During both the 2016 and 2017 reporting periods, assessment of rootstocks and in-row tree spacing was carried out through measurement of yield for each rootstock, spacing and training treatment in three existing orchards. A prototype mechanical over-the-row harvester was used to harvest fruit in high density tart cherry systems, and modifications were made to the harvester to improve effectiveness. Graduate student Sheriden Hansen began working on the project in June 2015. Her efforts focused on: (1) evaluating renewal pruning techniques in high density orchards to facilitate over-the-row harvesting, (2) evaluating the effectiveness of mechanical summer pruning in high density orchards, and (3) quantifying the relationship between light micro-environment and fruit quality in both conventional and high density orchards. She also carried out experiments to evaluate the effects of training system on spray droplet distribution within the canopy as well as total light interception. During Fall 2017, Ms. Hansen analyzed the data for her renewal pruning and summer hedging studies, and wrote and successfully defended her M.S. thesis.
1) Determine the optimum combination of rootstock, row spacing and tree training.
2) Compare the distribution uniformity of crop protectant applications.
3) Determine the response of ‘Montmorency’ tart cherry to mechanical summer pruning.
4) Determine the relationship between light micro-environment and fruit quality in tart cherry.
5) Develop enterprise budgets for both conventional and high density systems.
6) Provide high-density cherry management experience to several early adopters.
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Tart cherry production is based on a low-density system that does not come into production until 5 to 7 years after planting and only reaches full production in years 10 to 12. We hypothesize that a high density management system will allow for fruit production earlier in the life of the orchard, that the fruit will be higher quality, and that the orchard will be more conducive to pest and disease management.
The 2010 orchard is an incomplete factorial of 4 rootstocks, 4 in-row tree spacings (4, 6, 8 and 10 foot) and three tree training systems. Each rootstock-training system-spacing combination is replicated in four plots that are each approximately 30-feet long. With the experimental unit consisting of uniform plot length (varying number of trees per plot), better facilitates machine harvest and offers a more direct comparison of systems. The rootstocks included are three dwarfing rootstocks imported from Germany (Gisela®3, Gisela®5 and Gisela®6) and the current industry standard ‘Mahaleb’, which itself is slightly dwarfing compared to the industry standard sweet cherry rootstock ‘Mazzard’. The design is an incomplete factorial because not every rootstock or training system is included in every spacing. For example, the large ‘Mahaleb’ rootstocks and the multi-leader systems are not included in the closest spacings, and the very dwarfing Gisela®3 is not included at the widest spacings. The training systems are based on “columnarized” pruning, where renewal cuts are made back at the main leader on approximately a 3 to 4 year cycle. The targeted result is permanent leaders with weaker fruiting lateral shoots that are frequently replaced. The key difference among the three training systems is the number of leaders per tree. The “tall spindle” system having a single central leader, the “parallel vee” having two leaders that are both in line with the row, and the candelabra having three to four leaders, also oriented within the row. Multi-leader divide the vigor across multiple growing points to reduce tree growth and more easily maintain an orchard size suitable for the canopy-shake berry harvesters.
Clearly the attention to detail in this pruning process is much less intense than for a higher value crop such as peaches or apples. For a processed crop like tart cherries, pruning focuses on 4 to 6 renewal cuts per tree per season.
The 2012 planting has two rootstocks (G.5 and Mahaleb) but includes closer spacings and less intensive pruning strategies. Tree spacings range from 3 to 6 feet in row. Trees were either left unpruned or pruned back heavily at planting. Subsequent pruning will be mechanical. There are a total of 11 treatments, also replicated four times in 30’ plots. The first harvest of this planting was in 2014.
The 2013 planting features the same rootstocks and similar training approaches as the 2012 planting, but is scaled up to 250’ plots, and is on a commercial tart cherry farm. The site tends to produce less vigorous trees than at Kaysville, so it will also provide a test of soil conditions. Custom-propagated trees were ordered in 2014 for delivery in 2016 and will feature several new rootstocks from the Michigan State University breeding program. Two Utah orchards will be established, one on a commercial farm in Utah County and the other at the Kaysville Research Farm. Additional orchards will also be established at locations in Wisconsin, New York and Michigan as part of an NC-140 rootstock trial.
Economic feasibility of the HD tart cherry management system is examined in the research of the enterprise budget. Investigation of economic feasibility is not a simple computation as tart cherry yield, price, and sales are stochastic and the two production systems have different pre-productive periods and total orchard lives, where the HD system may result in earlier yields in the life of the orchard. The enterprise budgets for both conventional and low density systems will be created for the estimated life of the orchard, including the initial planting costs, pre-productive period, and various expected yields over the productive life. Time value of money techniques such as net present value will be used to examine the effects of the timing of the expected yields and costs over the life of the orchard for the two systems.
Generally farmers who are risk-averse would be concerned with the risk of adopting a new management system. Simulation, which incorporates stochastic components, is used to assess production, price, and sales risk between the HD tart cherry management system and traditional management system. Simulation based on data from objectives 1-4 and enterprise budgets allows for a variety of situations to be considered by combining price, yield, and sales risk and produces a probability distribution of economic return, showing the likelihood of differing levels of profit. Risk analysis provides farmers valuable information about adopting the HD tart cherry management system.
Objective 1. Rootstock, row spacing, and tree training were evaluated in two experimental orchards at the Kaysville research farm. Treatments were harvested in July of 2015, 2016, 2017 and 2018 using a prototype over-the-row harvester. Multiple problems were experienced with the harvester in the first three years that required both repairs and modifications. Most of these repairs and modifications involved working with 3rd party fabricators and suppliers, as the company that built the prototype harvester had gone out of business.
During 2016, 2017 and 2018, the harvester was also used in a grower cooperator orchard in Santaquin, Utah that was established in 2013. Local growers were invited to observe the harvest and provide feedback. Approximately 30 growers observed the 2016 harvest, with approximately 15 growers attending in 2017.
Findings: Yields in the earliest orchards plateaued at 15,000 pounds per acre, which is inadequate for a mature tart cherry orchard. The time to reach this plateau is related to rootstock, tree density and training system. Trees under single leader training, on Gisela®5 and Gisela®3 rootstocks, with 4’ or 6’ in-row spacing were the first to reach full production but also required heavier pruning in the later stages of the experiment to maintain size conducive to mechanical harvest. For the Kaysville location, the most dwarfing rootstocks appear to be best for maintaining productivity in the allotted space. More dwarfing rootstocks may be better suited to the system. Michigan State University has been developing some new dwarfing cherry rootstocks that may prove to be more suited to a high density system. A set of these rootstocks grafted to ‘Montmorency’ tart cherry became available in 2017, and two plantings were established to evaluate these under Utah conditions. One of these plantings is on a commercial farm near Genola, UT. The second is at the USU Kaysville Research Farm. Plans are to evaluate these rootstocks through 2027.
Objective 2. In 2016 and 2017, water sensitive paper targets were placed within the canopy of tart cherry trees on multiple rootstocks and trained to multiple training systems. Targets were placed at multiple heights and locations within each canopy and then the trees were sprayed with water using a commercial speed sprayer delivering 50 gallons per acre, to simulate distribution patterns of crop protectants. The targets were collected, scanned and droplet patterns analyzed to compare the effects of rootstock and training system on spray distribution in the canopy.
Findings: Spray distribution was generally quite uniform across the canopy among the different pruning and training systems. There did appear to be more uniform spray distribution in the hedged single leader training system than in the unhedged comparison. The degree of uniformity indicates that pruning to maintain light distribution, and matching the appropriate sprayer to the size of the tree are the best approaches for getting uniform spray coverage and minimizing non-target pesticide exposure.
Although spray distribution was most uniform in the hedged treatments, continued hedging in led to some noticeable increases in powdery mildew. This increased incidence was likely due to two factors. First, the overall canopy density is increased which reduces air movement in the canopy creating an environment more conducive to foliar diseases. Second, the hedging causes a flush of new shoots in the vicinity of the hedging cuts. This proliferation of new shoots appear to be more susceptible to the disease. Any benefit of reduced labor and concentration of fruiting wood will need to be weighed against powdery mildew disease pressure.
Objective 3. Response of ‘Montmorency’ tart cherry to mechanical summer pruning was again assessed. A Gillison Sickle Bar Hedger was provided by grower-cooperator David McMullin of Payson, UT for the 2015-2017 seasons. USU was able to obtain a small hedger for the 2018 season. Replicated research plots included: delayed dormant hedging, a mid-season hedging, alternate side hedging, and an unhedged control. These treatments were initiated in Spring 2015 and repeat hedged in 2016, 2017 and 2018, with plots harvested for yield using the prototype mechanical harvester. A small planting in Santaquin was also subjected to hedging using a hand held trimmer and vertical guides. These plots were hand harvested.
Also under objective 3, a study was carried out to evaluate the response of ‘Montmorency’ tart cherry to different renewal pruning cuts. Branches that needed to be removed from the 2010 planting were marked, classified by diameter, and then cut to one of several pre-determined lengths. These marked branches were then monitored through the season to determine number and length of new shoots. This experiment was carried out in both 2015 and 2016.
Results: Results indicate that branches cut to 10 cm or longer tend to provide adequate renewal growth, but that this critical length varies with rootstock, branch diameter and the severity of other pruning cuts on the tree.
Light distribution patterns in these treatments were also compared in 2016 and 2017 within the various treatments using a trailer mounted ceptometer (described below). Analysis of light distribution data indicate that canopy uniformity is impacted more by rootstock and maintenance pruning than by initial training system or hedging practices.
Results from these studies were published in a peer-reviewed journal in January 2019. This paper was selected by the journal as the winner of the U.P. Hedrick award for best student paper.
Objective 4. Sampling was carried out in 2015 and 2016 to determine the relationship between light micro-environment and fruit quality in commercial orchards. Samples were collected in five commercial orchards in Utah County. Fruit samples were collected at weekly intervals from 24 June to 15 July. Fruit was assessed for whole fruit fresh weight, pit fresh weight, fruit sugar content, LCH surface color, as well as whole fruit dry weight and pit dry weight.
Based on variability observed in these spot samples, it was decided that examining this relationship on a larger scale might be warranted. During the summer of 2016, a mapping ceptometer was custom built to map light distribution on an orchard scale. A small scale boom sprayer was repurposed, with light meters placed along the boom, and a GPS receiver and data logger set to measure light interception as the device was towed through the orchard. (Funding for this apparatus came from a companion grant received from the Utah Department of Agriculture and Food, along with discounted pricing from environmental sensor manufacturers interested in the work) Several test runs were carried out in Fall 2016, the machine was modified, and additional measurements were taken in 2017. Data for light distribution in the two high-density tart cherry orchards at Kaysville, along with a conventional orchard have been collected. The rootstock-training system combinations had light interception values ranging from 70 to 90%. Preliminary analysis indicates that optimum light interception is between 70 and 80%. However, we plan to use the equipment to further evaluate this relationship.
Objective 5. During 2016, Michigan State University conducted focus groups and analysis to develop updated cost-of-production budgets for the Michigan tart cherry industry. Since Michigan is the only other state with significant tart cherry acreage, crop budgets for this crop have not been developed for any other state. MSU economists agreed to cooperate with us and recently shared both their results and survey methodology, which we will adapt and use to develop Utah-specific budgets in 2017. USU Ag Economist Ryan Larsen has surveyed Utah growers in order to adapt the MSU budgets to Utah conditions. These will provide a usable budget for current commercial practices. Because yields in the high density systems were well below average yields in conventional systems, we did not carry out a complete economic analysis for this system.
Objective 6. To date, four test plantings have been established on commercial farms to give growers experience with this management system. One is a small scale test plot established in 2010 that was designed for hand harvest, one is a larger scale planting for mechanical harvest established in 2013. The third is a rootstock trial (MSU rootstocks discussed above) planted in 2017. These first three plantings are all in southern Utah County. An additional test planting including multiple rootstocks was established in 2018 on a commercial farm in western Idaho, by a former USU student that helped in the early years of this project.
Findings: Growers that have observed the plantings were impressed with the fruit density and the harvester efficiency. The cooperating grower pointed for the 2013 planting has noted the challenge of managing fruit closer to the ground than in conventional orchards, but also pointed out that this is partly due to equipment that has not been properly adjusted for the change in tree size and shape.
The primary conclusion is that the high density system is not yet productive enough to be economically viable. It may become so with a combination of factors including better adapted rootstocks, pruning systems that concentrate production within the canopy, and plant spacing and tree size that are not currently possible due to the limitations of available machinery.
As part of this research, we have taken on the evaluation of newer rootstocks, which only became available near the end of this project and will need at least 10 seasons to appropriately evaluate.
Optimum renewal pruning for maintaining adequate productivity with the commercially available rootstocks was determined as part of this project. The results are published in a peer reviewed journal article.
Mechanical pruning systems were tested as part of this project, but results will not be published until we have collected two additional years of yield data to better determine the long-term effects of the approach.
Part of the research is conducted at the Kaysville Research Farm, owned and operated by the Utah Agricultural Experiment Station Farm. The other part of the research is conducted on commercial farms belonging to producer-cooperators. This project is utilizing multiple educational approaches:
First, research reports are presented at two annual grower meetings, the Utah State Horticulture Society annual convention, and the Northern Utah Fruit Growers Meeting.
Second, growers are invited to field days and farm tours where the methods are being demonstrated. In even-numbered years, these tours are at the Kaysville Research Farm, and in odd years the tours are in Utah County and feature one of the two commercial orchard sites.
Third, the two commercial orchard sites are managed by the farmer, and provide hands-on practical experience that they can then share with other producers.
Educational & Outreach Activities
Presentation at the annual conference of the Utah State Horticulture Association (USHA): 22 Jan 2016; 19 Jan 2017; 19 Jan 2018
Presentation at the winter Northern Utah Fruit Meeting: 3 Feb 2017
Featured stop on the USHA summer farm tour: June 2015; 29 June 2017;
Featured stop on the Kaysville Fruit and Vegetable field day: 28 June 2016, 20 June 2018
Featured stop on the USHA winter orchard tour: 18 Jan 2017
Presentation at the Northwest Michigan Orchard and Vineyard show: Jan 2015
Presentation to a symposium on cherry research in Traverse City: August 2018 (mixed audience of growers and researchers
Popular press articles: Research was featured in national popular press articles in two different publications (Good Fruit Grower and Fruit Grower News), along with a companion interview video that was posted online.
- The importance of early canopy establishment to optimize yields.
- Renewal pruning strategies to maintain productivity
- The importance of maintaining adequate light distribution for maintaining fruit quality and continued productivity
The principles of high density orchard management that were illustrated in this project also apply to other crops such as apple. Growers attending the winter and summer field tours (65 participants) engaged in lively discussions about these principles and how they could integrate the concepts on their own farms
This management system is still very much experimental and so it can not be recommended for adoption on a large commercial scale. However, results were promising enough that two growers established experimental plantings. Three additional growers were willing to plant test plots, but the nurseries were unable to generate sufficient quantities of trees. This progress can be seen as the recognition by Utah’s tart cherry producers that their production practices should be examined, and new approaches tested in order to remain sustainable in the presence of increasing development pressure on available orchard land.
Results on pruning practices are targeting ways to reduce labor inputs, which are increasingly a limitation to the sustainability of fruit crops. Some of these approaches could also be applicable to other fruit crops besides tart cherry. The work also provided a better understanding of the variability in fruit quality within the tree canopy and across the orchard. This needs further investigation to refine management practices in order to maximize the quality and marketability of the crop.
As outlined previously in this report, we are looking at several methods of refining this system to bring yields in line with commercial requirements to ensure economic sustainability.
One other component of orchard sustainability highlighted through this work was the problem of excessive cull fruit in some seasons. The amount of waste that results from sub-standard produce is a significant barrier to improved sustainability. We observed significant variation of fruit quality within the tree canopy as it relates to light distribution, and that this variation, along with yield variations exists throughout a given orchard. As a result of this work, we are looking at mapping entire orchards for variability in yield, fruit quality, light interception, as well as soil characteristics. The aim of this work is to consider how site-specific and variable-rate management (“Precision Ag”) approaches that might be appropriate for minimizing inputs such as hand labor, fertilizer and irrigation water, while maximizing the quality and value of the crop produced. These methodologies could be immediately applied to conventional systems, as well as in the refinement of high density approaches.