Following rapid expansion between 2014 and 2019, most of South Africa’s macadamia nut orchards have reached maturity. The larger trees and denser orchards require a different approach to management in order to get the full yield that mature orchards promise.
Mulch is added to the rows to improve microbial activity, which improves soil health and increases nutrient uptake.
Photo: Lindi Botha
Bigger is not necessarily better. While mature macadamia orchards can deliver higher yields, improper care will result in trees with high input requirements but low outputs.
For Denys Snyman, farm manager at Barberton Valley Plantations in Mpumalanga, regular pruning and root health are central to his care strategy for the farm’s 807ha of macadamias. The orchards vary in age, with some over 20 years old.
“The best time to start pruning macadamias is a year after planting,” says Snyman. “This is when you start establishing the strategic frame of the tree by removing unnecessary branches. Branches that are not productive are just consuming fertiliser and water, but don’t give anything in return. If the focus is on vegetative growth, yield is reduced, and the tree takes that much longer to get into full production.”
Denys Snyman, farm manager at Barberton Valley Plantations in Mpumalanga, focuses on pruning and root health to achieve high yields from mature macadamia nut orchards.
Trees that are left unpruned present multiple problems, all of which reduce a farmer’s income.
“Trees that are overgrown and dense prevent sunlight and chemical penetration, reducing yield and quality. By constantly pruning the tree, it is renewed. We get our best nut set on the new flush from branches that were pruned the previous season. Annual pruning is therefore not negotiable. If cash flow is an issue, then I’d rather cut back on fertiliser,” says Snyman.
Optimal pruning centres on more than just cutting windows for better light and chemical penetration. He also focuses on removing branches that have grown vertically, since these increase density without producing nuts.
“Nuts grow on horizontal branches, so it is important to stimulate horizontal branch growth from the central leader,” he explains.
Where trees have not been pruned from early on, secondary leaders are common, but should be removed to create the required windows for sunlight.
“If these branches are old and thick, it may seem counterintuitive to remove such a big part of the tree. But I’ve seen yields pick up the following year when we have done this.”
Aside from vertical branch removal, trees are also layered.
“Horizontal branches should be layered with at least a 600mm gap between lateral branches. I want to be able to see straight through the tree when I walk around it, with no dense, dark patches,” adds Snyman.
With this kind of selective pruning, he has limited use for hedge trimmers, which are often used to cut back overgrown orchards. However, he says there is one exception: the 741 cultivar.
“A 741 needs to be topped regularly because it grows very tall. A hedger is useful to manage the height, but internal branches must still be removed individually to prevent the tree from becoming too dense,” he says.
Tree spacing also plays a role in optimal light and chemical penetration. Barberton Valley Plantations’ older orchards are planted at an 8m spacing between the rows, and 3,5m between the trees. This results in 357 trees/ha. New orchards are planted at a 9m spacing between rows and 3m between trees, resulting in 370 trees/ha.
While both spacing configurations work well, the latter provides more sunlight in the row and more trees.
On top of the above-average size of Barberton Valley Plantations, which requires careful management of tasks to ensure each tree receives the care it requires, the various cultivars add additional challenges.
The farm has a mix of 14 cultivars, including 816, 741, Nelmac, A203, A268, H2, 344, 788, 814, A4, 695, Daddow, A16, and 842. Yields vary depending on the cultivar and soil type, but average 3,5t/ha across the farm annually.
Snyman notes that while the 741 provides good yields of up to 4,5t/ha, the total kernel recovery (TKR) is below average. The 816 cultivar, on the other hand, provides above-average TKR, while yields average 2,8t/ ha.
“It’s a fussy tree and does not like to be pruned. Just about every ailment that can affect macadamias is drawn to this cultivar, so it can cost you a lot to keep going. But if you treat it well, you can attain yields of 3,2t/ha, with a high TKR.”
He aims to increase his yields by 15% to 20% each year, based on tree growth and better management.
The consistent pruning regime has reduced chemical applications, since penetration is improved. While he previously needed to apply pesticides using 3 000ℓ of water per hectare, it has now been reduced to 2 200ℓ.
“Before we embarked on this pruning programme, we just couldn’t reduce the macadamia nut borer numbers, despite the high pesticide application rate. I realised that the chemicals couldn’t penetrate the wall of vegetation.
“Once the trees were opened up through pruning, the pesticides became far more effective. Now the yield and quality are higher, while the pesticide costs are lower,” he says.
While mature trees are better able to weather high temperatures and hot winds, they are not immune to them. These climatic conditions are prevalent in most production areas in late spring, at a time when the orchards can least afford it.
Fragile flowers, some of which have already started setting nuts, can be burnt by the heat and wind, significantly curtailing the harvest.
Snyman laments that the only mitigation available is to increase irrigation to help the trees cope with the heat. But this is easier said than done, since most farms’ irrigation infrastructure doesn’t allow for such increases.
“Optimal water management is most critical during nut set. You need to be on the ball during this time to ensure that, at the very least, the first 300mm of soil stays wet. A sign that the trees haven’t received enough water is the appearance of sticky water-like droplets on the flowers. If the flower flush is bigger than usual, but the irrigation wasn’t adjusted accordingly, this is also likely to happen,” he explains.
If these droplets appear, Snyman responds by adding a kelp supplement to the first foliar feed, which would usually only contain boron and zinc. The kelp helps the trees manage stress, and is applied once per season at 2ℓ/ha.
However, if the trees show signs of stress that has resulted from a Phytophthora infection, Snyman does another kelp application.
While the exact water requirements for macadamia nut trees are widely debated, Snyman follows the generally accepted norm of 400ℓ/tree/week.
“Looking at research from Australia, it is clear that irrigation needs to be increased at critical times, such as during nut set and hot spells. Then, between 500ℓ and 600ℓ/tree/week is advisable.”
The timing and application method of irrigation requires further thought. Snyman has found that keeping the soil too moist just before flowering will result in a tree that is too comfortable.
“The tree then won’t see the need to produce nuts to reproduce, since it doesn’t perceive any threat. Irrigation is therefore held back, creating light stress to induce flowering. Once flowering has commenced, we start irrigation, keeping the soil profile filled once the nuts have started setting.
“During the nut set and nut swell phases, a tree can use nearly double the amount of water than usual, so keeping an eye on moisture levels is crucial during this time,” he says.
With much of the Barberton Valley Plantations farm having gravel soil, Snyman has had to alter management practices to prevent over-compaction of the soil. This includes a change in irrigation practices, switching from micro-sprinklers with orange nozzles to those with blue ones. The former delivers water at a rate of 100ℓ/ hour, while the blue nozzles deliver 45ℓ/hour.
“With the orange nozzles, I used to irrigate in a three-hour cycle once per week, which resulted in a lot of water being dumped all at once, but leaving the soil to dry out over six days. This, coupled with mechanised harvesting practices where the soil is swept clean, created a hard crust in the top soil.
“I’ve now switched to blue nozzles, irrigating 45ℓ/hour over three hours, three times per week. This keeps the top soil moist, which is important to nourish the macadamia’s shallow roots. Macadamias have a proteoid root system, which means all the nutrients are absorbed by the fine roots close to the surface,” he says.
A conundrum that farmers face with maturing orchards is the on-farm bottlenecks created during the harvest season as yields increase exponentially.
Bucking the trend of mechanised harvesting, Snyman has reverted to a manual system in a bid to reduce soil compaction. Aside from the compaction caused by additional wheel traffic in the orchards, the mechanised harvesting process also necessitates the removal of much-wanted mulch.
“The sweeper needs to remove all the leaves and twigs from the nut bed so that the machine can pick up the nuts. We spend so much time and money adding compost, but then clear it all away during harvest. So, we’ve reverted to manual labour,” explains Snyman.
However, during peak times, the staff are aided by mini harvesters, which are pushed like a lawnmower. Nuts collect in a crate attached to the front of the harvester, which can then be tipped into bigger bins at the end of each row.
Hand-pushed mini harvesters reduce harvest time when the nut bed is full.
“This saves a lot of time when the nut bed is filled with nuts, as the mini harvester can collect at double the rate than having to manually pick up each nut. But staff need to understand that it can’t get to every nut, and going backwards and forwards across the whole orchard to collect every nut with the mini harvester is not time efficient. Once the bulk has been collected, or when the nut bed is not full, staff need to walk through and pick up the nuts individually.”
Although the mini harvesters save time in peak harvest season and don’t result in compaction, leaves and twigs on the nut bed still need to be removed to allow the harvesters to work efficiently.
“We use a three-point hitch blower, angled so that the wind just scoops the debris off the nut bed and into the interrow. This way it does not disturb most of the compost. Once the harvest has been completed, we go through the rows with a mulcher to break up the material, and then blow it back into the row again,” adds Snyman.
Optimising the harvesting process has become more complicated as farmers have increasingly started moving away from bare orchard floors, embracing weeds and cover crops. While Snyman leaves natural grass to grow in the orchard, he does not believe in allowing natural vegetation to run rampant.
“There are practical considerations one needs to keep in mind. Firstly, my irrigation staff are not keen to walk down rows where the weeds are waist high and risk encountering snakes. They are likely to skip over the rows, and not do a thorough check to ensure all the sprinklers are functioning properly.
“The second, and perhaps biggest issue, is that when weeds grow higher than the sprinklers, the water sprays against the weeds and I don’t get a good spread of water on the ridge. If the weeds have grown too high, I can’t go in directly with a spray cart or knapsack sprayer before harvest, and would need to slash the weeds first. This increases costs.”
Snyman therefore allows controlled weed growth, keeping the rows clean. A narrow lane alongside the row is also kept weed free to allow staff to move freely in the orchard. The pre-emergence herbicide Alion is used to control the weeds. This is applied after harvest, and provides enough of a knock to limit re-emergence in spring. Another application is done once the nuts have set.
Snyman says Alion has been shown to be less harmful to soil organisms than glyphosate, and does not adversely affect the shallow proteoid roots of the macadamias.
To handle the large harvest and prevent bottlenecks, Snyman has developed a schedule, aided by applications of the plant growth regulator ethephon to stagger nut drop. ‘Stick-tight’ varieties Beaumont and 816 require ethephon applications to force the trees to release their nuts.
While most early varieties drop their nuts when mature, this harvesting window starts overlapping with late-season varieties like Beaumont. By applying ethephon to 15ha of the early varieties at a time, at two-week intervals, Snyman ensures that the harvest is staggered and more manageable.
He notes that it is important to conduct maturity tests on the nuts before applying ethephon, and only to proceed once 90% maturity has been reached.
The seven-year wait for macadamias to reach maturity and produce viable yields does not mean the harvest is a given after year eight. Proper management from day one, and every year thereafter will result in trees that are able to flourish, producing yields befitting of their age.
