Good Fruit Grower

March 15

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THE SPIDER POLE Cherry Thinner TM TM TABLE 2 Thinning effect of abscisic acid on Bartlett pears Fruit no. per tree (after thinning) 212 ProTone Treatments Fruit no. per tree (before thinning) 158 0 N NO MORE L Yield Fruit lbs. per weight tree (g) 69 Call Foothi l Today ls ! 214 0 + surfactant 262 173 73 202 125 ppm 136 128 59 219 250 ppm 19 17 8 230 500 ppm 0 0 0 S! — Data are means of 4 whole-tree replicates. photos courtesy of todd einhorn SOURCE: Oregon State University lowest concentration produced a nearly equivalent amount of fruit as a hand-thinned control (see Table 2). Final fruit size at harvest was similar between the control and most efficacious abscisic acid treatment. A rate-dependent drop in leaf photosynthesis was measured for a period of two weeks following the growth regulator applications, likely creating a carbohydrate deficit during a period when fruitlets have a high carbon demand. Although ProTone is not currently labeled for pear, these preliminary results are highly encouraging. More intensive testing will occur in 2013. ' #% & ) &##!($ • Untreated d'Anjou control tree. At harvest, fruit from treated trees were significantly smaller than control fruit—an indirect response attributed to excessive croploads of treated trees. However, limited drop of weaker fruit, which would have otherwise abscised, cannot be ruled out as a factor contributing to the smaller fruit size at harvest. A pronounced reduction of vegetative growth was seen on d'Anjou trees treated two weeks after full bloom (see photo), indicating a strong cropload influence on carbohydrate partitioning to shoots. Fruit of ReTain-treated trees had a similar number of seeds as control fruit, confirming that pollination and/or fertilization were not limiting factors controlling fruit set, or drop, in d'Anjou or Comice. Interestingly, in our trials there was a very poor relationship between seed count and final fruit size of fruit of either cultivar. The potential to transition nonproductive, young d'Anjou trees into bearing while simultaneously controlling vigor is an intriguing option for achieving manageable, higher-density d'Anjou plantings. Caution is required when interpreting these results, as they are based on one year of data and do not take into account environmental factors that may contribute strongly to the response. Return bloom and fruit set will be monitored in 2013, in addition to more detailed experiments on new plantings. Chemical thinning In order to produce profitable fresh Bartlett crops, good fruit size is mandatory. A reliable and predictable thinning agent would markedly improve Bartlett profitability through reduced costs for hand thinning. Further, a postbloom thinning agent can significantly reduce the early and negative impact of high fruit set on harvestable fruit size. In 2012, we applied the abscisic acid growth regulator called ProTone to whole Bartlett trees about three weeks after full bloom and observed a highly significant, ratedependent thinning response (see Table 2). The highest concentration of ProTone removed every fruit, while the www.goodfruit.com " ! " ! ! ! ! #! " ! "$ "% ! ! # "! " $ ! !! ! GOOD FRUIT GROWER March 15, 2013 43

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