Issue link: http://read.dmtmag.com/i/560612
www.goodfruit.com GOOD FRUIT GROWER SEPTEMBER 2015 9 bins per acre, so we decided to regraft the Packham trees to Nijisseiki. In the 11th year, when the Nijisseiki trees had suffi- cient flowers and beehives were introduced, the Bartlett trees were sprayed with 15 ppm ProGibb SG (gibberellic acid) at 70 percent full bloom, RDI was applied and the tops were delay-headed six weeks after full bloom to maintain canopy height at 2.7 meters (9 feet), measured vertically, which was 60 percent of row width. Yield increased four-fold (from 19 to 81 tons per hectare/bins per acre), vigor slowed down, and floral buds developed mainly on spurs, not laterals as before. However, as a result of the long non-productive years, vigor of the Bartlett trees was still a concern. Regalis (pro- hexadione calcium), which is sold under the brand name Apogee in the United States, was not recommended for pear, partly because of concerns about effects on return bloom and vigorous regrowth, so we experimented in the 12th year with foliar sprays of the growth regulator paclobutrazol (PP333). The first application was made ten days after petal fall when new shoots were about Environmental effects on fruit set F ruit set of Williams Bon Chretien (Bartlett) has been well documented. For instance, it is known that Bartlett is variably parthenocarpic, which means it sets fruit without pollination and pears grow to full size without fertilization. The rate of parthenocarpic fruit set is genetically determined among pear varieties, but is greatly affected by the environment. In Australia, it was believed that Bartlett flowers set fruit by vegetative parthenocarpy and fruit grew without any external stimulant, such as pollination or plant growth regulator. However, trees often took seven to nine years before enough fruit could be harvested, and free-standing trees took at least 17 years to settle down to a modest 40 to 45 tonnes per hectare (40 to 45 bins per acre). This was partly because trees were planted at low-densities of between 278 and 330 trees per hectare (equivalent to 109 to 134 trees per acre). Also, the seedling root- stock Pyrus calleryana was used and young trees were pruned hard with many heading cuts made in winter, which resulted in mature trees becoming over-limbed and over-shaded. Most research on pollination and fruit set of Bartlett showed that cross-pollination increased fruit set compared with self-pollination. Cross- pollination often led to fertilization, but fruit remained seedless when ripe, because the seeds did not mature, but left small seed-like structures called integuments. The hormones auxin and gibberellin are pro- duced in seeds in most fruit, and are also produced in high enough concentrations in the fruitlet's peri- carp (the tissue surrounding the seeds) to induce fruit set and maintain fruit growth. —Bas van den Ende and Mick Conti A change in tree management, not the rootstock, has made these Bartlett trees on Tatura Trellis very productive at an Ardmona orchard in Australia. COURTESY BAS VAN DEN ENDE