Dr Schalk Schoeman of Sonbesie Consulting offers valuable insights into the challenges and progress within South Africa’s macadamia industry. Drawing on years of field experience and research, he unpacks current pest management trends, the impact of shifting climatic conditions, and the importance of sustainable orchard practices. His analysis provides growers with practical, science-based guidance to strengthen resilience and maintain productivity in a changing agricultural landscape.
Five aspects of macadamia crop protection have changed significantly during the past decade, namely:
- Co-ordinated reorganisation of the chemical crop protection industry globally.
- Entry of several biological control companies into the market.
- The outbreak of the macadamia felted coccid linked to bark borers as well as stem and tree dieback pathogens.
- Loss of sensitivity of certain organophosphates and synthetic pyrethroids against stink bugs.
- Cost of insect management has increased substantially.
When the abovementioned factors are considered, it is very clear that a new way of thinking supported by strong leadership is now urgently needed in the field of crop protection. Additionally, it is self-evident that any proposed solution will have to comply with the principles of financial and ecological sustainability.
The stink bug complex can be regarded as the key pest of macadamias in South Africa. If left uncontrolled, it is the only group of pests that will make the production of high-quality macadamia nuts impossible.
Traditionally, this complex has effectively been managed by the application of broad-spectrum organophosphates and synthetic pyrethroids. It is also precisely against these two pesticide families that a loss of sensitivity (resistance) has been recorded during the previous two seasons in Mpumalanga regions.
Additionally, the macadamia felted coccid (MFC) is known to become troublesome even in Australia (host country) if too many broad-spectrum products are applied in relatively close succession. To initiate classical biological control, the macadamia industry is currently busy with the importation of Metaphycus macadamiae, and frequent applications of broad-spectrum products for stink bugs will disrupt these expected levels of biological control.
Protection via alternatives
Alternative options for stink bug management are therefore the key for unlocking the entire macadamia crop protection dilemma and should be regarded as the highest research topic possible.
What are our options?
- Mass releases of the commercially available parasitoids Trissolcus basalis and/or Telenomus sp.
- Ant control – does it influence biological control of stink bug egg masses?
- Treatment with entomopathogens (viruses and fungi). This could be done as stand-alone treatments but preferably in combination with certain pesticides, as synergistic effects are known to occur.
- Evaluation of the indigenous Tachinidae parasitoid Cylindromyia eronis for supplementary control as well as the reimportation of two parasitoids that were previously released viz: Trichopoda giacomelii and Trichopoda pennipes.
- There is also a very exciting possibility that defensive volatile compounds can be used to deter stink bugs.
- Integrated pest management (IPM) = knowledge. Although there are several monitoring methods, the most ideal method to determine the presence of bugs in the orchards is to use pheromones. Good news is that the main component of the two-spotted bug pheromone has already been isolated and patented, and research into commercialisation of this product should be regarded as the highest research priority possible. The macadamia industry should support this research as it will have significant economic benefits for the growers.
Holistic approach to orchard management
It is very clear that we must deal with macadamia orchards as ecological units and that mitigating practices applied against one pest will very likely have downstream effects on other pests as well. As such, it is of critical importance that improved production systems and products be independently tested and demonstrated to farmers.
Manipulation of factors to enhance natural plant resistance is already playing an increasingly important role in macadamia production. Not only does the optimisation of certain elements such as silicone have a direct and measurable effect on notorious pests like thrips, but the last few winters also showed us that plants with a higher inherent immunity tended to survive cold snaps much better.
The elephant in the room is the link between macadamia felted coccid/shot hole borers and branch and tree dieback, as the incidence of pest-related tree mortalities increased significantly during the past two seasons. Botryosphaeria species are latent, endophytic fungi that can live asymptomatically in healthy trees. They become pathogenic when trees experience stress from factors like drought, heat, nutrient deficiency, mechanical injury or insect damage.
Stressed trees have weakened defence mechanisms, and this allows Botryosphaeria fungi to transition from a dormant state to an active, disease-causing phase, leading to dieback.
The fungi often enter trees through wounds, insect tunnels (e.g., from bark borer beetles of the family Scolytidae), or natural openings. Stressed trees are less able to seal off these entry points, facilitating fungal colonisation of vascular tissues, which disrupts water and nutrient transport.
Bark beetles are also highly attracted to trees that are stressed. These trees emit volatile organic compounds, which serve as chemical cues for beetles to locate suitable hosts. Stressed trees have compromised defence systems and are more vulnerable to successful colonisation.
Bark beetles use pheromones to co-ordinate mass attacks on stressed trees. This overwhelms the tree’s defences, allowing beetles to bore into the bark and establish tunnels for reproduction. Due to these mass attacks infected trees often succumb very quickly.
Many Scolytidae beetles carry symbiotic fungi that they introduce into the tree. These fungi disrupt the tree’s nutrient and water transport, further weakening it and aiding beetle success. Stressed trees are less capable of resisting fungal spread.
The simultaneous presence of all three pathogens will create a negative feedback loop, as dead trees provide breeding grounds for more beetles, increasing the likelihood of attacks on nearby stressed trees. While certain chemical treatments can be considered for Botryosphaeria and shot hole borers, they are not spectacularly effective, and the best method of control would be to enhance tree health.
Dr Schalk Schoeman – Sonbesie Consulting
What is happening on our farms to mitigate risks from pests and diseases?
- South African farmers are known for their resilience and the following are becoming mainstream basic farming practices:
- Supplementary releases of parasitoids and predators for major macadamia pest insects.
- Orchard floor management with cover crops/grasses/weeds to make our orchards more parasitoid-friendly. Remember that adult parasitoids need to feed, and flowering cover crops will provide these insects with a rich resource for energy.
- Installation and establishment of bat boxes, raptor perches and fallow fields for the enhancement of biodiversity, which will have positive downstream ecological consequences in the macadamia ecosystem.
- Supplementation of soil ameliorants/compost for the more holistic management of tree health.
- Establishment of various grazing animals in the orchards for weed management and for more rapid and effective nutrient cycling, to reduce our reliance on synthetic chemicals.
- Some farms are even re-establishing the critically endangered Aloe simeii in wetlands.
- While these practices are something of which to be immensely proud, unfortunately they are yet to form any part of a co-ordinated drive to improve general sustainability on farm level.
Active consequence monitoring to ensure a positive feedback loop is very important as it will help to sustain South Africa as the current global leader of high-quality nuts produced according to the highest environmental standards.
Dr Schalk Schoeman – Sonbesie Consulting
