AusBonsai

MYRTLE RUST, aka - The Dirty Mirty.

Rory's history:

A few years ago, I had the unfortunate displeasure of being introduced to this horrible disease. It decimates certain native material in the wild and is unfortunately now considered endemic here on the central coast of NSW. It thrives in areas that lack sun, have high humidity and thrives on the family Myrtaceae. (Melaleuca, Eucalyptus, Corymbia, Callistemon etc, pretty much nearly all my favourite varieties). It can be devastating if not managed or dealt with quickly. Fortunately it has no known affects on Casuarina (thank goodness).

Rory's sadness at what it attacks:

I am to blame for the widespread attack on my collection a few years back , as I presumed at first it was just a slight dying off of leaves or burnt leaves and neglected to look into it further. It was about a good month later that I noticed the seriousness of the problem. Basically, it attacks the foliage first, which you don't realize is as serious as it can be. It just looks like the foliage is slightly browning off. But it essentially is getting a stronger foothold on the tree. I don't grow a lot of the species that are on the list, but from my experience, I can tell you.... the first ones most likely to die are Melalueca. It is ruthless on these, then the Eucalypts and Callistemon, and then others. The Mels just seem to have no resilience at all to it. Mel Quinquinervia was the most hardy at fighting it. Every other Mel had very little hope of fighting it. I lost 6 different varieties of Mels due to the Dirty Mirty. Of the Eucalypts, Eucalyptus crebra was also very affected and died quite quickly. Eucalyptus saligna was very strong against it, but robusta was not very tolerant. Corymbia were quite strong against it, and seem to respond quite well to the Triforine spraying too with little side effects.

Rory's plan of attack:

So, thinking the best form of defence was to attack, I rang local nurseries and found out their solution to the problem. I Quote "oh, that's the easy part, just throw away the infected stock and spray the rest". Okay, so not very helpful. I rang the exotic pests hotline, and they were more helpful, she advised that I will probably lose the Mels and Cals, depending on how long the disease has been on them for. Remove ALL affected areas, over a spread newspaper or something to catch the disease if it falls, then spray with Triforine every 2 weeks for many, many months and then to reduce down to spraying every couple of months and then once every 3 months and should completely kill it off. Obviously bag the newspaper with the affected material in a tight bag for 8 weeks too. So I did this, and yes, many of the Mels died. So too did the Eucalypts and one Corymbia. I sprayed every 2 weeks like she said, (not full strength), I sprayed at 20% - 30% strength diluted with water. It can seriously harm or deform new growth, depending on how new the growth is. But not spraying and waiting for new growth to harden is not an option if you want the tree to stand any chance at all.

Rory's advice on what to look out for:

More often than not, you will probably just have rust, and not Myrtle Rust, but in case you do, this is to help you.
So, if you have a period of continual rain or humidity, it fuels the disease and spreads it further and faster. Lack of sun also is a booster for this disease. Hence why the central coast has such a high rate of it occurring. So, what sets it apart from normal rust is that the pustules you will see that form usually underneath the leaf is quite unusual, and looks like puffy yellow wattle. These puffy yellow spores are very fragile and if you flick it or bump it, it releases clouds of this yellow spore of doom, which will spread the disease further to other trees. Hence why some horticulturists will simply recommend bagging the plant for 6 weeks to kill it completely. However, for bonsai this is obviously not a recommended option. You need to remove ALL affected foliage and ALL affected branches, which can sometimes mean a complete defoliation. If you have branches you don't want to lose, spray a sponge with the triforine and wipe away the affected area and you will have to do this continually every 2 weeks as well. Then a 2 weekly spray cycle, which will inevitably harm the new growth when it shoots, so try to wait a week after the new growth has appeared before the next spray of Triforine if you can help it.
If it has really got a foothold, it will look like a thickich film of the gunk (about 1mm thick) all along the branches in random areas.

So, in summary: Place the affected tree into the sunniest position you have, don't over-water the stock and spray the stock every 2 weeks with Triforine. Spray the soil as well. Bin ALL affected foliage or trees that are beyond saving into a garbage bin, and keep it completely air tight and tied up and in the dark for 2 months, to completely kill the disease inside the bag. Then bin this in the green waste, otherwise you will spread it further into your community.

Images of the disease:

http://www.dpi.nsw.gov.au/biosecurity/p ... ge-gallery

Notes about the disease:

http://www.dpi.nsw.gov.au/biosecurity/plant/myrtle-rust

List of affected species:

https://www.anbg.gov.au/anpc/resources/Myrtle_Rust.html

Gday Rory
I too have been battling myrtle rust for the last couple of years
I found spraying with full strength triforine early in spring and then about every 3 or 4 weeks keeps it at bay.
Unfortunately this year it started early so I had a fair few pustules present when I noticed it ( on a weeping mel) I have found I don't have to remove the infected leaves to get control -- I might have to spray two or three times at weekly intervals then I pick the most distorted leaves off and continue with my spray cycle.If I picked off the diseased leaves I would be doing the best part of a defoliation.the spray does affect the new growth but it is easily pruned after a couple of weeks.
Regards Steve

I will have to get some of that spray, even though my balcony turns into a BBQ in summer. Err on the side of caution I say.

Cheers Rory.

Gee whiz Rory
I can't believe we are the only people with the dirty mirty
Steve

Yeah, there might be others who just haven't commented. So far, moving my collection to a sunnier position and having sprayed and removed anything with infected signs has worked. I haven't seen any sign of the rust come back since about May/June. I did purchase two beautiful Melalueca from a nursery on the coast that had it ( I couldn't put them back), but I sprayed the bark out of them with triforine and had them in a secluded area and so far it hasn't returned ..... . Will be interesting to see how long my collection stays mirty free for. The problem with living on the central coast will often see the spores spread in the wind, so if you are closer to bush you are probably closer to infected areas.

It is kind of like trying to avoid the flu for humans - you can vaccinate, but it won't necessarily guarantee immunity.

Hi Rory
I keep getting it when I forget to spray!
I'm surrounded by a couple of thousand acres of bush so I keep getting the spores
Keep on spraying!
I found spraying once a month from now until autumn works for me although this year it hit a month ago
I think if people had it they would know - the pustules are unmistakable
Steve

I've had it in my trees. I've had a Bachousia citriodora (Lemon Myrtle) and Syzygium jambos, both in the ground, covered in it. 3 years of very dry winters and springs and both are going gang busters with no sign. No treatment. I also have a a Backhousia citriodora in a pot that has had it for the last 3 years and is the only tree originally infected that I have kept as it has a great nebari. Last year it was ok but this spring is showing signs again so I'll probably just ditch it. I have seen it in the bush around here quite a bit a few years ago and some trees covered in it. One I have checked out recently seems to have recovered. I can only put it down to the lack of humidity through winter and spring. The 3 years before that we had nearly double our annual rainfall. Will have to keep and eye out if we get a wet summer. About due for some more floods!

First saw it last year. Started as reddish circle on the leaves. Then came the yellow spots, mostly on the new growth. Then the yellow spots started to spread, first over the leaf then the branch then onto the leaves close by. It died off over winter especially after I cut off all the infected bits. I was told by a horticulturist that it is myrtle rust, a fungal disease from South America which only arrived into Australia (or was first noticed) in 2010. It has now spread from Sydney to Brisbane and is aggressively marching ever onwards. It is effectively changing the balance of the native trees and shrubs in the bush which will impact the animal life which feeds on or breeds in those trees.
It attacks plants from the Myrtaceae family- Eucs, coryimba, callistomans, Melaleucas etc. The many species in this group have varied resistance from completely unaffected to dead in a few weeks. As it spreads by spores you really can't stop it however you can prevent it by spraying with various anti fungal sprays. You need to spray every few weeks as the spores die within a few days of spraying however you get more spores with every breeze.
You may want to remember this story next time you take offence at being fumigated on a flight into Australia or have some of your items confiscated at the airport.

Also remember it next time you are tempted to buy seed from overseas.

I just tossed out two trees, a Mel. quinquinervia and a lily pilly. Both were infected with the myrtle rust and anti fungal spray had little if any effect. I don't think it is worth keeping trees that get smothered in air born fungal diseases that they are very prone to catching. I also have a NZ Christmas bush that had a few red circles on the leaves (these are the start - then comes the orange spores). This tree is not as prone to catching the fungus however I still need to keep a look out.
Not a happy camper!

EdwardH wrote:I just tossed out two trees, a Mel. quinquinervia

That is a shame. That species of Mel is usually quite responsive once it gets a full defoliation and scraping off of the infected areas. For mels you have to act early in the start of the progression. I would have done this if it were mine, just make sure you are using triforine, not a reuglar anti-fungal spray. A regular stock shelf anti fungal spray probably wont do anything to the Myrtle Rust.

You can buy triforine from bunnings or probably specialty nurseries. Though more likely bunnings, which is the only place I found it at.

I work with the Lismore Rainforest Botanic Gardens and have recently been spraying our collection of the family Myrtaceae with Triforene in an attempt to contain the damage from Myrtle Rust. Our approach has been to fertilise and spray in spring as new growth emerges and repeat until the new growth has hardened. I am reluctant to spray beyond this because of the damage copper based fungicides pose to earth worms and soil health. In general we have found that all of our plants have benefited from this regimen and are surviving and putting out new growth.
Now all of our plants are in the ground and largely unpruned so anything I say may be less applicable to bonsai (and other container plants) but there are couple of observations which I think can be applied more generally. The first is that I find Triforine to be effective against Myrtle Rust. On all the trees I have sprayed over the past month the live rust has disappeared and new growth which has emerged has been vigorous and healthy. The second is that the most susceptible species in our collection are the Rhodamnias and Rhodomyrtus. Both are important bird foods and could become extinct, or extremely rare in the wild. Some Gossias and some species of Syzygium are also very susceptible to damage. We've had less damage to our Melaleucas, Callistemons, Corymbias and Eucalyptus.
I got a few members of the Myrtaceae in my bonsai collection and haven't had any problems as yet even though several Rhodamnia rubescens (Scrub Turpentine) on my property have suffered very heavy damage from Myrtle Rust.
I note that some commentators have said that Myrtle Rust thrives in sheltered, shaded and humid environments but my own observations would tend to contradict that. I have a stand of Rhodamnia trees on my property which would have to be related and thus genetically pretty similar and which vary in the level of defoliation from Myrtle Rust they show, and it is the more exposed trees which show the most damage. I suspect this is because the more sheltered trees have a healthier beneficial fungal community occupying the leaf surface, the more exposed trees less so, and thence the Myrtle Rust has more free space on which to propagate. I want to stress that I haven't done any real scientific trials on this aspect of Myrtle Rust and these are personal observations only... but I think there is still a lot to be learnt about how Myrtle Rust spreads, why some plants are more impacted than others and it's interactions with the native fungi and bacteria which occur on the leaves of native plants.

You can buy triforine from bunnings or probably specialty nurseries. Though more likely bunnings, which is the only place I found it at.

I'm surprised Rory There are at least 4 companies selling Triforine in Australia. I thought it was the most common Rose black spot spray and should be available at most nurseries. Maybe all your local outlets up there have sold out with the rust spreading through your area?

shibui wrote:

You can buy triforine from bunnings or probably specialty nurseries. Though more likely bunnings, which is the only place I found it at.

I'm surprised Rory There are at least 4 companies selling Triforine in Australia. I thought it was the most common Rose black spot spray and should be available at most nurseries. Maybe all your local outlets up there have sold out with the rust spreading through your area?

Haha, possibly, but when I first was told to acquire triforine, I remember the blank stares I got when I asked them for it at nurseries. This may also explain the melaleuca stock that I purchased later was infected with the dirty mirty. The bunnings at west Gosford had actually been hit with an outbreak of myrtle rust and they just binned all the infected stock. So this was possibly the reason why they also were quite knowledgeable on it.

In response to the previous poster, that is interesting that you say it had less impact on the same plant in a wetter more humid position. The recorded evidence thus far and what I have also been told from exotic pest hotline, combined with what is known online seems to all agree with the ehanced stage of the problem due to excess humidity and rain and damp periods. Perhaps the spores were simply on the plants in the sunnier position prior to the other area and you simply didn't notice. I wouldn't think we have imported 2 strains of the dirty mirty, but it will be interesting to see others' experiences.

Generally speaking, a tree exposed to more sun would usually be in better health than one in long periods of shade or dampness, depending on the species of course. But having moved all my stock to a sunnier position appears to have helped (obviously this is an assumption). It is also interesting that you say triforine has no ill affects on young shoots. I was using it at 20% strength initially and it killed / mutated all the brand new growth on my melaluecas as I sprayed when buds were bursting. What strength were you using? What Mel's were u spraying? How did you acquire the triforine, is there a specific brand you used that was just this or with additives?

I also thank you for your contribution as with bonsai it is essential that we all combine our experiences on this one. I'd love someone to have the magic wand solution..... Apart from not growing myrtacae, trials and success stories are needed.

"It is also interesting that you say triforine has no ill affects on young shoots. I was using it at 20% strength initially and it killed / mutated all the brand new growth on my melaluecas as I sprayed when buds were bursting. What strength were you using? What Mel's were u spraying? How did you acquire the triforine, is there a specific brand you used that was just this or with additives?"
I've been using Yates as it is provided free to us through a sponsorship deal. I am a bit surprised that you say you have applied it at 20%! The recommended rate is 14ml per litre or 1.4%. Could explain the damage to new to new shoots!