High-threat Merri weeds - call the professionals

Weeds are one of the most visible and familiar threats to the health of Merri Creek, and one that countless hours are spent battling every year. 

Following on from FoMC President Nick Williams’ previous article on woody weeds, in this article we take a look at some requiring a co-ordinated and professional approach to achieve effective control and what this means for volunteers wanting to lend a hand.
Dedicated FoMC volunteers and individuals play a crucial role in slowing the spread of weeds, through both organised working group events and informal moments pulling out weeds on their regular creek walks. However, while even folk with limited experience can meaningfully contribute by hand weeding common weeds like Sow Thistle and Panic Veldt-grass, some of the more tenacious species on the Merri will require ongoing and specialised treatment to control. This is where the enduring partnership between the Friends and Merri Creek Management Committee (MCMC) comes in.

A key reason for MCMC’s formation was to provide a dedicated crew of skilled staff to develop and manage the Merri Creek Parklands. Green Links grant funding, received in 2024 has recently allowed the team to target several high-threat species along the creek. This is part of a broader project to connect existing areas of quality habitat between Northcote and Coburg. If you spent time on this section of the creek over summer, you may have seen our crew scrambling along the creek banks, or noticed signs warning you to avoid areas where herbicide has been sprayed, and wondered what we’ve been up to.

So let’s take a look at four of the most challenging species we’ve been working on and what makes them so difficult to control. For further detail, follow the links in species' names.

Wandering Trad - Tradescantia fluminensis

A trailing ground cover, with flimsy, succulent stems and oval to egg-shaped leaves, with pointed tips arranged on alternating sides. Flowers are white and arranged in groups, with three petals, yellow-tipped stamens and white filaments attached at a central point. Usually found in shady areas under trees and shrubs, large infestations smother entire sections of creek banks, leaving no space for other plants to survive. 

Challenges: Although it does not form seeds, in Australia Wandering Trad is exceptionally good at regenerating from small sections of stem. These can survive for up to a year without roots or soil contact. Segments readily break off and spread while hand weeding, as a result of flood events, or as people, animals or machinery move through infestations. Carefully timed herbicide treatments are effective, but repeated follow-up is required to completely eliminate. The steepness of the creek bank, proximity to water and sheer area to cover makes it particularly difficult to treat in many places along Merri Creek.

   
Image credit:  Wandering Trad - Tradescantia fluminensis, photos by Andre Messina.
 VicFlora (2026). Flora of Victoria, Royal Botanic Gardens Victoria.
Available online: https://vicflora.rbg.vic.gov.au (accessed on: 26 Mar. 2026). CC BY-NC-SA 4.0

Cape Ivy - Delairea odorata

Climber, or scrambler, with fleshy, semi-succulent leaves of varying shape, but generally with 7–9 points and an ivy-like appearance. Clusters of 15-50 small yellow flowers, each 2-3 mm wide and without petals. It is usually found climbing through shrubs and up tree branches in revegetated areas of Merri Creek. It can entirely smother smaller plants out if left unchecked. 

Challenges: Physically removing Cape Ivy plants can damage the native vegetation they climb through. Removal often results in small stem fragments being left behind, which can take root if they come into contact with soil. Unlike Wandering Trad, Cape Ivy also spreads by seed, which is plentiful and readily carried to new areas by wind, water or animals. Spraying foliage, or directly applying herbicide, to cut stems is effective, but thick native vegetation in some parts of Merri Creek makes it difficult to do so safely and without causing unwanted damage.

   
Cape ivy, Delairea odorata. Left, in flower; right, rambling over other vegetation, photos by Andre Messina.
 VicFlora (2026). Flora of Victoria, Royal Botanic Gardens Victoria.
Available online: https://vicflora.rbg.vic.gov.au (accessed on: 26 Mar. 2026). CC BY-NC-SA 4.0

Pampas Lily of the Valley - Salpichroa origanifolia

Scrambling, sometimes vine-like herb, with small, round and usually hairy leaves, 10-15 mm long, either in pairs, or alternating sides along stems. Nodding white bell-shaped flowers are attached where a leaf meets the stem, either individually, or in pairs. There are a few areas with denser infestations along the Merri, with occasional isolated plants in surrounding areas.

Challenges: The dense root system in Pampas Lily of the Valley is highly capable of reshooting, even where all above-ground parts have been poisoned, or removed. Complete manual removal of these roots is also not always possible on steep sections of creek bank, or in proximity to native vegetation. Herbicide application is showing initial signs of success on the Merri, but it is expected that at least some plants will continue to reshoot and require ongoing follow-up and potentially attempting physical removal were possible. Monitoring surrounding areas and removing isolated plants, before root systems get established, will help prevent further spread. 

   
Pampas Lily of the Valley - Salpichroa origanifolia. Left: photo by Andre Messina, CC BY-NC-SA 4.0. Right: photo by Neville Walsh, CC BY-NC-SA 4.0
 VicFlora (2026). Flora of Victoria, Royal Botanic Gardens Victoria.
Available online: https://vicflora.rbg.vic.gov.au (accessed on: 26 Mar. 2026). 

Blackberry - Rubus anglocandicans

Sprawling shrubs with upright, arching stems/canes covered in sharp spikes. Leaves alternate along the stem and consist of 5 smaller leaflets, arranged like a hand. Flowers with five white or sometimes pink petals in clusters at the ends of canes, followed by widely recognised fruit that changes from green, through red to black as they ripen. Blackberry is usually found on the edges of Merri Creek in wetter areas, often forming dense and impenetrable thickets. It can sometimes be confused with Rubus parvifolius, the Native Raspberry naturally found along Merri Creek.

Challenges: Anyone who has collected blackberries recreationally, will be familiar with the sharpness of the prickly stems and the difficulty of moving through areas when they constantly catch on your clothing. Unsurprisingly, hand-weeding is therefore not a viable option. In addition to being a physical hazard, dead stems often also obscure the fresh new growth that is most receptive to herbicide. As with some of the other species mentioned here, repeated follow-up treatments are usually necessary and may incorporate a combination of blade brush cutting and herbicide.

The challenges MCMC faces in controlling these weeds demonstrate the importance of having consistent, long-term management to restore bushland areas. This work is labour-intensive, requires specialised knowledge and equipment and can sometimes take many years to complete. Ultimately, there’s no shortage of weeds on the Merri, so having a paid team of professionals to properly tackle the tough ones, like these, means that Friends of Merri Creek volunteers can work more effectively on the others. As decades of this collaboration have shown, together we can achieve great things!

   
Image credit:  Blackberry Rubus anglocandicans. Atlas of Living Australia
Left: photo by MichaelMulvaney, CC BY 3.0 (Au). Right: photo by Jennybach, CC BY 3.0

Although some things are best left to the pros, here are some ways you can help prevent high-threat weeds:

• Next time someone offers you a cutting from their garden that’s “impossible to kill”, dig a little deeper and find out if there’s a risk of it becoming a weed. All four of these high-threat weeds were likely brought to Australia as they spread into the environment from garden plants. 
• Understand which weeds are worth your time hand weeding, so you don’t inadvertently spread the high threat ones. Attend weeding events with FoMC working groups to get familiar with common weeds and learn which ones can be effectively controlled by hand. 
• Keep an eye out for emerging infestations of these four high-threat weeds. If you’re confident in your ID and come across small, individual plants with no others in a 10m radius, it could be beneficial to manually remove them. Always wear gloves, and only attempt if you’re confident you can remove all parts, including roots.
• Ensure you dispose of high-threat weeds appropriately, either by burning, solarising in plastic bags until disintegrated, or bagging securely for disposal in landfill.

More to explore:
Weedspotters - state government program for volunteer weed spotters looking out for and reporting state prohibited weeds.
Weed Society of Victoria - for anyone interested in any aspect of invasive plants
Grow me instead - some weeds in the environment are garden escapees - this organisation promotes native plants that won't pose the same threat - bearing in mind that native plants can also become weeds if in the right conditions for them to become invasive.