Soursobs

There is one sure thing about Winter for gardeners and that is the annual invasion of Sour Sobs! The big question is - how do you control them?

At this time of year, Sour sobs can be 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 only grow from May right through to September. According to Herbguide, over 1.25 million hectares of land in South Australia is infested with Sour sob. Unfortunately, there is no simple or fast way to get rid of them however, with persistence, 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 chiropractor's friend, the sour sobs, were deliberately imported from Tasmania, whither the beastly things had been introduced!”

When Sour sobs first emerge, they can easily be mistaken for clover. There are several ways to identify a sour sob 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 Sour sob. 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 that is attached to the root. At the right time in the plant's 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 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 sour sob weed produces, on average 1 bulb and up to 20 bulbils making them highly invasive and hard to control.

An interesting point to consider when tackling sour sobs is that each bulb or bulbil can only produce one sour sob. Once you remove the sour sob, then the bulb dies. In this way, persistent removal of the weed will eventually conquer it, especially if you remove it while it's a juvenile and has not yet formed its own bulbils.

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 ultimately exhaust the bulbs that already exist in the soil.

Removal methods could include:

1) Hand-pulling them. I know- It sounds like a ludicrous idea, especially if you have heaps of them. As will all removal methods, it will take a few seasons of persistence,  but it will absolutely do the job in the long term. The goal is that you remove sour sobs as they appear, so in that sense, it doesn't matter by which means you do that (e.g. hand pulling, chemical or otherwise). This method is especially good for those that don't want to use chemicals. 

2) Spot spray with a non-selective herbicide such as Glyphosate (Roundup/zero etc).  Be careful, as chemicals like this will kill everything they come into contact with

3) Try a selective herbicide mixed with a wetting agent. such as Amgrow Bin-Die. Selective herbicides will target the weed and won't harm the lawn, provided that you spray at the recommended rate. Mix a wetting agent with the chemical for better results - use about 5-10ml per 5 litre mix you make up. You'll need to spray at least 3 times at monthly intervals to have any success with this method. 

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.  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. 

Persistence is the key. However you choose to remove sour sobs, do it often in order to win the battle. Expect to continue to treat for sour sobs for 2-3 seasons in order to achieve any level of control.  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.