The Cactus Working Group was established in 2012 to address the issue of invasive cacti species in South Africa. Managed by the South African National Biodiversity Institute’s Invasive Species Programme, the CWG meets biannually at the National Botanic Gardens in Pretoria.

The CWG is made up of scientists from SANBI, the Department of Environmental Affairs, the Department of Agriculture, Forestry and Fisheries and various universities, as well as certain stakeholder groups.

Successful working group with top scientists

The CWG has been a huge success with the organizational skills of Haylee Kaplan from SANBI. Dr Ana Novoa, a post-doctoral researcher based at the Centre of Excellence in Invasion Biology (CIB) at Stellenbosch University, has contributed significantly to our understanding of invasive cacti and the extent of trade in the nursery industry.

South Africa’s top biocontrol scientists, like Hildegard Klein from the Agricultural Research Institute (ARC), lead the field in biocontrol of invasive cacti form part of the CWG. Other top scientists include Dr Helmuth Zimmermann and Lesley Henderson, who have been instrumental in the success of this working group.

The CWG was privileged to have Dr Roberto Kiesling, a taxonomist and top cactus expert from Argentina, presenting at the April 2016 meeting.

In October 2014, the CWG held a workshop in the heart of historical cacti invasions – Graaff-Reinet in the Eastern Cape.

Members of the CWG, particularly Dr Ana Novoa, were instrumental in launching the International Cactus Working Group during a conference held in Hawaii earlier this year.

The latest meeting was held on Thursday 17 November, 2016.

• Iain Patterson gave an overview of cactus biocontrol research at Rhodes University.
• Madodomzi Mafanya spoke about using remote sensing techniques to detect Harrisia pomanensis.
• Travor Xivuri chaired the session and also reported back on his trip to Australia where he attended the Australasian Weeds Conference in September 2016.

Invasive cacti

Invasive cacti are a concern in South Africa, particularly in arid regions where they are fast taking over productive agricultural land and game farms. Various species of Opuntia have become serious invaders, but fortunately effective biocontrol such as cochineal have produced fantastic results in the control and spread of these cacti. Teddy bear cactus (Opuntia microdasys) is still often traded despite being listed under NEMBA as a Category 1b invasive species.

Some cacti also thrive in sub-tropical regions with high rainfall, such as Barbados gooseberry (Pereskia aculeata) – Category 1b and the climbing dragon fruit (Hylocereus undatus) – Category 2.