Blossom Thinning Research Articles

Mechanical blossom thinning of ‘Allstar’ peaches influences yield and quality

Peach trees can produce an overabundance of fruit when crop loads are not managed properly, resulting in poor returns due to small fruit size at harvest. Recently, mechanical thinning using string thinners at bloom has been investigated as a method for reducing crop load and labour costs. ‘Allstar’/‘Bailey’ peach trees grown in a supported spindle-type orchard system were subjected to three rates of mechanical blossom thinning (MBT) and hand blossom thinning (HBT) at bloom across two years, with a hand-thinned control added in the second year. Mechanical and hand blossom thinning were both effective in removing flowers and decreasing fruit set with increasing rates. In 2010, only the highest rate of HBT treatment reduced the time needed to hand-thin, but in 2011 nearly all treatments reduced hand thinning labour requirements. Differences in total yield and number of fruit harvested per tree were observed in both years of the study whereas differences in marketable yield were observed only in the first year. The results of this study highlight the benefits of mechanically string thinning peaches at bloom, but also the variability in response across years.

A Hand-Held Mechanical Blossom Thinning Device for Fruit Trees

<abstract> Abstract. Blossom or green fruit thinning is a common practice for producing larger and higher quality fruit in tree fruit production. Mechanical blossom thinning could decrease production costs when compared to hand thinning of either blossom or green fruit. In stone fruit, a few chemical thinning agents are available or reliable. In apple, chemical thinning agents are under regulatory scrutiny, and efficacy is highly dependent on weather. This study aimed to develop a hand-held mechanical thinning device suitable for thinning blossoms on fruit trees pruned to different architectures. Research prototypes of different configurations have been developed, fabricated, and tested in blossom thinning operations in commercial orchards. Results obtained from field tests verified that a hand-held mechanical blossom thinner could effectively remove blossoms from apple, stone fruits, and sweet cherry. Among all evaluated parameters, spindle speed appeared to have the greatest direct effect on the capacity to remove blooms. Field test results indicated that the test device could remove 61.1%, 30.8%, and 18.0% flowers on a single branch with a swipe around 0.5 m·s^-1 under high (2500-3000 rpm), medium (1500-1800 rpm), and low (500-800 rpm) speed settings, respectively. In trees trained to central leader architecture, 85 s was required to remove 50% of blossoms using the hand-held mechanical thinner and at least 180 s when the task was accomplished by hand. Field tests also revealed that a better ergonomic design of the device could further improve operational efficiency.

Influence of Mechanical String Thinning Treatments on Vegetative and Reproductive Tissues, Fruit Set, Yield, and Fruit Quality of ‘Gala’ Apple

The objectives of this experiment were to test the efficacy of a mechanical string thinner (Darwin PT-250; Fruit-Tec, Deggenhauserertal, Germany) on apple and to identify an optimal range of thinning severity as influenced by spindle rotation speed. Trials were conducted in 2010 and 2011 at the Pennsylvania State University Fruit Research and Extension Center in Biglerville, PA, on five-year-old ‘Buckeye Gala’/M.9 apple trees that were trained to tall spindle. A preliminary trail on five-year-old ‘Cripps Pink’/M.9 was conducted to determine the relationship between string number and thinning severity. As the number of strings increased, the level of thinning severity increased. A range of spindle speeds (0 to 300 rpm) was applied to the same trees for two consecutive years. As spindle speed increased, blossom density (blossom clusters per limb cross-sectional area) was reduced as was the number of blossoms per spur. In 2010, leaf area per spur was reduced 9% to 45%. In 2011, the fastest spindle speed reduced leaf area per spur 20%. Although increased spindle speed reduced cropload, injury to spur leaves may have inhibited increases in fruit size. The largest gain in fruit weight was 28 g (300 rpm) compared with the control. In both years, the most severe thinning treatments reduced yield by more than 50%. There was no relationship between spindle speed and return bloom. Severe thinning treatments (240 to 300 rpm) caused significant reductions in spur leaf area, yield, and fruit calcium and did not improve fruit size or return bloom. Spindle speeds of 180 and 210 rpm provided the best overall thinning response and minimized injury to spur leaves, but cropload reduction was insufficient in years of heavy fruit set. Therefore, mechanical blossom thinning treatments should be supplemented with other thinning methods. Mechanical string thinning may be a viable treatment in organic apple production, where use of chemical thinners is limited.

Hyperspectral waveband selection for automatic detection of floral pear buds

Thinning of fruit-tree blossoms is used to regulate the yearly tree bearing and to increase the fruit yield and quality. While this is still mostly done by hand, the increasing costs of manual labor have created a demand for mechanization. This has recently led to the development of several prototype thinning machines. The main disadvantage of these machines is that they are not selective, while the fruit bearing capacity of different floral buds is not equal. On-line information about the position and distribution of the floral buds on the tree can improve the efficiency of mechanized thinning. Therefore, the aim of this study was to identify the most informative wavebands to develop a multispectral vision sensor for detection of the floral buds of the pear cultivar Conference. Hyperspectral scans were taken from tree samples in five early phenological stages to create a database of reflectance spectra for the different tree features. A stepwise algorithm was then applied to this training set to select the best combination of wavebands having the highest discriminating power between the components of interest. Subsequently, canonical correlation analysis was used to create discriminant functions out of the selected wavebands. It was possible to correctly classify 95 % of the (pixel) observations with six selected wavebands. The discrimination performance was also tested as a function of the number of used wavebands. Analysis showed that when only the two most important wavebands were used, still over 90 % of the (pixel) observations could be correctly classified.

Vision-Based 3D Peach Tree Reconstruction for Automated Blossom Thinning

This paper presents research using a correlation-based stereo vision approach to 3D blossom mapping for automated thinning of peach blossoms on perpendicular “V” architecture trees. To this end, a calibrated camera system is proposed, based upon three synchronized ten megapixel cameras and flash illumination for nighttime image acquisition. A correlation-based stereo algorithm, suitable for parallel processing, is developed with the actual scene structure in mind using multiple camera pairs for validating 3D locations, three different certainty metrics, and does not require extrinsic rectification of the images. Results show that mapping accuracy of less than half of a blossom width ( ~ 1 cm) is feasible, and validates the approach as the sensor part of an automated selective blossom thinning system. Furthermore, the effects of the different certainty metrics are examined. They effectively improve the accuracy of blossom positions when the visibility of blossoms is good by removing insecure matches and through qualified selection of subsets of cameras for 3D triangulation. The proposed algorithm is compared and found superior to a popular global optimization algorithm, designed to perform well in another scene structure, demonstrating the quality of correlation-based stereo in practical applications.

Mechanical flower thinning improves fruit quality of apples and promotes consistent bearing

A novel device is presented for mechanical blossom thinning with first test trials in the US on seven-year-old apple [ Malus domestica (Borkh.)] ‘Buckeye Gala’ near Yakima, WA, USA. Trees were mechanically blossom-thinned with the novel string thinning device, developed by Damerow et al. (2007), at 260 or 360 rpm rotor speeds and a 2.5 km h −1 vehicle speed to improve fruit quality, reduce hand and chemical thinning and to prevent or overcome alternate bearing; manually thinned trees served as controls in a replicated, randomized block trial. The strongest mechanical thinning treatment (360 rpm, 2.5 km h −1) had a positive effect on apple fruit size (75 mm versus 72 mm in the hand-thinned control), firmness 9.0 kg cm −2 versus 8.9 kg cm −2, advanced ripening i.e. starch breakdown, sweetness 12.3-12.8 °Brix versus 11.9 °Brix in the control, contained the largest malic acid content 0.43% versus 0.37% in the control and more red blush, i.e. fruit coloration. The sugar:acid ratio was maintained particularly after the strongest 360 rpm mechanical thinning (29:1) and resembled that of the chemical thinning and the hand-thinned control (32:1), since fruit with higher sugar content also contained more malic acid. The best return bloom was achieved by the conventional chemical standard (105%), followed by the strongest mechanical thinning (92% with 360 rpm) then the combination of mechanical and chemical thinning (85%) compared to much lower values in the control (69%), showing the efficacy of blossom thinning to overcome alternate bearing.

Efficacy of blossom thinning treatments to reduce fruit set and increase fruit size of Ambrosia and Aurora Golden Gala™ apples

Hampson, C. and Bedford, K. 2011. Efficacy of blossom thinning treatments to reduce fruit set and increase fruit size of Ambrosia and Aurora Golden Gala™ apples. Can. J. Plant Sci. 91: 983–990. The usefulness of several blossom thinning treatments to reduce fruit set and improve the final fruit size of two new Canadian apple (Malus×domestica Borkh.) cultivars was investigated. Ambrosia and 8S6923 (also called Aurora Golden Gala™) apple trees in a high density commercial superspindle planting were used. Ammonium thiosulphate (ATS) at 1.6% vol/vol or Crocker's fish oil and lime sulphur (FOLS) at 2+2% vol/vol were applied at 20 and 80% full bloom with an airblast sprayer. The chemical blossom thinning treatments were compared with a positive control [hand blossom thinning (HBT)], done at open cluster to king bloom stage, and a negative control (no blossom thinning). All trees received follow-up hand thinning as necessary to end up with a commercial crop load (single fruits about 15 cm apart). Hand blossom thinning resulted in about 95% single-fruit clusters and obviated the need for further thinning, but required considerable labour. Both ATS and FOLS reduced initial set (fruit number per tree, mean fruit number per cluster), but neither eliminated the need for follow-up fruitlet thinning. The two chemicals had similar efficacy in many respects, but FOLS was superior in certain specific measures of performance. In 2009, ATS negatively altered the fruit size distribution for 8S6923. For 8S6923, HBT improved fruit size without reducing yield. Ambrosia fruit size was less responsive to blossom thinning, and in the second year, yield was lower for trees receiving HBT. No fruit russet occurred on either cultivar. Return bloom was sufficient for a full crop for both cultivars after both years. 8S6923 was more productive than Ambrosia but was more difficult to thin.

Efficacy of blossom thinning treatments to reduce fruit set and increase fruit size of Ambrosia and Aurora Golden Gala™ apples

Hampson, C. and Bedford, K. 2011. Efficacy of blossom thinning treatments to reduce fruit set and increase fruit size of Ambrosia and Aurora Golden Gala™ apples. Can. J. Plant Sci. 91: 983-990. The usefulness of several blossom thinning treatments to reduce fruit set and improve the final fruit size of two new Canadian apple (Malus×domestica Borkh.) cultivars was investigated. Ambrosia and 8S6923 (also called Aurora Golden Gala™) apple trees in a high density commercial superspindle planting were used. Ammonium thiosulphate (ATS) at 1.6% vol/vol or Crocker's fish oil and lime sulphur (FOLS) at 2 2% vol/vol were applied at 20 and 80% full bloom with an airblast sprayer. The chemical blossom thinning treatments were compared with a positive control [hand blossom thinning (HBT)], done at open cluster to king bloom stage, and a negative control (no blossom thinning). All trees received follow-up hand thinning as necessary to end up with a commercial crop load (single fruits about 15 cm apart). Hand blossom thinning resulted in about 95% single-fruit clusters and obviated the need for further thinning, but required considerable labour. Both ATS and FOLS reduced initial set (fruit number per tree, mean fruit number per cluster), but neither eliminated the need for follow-up fruitlet thinning. The two chemicals had similar efficacy in many respects, but FOLS was superior in certain specific measures of performance. In 2009, ATS negatively altered the fruit size distribution for 8S6923. For 8S6923, HBT improved fruit size without reducing yield. Ambrosia fruit size was less responsive to blossom thinning, and in the second year, yield was lower for trees receiving HBT. No fruit russet occurred on either cultivar. Return bloom was sufficient for a full crop for both cultivars after both years. 8S6923 was more productive than Ambrosia but was more difficult to thin.

Peach Blossom String Thinner Performance Improved with Selective Pruning

Hand-thinning of fruit is among the most labor-intensive orchard practices and consequently contributes significantly to peach (Prunus persica) production costs. Prior research conducted by the authors on string blossom thinners for managing peach tree cropload demonstrated that this new technology reduces labor requirement and also improves fruit size. Studies were conducted over two seasons in peach orchards trained to perpendicular V or open-center systems to evaluate possible pruning strategies to improve tree canopy access by string thinners. The objectives were to demonstrate if modifications in fruiting shoot orientation, pruning detail, and/or scaffold accessibility improved flower removal, reduced follow-up hand-thinning requirement, and/or increased fruit size. Blossom removal was improved by either detailed pruning or partial pruning (elimination of all shoots on the side of a limb inaccessible by the thinner spindle) in both training systems. Flower density and fruit set measurements revealed greater differences among pruning treatments compared with hand-thinned control treatments with both fruiting shoot orientation pruning modifications and detail pruning resulting in improved thinning. Thinning efficacy was unaffected by scaffold angle but increased as canopy accessibility ranking increased. Follow-up hand-thinning time was reduced by all treatment, system/cultivar, and year combinations except standard pruning in an open center-trained 2009 trial. Detail pruning consistently improved fruit size compared with hand-thinned control and other pruning treatments in both perpendicular V- and open center-trained orchard plots. The best treatments resulted in a thinning savings of $120/ha to $282/ha in perpendicular V plantings and $26/ha to $46/ha in open-center plantings. Realized economic savings beyond hand-thinning alone ranged from $473/ha to $2875/ha in perpendicular V trials and $28/ha to $293/ha in open-center trials.

BLOSSOM THINNING OF 'REDHAVEN' AND 'BABYGOLD 5' PEACHES WITH DIFFERENT CHEMICALS

BLOSSOM THINNING OF 'REDHAVEN' AND 'BABYGOLD 5' PEACHES WITH DIFFERENT CHEMICALS

Regulation of source: sink relationship, fruit set, fruit growth and fruit quality in European plum (Prunus domestica L.)—using thinning for crop load management

Demand for large fruit of uniform size is increasing in the market; thinning is a means to achieve consistently large fruit and to overcome possible alternate (biennial) bearing for the small-fruited European plum (Prunus domestica L.). However, chemical thinning agents for stone fruits are scarce and/or often ineffective. Hence, the objective of this work was to study possibilities of enhancing fruit growth and to improve fruit quality, viz size using plum as a model crop. Nine-year-old ‘Ortenauer’ plum trees, trained to spindles, with maximum flowering intensity (score value 9) near Bonn, Germany were mechanically, chemically or hand-thinned. Un-thinned plum trees in the same rows served as control. Trees were either mechanically thinned at full bloom on 20 April 2009 with a rotor speed of either 300, 400 or 500 rpm, and half of those trees additionally treated with ATS (15 L/ha) and an ethylene releasing compound 35 days after full bloom or manually thinned. The objective of 1/3 flower removal was successfully achieved even with the slowest rotor speed of 300 rpm. The number of fruit per branch was significantly reduced from 152 to 67–76, equivalent to a (source: sink) leaf: fruit ratio of 5:1. Mechanical thinning significantly enlarged fruit mass from 28 g in the un-thinned control to 30–32 g with rotor speeds of 400 or 500 rpm. Additional chemical thinning with ATS and an ethylene-releasing compound resulted in no further increase in fruit mass. Inner fruit quality (sugar) of the plums appeared unaffected by either mechanical or chemical thinning, except for fruit firmness: Plums thinned with an ethylene releasing compound were softer and ripened earlier than respective control fruit. The most efficient method of flower removal and fruit mass enlargement was mechanical blossom thinning with 400 rpm, which may provide a suitable replacement for chemical and/or manual thinning. Alternatively, the mechanical thinning can be combined with either of those options. Mechanical blossom thinning was as effective to overcome or avoid alternate/biennial bearing as the ethylene releasing compound in the previous year. The results are discussed with respect to stone fruit being more difficult to thin than pome fruit, because the former do not exhibit leaves at the time of blossom thinning. Stone fruits develop within a shorter time and a larger number of (smaller) leaves (source) are required for the same fruit growth and final fruit size (sink). A lower threshold of fruit removal has to be exceeded before the remaining stone fruit grow faster and final fruit mass and sugar (and possibly fruit firmness) increase, while acidity remains unaffected by fruit set. An upper saturation threshold is reached fairly quickly without further effects.

A Theory of Blossom Thinning to Consider Maximum Annual Flower Bud Numbers on Biennial Apple Trees

Tree fruit growers use chemical and mechanical thinning techniques in an attempt to maintain regular annual flower production and maximum repeatable yields of varieties susceptible to biennial bearing. If the percentage of floral buds an apple tree could produce without causing yield depression in subsequent years was known, it would be possible to better manage crop-thinning regimes. This study proposes that thinning is a partial transfer of potential flower buds from one year to the next year and estimates the maximum repeatable sequence of flower buds without biennial bearing. The conceptual framework is tested on a 50-year simulation with 0% to 100% transfer of thinned flower buds. Results indicate that the maximum repeatable sequence of flower buds rises sharply when the final years of the orchard approach and declines when the percent transfer of thinned buds is near 0%.

THE IMPACT OF BLOSSOM AND POSTBLOOM THINNERS ON FRUIT SET AND FRUIT QUALITY IN APPLES AND STONE FRUITS

THE IMPACT OF BLOSSOM AND POSTBLOOM THINNERS ON FRUIT SET AND FRUIT QUALITY IN APPLES AND STONE FRUITS

Mechanical String Thinner Reduces Crop Load at Variable Stages of Bloom Development of Peach and Nectarine Trees

Thinning of blossoms or fruitlets is a labor-intensive requirement in the production of peach and nectarine (Prunus persica) fruit of optimum size and quality. Prior research conducted by the authors on string blossom thinners for managing peach tree crop load demonstrated that this new technology reduces labor requirement and improves fruit size. The research reported in the current article was conducted over 2 years on ‘Sugar Giant’ peach and ‘Arctic Sweet’ nectarine to evaluate string blossom thinner efficacy at variable stages of bloom development ranging from pink to petal fall. Blossom removal at the pink stage of bloom development was lower than at other stages in 2008; however, a 150-rpm versus 120-rpm spindle rotation speed resulted in blossom removal similar to the 80% full bloom (FB) treatment in 2009. Blossom removal at the petal fall stage was similar to the open bloom stage with the exception of the 2009 ‘Sugar Giant’ trial, in which blossom removal was higher at 80% FB. Flower density and fruit set of the bloom stage compared with hand-thinned control treatments followed a similar trend with the exception that there were fewer differences in 2009 and in lower canopy regions. Follow-up hand thinning time was reduced by all string thinning/year combinations except ‘Arctic Sweet’ at pink in 2008 and 2009 and at petal fall in 2009. The best treatments reduced follow-up hand thinning time compared with green fruit hand thinning alone by 51% and 41% for ‘Sugar Giant’ and by 42% and 22% for ‘Arctic Sweet’ in Years 1 and 2, respectively. In 2008, the percentage of fruit in the “7.0 cm or greater” size category was increased by all bloom stage treatments in both cultivars. The 2009 size distribution of ‘Arctic Sweet’ fruit was unaffected, but the percentage of ‘Sugar Giant’ fruit in higher market value size categories was increased by the 80% FB and higher rpm pink treatments. Savings in hand thinning time and/or increases in fruit size in both years associated with the bloom stage treatments resulted in a net positive impact of $123/ha to 1368/ha compared with hand thinning alone.

Blossom Thinning in Apple and Peach with an Essential Oil

A series of experiments was conducted with apple (Malus ×domestica) and peach [Prunus persica (L.) Batsch] from 2003 to 2008 to evaluate the flower thinning efficacy of eugenol and a eugenol-based essential oil. Flower thinning effects by hand defoliation and alternative chemical agents were compared with eugenol in different years. Eugenol or the eugenol-based contact herbicide Matran 2 EC (or Matratec AG) produced noticeable phytotoxicity to floral parts and exposed leaf tissue within 15 min to 1 h after application and injury was proportional to rate. At the highest rates (8% and 10%), eugenol resulted in complete burning of all exposed tissue except bark tissue, in which there were no visible signs of injury. Within 3 to 4 weeks of application, phytotoxicity was difficult to observe even at the higher rates of eugenol. In companion experiments, hand defoliation of young leaves at bloom resulted in abscission of young fruitlets in apple, but not in peach, indicating that eugenol may cause thinning by multiple mechanisms. Ammonium thiosulfate (ATS) [49 L·ha−1 or 6.0% (v/v)] provided thinning in peach and showed little or no phytotoxicity, but the response was inconsistent. ATS was also inconsistent in thinning apple. The thinning response from monocarbamidedihydrogen sulphate (MCDS; Wilthin) at 3.2% (v/v) was inconsistent in peach. At the rate used, MCDS caused some phytotoxicity on peach. Applications of 1% to 2% eugenol appear promising, but good blossom coverage is critical for thinning. Furthermore, eugenol formulations need improvement to ensure uniform coverage for more predictable thinning.

String Blossom Thinner Designed for Variable Tree Forms Increases Crop Load Management Efficiency in Trials in Four United States Peach-growing Regions

Hand thinning is a necessary and costly management practice in peach (Prunus persica) production. Stone fruit producers are finding it increasingly difficult to find a workforce to manually thin fruit crops, and the cost of farm labor is increasing. A new “hybrid” string thinner prototype designed to adjust crop load in vase or angled tree canopies was evaluated in processing and fresh fruit plantings in varying production systems in four U.S. growing regions in 2009. Data were uniformly collected across regions to determine blossom removal rate, fruit set, labor required for follow-up green fruit hand thinning, fruit size distribution at harvest, yield, and economic impact. String thinner trials with the variable tree forms demonstrated reduced labor costs compared with hand-thinned controls and increased crop value due to a larger distribution of fruit in marketable and higher market value sizes. Blossom removal ranged from 17% to 56%, hand thinning requirement was reduced by 19% to 100%, and fruit yield and size distribution improved in at least one string-thinning treatment per experiment. Net economic impact at optimum tractor and spindle speeds was $462 to $1490 and $264 to $934 per acre for processing and fresh market peaches, respectively. Case study interviews of growers who thinned a total of 154 acres indicated that commercial adoption of string-thinning technology would likely have positive impacts on the work place environment.

Effects of self-incompatibility control substance and blossom thinner on fruit set and quality of apple (Malus domestica)

Effects of calcium nitrate (CN) and sodium sulfate (SS) blossom thinning agents applied after self-incompatibility control substance (SICS) treatment on the fruit set rate and quality of apple were investigated for 2 cropping seasons. CN and SS at 0.1% and 0.2% concentrations were applied once (3 or 4 days after SICS treatment) or twice (3 and 5 or 4 and 6 days after SICS treatment). Commercial Japanese flower thinning agent (FTA: Ekoruki) treated and untreated apple trees were used as treated and untreated controls. SICS was sprayed 7 days before full bloom. Both agents showed a fertilizing effect in 'Hongno', improving its fruit yield and quality. SS obtained 29.8% and 36.3% thinning rates in the central floret of 'Fuji'. Both CN and SS were effective in 'Gala', which induced a lower fruit set than SICS treated plants. Earlier and double applications of CN and SS at 0.2% concentration resulted in a higher thinning rate and improved fruit quality in 'Gala'. Results also showed similar thinning efficacies in Ekoruki, CN, and SS.

Evaluation of the Risk of Spreading Fire Blight in Apple Orchards with a Mechanical String Blossom Thinner

The risk of spreading fire blight in apples after mechanical thinning with a rotating string blossom thinner was evaluated in field and potted-tree experiments. In the field experiment, using the mechanical thinner on noninoculated trees immediately after operating the equipment on inoculated trees significantly (P &lt; 0.01) increased fire blight incidence resulting in 90 ± 20.01 (mean ± SE) infected shoots compared with 23.5 ± 8.97 diseased shoots in similar trees that were not thinned mechanically. A similar result was obtained in greenhouse experiments whereby healthy apple plants positioned adjacent to diseased plants before the group was subjected to the mechanical thinner developed more than twice the number of infected shoots as that on similar plants that were not thinned. These results indicate that under conditions conducive to infection, the mechanical blossom thinner significantly increases the risk of spreading Erwinia amylovora. The use of the thinner should therefore be limited to orchards with no history of disease in the last 3 years and on days when predicted weather is not suitable for tree infection by E. amylovora; otherwise, a severe fire blight epidemic could develop in the orchard.

Horizontal String Blossom Thinner Reduces Labor Input and Increases Fruit Size in Peach Trees Trained to Open-center Systems

Hand thinning of fruit is among the most labor-intensive orchard practices and consequently contributes significantly to peach (Prunus persica) production costs. Research reported in 2008 on a string blossom thinner for vertical tree canopies demonstrated that this new mechanical method has potential to favorably impact grower profitability by reducing labor requirement and by improving fruit size and quality. A string thinner prototype for open-center tree canopies was tested in six orchards in 2008. Peach blossom removal in upper canopy regions ranged from 23% to 69% with the new string thinner oriented in a horizontal or inclined position to thin the tops of vase-shaped trees. Optimal thinning with the horizontal string thinner was with a 2.0 km·h−1 tractor speed, reducing peach crop load by an average of 47%, reducing follow-up hand thinning time 32%, and increasing fruit in higher market size categories 22% to 31%. Net economic impact (realized economic savings) of mechanical thinning at 2.0 km·h−1 versus hand thinning alone ranged from $799 to $911 per hectare. Total yield was sometimes reduced by string thinner treatments; however, high-market-value yields were comparable across treatments. Two combination treatments—mechanical thinning followed by hand blossom thinning and thinning with a horizontal followed by a vertical string thinner—suggested additional strategies for achieving the most desirable thinning results.

Horizontal String Blossom Thinner Reduces Labor Input and Increases Fruit Size in Peach Trees Trained to Open-center Systems

Hand thinning of fruit is among the most labor-intensive orchard practices and consequently contributes significantly to peach (Prunus persica) production costs. Research reported in 2008 on a string blossom thinner for vertical tree canopies demonstrated that this new mechanical method has potential to favorably impact grower profitability by reducing labor requirement and by improving fruit size and quality. A string thinner prototype for open-center tree canopies was tested in six orchards in 2008. Peach blossom removal in upper canopy regions ranged from 23% to 69% with the new string thinner oriented in a horizontal or inclined position to thin the tops of vase-shaped trees. Optimal thinning with the horizontal string thinner was with a 2.0 km·h−1 tractor speed, reducing peach crop load by an average of 47%, reducing follow-up hand thinning time 32%, and increasing fruit in higher market size categories 22% to 31%. Net economic impact (realized economic savings) of mechanical thinning at 2.0 km·h−1 versus hand thinning alone ranged from $799 to $911 per hectare. Total yield was sometimes reduced by string thinner treatments; however, high-market-value yields were comparable across treatments. Two combination treatments—mechanical thinning followed by hand blossom thinning and thinning with a horizontal followed by a vertical string thinner—suggested additional strategies for achieving the most desirable thinning results.