Good Fruit Grower

September 1

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8 SEPTEMBER 2015 GOOD FRUIT GROWER A lthough we know a lot about the Bartlett pear, most orchardists, especially in Australia, have been concerned that trees take a long time to come into production, and yields of mature trees are relatively low and fruit is of poor quality. The use of a vigorous seedling rootstock was often blamed for the poor performance. No wonder much of the research was, and still is, focused on finding the perfect size-controlling rootstock. Many believe that the performance of Bartlett could only improve if trees were planted at high-density and on a size-controlling rootstock. Therefore, finding a hardy, size-controlling, precocious rootstock the equivalent of the Malling 9 apple rootstock has been, and still is, the Holy Grail. The pursuit of such a rootstock has been going on unabated for more than 60 years. Some may argue that progress has been made. Pollinizers When it became known that cross-pollination enhanced fruit set of Bartlett, orchardists in Australia began to interplant Beurre Bosc (Bosc), which flowered with Bartlett. However, copper sprays were usually needed to make the skin of the Bosc russet, while Bartlett pears had to remain russet-free. Packham's Triumph (Packham) trees were sometimes interplanted with Bartlett trees, but Packham was a poor pollinizer because it flowered earlier than Bartlett. It was later discovered that the Asian pear variety Nijisseiki (20th Century) was a much better pollinizer, because it started to flower just before Bartlett did, was very precocious, spurry and compact, and bees liked the nectar. Orchardists who interplanted their old free-standing Bartlett with Nijisseiki and introduced beehives saw that yield increased. Regulated deficit irrigation (RDI) helped to reduce excessive vigor, but the peculiar fruiting habit of Bartlett made it difficult to match the production of other spur-type pear varieties. Pyrus calleryana has been widely adopted in Australia since the 1950s. It is hardy enough for arid Australia, com- patible with all European pear varieties, easily propagated (from seed), and the scion can be made precocious if well managed. It was not until Bartlett trees on Pyrus calleryana rootstock were planted closely and trellised, Nijisseiki pollinizers were interplanted, beehives were introduced, RDI, drip irrigation and Ethrel (ethephon) were used to control shoot growth that precocity improved and trees could be brought into full production by year six (see Good Fruit Grower September 2008). Experiment In this article, we discuss our experiment where we significantly improved fruitfulness of Bartlett trees on Tatura Trellis, which had performed poorly for 11 years, and changed the traits of Bartlett to show the true production potential of this popular variety. We increased fruit set of Bartlett trees by improving cross-pollination, using a synthetic stimulant, and controlling vigor. We focused on tree management—not on waiting and hoping for the right size-controlling rootstock to turn up. In 2003, a 0.37 hectare (0.9 acre) block of Bartlett on Pyrus calleryana was planted on Tatura Trellis on a 4.5- by-1 meter (3-by-15 foot) spacing with 2,222 trees per hectare (968 trees per acre) at an orchard near Ardmona, Australia. Initially, Packham trees were interplanted (7 percent of trees) as pollinizers and two beehives were introduced during flowering. When eight years old, the trees had only produced a total of 37 tonnes per hectare/ Proliferating pears An experiment demonstrates how to increase yields of close-planted Bartlett pear trees by changing tree management, not the rootstock. by Bas van den Ende and Mick Conti GOOD TO KNOW

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