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Increase light interception for quality gains

Research & Extension

Maximising light interception and light distribution in orchards can help growers to maximise yield and quality, according to an international tree fruit expert.

Dr Stefano Musacchi, Endowed Chair of Tree Fruit Physiology and Management at Washington State University’s Department of Horticulture, recently visited Australia as part of the Future Orchards® program that is funded by Hort Innovation and delivered by APAL and AgFirst.

He presented at workshops across Australia in June, explaining to growers that the way light is distributed in the tree canopy can play an important role in quality.

“Particularly in the case of apples, light interception is everything because usually the more light intercepted, the more dry matter accumulated, especially in the fruit,” he said.

“Fruit usually accumulates 70 per cent of the dry matter produced by a tree and the more dry matter we drive into the fruit, the better the quality perception by the consumer.

“Quality is a dynamic concept and what growers consider good quality might not be the same as what a consumer perceives to be good quality. Ultimately though, the consumer’s perception is the most valuable definition of quality because if they are not happy then they won’t buy the product again.”

Dr Musacchi says achieving good quality is a matter of taking into account the cultivar, rootstock and environmental conditions.

Once these factors are understood, the best training system can then be determined to target the highest quality.

“In my opinion, the key word for fruit quality is balance,” he said.

“When the tree is out of balance the quality is in jeopardy. If there is excessive vigour not enough vigour then quality is immediately interrupted.

“Keeping trees in balance is a matter of good pruning, good nutrition and good irrigation.”

For Australian orchards, Dr Musacchi says between 65-75 per cent light interception is adequate.

Poor distribution of light in the canopy can have implications on size and fruit over-colour.

Pruning can play in important role in light distribution and keeping trees balanced, Dr Musacchi says.

He described pruning as an investment rather than a cost.

“Pruning is a tool which can help to control the growth of the tree and maximise returns for the grower,” he said.

“Pruning is not a cost – it is an investment to help growers derive more income from their orchards. Pruning can modify the growth of a tree and put it back in balance.”

Dr Musacchi has previously established pruning trials on vigorous varieties where the trees were autumn pruned to reduce vigour.

This, he said, had a very positive effect on light penetration in the canopy and on the following year’s crop.

“An open and well-exposed canopy can increase light penetration, meaning it is possible to have a good compromise between yield and fruit quality,” Dr Musacchi said.

“I believe a bi-axis system with a plainer canopy can really increase the quality levels of fruit because it makes the tree more efficient.

“For a variety like SweeTango®, which is grown in Washington, growers go out and remove all the leaves around the fruit 10-15 days before harvest to minimise over-colour problems otherwise they end up with unacceptable quality.

“SweeTango can become completely shaded by the leaves and for that reason it needs training systems that fully expose the fruit to the light. It requires a plainer canopy — three-dimensional canopies don’t give the fruit of SweeTango enough exposure to light.”

More information

Read through the powerpoint presentations shared during the Future Orchards® walks, winter 2018:

  • Optimize pruning and fruit quality in apple orchards, Stefano Musacchi (USA) – Part 1 |  Part 2
  • Optimize pruning and fruit quality in pear orchards, Stefano Musacchi (USA) – Part  1  |  Part 2  |  Part 3
  • Improving fruit quality, Ross Wilson and Steve Spark, AgFirst


Fruit quality and monitoring Future Orchards News Pruning and training

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