Blossom Thinning Research Articles

Regulation of crop load and quality in sweet cherry cv. ‘Sweet Heart’ using blossom thinning

ABSTRACT Self-fertile cultivars of sweet cherry (Prunus avium) produce heavy crop load that is often associated with small and poor-quality fruits. Therefore, a crop load-management strategy is required to improve the quality of the fruit. In this study, the effect of blossom thinners on fruit set, yield and quality of the fruits was evaluated. Three types of blossom thinners were used at three different concentrations viz., ammonium thiosulphate (ATS) (1, 1.5 and 2%), naphthaleneacetic acid (NAA) (20, 40 and 60 ppm) and corn oil emulsion (1, 2 and 3%). These were sprayed at 80% of the bloom stage. The vegetative, flowering, fruit set and yield parameters were observed and recorded. Fruit quality was evaluated by measuring the physical and chemical characteristics of the fruits at the harvest stage. Negative correlation was found between fruit set and quality of fruit. The reduction in the crop load was associated with enhanced vegetative growth, including higher leaf:fruit ratio, higher supply and availability of photosynthates to the remaining fruitlets and reduced fruit firmness and titratable acidity. Fruit size, weight, volume, hue value, chroma value, soluble solid content (SSC), total sugars, SSC/acid ratio, anthocyanin and ascorbic acid content were enhanced as a result of thinning. The foliar spray of ATS at 2% and NAA at 60 ppm, at 80% bloom proved to be the most effective in reducing crop load and enhancing the fruit quality.

UGV‐Based Precision Spraying System for Chemical Apple Blossom Thinning on Trellis Trained Canopies

ABSTRACTBlossom thinning is one of the key steps in apple crop load management that improves the quality of apples, reduces stress on the trees, and avoids the likelihood of biennial bearing. Conventional chemical blossom thinning such as air‐blast spraying can lead to excessive use of chemical thinner to ensure full coverage, which can also cause leaf damage fruit russeting. In addition, a well‐trained operator is required to use these chemical spraying systems. To address these challenges, a UGV‐based precision spraying system was developed for automated and targeted chemical blossom thinning for apples. The system is capable of automatically driving along the tree row in the orchard environment during blooming stage, locating apple flower clusters to be thinned using a real‐time machine vision system, and precisely spraying the chemical thinner to the targeted flower clusters. A set of field tests were conducted to evaluate the performance of the UGV‐based target spraying system by comparing it to a conventional air‐blast sprayer (ABS) and a previous prototype named the cartesian target sprayer (CTS). Tests showed that the flower cluster detection reached a precision of 93.8%. The UGV‐based spraying system used 2.2 L of chemical thinner to finish the chemical thinning for 30 apple trees, followed by the ABS and CTS with 4.2 and 2.4 L usage, respectively. The robotic system also obtained an average fruit set of 2.2 per cluster after thinning, which was comparable to that with the air blast sprayer. The findings indicated that the robotic thinning system demonstrated a 66.7% reduction in chemical usage compared to the ABS and exhibited a 43.0% faster operational pace than the CTS, while attaining a comparable fruit set per cluster. The outcomes of the study provided guidance for developing a full scale robotic chemical thinning system for modern apple orchards.

Design, integration, and field evaluation of a robotic blossom thinning system for tree fruit crops

AbstractThe United States (US) apple industry relies heavily on semi‐skilled manual labor force for essential field operations such as training, pruning, blossom and green fruitlet thinning, and harvesting. Blossom thinning is one of the crucial crop‐load management practices to achieve desired crop load, fruit quality, and return bloom. While several techniques such as chemical and mechanical thinning are available for large‐scale blossom thinning, such approaches often yield unpredictable thinning results and may damage the canopy, spurs, and leaf tissue. Hence, growers still depend on laborious, labor‐intensive, and expensive manual hand blossom thinning for desired thinning outcomes. This research presents a robotic solution for precision blossom thinning in apple orchards using a deep learning‐based computer vision system, a six‐degrees‐of‐freedom UR5e robotic manipulator, and an electrically actuated miniature end‐effector. The integrated robotic system was evaluated in a commercial apple orchard which showed promising results for targeted and selective blossom thinning. Two thinning approaches, center and boundary thinning, were investigated to evaluate the system's ability to remove varying proportions of flowers from apple flower clusters. During boundary thinning, the end‐effector was actuated around the cluster boundary, while center thinning involved end‐effector actuation only at the cluster centroid for a fixed duration of 2 s. Field evaluation results showed that the boundary thinning approach thinned 67.2% of flowers from the targeted clusters with a cycle time of 9.0 s per cluster, whereas the center thinning approach thinned 59.4% of flowers with a cycle time of 7.2 s per cluster. Upon further improvement for commercial adoption, the proposed system could help address problems faced by apple growers with current hand, chemical, and mechanical blossom thinning approaches.

Multi-scenario pear tree inflorescence detection based on improved YOLOv7 object detection algorithm.

Efficient and precise thinning during the orchard blossom period is a crucial factor in enhancing both fruit yield and quality. The accurate recognition of inflorescence is the cornerstone of intelligent blossom equipment. To advance the process of intelligent blossom thinning, this paper addresses the issue of suboptimal performance of current inflorescence recognition algorithms in detecting dense inflorescence at a long distance. It introduces an inflorescence recognition algorithm, YOLOv7-E, based on the YOLOv7 neural network model. YOLOv7 incorporates an efficient multi-scale attention mechanism (EMA) to enable cross-channel feature interaction through parallel processing strategies, thereby maximizing the retention of pixel-level features and positional information on the feature maps. Additionally, the SPPCSPC module is optimized to preserve target area features as much as possible under different receptive fields, and the Soft-NMS algorithm is employed to reduce the likelihood of missing detections in overlapping regions. The model is trained on a diverse dataset collected from real-world field settings. Upon validation, the improved YOLOv7-E object detection algorithm achieves an average precision and recall of 91.4% and 89.8%, respectively, in inflorescence detection under various time periods, distances, and weather conditions. The detection time for a single image is 80.9 ms, and the model size is 37.6 Mb. In comparison to the original YOLOv7 algorithm, it boasts a 4.9% increase in detection accuracy and a 5.3% improvement in recall rate, with a mere 1.8% increase in model parameters. The YOLOv7-E object detection algorithm presented in this study enables precise inflorescence detection and localization across an entire tree at varying distances, offering robust technical support for differentiated and precise blossom thinning operations by thinning machinery in the future.

Bloom and Postbloom Thinner Effects and Interactions on ‘Gala’ Fruit Growth Rate, Return Bloom, and Yield Responses at Three Locations

Multistep chemical thinning programs have been widely recommended in the eastern United States; however, adoption of bloom thinners is limited. With caustic blossom thinners, narrow effective application timings and concerns related to spring frost damage are barriers for commercial use in this region. If effective and safe, use of hormonal blossom thinners for apple would be an attractive alternative. We evaluated the effects and interactions of bloom thinners [6-benzyladenine (BA) and lime sulfur (LS, or calcium polysulfide) + stylet oil (LS+SO)] and a postbloom thinner (NAA) in the context of a multistep, carbaryl-free thinning program across three locations. Experiments were conducted in 2017 and 2018 on mature ‘Gala’ in North Carolina, Massachusetts, and Pennsylvania, USA. In four of six studies, BA at bloom increased the efficacy of postbloom NAA and reduced crop density (P < 0.08). Postbloom NAA generally increased fruit relative growth rate (RGR) and reduced crop density. However, where NAA failed to reduce crop load, there was a negative influence on RGR. BA and LS+SO increased RGR in one of six studies; however, BA was generally ineffective as a blossom thinner, whereas LS+SO was more effective. Nevertheless, BA applied at bloom may have utility as part of a multistep thinning program. As a part of a multistep thinning program, BA applied at bloom may be useful in increasing efficacy of postbloom applications, particularly when use of caustic blossom thinners is not permitted.

Technologies and Equipment of Mechanized Blossom Thinning in Orchards: A Review

Orchard thinning can avoid biennial bearing and improve fruit quality, which is a necessary agronomic section in orchard management. The existing methods of artificial fruit thinning and chemical spraying are no longer suitable for the development of modern agriculture. With the continuous acceleration of the construction process of modern orchards, blossom thinning mechanization has become an inevitable trend in the development of the orchard flower and fruit management. Based on relevant reports in the past 20 years, the paper discusses the current level of development of mechanized blossom thinning technologies and equipment in orchards from three aspects: mechanism research, machine development, and intelligent upgrading. Firstly, for thinning mechanism research, three directions were investigated: the rope flexible hitting force, thinning agronomic requirements, and the fruit tree growth model between thinning and fruit yields. Secondly, for marketable machine developments, two types of machines were investigated: the hand-held thinner and tractor-mounted thinner. The hand-held thinner is mainly suitable for traditional old orchards with a messy canopy structure, especially in the interior and top of the canopy. The tractor-mounted thinner is mainly suitable for orchards with the same crown structure, such as the hedge type, trunk type, and V-type. Thirdly, for equipment intelligent upgrading, the research of the intelligent detection algorithm for inflorescence on the fruit tree was investigated, for species including the apple, pear, citrus, grape, litchi, mango, and apricot. Finally, combining the advantages and disadvantages of the research, the authors propose thoughts and prospects, which can provide a reference for the design and applications of orchard mechanized blossom thinning.

基于融合注意力机制的 YOLOv5 算法对梨花序的识别研究

Thinning is an important agronomic process in pear production, thus the detection of pear inflorescence is an important technology for intelligentization of blossom thinning. In this paper, images of buds and flowers were collected under different natural conditions for model training, and the images were augmented by data augmentation methods. Model training was performed based on the YOLOv5s network with coordinate attention mechanism added to the backbone network and compared with the native YOLOv5s, YOLOv3, SSD 300, and Faster-RCNN algorithms. The mAP, F1 score and recall of the algorithm reached 93.32%, 91.10%, and 91.99%. The model size only took up 14.1 MB, and the average detection time was 27 ms, which are suitable for application in actual intelligent blossom thinning equipment.

UAV Photogrammetry-Based Apple Orchard Blossom Density Estimation and Mapping

Thinning is an important routine for apple growers to manage crop load and improve fruit quality, which can be accomplished through manual, chemical, or mechanical manipulation of flowers and fruitlets. Traditionally, blossom thinning relies on human experts’ visual evaluation of the flower load, a leading indicator of crop load, which can be imprecise and prone to errors. This study aimed to develop an apple blossom density mapping algorithm utilizing point clouds reconstructed through unmanned aerial vehicle (UAV)-based red-green-blue (RGB) imagery and photogrammetry. The algorithm was based on grid average downsampling and white color thresholding, and it was able to generate top-view blossom density maps of user-defined tree height regions. A preliminary field experiment was carried out to evaluate the algorithm’s accuracy using manual blossom counts of apple tree row sections as ground truths, and a coefficient of determination (R2) of 0.85, a root mean square error (RMSE) of 1307, and a normalized RMSE (NRMSE) of 9.02% were achieved. The algorithm was utilized to monitor the blooming of the apple tree rows and was demonstrated to effectively show blossom density variations between different tree rows and dates. The study results suggested the potential of UAVs as a convenient tool to assist precise blossom thinning in apple orchards, while future research should further investigate the reliability of photogrammetry techniques under different image qualities and flight settings as well as the influence of blossom distribution on algorithm accuracy.

EFFECT OF FLOWER THINNING ON YIELD AND QUALITY OF ‘`STANLEY`’ PLUM (PRUNUS DOMESTICA L.)

Plum is the most important fruit crop for cultivation in Serbia. However, a small amount of plum fruit is sold as fresh fruit due to its poor quality. In order to improve fruit quality and obtain regular and high yield chemical blossom thinning agents were applied. The experiment was conducted on seven-year-old plum trees of cultivar `Stanley` which were planted on distance 5x5 m. Ammonium thiosulphate and ethephon were applied in the next treatments: 1) ammonium thiosulphate 1.5% (ATS); 2) ethephon 0.015% (E); 3) ammonium thiosulphate 1.5% + ethephon 0.015% (ATS + E); 4) hand thinning (HT); 5) untreated control treatment (UTC). Chemical thinning treatments were performed once during the phase of full bloom, while hand thinning treatment was performed after the fall of unfertilized fruitlets at the end of May. Parameters analyzed were yield, fruit size, fruit weight, pit weight, fruit firmness, fruit shape index, soluble solids content, total acid content and the amount of harvested fruits per time unit. The obtained results have shown that ATS + E, ATS and HT treatments significantly reduced the number of fruits on the trees compared to the control treatment. However, yield per tree was reduced significantly only in the ATS + E treatment. Other treatments compensated for the smaller number of fruits per tree with a significantly larger fruit size. Since the fruit size was larger on treated trees, the amount of harvested fruits per time unit was significant compared to control treatment. There were no significant differences among the applied treatments in terms of fruit firmness, soluble solids and total acid content.

An Advanced Robotic System for Precision Chemical Thinning of Apple Blossoms

Highlights A cartesian robotic spraying system was developed for precision apple blossom thinning. Flower clusters were detected and localized with deep learning model for target spraying. A communication algorithm was developed for positioning the spray end-effector to the target flowers. The cartesian robotic system greatly reduced chemical usage while maintaining thinning effectiveness in the final green fruit set. Abstract. Crop thinning, including blossom thinning, is one of the critical management strategies that determines the annual profitability of apple orchards. Challenges still remain for applying appropriate amounts of chemical thinner; if thinning is inadequate and too many fruits remain on the tree, fruit size will be small, fruit quality will be poor, and flower bud initiation for the following year’s crop may be either reduced or eliminated. Over-thinning also carries economic perils since yield and crop value in the year of application will be reduced. In addition, chemical thinning with excessive spray volume may cause leaf damage and fruit russeting. Thus, a robotic apple blossom thinning system was proposed, aiming to reduce the usage of chemical thinner while maintaining good thinning performance. The robotic system consisted of three major components: (1) a machine vision system that can identify and localize the apple flower clusters in tree canopies, (2) a cartesian robotic system with the guidance of a machine vision system to reach target flower clusters, and (3) a flat-shaped spraying nozzle connected with a solenoid valve as a spraying end-effector to deposit chemical thinner to the targeted flower clusters. A set of field tests was conducted to evaluate the performance of the robotic thinning system by comparing it to conventional air-blast and boom-type sprayers. In the test, the flower cluster detection reached a precision of 93.82%. The integrated robotic system used 2.3 L of chemical thinner to finish the chemical thinning for 18 apple trees, followed by the boom sprayer and air blast sprayer with 4.2 and 6.8 L usage, respectively. The robotic system also obtained an average fruit set of 2.4 per cluster after thinning, which was comparable to that of the air blast sprayer. The results showed that the robotic thinning system saved 66.7% and 45.5% of chemicals compared to the air-blast sprayer and boom-typed sprayers, respectively, while achieving a similar fruit set per cluster. The outcomes of the study provided guidance for developing a full-scale robotic chemical thinning system for modern apple orchards. Keywords: Apple orchard, Blossom thinning, Cartesian robot, Chemical thinning, Machine vision.

Alternative Approaches to Chemical Thinning for Regulating Crop Load and Alternate Bearing in Apple

In the past, chemical thinning dominated in fruit orchards. This paper for the special issue outlines alternatives to chemical thinning for crop load management (CLM) and its effect on fruit size, firmness, sugar, starch, and weight, indicating ripeness and fruit quality, yield, and alternate bearing. A total of 450 apple trees (Malus domestica Borkh., cv. ‘Roter Boskoop’; six years old) on M9 rootstock were used at the Klein-Altendorf experimental station (50° N) of the University of Bonn, Germany. As the first alternatives, trees were mechanically blossom-thinned at the balloon stage (BBCH 59) with a rotor speed of 320 rpm or 380 rpm at 5 km/h tractor speed or were chemically thinned at the full bloom stage (BBCH 65) with ammonium thiosulfate (ATS), ethephon (ETH), and/or 6-benzyladenine (BA) at 10–12 mm fruit size (BBCH 71) after applying ATS/ETH. Flower clusters and/or cluster leaves (source) were manually removed to determine the optimum sink-source ratio to achieve different ratios of fruitlets (sink) relative to the leaves (source) at fruit set (BBCH 67–69). Un-thinned, adjacent trees served as the control. The majority of CLM methods improved fruit size and weight. Removing cluster leaves at fruit set increased fruit size and weight of the remaining fruit, which has not been observed before. The most effective treatment for fruit size and weight and return bloom was the 75% flower cluster and complete cluster leaf removal. Removal of more than 50% of flower clusters successfully improved return bloom, indicative of alternate bearing. The mechanical blossom thinning had a positive effect on fruit size and weight with a return bloom similar to that of removal of 50% flower clusters.

Impacts of 1-Aminocyclopropane-1-Carboxylic Acid as a Late Post-Bloom Thinner on Fruit Set, Yield, and Fruit Quality in “Gala” and “Fuji” Apples

A few post-bloom thinners are available for apple (Malus domestica Borkh.) and the prospects for additional thinners appear to be limited. Application of blossom thinners may present a risk of overthining in the areas where weather is less predictable. Thus, we studied the impacts of various rates of 1-aminocyclopropane-1-carboxylic acid (ACC) in three strains of “Fuji” apple and different rates of ACC and one rate of Ethrel in “Buckeye Gala” apple, when fruitlet diameter was about 20 mm, on fruit set, yield and fruit quality attributes at harvest, and return bloom in southwest Idaho in the Intermountain West region, USA. In 2013, application of Ethrel at 300 mg·L-1 did not affect fruit set, fruit weight, diameter (D), length(L), or L/D ratio 34 days after application, or yield, fruit weight, color, russet, and starch degradation pattern (SDP) at harvest, while application of ACC at 150 mg·L-1 or higher reduced fruit set by 19% to 34% in “Buckeye Gala” apple. In this cultivar, application of ACC at 350 mg·L-1 significantly increased fruit weight, diameter and length 34 days after application, and increased fruit weight, color, and SDP at harvest time. Application of ACC at all rates reduced total yield per tree in “Buckeye Gala”. Application of ACC at 300 mg·L-1 significantly reduced fruit set but applications of 150 mg·L-1 or 300 mg·L-1 ACC did not affect yield or quality attributes of “Sun Fuji” apple in Sunny Slope area in 2013. Application of ACC reduced fruit set and slightly increased fruit size in “Top Export Fuji” in 2013. Application of ACC at 600 mg·L-1 significantly reduced fruit set in “Aztec Fuji” apple in 2014. Application of ACC in a season never reduced bloom density (return bloom) of the next season. Overall, we conclude that ACC is an excellent tool as a late-season post-bloom fruit thinner and can be effective when applied fruitlet diameter is about 20 mm.

Evaluation of Blossom Thinning Spray Timing Strategies in Apple

In the eastern USA and several other apple-growing regions, apple blossom thinning using lime sulfur is a relatively new crop load management strategy. This study sought to evaluate how application timing of lime sulfur + stylet oil blossom thinning sprays would influence thinning efficacy and crop safety of ‘Gala’ apples. This project occurred at two locations in the USA, Winchester, Virginia, and Mills River, North Carolina, during the 2019 growing season. Two main timing strategies were assessed: (1) model-guided sprays with the pollen tube growth model (PTGM), (2) fixed spray intervals with the first spray applied at a specified percentage of open bloom (20% vs. 80%), and the second spray applied at a reapplication interval (48 h vs. 72 h). Model-guided and 20% open bloom + 48-h treatments reduced fruit set and increased fruit weight, diameter, and length at both sites. Treatments with a delayed first spray at 80% open bloom or a more extended second reapplication of 72 h were generally ineffective. There was no conclusive evidence that lime sulfur + stylet oil blossom thinning spray timing influenced russet incidence/severity or leaf phytotoxicity. This study demonstrated that effective and safe blossom thinning can be obtained from applying two sprays at 20% open bloom and 48 h thereafter or using the PTGM.

Performance evaluation of mechanical blossom thinning in trunk type pear orchard

In order to yield a marketable product, hand fruit thinning (HFT) has become the major but costly management practice in modern pear planting. Two kinds of new blossom thinners for pear blossom thinning were developed, which are tractor-mounted three arms blossom thinner (TTBT) and hand-held electric blossom thinner (HEBT). Four treatments for 24 trunk type ‘Cuiguan’ pear trees (7 years) were tested. They are TTBT combined with HFT, HEBT combined with HFT, hand blossom thinning (HBT) combined with HFT, and HFT only. Pear trees were divided into 4 groups equally. Four indexes were used to evaluate the test: flower reserve rate, fruit set rate, work efficiency and cost, fruit yield, and quality. Pear canopy was divided into the inner, middle, and outer 3 layers in the top view. 20 inflorescence samples were selected for each layer. Field tests showed: there was no obvious difference in quality between mechanical blossom thinning and HBT, and the working stability of TTBT was higher than other treatments. Mechanical blossom thinning decreased the fruit set rate to a certain degree, but did not reduce the yield and quality of harvesting. TTBT could save 61.35% operation time compared with HFT, and the profitable area was 5845.76 m2. TTBT is suitable for large-scale sparse layer trunk-type pear orchards. HEBT could save 36.01% operation time compared with HFT, and the profitable area was 663.96 m2. HEBT is suitable for small and medium-sized trunk-type pear orchards. Blossom thinning can improve the average weight of high quality fruit and brix of sugar solids. Keywords: mechanical blossom thinning, pear orchard, trunk type, performance evaluation DOI: 10.25165/j.ijabe.20211404.6060 Citation: Lei X H, Lyu X L, Zhang M N, Lu D P, Wang S L, Chang Y H, et al. Performance evaluation of mechanical blossom thinning in trunk type pear orchard. Int J Agric & Biol Eng, 2021; 14(4): 106–112.

Efficacy of an Eco-Friendly Bloom Thinning Formulation on Mango Trees and Its Olfactory Effect on an Insect Pollinator, Apis mellifera

In various orchard fruit trees, thinning of blossoms and fruits is important to increase fruit size and quality and to promote a new bloom in the following season. Several chemical thinning agents are currently commercially available, but they are inconsistent and produce side effects in crop plants and insect pollinators. Because of environmental concerns, developing alternative eco-friendly bloom thinning agents is necessary. We developed an eco-friendly bloom thinning formulation (BTF) using minerals and extracts of various medicinal plants. Our BTF spray (0.1%, w/v) decreased the number of fruits per tree (46.5%) and fruit yield per tree (81.5%) but increased the fruit weight (196.8%) compared with the control treatment; the spray induced a small number of larger mango fruits in the treated trees. We also investigated the effect of BTF on the olfactory behavior of Apis mellifera L. (Hymenoptera, Apidae), a major insect pollinator. We analyzed the behavioral changes of adult workers at two different concentrations (0.1% and 1%) of nine different BTF spray components using a Y-tube olfactometer. The behavioral responses of honey bees to nine BTF components showed significant differences. However, honey bees showed no clear attraction or repellent behavior towards the tested BTF components. Our results suggest that the newly developed eco-friendly BTF is practically applicable in mango orchards without interrupting honey bee behavior.

Performance evaluation of mechanical blossom thinning in trunk type pear orchard

Performance evaluation of mechanical blossom thinning in trunk type pear orchard

Branched Secondary Alcohol Ethoxylate, Ammonium Thiosulfate, Calcium polysulfides-thiosulfate, and Fish Oil Effects on Blossom Thinning, Fruit Set and Quality of Peaches and Nectarines

Abstract Total crop load has an inverse relationship with fruit size, while larger fruit size is often demanded by the peach and nectarine markets. Hand-thinning is extremely expensive, and thus, crop load adjustment, using blossom thinners is a crucial practice to ensure production of commercially acceptable fruit size and yield efficiency in stone fruit. In this study, the influence of branched secondary alcohol ethoxylate (Tergitol TMN-6), ammonium thiosulfate (ATS), Crocker Fish Oil, (FO) and a mixture of calcium polysulfides and thiosulfate (lime sulfur) on fruit set and quality attributes in peaches (Prunus persica) and nectarines (P. persica var. nectarina) were studied. All blossom thinners reduced fruit set in 'Summer Lady' peach in both 2016 and 2017. Fruit sets in 'Summer Lady' peach trees with a double application of Tergitol TMN-6 at the rate of 7.5 or 10 mL.L-1, each rate applied at 40% and 80% bloom, were lower than those receiving the same rates of this chemical only at 80% bloom, but they were similar to those receiving a single Tergitol TMN-6 spray at 15 mL.L-1 at 80% or 100% bloom. 'Summer Lady' peach trees receiving Fish Oil at 20 mL.L-1 plus lime sulfur at 25 mL.L-1, once at 40% bloom and again at 80% bloom had lower fruit set as compared to Un-treated Control but the fruit set was higher than those with any Tergitol-TMN-6 spray. Tergitol TMN-6 at 12m.L-1 at 100% bloom or 10 mL.L-1 all stages of bloom reduced fruit set in 'Zee Lady and Snow Giant' peaches. Total yield was proportional to the severity of thinning and final fruit weight. In 'Snow Giant' peach, trees receiving Tergitol TMN-6 at all concentrations and blossom stages had significantly higher fruit weight as compared to the trees of Un-treated Control. Applications of Tergitol TMN-6 at all concentrations at 80% bloom reduced fruit set in 'Red Globe' and 'Elberta' peaches in Utah comparing with Un-treated Control. Overall, it is concluded that efficacy of blossom thinners depends on the rate of thinners, cultivar and stage of bloom development.

Chemical thinning of apple blossoms in organic production

An experiment on chemical blossom thinning on apple variety 'Summerred'/ M9 was performed in an experimental plantation in Brdo pri Lukovici. Different chemical thinners were applied on apple’s fruitlets in organic production. The experiment was designed in 7 randomized block with 13 treatments: 1. unthinned trees (as a control), 2. hand thinning in June, 3. 1% NaCl, 4. 1,5% NaCl, 5. 1% CH3COOH, 6. 3% CH3COOH, 7. 3% CaSx, 8. 1% rape oil, 9. 3% rape oil, 10. 3% of sunflower oil, 11. 3% soybean oil, 12. 5% dextrin, 13. emulsifier 100 + OCA 30. Chemical thinners were applied in a phenological stage at peak blooming with a manual knapsack sprayer. The best thinning of fruitlets (similar to hand thinned trees) was observed with 3% rape oil, however, relatively strong russeting of fruit skin was detected in this treatment. Statistically significant reduction of final fruit set also occurred when 1,5% NaCl and 3% soybean oil were applied, but with less fruit russeting.

Potential and Challenges of Branched Secondary Alcohol Ethoxylate and Fish Oil Applications as Blossom Thinners in Apples

Thinning excessive fruit in apples is an essential but expensive cultural practice and the use of blossom thinners can facilitate this practice. To assess the potential and challenges of branched secondary alcohol ethoxylate (Tergitol TMN-6) and Crocker Fish Oil (CFO) as blossom thinners, their impacts on fruit set, yield, and fruit quality of “Delicious”, ‘Top Export Fuji’ and ‘Early Spur Rome’ apples (Malus domestica Borkh)were studied. Application of Tergitol TMN-6 at all rates reduced fruit set, yield per tree, and fruit weight in ‘Top Export Fuji’. Applications of Tergitol TMN-6 at all rates in “Delicious” and at the rate of 3.12 mL.L-1 in “Top Export Fuji” apples were challenging and caused phytotoxicity, induced fruit russeting in both cultivars and resulted in smaller fruit and lower yield in “Top Export Fuji”. The exent of russeting was diercetly proporotional to the Tergitol TMN-6 rate. The use of CFO at 30 mL.L-1 alone did not have any significant effects on yield per tree, fruit weight, or fruit color, while significantly reduced fruit sunburn and increased fruit russeting in ‘Top Export Fuji’. In ‘Early Spur Rome’ apple, application of Tergitol TMN-6 at or higher than 1.87 mL.L-1reduced fruit set. Despite fruit set reduction, application of Tergitol TMN-6 at the rate of 1.87 mL.L-1 did not reduce total yield per tree, fruit weight, fruit color, or fruit russeting when compared to Un-treated Control and thus, this rate can be recommended for blossom thinning in ‘Early Spur Rome’ apple. Crop Regulation; Fruit thinning; PomeFruit Blossom Thinning; Malus domestica; Regular Cropping

Calcium Polysulfides-Thiosulfate, Ammonium Thiosulfate, and NC-99 Blossom Thinners Impact Fruit Set of Apples, Peaches, and Plums

Crop load adjustment, using blossom and/or post-bloom thinners is a crucial practice to ensure production of commercially acceptable fruit size and yield efficiency in apples and stone fruit. In a study with two apple, one peach and one plum cultivars, application of calcium polysulfides and thiosulfate mixture (lime sulfur), ammonium thiosulfate (ATS), and NC-99 (Natural-cal), applied during bloom, reduced the fruit set of apples and/or certain stone fruit. In most cases, higher concentrations or double applications of a bloom thinner resulted in more blossom thinning which led into lower fruit set. Double applications of ATS at a rate of 15 mL.L-1 or a single application of this chemical at a rate of 25 mL.L-1 resulted in adequate levels of thinning in ‘Fuji’ apple. Double applications of ATS at a rate of 25 mL.L-1 resulted in excess thinning on ‘Fuji’ apple. In ‘Gala’ apple, a single application of NC-99 at 3% or 6%, with and without refined oil, or double applications of lime sulfur, each time at 5%, significantly reduced fruit set in 2013. In ‘Jonathan’ apple, applications of ATS at 25 mL.L-1 significantly reduced fruit set and increased fruit size. Application of lime sulfur at 6% with or without refined oil significantly reduced fruit set in ‘Elberta’ peach. In plums, application of lime sulfur at 6% with 1% refined oil significantly reduced fruit set, while application of this mixture at 3% lime sulfur (3% lime sulfur plus 1% oil) did not affect fruit set.