22AWC report

Andrew Mitchell, WSWA Secretary

Reflections and recollections on the 22nd Australasian Weed Conference;

Adelaide 25-29 September 2022

This 22nd Australasian Weed conference was originally planned for 2020 but had to be postponed due to COVID. It was a time of serious stress for the organising committee. After it was first postponed, the original events organising company decided they couldn’t do the job and the South Australian committee had to engage another company and pick up all the pieces. Later, the committee had the perennial worry of not enough participants but there was a communal sigh of relief a month prior to the start of the conference, when there were 300 plus registrations.

The conference was held at the various meeting rooms in the Adelaide Oval [building], which is adjacent to the River Torrens in downtown Adelaide. The Adelaide CBD is on the other (south) side of the Torrens and the University of Adelaide is adjacent, as is the Botanical Gardens and North Adelaide. There is a lot of accommodation in this area. The only drawback to the Adelaide Oval was that the 4 meeting rooms were not all together and involved a 5 minute walk from one area to another. There were 2 breakout areas and one was used for meals and commercial displays and the other held the event organising office and poster displays.

The conference proper lasted 3 days with a plenary session for an hour and half at the start of each day with three speakers. Some conferences I have been to have plenary sessions that last half a day but as these were split over three days and they were all significant speakers that gave presentations of particular aspects of weed science; for example Rick Llewellyn CSIRO Adelaide, presented on the current and future developments in weed control. Most of the various crystal ball gazing in this conference revolved about being able recognise weeds from their spectral signature and restricting herbicide use to the weeds. Traditional Owners from the Adelaide area were significant participants in the last plenary session and in other parts of the conference and described how they were rehabilitating a swamp that had been cut off from its water source and infested with weeds.

A key feature of the conference format was that all presentations (oral and poster) were pre-recorded and available online. This change was introduced to ensure that participants would have access to presentations if COVID prevented travel. However, it is a feature worth preserving. It ensured that it did not matter which presentation you attended- you could see them all in the weeks after the conference if you so desired. The Proceedings are now available.

The Council of Australasian Weed Societies (CAWS) gives a medal at each Australasian Weeds conference to a person who has made significant contributions to weed issues. This year there were two outstanding candidates; Dr Louise Morin and Associate Professor Michael Walsh, who the CAWS committee considered were both well-deserved recipients. The committee not being able to choose one over the other, with the new CAWS president Rae Kwong awarding each a CAWS medals. Louise has had a long dedicated career in biocontrol whilst Michael has spent many years developing and promotion of, Harvest Weed Seed Control (HWSC), which significantly reduces weed populations in subsequent crops.

The presentations were run in three and sometimes four concurrent sessions that were organised by themes. CAWS ran group workshops and these were sometimes the main part of one of the concurrent sessions. My interests and experience lie in environmental, rangelands, tropical weeds and their early detection. The stand out developments for me at the conference was the extent of the cacti infestations in eastern Australia and the variety of responses to them. We were shown how important it is to have an understanding of the social forces in an area when organising a district wide control program.

I was frightened by the extent of the Hudson-Pear and Wheel-cactus infestations in eastern Australia. The Goldfields in WA have a serious problem with Coral-cactus near Leonora and no one reported on the situation here.  The entomologists have worked out that there are races of Cactoblastis moth and Cochineal bug (it’s a mealy bug) that are specialised to each cactus species.

Glass houses have been built to grow these cacti, where these insects have been bred up and spread by the land holders that want them. One organisation is offering landholders, a bucket of infected cacti if you bring in a bucket of uninfected cacti. The landholders then have to go and put the infected cacti segments out on their properties. The importance of social settings for weed control programs was rammed home to us by Sonia Graham, University of Wollongong in combination talks about the successes and failures of various cactus control projects.

Siam Weed (Chromolaena odorata) has been found in the top end of the NT south of Dundee Beach and unfortunately a delimiting survey has found that it is much more widespread than originally thought and it will not be possible to eradicate it. A stem galling fly that attacks Siam Weed has finally been introduced to north Queensland.

Eradication has been achieved in the NT for an outbreak of Cabomba in Palmerston and below the Darwin River Dam through an ingenious use of herbicide in combination with a novel underwater camera monitoring system. They were lucky that the main Cabomba infestation was wedged between the Darwin River Dam and its salt water estuary

The eradication of Striga asiatica in north Queensland is looking promising.

Grass weeds received significant coverage and ranged from a presentation about a new program that will attempt to rein in the spread of Gamba Grass in the NT. Unfortunately I think that horse has bolted. Has it been eradicated in the Kimberley?

We were told that the diversity of native plants and animals in Central Australia is being badly affected by Buffel Grass, due to it forming monocultures and as a result, there are no animals to hunt or available food plants. Buffel Grass continues to be controlled in South Australia where a number of new grass weeds have been recorded.

Results of a survey for biological control agents for African Lovegrass (Eragrostis curvula) in Africa did not appear to be promising at this stage.

We were told that a large proportion of newly establishing weed species seem to be the progeny of highly selected garden plants. This maybe because they are planted in large numbers in a range of areas. During the conference the “Garden responsibly” theme was launched as an alternative “to plant this, not that”, to promote responsible gardening that does not allow garden plants to jump the fence and become weeds.

I could not help compare the various State Government weed organisations, NSW were a stand out with large numbers of staff doing useful projects. Of the 320 participants, DPIRD had three staff at the conference.

There were 3 post conference tours;

  • northern Adelaide Plains and the Barossa Valley wine region
  • southern Adelaide Rivers and McClaren wine region
  • Belair National Park and Adelaide Hills wine region

I went to the Belair National Park tour.  Our first stop was at the Waite Institute, Adelaide University greenhouse where Dr Peter Boutsalis demonstrated how, for a fee, they test for herbicide resistance on freshly dug out weed samples sent in by farmers.

We then went to the escarpment of the Belair National Park to a grassy woodland where feral European Olives were being controlled using a stem injected herbicide. Nearby, we were then shown an area that had been invaded by weedy annual grasses. They had used a chemical, Esplanade, to suppress the germination of the weedy annual grasses but it didn’t kill the perennial grasses. Lunch was provided by volunteers at the park headquarters in an area that had been planted with a large number of exotics, many years ago. After lunch we walked from the bottom to the top of the escarpment, looking at the environmental weeds. Their main weeds were Boneseed (Chrsanthemoides monilifera subsp. monilifera) and Broom (Genista monspessulana). The hill was either sandstone or siltstone and there wasn’t a lot of exposed rock and the vegetation was a eucalypt woodland with a grassy understorey. There was no gravel and no myrtaceous heath, blackboys or sedges as per the Perth Hills. To end a very pleasant and interesting day, we were taken to a winery for wine and nibbles and then returned to Adelaide Oval.

This weed conference was an event that provided a wide range of interesting presentations, opportunities to network and was well organised, accommodated most interests and the catering was excellent. Many thanks to the Weed Management Society of South Australia.

Feature Weeds

Euphorbia paralias


Ecologist Peter Heyligers reported in The Western Australian Naturalist (Vol 18(1)) in his article Sea spurge (Euphorbia paralias), a strandline pioneer new to the Perth region:

In October 1987 I found a single plant of another introduced strandline pioneer, Sea Spurge, established at Coogee Beach, not far from Woodmans Point. Its presence there, however, was short-lived; when I visited this beach again in September 1988, severe erosion of the upper beach and foredune was evident and the Sea Spurge plant, along with the neighbouring vegetation, had disappeared. No seedlings were found, and an inspection of beaches in the vicinity of Woodmans Point located no other Sea Spurge plants. Nevertheless, I expect that sooner or later this species will turn up again in the Perth region”

His observation ran true, and it’s now a dominant foredune invader as far north as Lancelin, while was previously known to be in the east to Eucla.

Euphorbia paralias, sea spurge, is native to southern Europe and north Africa and was first recorded in Western Australia herbarium# in Albany in 1927 on the shores of King George Sound.  Seeds are buoyant and its quite likely that seeds arrived with shipping movements to the Port of Albany as the weed was soon after found at Port Victoria in South Australia (Heyligers 1989).   

Ecology biology and phenology

Sea spurge is a perennial coastal coloniser, surviving well on beach sand and has a deep tap root that enables it to survive the extremes of coastal dune movement.  Its not uncommon to find clusters of what appear to be sea spurge seedlings, only to find they are the tips of a mature plant deeply buried in sand.  Bushes are between 20cm-1m high, depending on the sand.  Like most Euphorbia species, sea spurge is not palatable to vertebrates as they exude a toxic, and bitter latex sap that can cause irritation to skin and eyes.  Sea spurge is a prolific fruiter, with 1000s of seeds produced each year in summer.

Sea spurge in Western Australia is found on most southern beaches and can form dense stands.  In eastern Australia, particularly Tasmania sea spurge deprives shore birds of habitat, and is a direct threat to at least three migratory birds. 


Sea spurge is not a declared species in Western Australia.

Control Options

Sea spurge is often controlled with herbicide and hand weeding, but a persistent seed bank will mean ongoing efforts are required. 

Sea spurge is a target for biological control, with a rust fungus released in 2020 (  Trial sites for rust establishment are being monitored in Tasmania, Victoria and NSW.  It is anticipated that sites for rust establishment will be set up in Western Australia in late 2023.

#Notes in Heyligers (1989), but this record is not available on the Atlas of Living Australia.


Heyligers, P (1989).  Sea spurge (Euphorbia paralias), a strandline pioneer new to the Perth region.  The West Australian Naturalist 18(1) p1-6.

Feature Weeds

Passiflora foetida

passiflora stinking passionfruit

Feature Weeds

Paddy Melon

Feature Weeds

Italian buckthorn Rhamnus alaternus

Feature Weeds

Ice plants (Mesembryanthemum crystallinum)

Feature Weeds

Calotropis procera

Feature Weeds



Carpobrotus sp. (Aizoaceae) are commonly called pigface in Australia, and it’s a complex genus that consists of several species, that most people think all are native.  Carpobrotus edulis, commonly called Hottentot fig or Cape fig, is a widespread perennial succulent that originates in South Africa and has naturalised in most Mediterranean countries in the world.  Its particularly weedy on sandy soils in coastal areas, and can form monocultures in winter-wet depressions and sandy paddocks.  Its spread in Western Australia has been assisted by widespread amenity plantings facilitated by several local government areas and contractors.  Carpobrotus aequilaterus commonly called Chilean pigface is less common, but not less aggressive as an invader.  Also widespread throughout Mediterranean, but its origin is less clear.  Most likely to be from South Africa, but it’s seen as a species unique to California and has been present there the 1600s (Vila et al 1998). 

The native Carpobrotus species in Western Australia are:

Carpobrotus modestus.  Inland pigface see

Carpobrotus rossii, Krakalla,found near Shark bay  see

Carpobrtus virescens, found in southern coastal dunes from Shark Bay to Esperance see

All three species will hybridise with the exotic Carpobrotus, and there is concern amongst botanists that it will eventually be impossible to discern native species form hybrids.

Ecology, biology and phenology

When not in flower, C. edulis is a low growing succulent with deep green leaves that resemble fingers.  Usually triangular in section, leaves are variable in length from 1-15cm.   Flowers are large, 5-6cm wide, yellow and present from September – January.  Individual flowers persist for about a week, and then petals wither and the fruit can persist for several months where its either eaten by wildlife or falls below the plant.  Carpobrotus fruits are edible and can sometimes be found pickled at specialist gourmet food stores and recipes online.   

C. edulis readily hybridises with native species, and back again and therefore much of the Carporbrotus seen in gardens are a hybrid of unknown ancestry.  Due to challenges in taxonomy, its only in recent years that revegetation programs have ensured Carpobrotus used in coastal revegetation are sourced from stock propagated from the native C. virescens and not C. edulis or hybrids.  

Hybrid Carpobrotus flowers are variable in colour, from apricot to deep purple.  C. edulis in its pure form is always yellow.


Unfortunately, it’s not a reportable plant, but its still sold in mainstream nurseries. 

Control options

C. edulis is shallow rooted, so can be easily hand pulled in small areas but will regrow from any fragments.  Herbicide may be required for larger areas.  The seed is short-lived but may persist for 2-3 years.  Succulent species aren’t often successfully managed with control burns.

Found Carpobrotus edulis?

If you find Carpobrotus edulis, report it to DPIRD by MyPestGuide Reporter or iNaturalist.  Reporting contributes to knowledge of the species range. 


Hussey, B.M.J., Keighery, G.J., Dodd, J., Lloyd, S.G. & Cousens, R.D. (2007) Western Weeds. A guide to the weeds of Western Australia. 2nd Edition. The Plant Protection Society of Western Australia, Victoria Park.

Vila, M., Weber, E., & D’Antonio, C.,M. (1998). Flowering and mating system in hybridizing Carpobrotus (aizoaceae) in coastal california. Canadian Journal of Botany, 76(7), 1165-1169.

Feature Weeds


Feature Weeds

Mexican poppy

Mexican poppy in Western Australia is the common name for two species of invasive poppy from the Papaveraceae family: Argemone mexicana and Argemone ochroleuca subsp ochreleuca.  Both species originate in Mexico and the range extends to central America and into southern Texas.  Both species have similar in appearance but A. mexicana petals are orange in colour while A. ochroleuca is pale yellow to white.  First recorded in Australia herbaria in 1882 around Moree and Gunnadah, it has thought to have arrived as a contaminant in imported wheat (Parsons & Cuthbertson, 2001).  First recorded in Western Australia in 1921 at Beverley in the Avon Valley catchment in southern Western Australia, but its highly invasive range is Pilbara region, particularly along water courses.  Occasional plants are found in southern WA but populations rarely persist.


Argemone ochroleuca Sweet subsp. ochroleuca, Argemone Mexicana L.

The most prevalent species in Western Australia is A. ochroleuca subsp. ochroleuca.  From Florabase:

Annual, herb, 0.3-1 m high, spiny, with yellow latex. Fl. white-cream-yellow, Feb to Mar or Jul to Nov. Red/white/grey sand, red-brown clay loam. Creek edges, riverbanks, roadsides.

Ecology, biology and phenology

Mexican poppy has naturalised throughout Australia and in southern Africa.  Its commonly a weed of highly disturbed areas such as roadsides and mining areas, but large infestations are found along seasonal sandy river beds and poorly managed pastures.  The sap is toxic, but it’s not usually grazed by livestock due to the numerous spines on all plant tissues and the bitter sap, but the seeds could result in animal poisoning if introduced in ground feed.  Primary concern for agriculture is the contamination of cereal crops, and in southern India and southern Africa and there have been several cases of human poisoning and death following ingestion of wheat flours made with high levels of mexican poppy seed.  It is also associated with epidemic dropsy, a lymphatic condition resulting in fluid retention in the legs and feet (see

Mexican poppy is an annual species, germinating in late Autumn and producing flowers between November and December.  The species is self-fertile and after flowering, an ovoid seed pod forms containing up to 400 seeds that can persist for several years.  In northern Australia, germination could be variable depending on rainfall and it’s not uncommon to have huge flushes of germination following cyclonic events. 


Argemone mexicana is a declared pest in the state, prohibited entry although it has been recorded from several locations.  Argemone ochroleuca is a permitted species, and although its highly undesirable weed there is not control category assigned. 

Control options

Several control options are listed on the DPIRD website

Found Mexican poppy?  Report it