba

I saw my first case of Myrtle rust this week.
I hadn’t expected to see it in the Toowoomba area until spring. Our typically cold, dry winter would slow it down, and I thought we would be able to enjoy a brief respite before it started to spread in earnest with the warmer weather and the first summer rains.

Here it is already, however, at a friend’s place at Mt Kynoch.

It is on a malabar apple Syzigium jambos, a species which is already known to be particularly susceptible to the rust. Malabar apple has been brought to Australia from south-east Asia, and is grown for its edible fruits and its creamy powder-puff flowers. Closely related to our native lillypillies, it has become an invasive weed in some areas.
Myrtle rust is still so new to Australia (it’s only been known here for 14 months, though it may have gone undetected for a year or two before that) that we don’t know, yet, to what extent our various local native plant species will be affected. Some have already proven to be very susceptible, others less so.
One thing we do know, is that the disease is so easily spread, by insects and the wind, that it is inevitable that it will find every susceptible plant in Australia no matter what we try to do to prevent it.
Myrtle rust is restricted to members of the myrtle family (Myrtaceae). They are all trees or shrubs, so a disease which affects them has the potential to have a major impact on the Australian landscape. The likelihood is that it will make mature plants look ugly, and affect seedlings badly. A worst-case scenario is that seedlings will die en masse, and extinctions of more susceptible species will result.
Plants from this family have been very popular in gardens. The rust is going to affect the decisions we make about what we plant. We will also find ourselves deciding to remove many of them, and replace them with plants from some other family.
So far, myrtle rust has been identified on 73 Queensland species. Unfortunately there are likely to be still more species affected.
Here is a site that gives advice about what to do if you find myrtle rust in your garden.
Don’t overlook the importance of reporting affected plants to Biosecurity Queensland on 13 25 23. They can’t prevent it or cure it, but their research will be our future guide as to what Myrtaceae are really worth planting in our gardens.
To this I would add that I believe home gardeners have a responsibility not to let their plants act as carriers which might make a bridge for the fungus to reach native bushland or commercial growers whose livelihoods are under threat.
There are some plants which I think we should remove even if they are not yet infected. I leave it to you to decide which ones, but they would obviously include any Myrtaceae that we just don’t love very much, particularly those which are still small enough to remove easily. Perhaps they should include any others of species which are already known to be very susceptible. Realistically, we have to accept that these plants’ period of beauty will end shortly, and they are certainly easier to dispose of without spreading infection if it’s done before they get it. The sooner they go, the sooner we can be planting something in their place.
There are others which we should remove as soon as they show symptoms. These certainly include the very susceptible ones. No matter how hard we fight to save them, they are always going to be reinfected. We might as well bite the bullet sooner, rather than later. It will save quite a bit of effort and money which might be put into pouring poisons into the environment to no purpose.
(Note the DPI advice on how to dispose of infected plants )
So am I.
I try to cheer myself up with the thought that only 10% of Australian plants are in the Myrtaceae family. Those popular Grevilleas and other Proteaceae will be unaffected, and there are a great many garden-worthy plants from other families which have never even been tried in our gardens.
Meanwhile, some Myrtaceae may prove to be resistant. I find it reassuring that there are no Eucalyptus species on the list so far. I hope I am not being premature.

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