Good Fruit Grower

March 15

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GOOD TO KNOW A research report from Todd Einhorn, Mateus Pasa, and Janet Turner, Oregon State University Promotion and management of pear fruiting A new chemical thinning agent looks promising for Bartlett. D ifferent pear cultivars have unique challenges associated with their fruiting habits; young d'Anjou trees can bloom profusely but set relatively few fruit, while Bartlett trees are fairly precocious and productive. Mature d'Anjou trees typically produce large fruit, despite the crop being unthinned. Bartletts require thinning to size fruit to commercial standards. Comice is a conspicuously shy bearer. To improve production efficiencies of d'Anjou and Comice, bloom and postbloom applications of the plant growth regulator ReTain (aminoethoxyvinylglycine) were tested to promote fruit set. For Bartlett, we have recently explored a new chemical thinning agent. ReTain Ethylene is a naturally occurring plant hormone that promotes senescence in plant organs, such as flowers and fruit. The active ingredient in ReTain inhibits ethylene synthesis and, therefore, could potentially be used to improve fruit set when limitations are due to a short ovule longevity period or high fruitlet abscission. In the case of a short ovule longevity period, ReTain applications made during bloom could potentially improve fruit set by extending the life of the ovule, thereby increasing the chance for fertilization. However, when early fruitlet abscission reduces set, ReTain is used in a postbloom application. We were interested in evaluating ReTain for Comice due to its reported short ovule viability. For d'Anjou, we were aiming to affect the characteristically poor fruit set of younger trees, despite their often profuse bloom. The processes regulating d'Anjou fruit set are unclear. ReTain was applied in 2012 to whole canopies of Comice and d'Anjou trees at a rate of 40 or 80 ppm D'Anjou tree sprayed at two weeks after (equivalent to approxibloom with 80 ppm ReTain (left) relative to mately 2/3 or 1-1/3 an untreated control. pouches of ReTain per acre, respectively). Applications were timed to coincide with 30 to 40 percent bloom, but bloom advanced from 20 to 80 percent in one afternoon. An alternative timing was applied at two weeks after full bloom. ReTain applied during bloom did not improve fruit set of d'Anjou. Fruit set of Comice was improved from the bloom application timing, though a rate response was not observed. However, when ReTain was applied at two weeks after full bloom, fruit set was increased in a rate-responsive manner for both cultivars. An application rate of 80 ppm increased fruit set more than threefold for d'Anjou (see photo) and doubled the number of fruit on Comice trees, relative to controls (see Table 1). TABLE 1 D'Anjou and Comice data following ReTain treatments D'Anjou treatments Yield per tree (lbs) (fruit no.) Projected yield (bins per acre) Fruit size (no. per 44-lb box) Seeds (no. per per fruit) Untreated control 88 172 24 90 4.9 44 ppm ReTain (80% FB) 57 118 16 90 3.5 80 ppm ReTain (80% FB) 52 111 14 90 3.2 40 ppm ReTain (2 WAFB) 160 409 44 110 4.0 80 ppm ReTain (2 WAFB) 198 558 55 120 4.0 Projected yield (bins per acre) Fruit size (no. per 44-lb box) Seeds (no. per per fruit) 80 5.4 Comice treatments Yield per tree (lbs) (fruit no.) Untreated control 77 138 21 44 ppm ReTain (80% FB) 95 189 26 90 4.5 80 ppm ReTain (80% FB) 106 235 29 100 3.9 40 ppm ReTain (2 WAFB) 100 215 28 100 5.6 80 ppm ReTain (2 WAFB) 127 269 35 100 5.8 Data are means of 4 whole-tree replicates. SOURCE: Oregon State University 42 March 15, 2013 GOOD FRUIT GROWER

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