Good Fruit Grower

February 15

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GOOD TO KNOW A research report from Todd Einhorn, Oregon State University Vigor control and promotion of fruiting of pear trees Inducing early fruiting of pear trees while controlling vigor may require multiple strategies. C Apogee Photos courtesy of oregon state university onsiderable time is required to recoup the increased establishment costs that accompany higher density plantings given the precocity challenges associated with commercially available pear rootstocks and scions. Limited fruiting and excessive vegetative growth create an unprofitable scenario that can be difficult to manage. The main objective of our current research is to control vigor and/or induce early fruiting of pear trees to facilitate a balanced canopy compatible with high-density plantings. To achieve this, we have recently explored several approaches, of which two are described in the first of a two-part series: ��� Treatment with Apogee to control vigor ��� Root pruning to control vigor and promote fruit set D���Anjou pear trees in the Apogee trial are shown in November 2012. Left tree is untreated, middle received single application of Apogee during the growing season when shoots were two inches Apogee (prohexadione calcium) is long, and right tree received two Apogee applications (second applied when regrowth observed). used successfully on apple to manage vigor. Apogee reduces shoot growth by interfering with the plant���s production of the growth-promoting horshoots were about 2 inches (5 cm) in length at a rate of 250 parts per mone, gibberellic acid. In pear, previous research by Drs. Don Elfvng, million (Figure 1). David Sugar, and Gene Mielke demonstrated that Bartlett fruit size was In most cases, only one application was required to control d���Anjou directly limited by Apogee in the year of application, while Bosc return shoot growth for the entire season, but in several cases a second applicabloom and yields were markedly reduced the year following application; tion at the same rate was needed about 60 to 80 days after the first. This d���Anjou fruit growth and return bloom, however, were not similarly application coincided with a marked increase in the rate of shoot growth, affected. presumably due to the cessation of activity of Apogee in the plant. FavorWe recently evaluated Apogee on multiple d���Anjou orchards over the able environmental conditions, however, likely play an important role in past three years. Additionally, we tested Apogee on Starkrimson, given stimulating this regrowth, since we did not observe it in most years or trithe cultivar���s vigorous growth habit. We consistently observed an approxals. Starkrimson trees did not require multiple applications of Apogee imate 50 percent reduction in the annual growth of shoots relative to (Figure 1). In all years, total tree yields of d���Anjou and Starkrimson were untreated trees, irrespective of the cultivar or year. The strongest either slightly improved on trees sprayed with Apogee or similar to response occurred when applications were made in early spring when untreated trees (Table 1). FIGURE 1 FIGURE 2 Effect of Apogee on shoot growth Root pruning in sixth-leaf d���Anjou pears Apogee reduced annual shoot growth rate by about 50 percent. 20 - July 31 - July 24 - July 17 - July 10 - August 7 - SOURCE:Todd Einhorn, Oregon State University July 3 - June 26 - June 19 - 0- June 5 - 10 - June 12 - 171 - 30 - August 14 - SOURCE:Todd Einhorn, Oregon State University 40 - May 29 - Note: An additional control (water plus the surfactant used with the Apogee treatments) was included for d���Anjou trials to determine if the surfactant affected shoot growth. Untreated control 1-side root pruning 2-side root pruning May 22 - DAYS AFTER FULL BLOOM 129 - 122 - 115 - 109 - 93 - 100 - 86 - 80 - 72 - 65 - 0- d���Anjou pear 50 - May 8 - DAYS AFTER FULL BLOOM 10 - 58 - 14 23 30 37 42 51 58 65 72 79 86 93 100 107 114 121 129 136 170 0- - 10 - 51 - Arrow signifies the second application for the multiple application treatment. 20 - 45 - 20 - 30 - 37 - 30 - 30 - 40 - 40 - 23 - (2 applications) 60 - Apogee May 15 - Untreated control 50 - 6- 50 - Seasonal shoot growth was significantly reduced for root pruned treatments compared to control trees. Starkrimson pear 16 - 60 - SHOOT LENGTH (cm) 60 - Untreated control Water + Surfactant Apogee Apogee SHOOT LENGTH (cm) d���Anjou pear SHOOT LENGTH (cm) 70 - GOOD FRUIT GROWER FEBRUARY 15, 2013 35

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