Pictured above: Dead bees on flowers are becoming a common occurrence with the increase in pesticide use in orchards.

For at least two years, South Africa’s national macadamia crop estimates have failed to meet forecasted yields by several thousands of tons. While the reasons underpinning the shortfall are seemingly under-researched, notable trends are emerging.

The relative infancy of the industry has meant research into the complexity of orchard management and yield influences has yet to fully mature. And while macadamia farmers have continued to operate relatively successfully within known best practice, the knowledge vacuum is now affecting production efficacy and the environment, say experts.

For example, scientists, beekeepers, and growers are yet to agree on the optimal beehive density or the crucial role played by insects in securing top yields, while research remains outstanding on the long-term influence of high chemical loads used to prevent disease and pest load on the orchard environment.

What is clear, however, is that the 4.5 tons-a-hectare mature tree yield first touted by the industry just a couple of years ago has now dwindled to just 2.5 tons per hectare. Crop estimates for the past two harvests have failed to reach the predicted heights as growers and processors continuously revise tonnages downward as the seasons progress.

For example, predictions for this year’s harvest started out at more than 57 000 tons, but this was then revised in May by the South African macadamia representative body, SAMAC, to just more than 56 400 tons. In August this number was further revised down to 54 174 tons in shell, measured at 1.5% moisture content.

Barry Christie

Green Farms Nut Company Group Agricultural Technical Manager Barry Christie said this year the industry grossly miscalculated the yield.

“Furthermore, we can’t say definitively why the yield was that much lower,” he said. And while he accepts the impact of adverse weather conditions on the crop at crucial stages of nut development, he believes the vagaries of the climate were not solely to blame for the decline in harvest.

“In 2019 we had hot and dry weather in October, which affected the flowers ahead of the 2020 crop. Last year, we had wet and cold weather in October, which resulted in a fungus spreading among the flowers. But what is more concerning for the future crop, however, is the way our orchards are being managed. Immature nuts are increasing, yet there is no correlation with germination, which means the problem is more likely macadamia nut borer (MNB), rather than out-of-season nut development. I have never seen such a high incidence of the borer as this past year,” he said.

Pest load increase

The fight against stinkbug infestation has remained since the very first tree was planted in the country. What is of concern, however, is the increase in new insect “plagues” in the orchards.

The felted coccid, for example, first made its appearance nearly four years ago when contaminated trees were imported from Australia. The pest has since spread through the orchards at pace.

Dr Schalk Schoeman, research manager at Macadamias South Africa (SAMAC), said the tiny pests were easy to miss, which meant often, by the time they were detected, the trees were already severely pest-ridden. Also, general pesticides remained ineffective in fighting off the bug.

Dr Schalk Schoeman

Dr Schalk Schoeman

Just last month, the scientist said, he had received the first batch of parasitoids from Hawaii, which were now under test before being released into the orchards at scale to make sure they weren’t harmful to existing but harmless scale insects.

But, Schoeman said, the introduced parasitoids were no silver bullet and would require careful management by farmers, particularly as pesticide applications had to reduce to make sure the Hawaiian visitors were not killed off along with the stinkbugs.

Another villain – which is becoming more and more prevalent – he said, was the shot hole borer, which eventually destroys almost all types of trees, including avocados and citrus.

“It seems to be spreading very quickly in South Africa and is already found in most macadamia production regions. Every year the numbers are escalating, and we have no idea why. What we do know is trees under stress are more susceptible to infection. And since climate change is playing havoc with the weather, which induces stress in the trees, shot hole borer and climate change are connected,” Schoeman said.

Thrips were also on the increase, but of less concern. Problems arose, however, when the pest threshold got too high and tiny leaf syndrome caused by thrips reduced the trees’ carbohydrate reserves.

Schoeman said it would be better if farmers refrained from applying pesticides for thrips, as the disadvantages outweighed the benefits.

“For production to flourish, there must be life in the orchards. Chlorpyrifos does not control thrips but makes them worse. We have been using these products for decades and the insects are immune. Instead, farmers might consider a winter orchard floor treatment with a pathogen to control soil dwelling stages of any overwinter species,” he said.

And, although pests in the orchards were on the increase, farmers would be remiss in thinking increasing pesticide applications was the answer for increased yields. Schoeman said improved penetration of the chemicals that the farmers were already applying, coupled with sufficient sunlight, appeared to be a better solution.

Immature nuts are increasing, signalling a greater prevalence of macadamia nut borer.

Pruning holds the key

Christie said insufficient pruning was the cause of so many issues, which were directly linked to yield as pests, such as the nut borer, preferred the lower and deeper aspects of the tree where they were shielded from the elements. Correctly pruning trees meant they had little place to hide and spray applications were able to effectively reach them.

“At the moment the industry in South Africa has a very high ratio of trees that are too big to manage. This means ineffective pesticide applications then result in farmers suggesting the chemicals are not working, when in truth, it is ineffective spray penetration,” he said.

He added that the effective and responsible use of chemicals was to make sure spray rigs were accurately calibrated, chemicals were mixed and combined properly, and the target area was reached. The efficacy of the spray could be measured by using water-sensitive paper in trees at different heights during the spraying, he said

The lack of good pruning was also one of the reasons big, mature trees were not achieving the expected yield potential.

“The nuts grow on the thinner, outer branches and not the big trunks on the inside of a tree. As the trees grow and become woodier, so their capacity to bear nuts declines if they are not properly pruned. The nuts on the outside of the tree on the newer branches can make it look as though the tree is bearing at optimum, whereas in reality, the inside of the tree is devoid of nuts. This is where many crop estimators get it wrong,” Christie said.

Schoeman agreed farmers could manage pests more effectively by increasing the sunlight in their orchards.

“This creates a stable eco-system as grass and weeds can grow between the trees and provide higher biodiversity. Tree density plays a big role in pest load and the higher the density, the higher the pest load. Less density means it’s also easier to spray if the need arises,” he said.

Chemical overload

The full impact of chemical loads on orchard health has yet to be fully researched and understood. What is known, however, is the higher prevalence of micro-organisms, beneficial insects, pollinators and parasitoids equals happier trees, and happy trees produce top nut yields.

Neonicotinoid residues in flowers were far higher than the lethal dose, nearly 12 months after the chemical was applied.

Christie said he had now seen for himself how farmers were changing to practices more in keeping with best biological farming methods and how they were reaping the rewards.

“When looking at the Unsound Kernel Recovery (USKR) percentages I can definitely see a pattern where those moving towards biological approaches are achieving lower incidents of nut damage. These farmers are not necessarily 100% biological in their approach, but they have a fully developed integrated pest management approach where chemicals are only used as a last resort and don’t make up 100% of their spraying programmes.

Improved integrated pest management

Both Schoeman and Christie agree the more biologically empathetic approach to pest managements starts with a proper integrated plan, which aims to move away from a calendar spraying programme and opt instead for more regular scouting, coupled with an understanding of when the pest become so rife it is no longer economically viable to spray: in other words, what is economically viable when deciding whether to spray or not. A greater focus on orchard health is an added priority to guarantee the trees are strong enough to withstand pest invasion.

There is an increasing trend showing that a biological approach increases nut quality.

Schoeman also advises an increased focus on precision farming. “Our levels of precision are not very good in macadamias. When it comes to pesticide applications, we blanket spray and hope to hit a few insects along the way. Training will become crucial in the future to improve management practices. Many farmers are at the mercy of chemical reps and consultants, so we need to empower the farmers to make their own decisions and understand better how to scout, when to spray, and how.”

He said integrated pest management was nothing less than access to good information and then applying that information accurately.

“You can’t practice IPM if you don’t know how the insects operate. Years ago, we believed in cleaning up the orchards with chemicals just after winter. Now we know such an application has no effect on the eventual stinkbug numbers because their numbers are so low at that point in the orchard.

“The way we handle thrips must also evolve. We did a trial during flowering where we removed 30% of the flowers in an orchard against a control where no flowers were removed. When it came to the harvest, we found there was no difference in the yield between the two orchards. This tells us that even if thrips affect 30% of the flowers, it will have no bearing on the final yield. So, spraying for thrips is not only unnecessary, but harmful to other beneficial insects in the orchards. Since this is also the time bees are most prevalent, it is especially important to limit chemical applications,” Schoeman said.

Targets to cut chemicals

While Schoeman said organic nut production seemed an unlikely solution, greater effort had to be made by farmers to reduce chemical use, as not only was it the right thing to do from an environmental perspective, it would also result in healthier orchards., But, he added, consumers were also dictating what they would or would not tolerate when buying their food.

“The world is clamping down on chemical use, and farmers must remain mindful of a possible future ban on endocrine disruptors, glyphosate, neonicotinoids, pyrethroids and organophosphates. Farmers therefore need an alternative strategy to pest control, not just a spray programme,” he said.

The European Union (EU), which is a significant market for South Africa’s macadamia nuts, has set a target to reduce pesticide usage by 50% by 2030. This is valid for countries within the EU and those exporting fresh produce to the Union.

Schoeman said it would be very difficult for South Africa’s macadamia industry to comply with this reduction presently. “We need to start planning for the future now and have alternative pest control strategies in place. Relying on chemical companies to come up with alternatives is not a foolproof method either, because of the long regulatory process to bring new products to market. It can take up to seven years to register a new product. Any new products are likely to be far more expensive than anything on the market currently since the companies need to recoup their development costs.

“On the other hand, there are very effective parasitoids available, which are vastly underutilised. It takes a more biological approach to farming and a different management style, but it is one of the few options that will be available to farmers in the future,” he said.

Schoeman stressed the importance of returning life to the orchards, to increase tree health and their ability to produce.

“We must bring back the balance to the orchards and move away from our monoculture mentality by planting cover crops, not killing all the insects, and by getting off the pesticide treadmill. Farmers might fall when they first get off the treadmill, but I believe they will get up and be better for the experience in the future,” he said.