Friday, October 28, 2011

Killing Typhoid Mary

I found myrtle rust in my garden yesterday.

We knew it was coming, of course, and I had been keeping a special eye on my brown malletwoods (Rhodamnia dumicola).

Although almost all members of the myrtle family (Myrtaceae) can potentially be affected by this nasty disease, I was aware that my malletwood is one of the most susceptible species, likely to be my “miners’ canary” for myrtle rust.
Having seen the new disease a few months ago in a nearby suburb (see posting on myrtle rust, July 2011) I had anticipated that it would probably arrive at my place, blown by spring winds, when the weather warmed up. So I was saddened but not surprised to find it infesting two little malletwoods on the eastern side (the upwind side) of our block. Only last week I posted new photos of them, in blooming good health. This week, hundreds of leaves were heavily infected!
A third plant in a somewhat more sheltered spot to the west of the block is (as yet) clean.
I rang Biosecurity Queensland and reported it. (They still want us to report new sightings at 13 25 23). Then I looked at the website which advises us on what to do with infected plants.
The site offers householders a choice of options ranging from taking no action at all, through the use of fungicides, to removing healthy plants as a preventative measure.
Because malletowoods are so very prone to myrtle rust infection, I decided that the plants should go, but cutting them out this morning has made me feel quite miserable!
I don’t plan to remove all infected species in the future, but in the case of these very susceptible plants I felt that attempts to save them by spraying with poisons would probably always be followed rather rapidly by reinfection. I just don’t want a heavily diseased plant in my garden - a continuous source of copious quantities of rust spores putting all my other Myrtaceae at risk (not to mention those of my neighbours, with whom I would rather be on good terms).
I went and contemplated the healthy malletwood, but couldn’t face the thought of removing it today after the emotional stress of cutting out the other two.
I probably should, though.

The Miners’ Canaries
There has been a lot of research done on myrtle rust since it was first found in Australia last year. There is a potential for it to infect almost all of the Australian species of Myrtaceae.
So far, over 100 species have been affected in the wild. There are likely to be many more plants which will suffer to a greater or lesser degree, and growers of Australian natives should become aware which of the plants in our gardens are members of the Myrtaceae family so we know where to look for the disease.
Scientific testing has been established that some species (such as the malletwoods) are very susceptible, some only moderately so, and a few species seem to be immune to it.
If we are looking for it in our gardens, the plants to check most regularly are the most susceptible ones. Some plants known to be badly affected are:
Willow Myrtle Agonis flexuosa (including cultivars “Afterdark”, “Burgundy” “Jedda’s Dream”)
Brown Myrtle Choricarpa leptopetala
Silky Myrtle Decaspermum humile
Beach Cherry Eugenia reinwardtiana
Thready-barked myrtle Gossia inophloia (with popular cultivars like “Blushing Beauty”)
Broad-leafed paperbark Melaleuca quinquenervia (our most familiar paperbark)
Malletwoods Rhodamnia sp. (also called scrub turpentines)
Native Guava Rhodomyrtus psidioides
Aniseed Myrtle Syzygium anisatum (Backhousia anisata)
Rose Apple Syzygium jambos (not native)
Water Gum Tristania neriifolia
Southern penda Xanthostemon oppositifolius
Sadly, these are likely to be plants which may become unpopular in home gardens, because of their higher susceptibility to the ugliness of myrtle rust.

Myrtle Rust Immunity
Early this year I decided not to plant any further Myrtaceae in my garden until more was known about myrtle rust. I had been hoping to hear that some of our locals might be found to be immune to it
The bad news is that the more it spreads, the more species are found to be susceptible.
The good(ish) news is that some plants, though they are infected, are not too badly damaged by it. Seedlings cop the worst dose, though, and we still don't know whether it will affect these species' ability to have babies.
The best news is that 11 species have so far been found to be immune. It’s not many, compared with the plants that have succumbed, but it’s better than none!
They include three locals - Brush box, Lophostemon confertus, Swamp Box Lophostemon suaveolens, and Gum-topped box, Eucalyptus moluccana.
Those of us who have been avoiding planting any new Myrtaceae can now go ahead with these species, happy in the knowledge that they are likely to continue in good health.
In the case of the gum-topped box, the koalas will be pleased, too.


koolkatquilting said...

Here's hoping this disease doesn't cause too much set-back to the willingness of people to plant Myrtaceae. Thanks for the info on resistant species. I guess we have to hope we get our trees and shrubs sufficiently advanced to live with ravages of the disease. Geoff, Crestview Crescent, Blue Mountain Hts.

Patricia Gardner said...

Hi Geoff.
Yes, it is a problem to know what is the best course, isn't it? My willingness to plant the most vulnerable species may not have been quite killed, but has definitely gone into suspended animation for the time being.
With some of the other Myrtaceae it may take considerable persistence by gardeners to nurse them through the vulnerable baby stages. I'm with you in hoping that there are plenty of native plant lovers who are willing to do this.
Meanwhile, it could be time for growers of Australian native plants to review the species that are most popularly grown in gardens. Till now, there has been an over-heavy emphasis on growing plants from just a few families. This disease could be the stimulus for some broadening of scope. Imagine what would happen if we got another disease which attacked Proteaceae! There would be few Australian plants left, in some gardens. Myrtaceae is a major family, but there are lots of others, containing lots of desirable plants.