This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

Canopy management is a significant challenge for the Australian avocado industry. The avocado tree must produce new growth each year to remain productive. However, if left unchecked the orchard eventually becomes crowded with a loss in fruit quality and yield. Large trees are also difficult to harvest and spray. Flowering and fruiting occur in well-lit terminal sites on the surface of the canopy. In crowded orchards the productivity of side canopies is lost due to insufficient light reaching lower levels of the tree.

The ‘Avocado Canopy and Orchard Floor Management (AV00007)' project was carried out to develop pruning systems that controlled tree size but with minimal negative effects on tree yield and fruit. Mechanical pruning systems were used because of their cost efficiency. Factors such as the time of pruning were investigated. Several chemicals that are known to reduce tree growth were also evaluated. Other treatments to improve fruit quality from pruned trees were studied, including calcium treatments and mulching.

Research was primarily conducted on ‘Hass’ grown in warm subtropical southeast Queensland (Childers/Bundaberg). Pruning trials were also conducted on ‘Shepard’ on the Atherton Tableland in north Queensland. The research found that:

• Pruning can control tree size, however the timing of pruning will determine the success of this canopy management strategy
• Yield was reduced in trees pruned for the first time, but this effect was minimal after 2-3 years
• Trees should be pruned after harvest and prior to the onset of flowering to minimise flower removal and maximise yield
• Pruning can stimulate vegetative growth, and the timing of the post-harvest prune will influence the amount of regrowth during flowering and fruit set. Pruning trees 1-2 months after harvest reduced vegetative growth and maintained fruit quality
• The success of summer pruning is dependent on establishing a tree shape at fruit set so that further pruning can be implemented in the presence of the crop
• The timing of the summer prune influences the length of shoot regrowth and the size of the canopy. Trees should be pruned no later than December to avoid reduced flowering in shoots the following spring
• Foliar application of Sunny® at flowering increased fruit size by 7-16 per cent but generally did not increase final tree yield. Sunny® applied to the regrowth following summer pruning can reduce shoot length and increase flowering the following spring.
• Pruning can reduce the concentration of Ca in the fruit. Low fruit Ca has been associated with poor fruit quality
• Apogee® (prohexadione-calcium) when applied at flowering increased fruit quality. Application of NAA to branches following pruning reduced regrowth in the treated area however regrowth occurred further down the branch
• Mulching enhanced root activity and improved fruit quality, but no increase fruit size or yield was observed.

The results of this research provide information on canopy management strategies involving pruning and growth regulator application on ‘Hass’ and ‘Shepard’ avocado in warm subtropical climates. Further work was required in other production areas before industry-wide recommendations can be made.