Research and development on pest management using biocontrol in South Africa’s macadamia orchards is at an advanced stage, despite supply and demand pressures in the sector, says SAMAC’s top researcher Dr Schalk Schoeman.
Schoeman was the headline speaker at the recent KZN Bee Farmers’ Association Symposium at the Royal Showgrounds in Pietermaritzburg.
He warned, however, that farmers were in a negative pricing cycle and were keenly focused on producing high-quality kernel to capture the high-end ingredient market. This, he said, might slow the trajectory to increased biocontrol in the orchards in the short term.
Dr Schalk Schoeman, research extension manager at macadamia industry body SAMAC.
But within two to three years, pest control in the macadamia sector would look entirely different from what had gone in the past, he added, describing the progress as a “good news story”, which wasn’t grabbing the headlines as it should.
“A lot of broad-spectrum products were used in the past, consisting of three main groups of pesticides that included pyrethroids, organophosphates and neonicotinoids. We are now on the cusp of great change. It is very exciting,” he said.
The main pests affecting South African’s macadamia crop include the two-spotted stinkbug, (Bathycoelia distincta), Thrips (Thysanoptera), the Felted Coccid (Eriococcus ironsidei) and the nutborer complex (Lepidoptera: Tortricidae).
Schoeman said effective pruning remained the primary deterrent for pest infestations on macadamia trees above and beyond any artificial controls, whether biocontrol or pesticides.
“Integrated Pest Management (IPM) is not just one product, but rather a process that includes a range of practices. Farmers should start disease control by pruning – a message which is now broadly accepted by our farming community,” he said.
While the two-spotted stinkbug was an indigenous species – there are more than 50 sub-species and counting – Schoeman said biocontrol methodologies were being used effectively, such as the release of parasitoids and pheromones to disrupt the insect’s life cycle.
Game changing fungus
“We have also identified a game-changer fungus in Beauveria bassiana, which has shown itself as effective in the control of stinkbugs. We are negotiating with a company in Kenya to mass manufacture and commercialise it,” he said.
The Felted Coccid, however, was spreading “like wildfire” in the Nelspruit region and in orchards on the KwaZulu-Natal North Coast.
“The Agriculture Research Council, in collaboration with the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria, is importing a parasitoid from Hawaii, but it is not yet in the country and will be in quarantine for some time,” he said.
Coccid infestations put macadamia trees under great stress in the early stages of infestation. “We are seeing massive die-back in orchards and it will take years for yields to return to previous levels in these orchards,” he added.
For the nut borers, Schoeman said South African scientists had developed a “very effective” parasitoid that was being used successfully on commercial farms in Australia.
But South Africa’s farmers, he said, were tackling the pest threat from a range of angles. “We must brag about what our farmers are doing. They are installing raptor perches for owls and Long Crested eagles in their orchards. One farmer is restoring 40ha of natural habitat in a bid to provide a place where the threatened Aloe simii can again grow in abundance. There are only about 400 of these aloes left in the wild, as they have been uprooted and destroyed through urban development and commercial forestry.”
All of these efforts, he said, were combining to create increased and preferred natural habitat for, particularly, the indigenous stinkbugs alongside the macadamia orchards.
EU Green Deal
Schoeman also warned that the European Union’s Green Deal on the use of various insecticides and pesticides in the orchards would dramatically change current practices.
“Added to this, the chemical industry has decided there are three things they want to eliminate from their products:
- Anything that causes cancer, or
- Cell mutation, or
- Influences the endocrine glands.
“We can expect the withdrawal of any chemicals with these effects by June next year,” he said.
And while this was not overly impactful on the industry, a further 14 co-formulants and oils were on the EU’s banned list.
“If these exclusions change the product by more than 10% then the product has to be submitted for re-registration. Most of these are old broad-spectrum products, so I can’t see companies wanting to go to that trouble and expense. In short, by June next year there will be fewer products available to us.”
Responding to a question from a delegate at the symposium on the Shothole borer, Schoeman said: “I am very, very scared.”
He said the pest had a very wide host range, meaning indigenous trees were also under threat, and it was deceptively efficient in killing off its host trees.
“The trees look happy and healthy on the outside, but when you cut them open, you can see the devastation. It’s a case of slowly, slowly before the tree dies quickly. Macadamias are currently not a reproductive host plant, but this beetle has the ability to adapt very quickly and we have to be vigilant.”
A recent report showed an alarming increase in the beetle numbers, which were now being detected in Nelspruit, Hibberdene, Port Shepstone and Umhlanga on the KwaZulu-Natal North Coast, he added. They were first found in plane tees in the Pietermaritzburg Botanical Gardens before being discovered in macadamia orchards in White River seven years ago.
Cover crops
Also at the meeting, Simon Hodgson, GM of AGT Africa Cover Crops and Forages, agreed that macadamia farmers were on a much more environmentally sustainable trajectory than previously.
Simon Hodgson, GM at AGT Africa Cover Crops and Forages
He said cover crops, which provided diverse foraging opportunities for pollinators, reduced soil moisture loss and improved the quality of soils generally, and were now widely used by producers who were reporting on their benefits.
“There are many ways of looking at the use of cover crops. I am urging farmers to include indigenous plantings as well, particularly where they don’t spray, along the fence lines, for example, where the tractor might turn,” he said.
He warned however, that there wasn’t a one-size-fits-all approach to cover crops.
“There are so many variables, which include what pollinators the farmer wants to attract, the different climatic conditions in different areas, and what grows well in the soils of a particular farm or orchard. We must consider management styles and probably the most important of all, profitability. Farmers must be able to measure the value they are getting from the use of cover crops.”
Cross-pollination
Meanwhile, pollination specialist and scientist Dr Sascha Beck-Pay told delegates that cross-pollination in macadamia orchards was proving successful in increasing yields. She said in-field grafting of different cultivars to encourage varieties to cross-pollinate was becoming more common. “On some farms, where Beaumonts and A4s are planted in blocks close to each other, the first two to four rows where the blocks meet have greater yields because of the natural cross-pollination,” she said.
Some unique products were under investigation to improve pollination, including a “wax-type” formulation that acted as a marker pheromone on each tree.
Research scientist and independent consultant Dr Sascha Beck-Pay
“I am testing this product over the next couple of weeks. We apply it on the stem of every tree where it sticks for four weeks. The product, which was developed in the United States, is designed to encourage bees to fly throughout the orchard to secure consistent yield across all of the trees. It has already been proven on blueberries and kiwis, and now we are testing it on avocado and macadamia trees.”
