Soursobs

Author: Stefan Palm   Date Posted: 20 May 2020 

I've done a few blogs on weeds over the past few weeks but there is one I need to talk about in some more detail. Soursobs have begun their annual invasion and we're getting a lot of questions on how to control them.

At this time of year, Soursobs  are a serious problem in lawns and gardens. They are one of the most common weeds in South Australia and are classified as a noxious species. 

They are seasonal and grow from May right through to September. According to Herbguide, over 1.25 million hectares of land in South Australia is infested with Soursob. Unfortunately there is no simple or fast way to get rid of them however with persistance, you can win the battle!

Most authorities on the subject agree that Soursobs were introduced into South Australia from South Africa in 1841, recognised as a weed in the 1850′s and by 1879 was a serious weed of wheat and gardens.

Geoff Manning writes in his Insight into South Australian History, “Aching gardeners will be enchanted to know that the chiropractors friend, the soursobs, were deliberately imported from Tasmania, whither the beastly things had been introduced!”

When Soursobs first emerge, they can easily be mistaken for clover. There are several ways to identify a soursob when it is young but by far the easiest is to pull one out. If the weed looks like clover and has a single, long, white, tuberous root, then it is almost certainly a Soursob. Of course, as they mature, they send up a familiar yellow flower which will give them away straight away.

What makes Soursobs so persistent is that they have bulbs and bulbils attached to their root systems. Most people have heard of a bulb but maybe not a bulbil. A bulbil is a small secondary type bulb which is attached to the root. At the right time in the plants life cycle, it will detach from the main plant and produce a new sour sob of its own. When the weed is physically removed, mown off or poisoned, the bulb and bulbils remain in the soil and simply send another stand to the surface which is less than outstanding news for anyone wanting to get rid of them. Each soursob weed produces, on average 1 bulb and up to 20 bulbils making them highly invasive and hard to control.

There are many methods of removal, some more effective than others. Eradication can take several years of repetitive removal, either by physical or chemical means before you kill off all the bulbs and bulbils in the soil. The aim of the game is to restrict the weed’s capacity to produce bulbils and to ultimately exhaust the bulbs that already exist in the soil.

My eradication tips would include:

  • Try not to let the weed excessively flower. This is when it is most likely to produce bulbils which of course leads to more weeds.
  • There are non-selective herbicides that can be used such as Glyphosate (Roundup/zero etc) to poison them. Another non-selective chemical to use against soursobs is metasulfuron methyl which is contained in products such as Esteem and Brushoff however if you use metasulfuron methyl, make sure you research the product thoroughly and attain a clear understanding of how, when and where to use it.
  • When it comes to controlling sour sobs in a lawn, there are no quick fixes. Regular mowing so that they don’t excessively flower is helpful . Spot spraying with glyphosate or metasulfuron methyl will help (be care full as these chemicals are non selective and will kill your lawn too). You can use selective control measures too such as broadleaf herbicides containing MCPA combined with bromoxynil.
  • Persistence is the key. However you choose to tackle soursobs, do it often in order to win the battle. Remember that you will no doubt have an extensive collection of bulbs and bulbils that will progressively come up during the cold months. You want to kill these weeds before they produce bulbils of their own.

Comments (9)

Does adding soap to Bin-die help ?

By: on 29 May 2020
When spraying soursobs in a lawn with Bin-Die, does it help the uptake of the poison if you add a little dish detergent to the mix ?

Paul Munns Instant Lawn Response
Hi Steve Yes, you can add a few drops of it in the mix. This can help it stick to the leaf for better results

How to get rid of soursobs in a lawn of couch gras

By: on 10 May 2020
My lawn in mainly couch grass, kikuyu and over a week soursob came to the surface. I do not wish to kill the couch grass/kikuyu with Round Up but would like to control the soursob. What is the best way to control the soursob without harming the lawn?

Paul Munns Instant Lawn Response
Hi Don Thanks for your query You can use a product called Amgrow Bin-Die killer. This won’t hurt your Couch/Kikuyu lawn but will control the soursobs and other broadfleaf weeds. The product will need to be applied every 2-3 weeks until you exhaust it out of the lawn. One application won’t be enough as the soursobs have multiple bulbs. Thank you Andrew

Spot spraying with glyphosate

By: on 8 May 2020
Hi I have soursobs coming up everywhere in my very poorly santa anna couch lawn which i have overplanted with 30cm x 30cm patches of kenda kikuyu (which is going well thanks!). Would it be okay to spray some of the worst patches of soursobs with some glyphosate and put up with the dead patches knowing that good old rock solid kikuyu will get in there eventually and fill the holes? Maria from Glenelg North

Paul Munns Instant Lawn Response
Hi Maria Thanks for your query I would recommend using a product called Amgrow Bin-Die killer. This is safe to use on Kikuyu and Couch and will control soursobs in your lawn. As soursobs have multiple bulbs you just need to repeat the spray every 2-3 weeks until it is exhausted out of the lawn. Hope this helps Andrew

Paving an area where sour sobs had been growing

By: on 5 October 2019
We had a 63 square meter area paved. The paving guys didn’t poison they said there was no need to. 1 month later the pavers were moving and had risen. When they pulled them up there was a mass of white roots from the sour sobs underneath which had made nearly all the pavers move. We have poisoned the ground many times with round up and no sour sobs have come through. Worried that we will have paving redone and the same will happen again due to the roots being so far down. Not sure what to do. Can you please help.

Paul Munns Instant Lawn Response
Hi Chris Thanks for your query You can try a product called Bantox. This controls weeds and grasses and also prevents them from coming up long term for a few seasons Hope this helps you out. Andrew

Is now too late

By: on 9 August 2019
Hi! Is now a good time of year to try to tackle the sour sob invasion? They’re everywhere at my place and I’m not sure if I should leave them to just die later to try to spray and eradicate them now? Thanks!

Paul Munns Instant Lawn Response
Hi Marianne, It's not too late to tackle sour sobs. Because it can take up to 3 Winter seasons to get on top of them, you should definitely start now. The longer you leave them untreated, the more they will multiply.

Is a flame Weeder an effective method of controlli

By: on 2 August 2019
Hi I'm not trying to contain them in lawn but in other area's and paths....is a flame Weeder an effective method of controlling soursobs? IE will the heat effect the bulds/bulibils? I don't have one but would consider getting one if it was an effective treatment

Paul Munns Instant Lawn Response
Hey Simon, Using a flame weeder will kill off the sour sob plant above the surface but will not have any effect on the bulb or bulbils. Like most control strategies with Sour Sobs, you will need to continually remove the surface plant until you have exhausted all the bulbs and bulbils in the soil.

Soursobs

By: on 2 August 2019
We had soursobs throughout a block of land we bought at Middleton (along with almost every other weed known to mankind, including Apple of Sodom!) We have landscaped exclusively with Australian natives, including the lawn which is a variety of Wallaby Grass. Mulching helps in the garden as the soursobs grow long stems before the rosette of leaves develop, making them easy to hand pull. In the lawn, we also handpull/cut below the rosette. We did this just before they flowered over the past two years, and it has made a definite difference. This year it hasn't been as big a job - just keeping an eye out for the first glimpse of yellow, and out it comes. Good hygiene is important. The pulled plants go straight into a bag or bucket and into the bin, just in case there are any bulbils or seed. No, there is no easy fix, and it requires persistence, probably for years(!), but I think we're winning...

Paul Munns Instant Lawn Response
Hey Iris, Thanks for your comments on our blog. You’re definitely on the right track – your approach will definitely see you win if you keep at it!

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