Pictured Above: In this orchard of 788s one line was selected as a trial. Every second tree was cut back post-harvest. Some trees will be left as 788s to rejuvenate them, to see how long they will take to come back into production. The remainder of the 788s that were cut will be ‘top-worked’ to 816s.
Australian pruning methods adopted a year ago to bring young trees into harvest earlier and grafting methodologies to rejuvenate harvests in older macadamia orchards are under way outside Port Shepstone, in KwaZulu-Natal.
Bruce and Kyle Pepworth visited the macadamia-producing regions of Queensland and Northern New South Wales expressly to learn orchard management methodologies used by the Australian growers.
The Pepworths have two strategies under trial, which include, first, how a hedge trimmer is used to prune younger trees to generate improved tree complexity, and how to rejuvenate older trees where yields are in decline.
And second, in some orchards where blocks were planted to single varieties more than 25 years ago, the trees have started to show a marked decline in yield. This is prevalent in A4s and particularly in 788s.
Kyle Pepworth shows where the tips of more mature trees were clipped using pruning shears to allow for more robust re-growth.
Kyle Pepworth said the Australian tree management methods were being adopted to make sure:
- Newly planted or younger trees grow more uniformly and are more complex. Hedging promotes earlier production and makes for a stronger and more resilient tree in adverse weather conditions.
- The grafting or ‘top working’ provides an opportunity to convert the orchard to a more consistent bearing variety and;
- cutting out every second tree allows for those left behind to keep on bearing until the ‘new’ or ‘topped’ variety begins to bear. This method also provides shelter for the newly ‘top-worked’ tree. Those left uncut will be cut down once the new variety begins to bear. The same procedure of ‘top-working’ will be done with the remaining undesired variety. A further aim is to introduce different varieties into existing mono-varietal blocks to promote cross pollination.
In this practice, for the first five years from the time the young trees are planted, they are hedged roughly every six months. A hedge trimmer is used to cut about 15cm off the circumference of the young tree. The direct aim is to improve its “complexity” in the early years. Or, put more simply, the different aged wood or re-growth after the half-yearly cut “builds” the tree in such a way that it creates numbers of complex branches right around the tree, creating layers of different age-bearing wood throughout.
Added benefits of hedging:
- More leaf area is created within the tree canopy, allowing for higher rates of photosynthesis and carbohydrate production.
- The orchards become more uniform or aesthetically more pleasing and easier to maintain.
- Larger tree stem diameter is noticeable and allows for larger root development, which then anchors the tree in adverse weather conditions.
Once the tree has matured past the age where hedging is not needed and has grown too big, then a simple transition to limb removal is adopted as all of the branches are the same size. The ‘topped’ trees also start producing earlier.
Clipped branches on Beaumonts show strong re-growth.
Pepworth said he and his father had seen three-year-old ‘topped’ trees laden with fruit during their visit Down Under.
“A further benefit is that the stems and branches thicken up, making the trees more resilient to high winds. Added to the usual annual pruning, they were using pruning shears to shape and top trees that were older than six years to also improve their complexity,” Pepworth said.
Macadamia orchards are a long-term investment, he added, and the market crash since 2021 and climbing input costs had emphasised the real need for a quicker return on investment.
“Our main objective here is to try to bring the young orchards into production a lot sooner and realise an income as soon as possible to offset capex and input costs,” he said.
Top working
Australian macadamia expert Chris Searle said ‘top working’ also assisted in promoting cross pollination, as a diverse selection of varieties could be grafted on to the stumps of the mature trees, thus promoting yield.
“This is a very old technique which is used in a lot of other tree crop industries. It has been used in a small way in the Australian industry since the early 1990s but has never really taken off, due to our labour costs,” he said.
He added that it was also a very effective way of rapidly introducing pollinators into large single variety blocks
Essentially, cross pollination between different macadamia varieties has recently proved to significantly improve yields and total kernel recovery. In the early development of the industry – particularly in South Africa – orchards were planted up as solid blocks of singular varieties across the developing orchards, which is not ideal for better quality nuts or an increased nut set.
Top working or grafting younger trees on to old macadamia varieties has given farmers options, particularly in such a young industry where research is regularly bringing up new and improved orchard management strategies.
More mature macadamia trees in the orchards are showing an improved nut set after outside branches were cut back with pruning shears.
How does ‘top working’ or grafting work?
Searle said the trunk of the replacement tree is first painted with white plastic paint up to the height where it will be cut off, to prevent sunburn. The top of the tree is then cut off to about 1m to 1.3m. A nurse branch is left behind, generally on the northern or western side of the trees. The aim is to provide shade for the new shoots and grafts while allowing the stump to re-shoot. The replacement variety is grafted on to the new shoots, effectively converting the above-ground portion of the old tree to another variety.
“The nurse branch, while providing shade, also provides energy to the roots, keeping them alive until the new grafts have taken. Once the grafts have taken and are growing vigorously, the nurse branch is cut off. So, what you have is a ‘new top’ on an old established trunk with all of its reserves and energy,” Searle said.
And because of the existing “huge” root system, the “new top” can come into production within two years because unlike in young trees, the new tree doesn’t have to put energy into growing an extensive root system, he added.
The practice is labour intensive and as a result is impractical in Australia, due to extremely high wage costs. However, Searle said in South Africa it was practical.
“I will be working with several farmers in the South African industry to remediate old or large single variety orchards to introduce the right pollinator varieties that improve both yields and potentially nut size.
“A focus in coastal orchards will be topworking existing Beaumont orchards to suitable cross pollinators like Nelmac 2 and A4, which are ideal for this cultivar,” he said.
