Getting rid of Oxalis from your pot

We have some unique pests to deal with in Australia. Post your experiences and treatments here for others to learn from.
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Phil Rabl
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Getting rid of Oxalis from your pot

Post by Phil Rabl »

Here is a photo of a piece of Oxalis (don't know the species - apparently there are 500 or so species) that I weeded from a bonsai pot the other day. Look at the length of the tap root!!
IMG_1521.jpg

I recently moved from Canberra, where this @*#% weed is a real pest. Almost impossible to eliminate from gardens and very difficult to get rid of if it gets into your bonsai pots. I don't seem to have Oxalis in my new garden in Ballarat so I am going to make a big (lockdown project) effort to weed it out and stop it from escaping into the garden. It will re-shoot from bits of broken root and from little bulb-like nodules it grows on its roots.

Just thought I would share this. And if anyone has a good plan for killing it, please let me know.
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Re: Getting rid of Oxalis from your pot

Post by Jow »

It can be a problem in Ballarat too ;)

Glyphosate seems about the only solution.

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Re: Getting rid of Oxalis from your pot

Post by treeman »

Yep, paint it with glyphosate
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Re: Getting rid of Oxalis from your pot

Post by Phil Rabl »

I am sure glyphosate will do the job. But I am very cautious about using glyphosate in my pots and I am even moving away from using it in the garden. There are two main reasons: first, the possibility that it can cause cancer (there was a $10 billion lawsuit in the US a few years ago); and second the fairly large body of scientific studies that show glyphosate can accumulate in soil and be taken up by other plants.

The following quote comes from an article on the US National Institutes of Health website titled Glyphosate: Its Environmental Persistence and Impact on Crop Health and Nutrition. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6918143/

“Another potential route for glyphosate accumulation and stabilization in soils is represented by the release of glyphosate from plant residues of glyphosate-treated weeds. As glyphosate is fairly stable and not immediately metabolized in many plant species, substantial amounts can be extensively translocated to regions of active growth and accumulate, particularly in young tissues. After weeds eventually die, it ends up in the soil following the decay of plant parts. … From the soil, glyphosate may also be reabsorbed by the target or non-target plants back through the roots after the initial application.”

There does not appear to be much evidence that other plants (such as the bonsai) will take up glyphosate at fatal levels, but there is mounting evidence that plants adjacent to the sprayed plants lose vigour. So, I will only use glyphosate in my bonsai pots by carefully painting it on to the leaves of the weed. I will never spray. And I will only use it where the weed is unable to be dug out.
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Re: Getting rid of Oxalis from your pot

Post by shibui »

Copper oxalis is a weedy pest of pots and gardens all over.
That tap root is probably not. Much more likely a stolon sent out from the mother plant. New plants from the end of stolons is one way this plant propagates itself. Explosive seed pods is another way it spreads. Seeds can fly several metres when the ripe pods burst.

The only way I have been able to beat it here is paint glyphosate on the leaves. I try to get even the very smallest before they get a chance to flower or send out runners. I've just found 3 copper oxalis plants this year after a 6 year war on weeds so it is possible to get on top of it but you will need to be vigilant and persistent.

Another strategy you could try if you really don't like glyphosate is to constantly pull anything above ground. No plant can live forever without leaves and they should gradually weaken and eventually die. The problem with this strategy is that few bonsai growers are as persistent as copper oxalis so the weed usually wins in the long run.

Obviously remove as much of the plants as possible when repotting so there is less to work on through the season.

Another little known herbicide is spray on personal insect repellent. I've tried several different brands with different active ingredients and they all seem to kill weeds within hours. Not sure why or how it works but it does. I'm guessing it is just has a contact effect so persistent weeds like copper oxalis will just come up from the roots afterwards but it may give you enough breathing space to keep them in check until you can use another strategy. The big problem is that we do not know any side effects or long term problems. I have not seen any affect on non target plants so far but I have not used much or very often.

:fc: for your war on oxalis Phil
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Re: Getting rid of Oxalis from your pot

Post by Beano »

I second the spray on insect repellant. Don’t get it on your bonsai leaves though - it won’t kill the tree but the leaves will be burnt and look unsightly. No good on a windy day.


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Re: Getting rid of Oxalis from your pot

Post by Phil Rabl »

Very interesting about the insect repellents. Thank you. I am going to have a guess as to what is going on.

A couple of years ago I needed to get rid of a huge flourishing of marshmallow in a horse paddock. I wanted something that acted quickly and didn’t require keeping the horse out of the paddock for an extended withholding period. My research came up with LocalSafe Weed Terminator. It is manufactured in Melbourne. It is acid-based and works by quickly drying out the leaves. The marshmallow wilted within minutes and was effectively dead the next day. Oh, and the horse went back into her paddock after only two hours. Here is a link to the LocalSafe manufacturer: https://www.contactorganics.com.au/loca ... HeEALw_wcB

Since the insect repellent kills the weed in a couple of hours, my guess is that it desiccates the leaves like LocalSafe does. I’m going to try it.
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Re: Getting rid of Oxalis from your pot

Post by shibui »

We used a pine oil bio-herbicide in the local community garden for a few years. It also desiccates the leaves quickly but not sure of the exact process.
The biggest problem was that it also dissolves rubber and plastic seals in the sprayers.

Note that all these treatments are non selective. They will affect any leaf they come in contact with so need to take care when spraying near plants you want to keep. On the positive side they should not be systemic so if there is some accidental over spray it should only damage the leaf it touches rather than the entire tree
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Re: Getting rid of Oxalis from your pot

Post by Jow »

Phil Rabl wrote: September 16th, 2021, 5:44 pm I am sure glyphosate will do the job. But I am very cautious about using glyphosate in my pots and I am even moving away from using it in the garden. There are two main reasons: first, the possibility that it can cause cancer (there was a $10 billion lawsuit in the US a few years ago); and second the fairly large body of scientific studies that show glyphosate can accumulate in soil and be taken up by other plants.

The following quote comes from an article on the US National Institutes of Health website titled Glyphosate: Its Environmental Persistence and Impact on Crop Health and Nutrition. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6918143/

“Another potential route for glyphosate accumulation and stabilization in soils is represented by the release of glyphosate from plant residues of glyphosate-treated weeds. As glyphosate is fairly stable and not immediately metabolized in many plant species, substantial amounts can be extensively translocated to regions of active growth and accumulate, particularly in young tissues. After weeds eventually die, it ends up in the soil following the decay of plant parts. … From the soil, glyphosate may also be reabsorbed by the target or non-target plants back through the roots after the initial application.”

There does not appear to be much evidence that other plants (such as the bonsai) will take up glyphosate at fatal levels, but there is mounting evidence that plants adjacent to the sprayed plants lose vigour. So, I will only use glyphosate in my bonsai pots by carefully painting it on to the leaves of the weed. I will never spray. And I will only use it where the weed is unable to be dug out.
You are absolutely right, Glyphosate should be used with care but sometimes it is the only thing that gets the job done. I used to work with a council and people got so fixated on glyphosate when the contractors were spraying much worse stuff on a daily basis (Grazon, garlon etc). While i don't think you should be blasé with glyphosate I think the risk is Ok prepared you manage it wear a mask, cover up and manage overspray concentration etc.

I think you will struggle to eradicate certain weed species without it.

Its worth noting that most things we spray on bonsai are not great for you. Lime sulphur is not great for you not to mention pesticides and fungicides. When ever using any product you should take appropriate precautions.
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Re: Getting rid of Oxalis from your pot

Post by austindrake »

Thank you everyone for the detailed summaries/experiences. Oxalis had become quite a problem for both my trees and my lawn in the backyard last year, and during my bare-rooting this year I was flabbergasted at how pervasive it's roots were in my trees. I kept pulling small taproots out of the root-balls of my trees and thinking to myself, 'surely that's the last of it' only to find another taproot on the other side, and another, and another!
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Re: Getting rid of Oxalis from your pot

Post by greg27 »

I wonder how effective something like Slasher would be against oxalis - a bit of a less-aggressive method than glyphosate.
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Re: Getting rid of Oxalis from your pot

Post by Alan Peck »

Try a zap with Aeroguard, works on everything else that you cant get at between the nebari roots.
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Re: Getting rid of Oxalis from your pot

Post by melbrackstone »

Just an FYI, if you have oxalis in your lawn, and it populates the edges where you use a whipper snipper, you're likely to be spreading it far and wide every time you do the edges. I've learned this the hard way....hopefully it'll stop it happening in your garden.
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Re: Getting rid of Oxalis from your pot

Post by Akhi »

I tend to ignore it :-) take off the leaves when they show up.
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Re: Getting rid of Oxalis from your pot

Post by Phil Rabl »

A couple of days ago, I bought some Aeroguard and sprayed it (lightly) on some Oxalis that was all tangled up in the roots of a corky bark elm. The Oxalis wilted within minutes, and two days later appears to be dead. It will be interesting to see if it re-shoots. Thanks for the tip people.
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