​The Grootvadersbosch Conservancy has worked on the removal of Pereskia aculeata over the past few years and knows how problematic an alien invader it is. The conservancy used to burn off every stem of the plant which was quite an expensive process. The Grootvadersbosch Conservancy has been working with the Swellendam municipality to manage alien invasives and noticed an invasion in the centre of town. We urgently required an easier way of eradicating the pesky Pereskia, so we contacted Dr. Iain Paterson to aid us with some biocontrol. He posted the biocontrol to us where we could release it at two sites – the first site is at a Swellendam municipality near the mall and the second site is at the Buffeljags Dam.

​Pereskia aculeata originates from Brazil in South America and thus it has no natural predators in South Africa. It is a creeper plant that can easily outcompete and overgrow indigenous plants especially in forest and plantation areas, leaving them with no access to sunlight, natural pollinators, and water (Invasives SA, 2014). The spread of Pereskia aculeata is problematic as the areas with the infestation will become degraded and will have little growth of indigenous plant diversity over time. 

​Biological control (Biocontrol) is the use of a natural enemy, usually an insect or pathogen, to control and/or eradicate an alien invasive plant species (ARC, 2014). Biocontrol is an alternative method to control and eradicate alien invasive plant species and is very effective and often used in combination with mechanical control

Luckily for this Pereskia invasion, both biocontrol agents were delivered to us, Pereskia Flea Beetle (Phenrica guérini) and Pereskia Stem-wilter (Catorhintha schaffneri). We released both at the Swellendam municipality site and only the Pereskia Stem-wilter at the Buffelsjag Dam site. Both agents can only survive by feeding on Pereskia. The Pereskia Flea Beetle feeds on the leaves, forming big holes while leaving a trail of brown faeces. The Pereskia Stem-wilter feeds on the plant shoot tips, splitting them open and/or rotting them. 
 
We are very grateful for the incredible scientists who work so hard in developing these agents and so we decided to interview Dr. Iain Paterson who shares his experience in developing a biocontrol agent for Pereskia aculeata.
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​Dr. Paterson has always had a passion for nature, he loved plants and animals since childhood. Once he started university, he decided to study both Zoology and Botany. While studying, he discovered an interest in insects, he was fascinated by the idea of using insects as a biocontrol agent, consequently, he decided to pursue Entomology and he then did his Ph.D. on Pereskia aculeata.

​Dr. Paterson explained that they experimented with potential Biocontrol insects, which are all indigenous to South America. Five insects were used in the experiment and only two were found successful as a biocontrol. It took him 2 years to prove that the Pereskia stem-wilter beetle (Catorhintha schaffneri) will only feed on Pereskia aculeata and not on any other indigenous plants of Africa. 

​Pereskia aculeata is an alien-invasive vine plant species. Vine plants are almost impossible to remove successfully using chemical or mechanical methods without damaging the surrounding indigenous vegetation. Pereskia aculeata also has a nasty habit of resprouting where it has broken off and any present stem fractions will eventually develop into a new plant. Dr. Paterson once brought a Pereskia stem fraction from overseas within a clip file and, with no soil or water, the fraction grew leaves, displaying its remarkable survivability and durability.

​In general, insects are selective feeders, they always seek and select the plants with the most nutrients that their bodies can absorb. In their natural habitat, the Pereskia stem-wilter evolved by only feeding on Pereskia. Here in Africa none of our insects are familiar with Pereskia aculeata and will not feed on them. Without natural pests, Pereskia will outcompete our indigenous plant species and spread rapidly. 

​The public is advised to learn how to identify Pereskia aculeata and not to plant and grow it within their gardens. In the past, Pereskia was used as a hedge plant in the garden because it grows so effortlessly. If the Pereskia aculeata is removed by hand, all the biomass that is removed and disposed of will resprout. Wherever it ends up, it will create a new infestation so it is advised to let the biomass dry out, or even better, spray it with herbicide and once it turns brown, it should be burned.

​Dr. Paterson states that the Pereskia biocontrol will not immediately eradicate the whole alien plant, the beetles must first establish their population. Once established, the Pereskia infestation will slowly deteriorate over time as the beetles feed on the shoots and roots. This will decrease the spread of the plant and reduce the Pereskia infestation.

​The biocontrol is funded by the Department of Fisheries, Forestry, and the Environment (DFFE) and is provided by the Centre for Biological Control (CBC) of Rhodes University.
 
The Grootvadersbosch Conservancy can also be contacted if Pereskia is observed so we can track its spread and the success of the agent in its control.

​With the help of Dr. Paterson and the biocontrol agents, we are doing all we can to remove Pereskia aculeata!
 
We thank Dr. Paterson for his time and knowledge regarding Pereskia aculeata and the tremendous journey in creating a biocontrol agent!

​The continuous effort of clearing mountain slopes of alien species is rewarding but challenging work. With the continuous effort of our mountain clearing teams and the support of the DFFE, LandCare, Gouritz Biosphere Cluster Reserve, and landowners, it will be possible for the conservancy to reach our end goal of controlling alien species in our precious mountain catchments.
 
 
                                            THANK YOU TO OUR CLEARING TEAMS AND FUNDERS

​Currently, the Grootvadersbosch Conservancy is part of a high mountain alien clearing project located in Langeberg Mountain, between Heidelberg and Swellendam. The Grootvadersbosch Conservancy covers over 30 000ha of private land which includes high mountain catchment areas. This project involves the clearing of alien species (mainly Hakea and Pine) in an estimated area of 6000ha, on the mountain slopes and their catchment areas.

​These catchment areas are essential in sustaining river systems due to the high runoff and groundwater recharge capabilities.
The dominant vegetation type in Langeberg Mountain is mountain fynbos, a fire-driven ecosystem that must burn every 10 – 15 years. However, with alien invasions, fires become more frequent and intense. These intense fires do harm to the natural vegetation and wildlife. The project's goal is to control alien species within these catchment areas to improve groundwater recharge and catchment runoff and reduce the intense fire outbreaks that can threaten infrastructure and natural vegetation.

​In 2020, the Grootvadersbosch Conservancy started working on a management plan to remove the alien species in the high mountain areas. The initial plan was developed in 2020 by our General Manager, Aileen Anderson. She did this by camping out in the mountains with countless hours of scouting and assessing the area’s infestations, prioritizing each area, and identifying access routes and suitable camping sites. From this information, a plan was developed with the help of photographs and drone footage to show the priority areas. This plan formed the basis of our ongoing High Mountain Project.   

FUNDING
In order to execute this project, funding was needed, and partnerships were required. In 2021, funding was initially secured from landowners and the Department of Environment, Forestry, and Fisheries (DEFF). In later years, the Gouritz Biosphere Cluster Reserve and LandCare also provided additional funding for the high mountain project.


TEAMS
​This project required the establishment of a high mountain clearing team. In order to work in these remote conditions, each member underwent training. These training courses included ‘Overnight wilderness camping’, ‘first-aid training, and ‘snake awareness and response’. 45 people underwent this training in September 2020 and again in July 2022.

The mountain team took on this project with creative enthusiasm. In order to be efficient, the team camps out for continuous days in the mountain. They are provided with camping equipment (that needs to be durable and lightweight) such as tents, backpacks, sleeping bags, sleeping mats, flashlights, and cooking stoves. 

The first team was operational in February 2021, the team had to come to terms with clearing aliens at high altitudes and all the challenges that these types of projects come with. These include working in harsh weather conditions and being temporarily cut off from public communication. The team has a radio to communicate with the conservancy. Despite the difficulties, the mountain team never feared these challenges and they continuously appreciate the view that this work comes with (as shown here in a video). 

This project includes initial inspections, internal inspections, and follow-up control. Initial inspections are done beforehand by the conservancy team to determine the workload, and days needed to camp out on the mountain slopes. Then, final inspections are done to observe the clearing team’s progress. In some cases, drones are used to assess and document progress. 

CHALLENGES AND LIMITATIONS

1. Weather is the biggest challenge; the teams must have at least four days without mist and rain to do the job efficiently.
2. Inspection and management of this project are time-consuming.
3. Removal of large pines is done by a small petrol chainsaw (that needs to be carried up the mountain).
4. Daily communication and check-ins done via radio are essential for the safety of our teams.
5. The use of drone footage assists in inspections but cannot replace in-person inspections.
6. Continuous follow-up procedures are done for small pine and hakea because it is not easily seen in walk-throughs.