Winning the War Against Sour Sobs in South Australia

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?

In Short: Sour sobs (Oxalis pes-caprae) are one of South Australia's most common and invasive winter weeds. They spread underground via bulbs and bulbils, making them difficult to eradicate quickly. Early identification is key—juvenile plants resemble clover but have a distinctive white tuberous root. Soursobs are much easier to kill when they are juvenile. Persistence pays off: repeated removal before flowering will gradually reduce infestations. Control options include hand-pulling, selective herbicides, and regular mowing to prevent flowering. Full control can take 2–3 seasons, but it is achievable with a consistent approach. Chemical-free options are available for gardeners who prefer not to use herbicides. You’ll need to treat them multiple times during the growing season (May–September) to break the cycle.

 

According to Herbguide, over 1.25 million hectares of land in South Australia are affected by sour sobs. Most experts agree that they were introduced from South Africa in 1841, and by 1879, they had become a serious agricultural pest. Geoff Manning, in Insight into South Australian History, humorously notes that they were “deliberately imported from Tasmania, whither the beastly things had been introduced!”

How to Identify Sour Sobs

When sour sobs first emerge, they can look deceptively like clover. The easiest way to tell them apart is to pull one out. If it has a single, long, white, tuberous root, it’s almost certainly a sour sob. Once mature, they produce the familiar bright yellow flower, which is a dead giveaway.

Why They’re So Hard to Kill

The resilience of sour sobs lies in their underground survival structures—bulbs and bulbils. While bulbs are well-known, bulbils are smaller, secondary bulbs that detach and produce new plants. Each weed can generate up to 20 bulbils, making them extremely invasive. Even if you remove or poison the main plant, the bulbils often remain dormant in the soil and sprout later.

However, here’s the good news: each bulb or bulbil can only produce one plant, and once that plant is removed or dies, the source is exhausted. This means persistent removal really works—especially if done before the plant matures and forms its own bulbils.

Control Methods: What Works and What Doesn’t

There’s no silver bullet for removing sour sobs, but there are several effective strategies you can use:

Hand Pulling

It might sound crazy—especially if your lawn is full of them—but hand-pulling can be extremely effective. Do it regularly before the weeds flower and form bulbils. It’s a great method for chemical-free gardens and provides long-term results if you're consistent over multiple seasons.

Spot Spraying with Non-Selective Herbicides

Products like Glyphosate (e.g., Roundup or Zero) can be effective but must be used with care—they’ll kill anything they touch, including your lawn.

Using Selective Herbicides

Using selective herbicides on Soursobs isn't a direct way of controlling them, but it will help slow them down and can eventually get rid of them. For lawns, use a selective herbicide like Bow and Arrow, which targets broadleaf weeds without harming grass. Always mix with a wetting agent for better absorption and apply monthly for at least three treatments. Soursobs are painfully slow to react to herbicides, so be patient.

Regular Mowing

Preventing flowering is crucial. Once the weed flowers, it’s much more likely to form bulbils and spread. Regular mowing helps stop this reproductive cycle.

Patience Pays Off

Whichever method you choose, persistence is key. You’ll need to treat sour sobs across 2–3 winter seasons to significantly reduce or eliminate them. Expect a steady emergence of new weeds throughout the cooler months as existing bulbils germinate.

Remove them before they mature, and over time, you’ll dramatically reduce their population.

Need Help? Let’s Chat!

At Paul Munns Instant Lawn, we understand how frustrating weed control can be—especially with something as persistent as sour sobs. If you'd like tailored advice or help choosing the right herbicide, feel free to call us on (08) 8298 0555 or email info@paulmunnsinstantlawn.com.au.

Frequently Asked Questions About Sour Sobs

• Q: What’s the best time to start treating sour sobs?

A: The best time is as soon as you see them emerge—typically in May or early winter. Acting early prevents them from flowering and producing more bulbils.

• Q: Can I get rid of sour sobs in one season?

A: Unfortunately, no. Due to the presence of bulbs and bulbils in the soil, full eradication typically takes 2–3 seasons of consistent treatment.

• Q: Will regular mowing help control sour sobs?

A: Yes. While mowing won’t kill them, it helps prevent flowering and the formation of bulbils, which is critical for long-term control.

• Q: Are selective herbicides safe for my lawn?

A: Yes, provided you use lawn-safe selective herbicides like Bow and Arrow, applied at the correct rate and with a wetting agent for better absorption.

• Q: What’s the difference between a bulb and a bulbil?

A: A bulb is the main underground storage organ, while a bulbil is a smaller offshoot that forms on the root and can grow into a new plant. Each sour sob plant can produce up to 20 bulbils.

• Q: Is hand-pulling really effective?

A: Absolutely—especially in small infestations or garden beds. If done regularly before the plants flower, it helps exhaust the underground bulbs and stop future growth.

• Q: Why do they keep coming back even after I spray them?

A: Most likely, you’re seeing new plants sprouting from leftover bulbils in the soil. That’s why repeated treatments across multiple seasons are necessary to fully control them.