Australian Rangeland Society

David Fitzgerald, John Morrissey, John Walsh, Ross Norrie and Don Burnside.  Contact email: david_0209@bigpond.com

 

Background and the threat posed by cactus infestations

The Leonora Shire is in the Western Australian Mulga Zone, and is dominated by mulga (Acacia aneura) shrublands and grasslands on extensive wash plains, interspersed with stony chenopod vegetation on greenstones, and halophytic vegetation on the margins of extensive slat lakes – normally dry.  It has been an important mining and pastoral area since the 1890s.

The cactus infestations in the Shire of Leonora were first reported in the RMN in Issue 09/1 March 2009 by David Fitzgerald (retired pastoralist, Nambi Station, via Leonora, and former President, Shire of Leonora) and David Wilcox AM (rangeland scientist and former President of the ARS, deceased).

As reported then, the cactus infestations are an unfortunate legacy of the many townships and camps established from the 1890s onwards by companies and individuals seeking gold, who introduced cacti as an ornamental plant in an environment where water is scarce.  Although most of these original towns and camps are long gone, the cactus has stayed!  Further, this large shire (32,189 km2) is still an important mining area, with many new mines and individual prospectors in the area.  Along with the cattle running on pastoral properties, the possibility of further spread of cacti is always a threat.

Most of the Leonora Shire lies within the catchments of Lake Raeside to the south and west and Lake Irwin to the north east.  These ancient river systems, now full of alluvial material occasionally flow – after very heavy rainfall events – several hundred kilometres onto the western fringe of the Nullarbor Plain.  If cactus plants eventually migrated down watercourses into the lakes, it is quite possible that infestations could occur all along these systems.  Preventing this migration is critical.

 

The formation of the ‘Cactus Hunters’

Led by David Fitzgerald, David Wilcox (until his untimely passing in 2015) and Cyril Linto (ex-Senior Stock Inspector, Department of Agriculture, Kalgoorlie), annual surveys of likely locations for infestations have been conducted since 2005.  The focus is on the two species that are ‘Weeds of National Significance -WONS’, being Coral Cactus (Cylindropuntia fulgida) and Riverina Pear (Opuntia elata).

The ‘Cactus Hunters’ – all volunteers – now comprise David Fitzgerald (Leader), John Walsh, John Morrissey, Ross Norrie and Don Burnside, all of whom have experience in and knowledge of the semi-arid mulga shrubland, and chenopod shrubland dominated landscapes in the Shire.

 

Activities to date

Although in a semi-arid pastoral area, remote from major settlements, the Leonora Shire is a hive of activity, with many large commercial gold and nickel mines, several smaller mines, numerous prospecting locations and camps, and many people just camping in the bush and doing a bit of metal detecting, all of this mixed in with normal pastoral activities (was sheep, now cattle).

The Cactus Hunters undertake an annual sweep through the shire, checking out areas around Leonora and Leinster towns, Gwalia historical townsite, abandoned townsites, old and new mining activities in the shire, numerous prospectors’ camps (current and abandoned), station homesteads  and tourist stops.  All locations visited are logged with GPS for latitude and longitude.

The Cactus Hunters have benefited from great support from Jim Epis, CEO Shire of Leonora (https://www.leonora.wa.gov.au/), who as well as being an enthusiastic supporter, provides all the resources (vehicle, accommodation, meals and other logistical needs) for the annual surveys, assists in identifying infestations around the town, and arranging for their control with spraying by Pilbara Environmental.

Other participants are :

  • the Goldfields Nullarbor Regional Biosecurity Association (https://gnrba.com.au/) who funded spraying of large stands of cactus away from town (2013-2015) and have since been spreading Cochineal (Dactylopious spp.) insects to kill cactus stands;
  • St Barbara Mines who have employed Pilbara Environmental to carry out spraying on their Gwalia leases (see results below); and
  • a growing number of local residents who have been alerted to the threat, and help identify infestations.

 

Progress is being made

Significant success has been achieved in using chemical spraying and spreading Cochineal (Dactylopious spp.) insects to kill four extensive stands of cacti:

  • Large stands near the old Gwalia mine and townsite (see before and after photos);
  • 300 hectares near the old Mertondale townsite (30km north of Leonora),
  • cactus within an area of 6,600 ha near a station homestead (with 5 ha of the rubbish tip fenced);
  • A large distribution of Coral Cactus near Slaughter Yard Mill just west of town; and

several other small stands located throughout the shire have also been sprayed, or have been populated with Cochineal (Dactylopious spp.) (Note – Cactoblastis cactorum insects were also introduced onto Riverina Pear but could not persist in the semi-arid environment).

 

Gwalia before (2008)

 

Gwalia after (2022)

 

The 2022 survey

The 2022 survey was conducted between 24 May and 1 June.  The survey had four objectives.

  • Revisits to check on the effectiveness of the kill in all areas previously sprayed or treated with insects, and to see if any recruitment is occurring.
  • Inspections of new sites, identified on Google Earth but not previously visited – mainly prospectors camps, woolsheds, and station outcamps.
  • Inspection of areas where local people have suggested cactus might occur.
  • Determining what further spraying is required.

 

During the 2022 survey, we visited 27 locations as shown in the table below.

 

Site category Number of locations Current status Actions
Extensive infestations (up to 6,600 ha) and fencing of 5 ha on a station rubbish tip 4 About 90% of cacti are dead, from spraying and/or insect attack.  About 10% still have some life Spot spraying to kill plants still alive, and annual checking to confirm complete kill, and to check for any recruits
Leonora townsite and adjacent common 3 Four new infestations treated with Tordon crystals Check to determine status of treated plants
Leinster townsite (town wholly owned by BHP) 1 Large Riverina Pears in a town garden. BHP to be requested to kill the plants
Previously visited small infestations at prospectors camps, old mines, station outcamps etc 4 Most cacti dead at previously treated locations. Some live cacti remain at some locations Spray team will revisit locations with cacti still alive.  Results will be checked
Prospectors camps, old mines, station outcamps, tourist locations etc 12 7/12 locations had cactus infestations.  Isolated plants treated with Tordon crystals Larger infestations will be sprayed.  Results will be checked
Current mines 2 No cactus seen
Other locations 1 No cactus seen

 

 

 

 

 

The photo to the left shows David Fitzgerald and John Morrissey looking at a large cactus (Opuntia sp.) at Wilsons Patch, about 60 km north of Leonora.  There are also several Coral Cactus plants at this site, and all these will be sprayed in due course.

 

 

 

 

 

 

 

 

 

The photo to the right shows John Morrissey with a healthy Coral Cactus located in the old Mertondale townsite area about 30 km north east of Leonora.  Outlying individual plants like this are often difficult to locate, and can be surrounded by many juveniles.

 

 

 

 

 

 

 

 

 

 

John Morrissey with dead cactus at Slaughter Yard well, showing the extent of the infestation in a mulga shrubland on an alluvial plain not far from Lake Raeside, and the effectiveness of the kill from spraying.

 

 

 

 

The work continues ….

Over the coming months, the Shire of Leonora will engage Pilbara Environmental to find and spray small plants that may have been missed on those sites already sprayed.  Larger infestations, such as the one at Wilsons Patch need to be sprayed.

The many newly identified small infestations have been treated with Tordon crystals which could take 12 months to kill the plants.  The Cactus Hunters will check these in 2023.

The pastoral leaseholders in the shire will be urged to comply with their lease agreements and take action to eradicate known infestations.  The public will be urged to report sightings of cactus, and signage will be placed in town showing the two WONS cactus species, with information about the threat they pose to the environment.

And next year – the existing known locations will be checked by the Cactus Hunters and new locations identified and visited.

And …. we hope that the work in the Shire of Leonora, supported by the Shire and others can serve as an example of what needs to be done and what can be achieved in other rangeland areas known to be infested with cactus.

 

Out in the bush ….

 

 

 

All the Cactus Hunters enjoy being out the bush, telling tall tales from the legendary past, stopping for lunch and billy tea and then enjoying refreshments and a good meal at the White House Hotel in Leonora in the evening, courtesy of the Shire.