Skip to main content

Australian Invasive Cacti Forum 24th May Hahndorf SA

By June 2, 2013June 22nd, 2018Archives, Research

The first speaker, Mike Chuck (Australian Invasive Cactus Network), spoke about the Australian Invasive Cacti Initiative and the recognition now that cacti are a national rather than local issue. He concentrated on the threat cacti pose to the rangelands of SA. The first National Rangelands Audit was conducted in 2009, with the first forum in that year. He spoke of cacti dispersion and forms of control. Discussion centred on conventional control methods (such as spray, stem injection and mechanical removal), the cost of one treatment being greater than the value of the land, retreatment may be needed over many years and the potential for biocontrol with Dactylopius (cochineal).

Helmuth Zimmerman, a recognized international expert from Pretoria, provided a global overview of cactus invasions and biocontrol. He presented a fascinating account of the history of biocontrol of cactus. It all began in 1880 with cactus invasions in South Africa, India, Australia and Madagascar. England desperately needed cochineal dye for its royal colours but Spain had the monopoly on red dye and had embargoed England. It was decided to produce it in the British colonies. The navy was used to find cochineal and take it to India to reproduce on the introduced cactus (Opuntia) now invading India. However, the cochineal produced inferior dye. The British had misidentified the cochineal variety – they mistook Dactylopius ceylonicus for D. Coccus. This mistake was fortunate in other ways because it triggered biocontrol, resulting in the destruction of the entire infestation of Opuntia cactus in India. Unintended biocontrol also occurred in Sri Lanka and Madagascar.

1914 saw the deliberate introduction of biocontrol in Australia but it was unsuccessful. From 1920-1940 biocontrol in Australia focussed on O. stricta (the pear cactus). Surveys teams in Texas, Argentina and Mexico identified 56 biotypes of cochineal and of the 56 cactus herbivore species introduced from 1927-39 only 17 became established. None were effective in the control of O. stricta. Cactoblastis cactorum, from South America, was only considered after cochineal proved to be unsuccessful.  It became the silver bullet for control of O. stricta and, to this day, there has never been a more successful example of cactus biocontrol.

John Heap (Biosecurity SA) talked about remote sensing of weeds, chiefly the main forms currently employed: landsat satellites and airborne platforms (including unmanned aerial vehicles). He spoke of the pros and cons of remote sensing for weeds. On the positive side, it can be cheaper than ground surveys, large areas are covered quickly, inaccessible areas can be surveyed and it allowed for digital manipulation. On the downside, small areas were expensive, cloud cover was problematic, availability of satellite data or aircraft and the need for specialist expertise.

Ben Chinnock, a cactus expert, talked about the good, the bad and the ugly in the Cactaceae (cactus) family. He described the family and its 4 sub-families: traits/characteristics, identification, growth habits, reproduction, distribution, weed status and potential for becoming a weed. There are 180 species of Opuntia and of the 18 in Australia most are identified. Some important points he made were that seed recruitment will take place for 10 years or more as not all the seeds germinate at once. The flowers incorporate pericarpel tissue (stem tissue) so if the flower is knocked off the plant it has the capacity to root and grow into a new plant.

Lorraine Edmunds spoke about her involvement in community action on Opuntia robusta (Wheel cactus) in the Flinders Ranges, with the catchy title “Where there is a wheel, there’s a way.” This community action has been taking place for 10 years, consisting of about 75 volunteers in 67 groups, 10 pastoral families and 1 contractor team. Trials have been conducted with foliar spray (Grazon) and stem pad injection with glyphosate. In the 1990’s Dactylopius opuntiae (cochineal) and Cactoblastis were introduced but they never flourished. Population numbers would increase in wet years and then rapidly decline during dry periods. After 5-6 years the cochineal was deemed unsuccessful as it had not spread. The plants with cochineal were dug up and piled on top of each other in a shed. To everyone’s surprise the cochineal flourished in the shed. This shed population was released into the field on 2-3 plants in 2008. Two years later the first cactus died. It took 3 years before widespread knockdown began to occur in the test area. Meanwhile, the cochineal population in the shed was fed fresh plants to keep it flourishing. Towards the end of 2011 hundreds of infected pads were taken to a 12 sq km core area infested with cactus and each healthy cactus was given one cochineal infected pad. The cochineal spread to thousands of cactus in the core area, even onto golf ball sized recruits, and then spread beyond the core area. But Lorraine stressed there was no such thing as eradication: it is a matter of manage, control and keep at low levels. O. robusta has seed recruitment for about 20 years and the plant is extremely versatile in terms of where it will grow, somewhat akin to rabbits.

Michaela Heinson and David Cooke (Biosecurity SA) then spoke about updating declared plant policies for Opuntioid cactus in SA. They provided a description of the Natural Resource Management Act 2004 and the risk assessment conducted before a decision was made to declare a plant a weed or not. This risk assessment included weed risk invasiveness, impact and potential range and feasibility in terms of control costs, persistence and current distribution. Risk assessment scores direct a declaration or not and also inform policy development and management actions.

The manager of NRM Biosecurity, John Virtue, discussed the national direction of weed management and the complexity of weed management.  Key stakeholders are federal, state, territory and local governments, intergovernmental committees, natural resource management bodies, industries (e.g. livestock, cropping, forestry, gardening), communities and individuals. The multitude of roles in weed management were covered, plus the risks posed by weeds (e.g. primary industries, biodiversity, ecosystems, amenity, public access, Indigenous, animal welfare, public health and safety, water, costs). He then spoke about Weeds of National Significance (WoNS). An initial 20 were declared in 1999 and an additional 12 in 2012. There are national strategic plans for each: revised plans for the original 20 weeds and 12 new plans for the 12 plant additions. Unlike the national approach to management, there is no national approach to weed research and no national weed research centre. However, by 2018 Caring For Our Country will develop a national surveillance framework for weeds that engages stakeholders for prevention, eradication and containment. John stressed the importance of the eradication of strategic outlier infestations in weed management and the need for this to be a core activity. It was important to start from the outside and work inwards, while maintaining containment lines.

Henry Rutherford, the National Coordinator for Opuntioid Cacti, finished the morning session by discussing the achievements under WoNS and the importance of research in biocontrol. He stated the University of Adelaide was considering DNA testing of cochineal biotypes for matching to host cacti.

Two workshops took place in the afternoon focussing on the assessment progress on the national strategic plan and implementation of a national approach.