Agriculture Victoria shares the results of their experiment within the Profitable Pears project to help identify the best rootstock, planting density and training system for blush pears.
Replanting or establishing new orchard blocks is a costly exercise. Decisions regarding cultivar, rootstock, training system and planting density have implications for not just potential profits but also management options.
Use of dwarfing rootstocks, 2-D training systems and high tree density are widely seen as the way of the future. Reported benefits include controlling vigour, simplifying pruning and harvest, enabling the use of picking platforms (or robotics) and decreasing the time to full production. However, for pears there have been few comparisons with more traditional orchard designs.
The Planting Systems experiment within the Profitable Pears project was designed to fill this knowledge gap, as a strategic investment of Hort Innovation. A blush cultivar, ANP-0131 (formerly known as Deliza™), was bench-grafted to D6, BP1 and Quince A (with Buerre Hardy interstem) rootstocks in winter 2013 and planted in the pear field laboratory at Agriculture Victoria, Tatura. Twelve training system by tree density treatments were compared for vegetative growth, yield and fruit quality performance. Row spacings were 4.5m and tree spacings were 0.5–3m in vertical and traditional systems and 0.5–2m in the Open Tatura trellis.
Trees were in their fifth leaf in 2017–18 with yields ranging 17–74t/ha. So, how did the different rootstock and planting system combinations perform?
Potential yield differences were established early in the 2017–18 season with significant differences in both flower density (clusters/metre row) and the proportion of flower clusters that set fruit. Trees on Quince A had a greater flower density than those on BP1 and a greater proportion of clusters set fruit than in trees on D6 or BP1.
Heavy crop loads on trees with Quince A rootstock compromised fruit size.
Yield (t/ha equivalent) was consequently similar for trees on Quince A and D6 rootstocks. Despite lower crop loads, trees on BP1 produced fruit of similar size to those on D6. Overall, trees on BP1 suffered a 10–13t/ha yield penalty.
Quince A rootstocks produced more flowers and set fruit well but the high crop loads increased the likelihood of needing a thinning intervention to ensure adequate fruit size. Conversely, in years with low fruit set, trees with D6 rootstock may lose packout yield due to oversizing of fruit. At this stage of the research, D6 is a preferred rootstock for use with ANP-0131 due to the tendency to set moderate crop loads and ability to size fruit. Longer-term studies are required to confirm this trend and identify appropriate crop loads for mature trees.
Yield increased with planting density. This corresponded with the development of tree structure. Leaders in ‘high’ and ‘ultra-high’ treatments reached the top wires (3.8m for vertical and traditional systems and 2.5m for the Open Tatura system) by their second or third leaf, whereas average leader height in the ‘low’ density treatments did not begin to reach the top wires until fifth leaf.
There was no yield benefit from increasing planting density from 2,222 trees/ha to 4,444 trees/ha. At low planting densities, trees on Quince A yielded well compared to those on D6 and BP1.
Yield tended to be highest in the ‘high’- and ‘ultra-high’- density Open Tatura trellis (on D6 and Quince A rootstocks).
Trees on BP1 performed poorly on Open Tatura trellis. Cordon and vase (low-density) treatments had low yields. Training cordons with six and eight leaders resulted in delayed tree establishment. Multiple shoots were allowed to grow in the first season; two of these were then selected to create the horizontal cordons and leaders did not begin to grow until the second season. Faster development of these systems should be possible by use of two-leader nursery trees at least 1.8m high so that cordons can be laid down at planting, removing downward- and inward-facing buds at green tip and cutting back strong vertical leaders close to the trunk in early summer.
There was little difference in blush coverage with the exception of reduced coverage in Open Tatura systems at ‘ultrahigh’ and ‘high’ densities and, to a lesser extent, in vase systems.
More intensive tree management may be required to ensure adequate colour development in Open Tatura systems. It is likely that colour development will become poorer in vase systems as the trees grow and shading of fruit increases.
Growers seeking to maximise yield should consider high-density (around 2,200 trees/ha) plantings on D6 or Quince A rootstocks. For growers wishing to remain with moderate planting densities (1,100–1,400 trees/ha), D6 is so far the most attractive rootstock option, with moderate crop loads and good fruit size. By contrast, in low-density planting systems (700–1100 trees/ha), crop load and fruit size of trees on Quince A rootstocks in fifth leaf was sufficient to maximise total yield while avoiding oversizing of fruit.
About the authors:
Lexie McClymont and Dr Ian Goodwin, Department of Economic
Development, Jobs, Transport and Resources (DEDJTR), Victoria
t: (03) 5833 5240 | e: email@example.com
Thanks go to David Cornwall, Wendy Sessions, Dave Haberfield, Madelaine Peavey and Susanna Turpin for technical assistance. This project is funded through the Productivity Irrigation Pests and Soils (PIPS) program (by DEDJTR) with co-investment from Hort Innovation using the apple and pear industry levy from growers and matching funds from the Australian Government and co-investment.