Shedding new light on macadamia production

A NEW study aims to shed more light on the biggest question facing the NSW north coast's $80 million macadamia industry - when and how to prune macadamia trees.

NSW DPI scientists at Alstonville's Centre for Tropical Horticulture are conducting a "back to basics" study of the fundamental physiological processes of the macadamia tree. The aim is to guide the development of a long-term strategy for maintaining the size of macadamia canopies.

"How you prune a tree dramatically affects the way it intercepts light - but we need to know more about how light interception and distribution within the tree impacts on shoot development, flowering and ultimately yield of nut-in-shell," said Dr David Huett, senior research scientist with NSW DPI.

Dr Huett said that due to the vigorous growth of macadamia trees, orchards planted at high densities of 300 to 400 trees per hectare were quickly facing problems with erosion, spray penetration and harvesting due to the shading produced by large trees.

"Some growers are intervening dramatically by severely topping trees or removing every second tree, causing a substantial reduction in short-term yield," he said.

"Gentler intervention, such as side hedging to maintain alley widths, has less effect on yields, but needs to be repeated more often.

"But there is no proven long-term strategy for maintaining the size of macadamia canopies."

He said the new study, funded by the Australian Macadamia Society and Horticulture Australia Ltd, would develop a better understanding of the physiological processes governing vegetative and floral shoot development in macadamias.

Recent work on lychee has shown that if the latest flush of shoot growth at the beginning of winter is immature, flowering in spring is reduced. Should a similar effect be shown for macadamia this would have implications for the timing of hedging and pruning treatments.

"A range of canopy architectures will be compared in a major field experiment at the Alstonville Centre for Tropical Horticulture and on some local growers' properties," said Dr Huett

"These treatments will produce a range of within-canopy light conditions.

"The results should help us understand the relationships between light, photosynthetic performance and longevity of leaves, fruitfulness of buds, flowering, and fruit set.

"This will help growers develop more efficient macadamia canopies and improve orchard productivity."

Media contact: Dr David Huett, NSW DPI, Alstonville (02) 6626 2400.