Soursobs

Author: Stefan Palm   Date Posted: 1 August 2018 

At this time of year, soursobs are a serious problem in lawns and gardens. Sour sobs 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 Sour Sobs 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 live cycle, it will detach from the main plant and produce a new plant 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.

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