Final report for GNC21-327
Project Information
Training fruit trees to high-density, planar canopy systems can increase sustainability by decreasing labor and pesticide inputs, while increasing fruit quality, yield per acre, and worker safety. However, high-density, planar systems are difficult to implement in peach (Prunus persica) because peach has very high vegetative vigor. This excessive vigor makes training difficult and increases labor costs.
This project explored how genetically-controlled differences in branch angle could be combined with innovative training strategies to facilitate high-density systems for peach.
First, we examined how altering the number of leaders in planar training systems affected yield, fruit quality, and vigor in the cultivar “Bounty”. We found that the single leader system (Super Spindle Axe; SSA) and the system with multiple (4-8) leaders (Upright Fruiting Offshoots; UFO) improved early yield (4th-6th leaf), when compared to a free-standing three-dimensional system (Quad-SSA; QSSA). This increase in yield did not come with any observed cost to fruit quality, which was not significantly different for any system. The amount of excess vegetative growth removed during pruning remained largely constant per row-foot regardless of the tree density. This suggests that increasing density may be as effective as increasing leader number at controlling vegetative vigor.
Second, we examined the performance of three varieties with different branch angles in two different planar training systems—one with two leaders, and one with six or more leaders. While significant differences in yield and fruit quality were observed among the varieties, no differences in performance were observed for any variety between the two training systems. An intermediate branch angle was observed to facilitate training activities such as pruning and tying.
Third, we engaged with growers to try to understand what they view as major obstacles to adopting high-density systems in peach. While presentations at grower conferences elicited interest in the training systems we trialed, we were unable to get sufficient responses to our survey to draw general conclusions about grower concerns about high-density, planar systems.
- Trial whether high-density, planar systems could improve yield and fruit quality in peach.
- Compare planar systems with differing numbers and densities of leaders.
- Test how branch angle impacts what training system works best.
- Understand what variation in architecture is available in commercial peach varieties.
- Identify growers’ concerns about high-density, planar systems in peach.
Cooperators
- (Researcher)
- (Researcher)
Research
We used three different peach plantings for this project. In order to compare the effects of differing leader numbers and planting densities in novel planar training systems, we utilized a 2018 planting of Bounty peaches in Clarksville, MI trained into three planar systems —upright fruiting offshoots (UFO) at 8’ x 12’ spacing, super slender axe (SSA) at 3’ by 12’ spacing, and dual SSA (DSSA) at 6’ x 12’ spacing —and a three-dimensional system, quad SSA (QSSA) at 8’ x 12’ spacing (Figure 1). Data was collected for three growing seasons (2021-2023; 4th -6th leaf). To assess productivity and efficiency of each system, we measured yield per tree, estimated yield per acre, and estimated excess vegetative growth, as measured by the fresh weight of pruned branches throughout the season. To evaluate the effects of each system on fruit quality and uniformity, we measured fruit weight and brix.
Second, in order to compare the effects of varieties with differing branch angle in different planar training systems, we utilized 2018 and 2020 plantings in Clarksville, MI of Bounty (spreading branch angle), Sweet N’ Up (upright branch angle) and Crimson Rocket (narrow branch angle). The 2018 planting was trained in UFO at 8’ x 12’ spacing (all three varieties) or SSA at 3’ by 12’ spacing (Bounty and Sweet N’ Up only). In the 2020 planting all three varieties were trained in DSSA in 6’ x 12’ spacing or Drapeau-UFO (DUFO) in 8’ x 12’ spacing (Figure 1). Data for the 2018 planting was collected from 2021-2023, and data for the 2020 planting was collected in 2022 and 2023 (3rd and 4th leaf). We performed the same yield and quality measurements as described for the training style comparison.
Third, in order to examine the variance in tree architecture available in commercial peach varieties, we utilized a variety trial at the Southwest Michigan Research and Extension Center (SWMRC) in Benton Harbor, MI. To develop a profile of the tree architecture, we measured branch angle and internode length and documented overall architecture characteristics and flower bud location.
Finally, to better understand the concerns and tradeoffs which influence growers’ decision-making process about training systems we developed a grower survey. The online survey consisted of twelve questions, including four demographic questions concerning grower age, grower location, acreage, and crops grown; two questions about their current methods of growing peaches; three questions about their experiences and views of planar systems in peach; and three questions about their experiences and view of high-density systems in peach.
For the comparison of training styles using Bounty, we examined the fourth-sixth leaf yields of the 2018 planting. Estimated cumulative yield per acre was higher for UFO and SSA than DSSA and QSSA (Figure 2). Between DSSA (two leaders) and SSA (one leader), both of which had leaders spaced at 3’ in the row, having only a single leader per tree (SSA) improved yield per acre, as would be expected from the vigor diffusion of having multiple leaders. However, UFO (6-8 leaders), with one leader every 12-18”, had higher yields than DSSA (2 leaders, 3’ spacing per leader) and QSSA (4 leaders). These preliminary results suggest that increasing leader density may improve early yield. Furthermore, in this study, this increase in yield did not come at the cost of fruit quality, as no consistent differences among the training styles were observed for fruit size or brix (data not shown).
The multileader planar systems (DSSA and UFO) had less excess vegetative vigor per row-foot (as measured by fresh weight of pruned branches) than the single-leader planar system (SSA; Figure 2). This is in accordance with the previous observations that multileader systems have more vigor diffusion. However, the multileader, three-dimensional system (QSSA) had the same amount of excess vegetative vigor as the single-leader planar system. It is not clear why this is the case, but it may have to do with the smaller amount of scaffold retained in planar systems.
For the comparison of Bounty, Crimson Rocket, and Sweet N’ Up, there were clear differences in cumulative yield among the varieties. For the 2018 planting in SSA, Bounty and Sweet N' Up had similar yields per acre (Figure 2). In UFO, Bounty had the best yield, followed by Sweet-N-Up, and then Crimson Rocket (Figure 2). Sweet N' Up and Crimson Rocket also had significantly lower fruit weight, although brix was not affected (data not shown). However, this planting had extensive bacterial gummosis that was more severe in Crimson Rocket and Sweet N' Up, and this may have impacted results. For the 2020 planting, Sweet N' Up had significantly higher yield per acre (3rd and 4th leaf cumulative) than Bounty (Figure 3). Bounty significantly outperformed Crimson Rocket in DUFO but the difference was less in DSSA (Figure 3). In this planting, only Crimson Rocket had significantly lower fruit weight than Bounty, no consistent differences among the varieties were observed for brix (Figure 3, data shown from 2023). Neither fruit weight nor brix was altered by training style.
For the assessment of architectural traits in peach cultivars, preliminary results suggest that there is moderate diversity in architecture among existing cultivars (Figure 4). Estimated branch angles for the 21 varieties measured ranged between 40˚ and 60˚, while measured average internode length ranged from approximately 1cm to about 1.5cm.
Responses to our grower survey were limited (10 respondents), and growers interested in planar systems are probably over-represented. We had good representation of growers with different sizes of peach acreage, ranging from less than 10 acres to 40-59 acres. Most respondents also grew other tree crops, particularly apple and cherry. Almost all growers had at least some peaches trained in open-vase. Half of the growers had either perpendicular-V or Quad-V trained peaches, and a couple growers had tried planar systems in peach, particularly bi-axe (essentially the same as our DSSA) and Palmette. One unexpected result is that almost half of the growers who responded had not tried planar systems in any tree fruit.
Educational & Outreach Activities
Participation Summary:
- Consultation: Discussion with grower about starting a planar peach planting on his farm.
- Fact Sheet: A description of the research project was included in a booklet for the 2022 Ridgefest Tour at the Michigan State University Clarksville Research Center.
- Press: An article describing the research project and results written by the PI was included in the July 2023 issue of Good Fruit Grower Magazine.
- Tours: The research planting was included in the 2023 "Ridgefest" tour for Michigan tree fruit growers.
- Presentations: Research was presented on posters at the Great Lakes Fruit, Vegetable, and Farm Market Expo (for growers) in both December 2021 and 2023 (See attached poster presentations), as well as on a poster at the ISHS 10th international peach symposium in Naoussa, Greece in June 2022. An oral presentation was also given by the PI's advisor (Courtney Hollender) at the 2022 Great Lakes Fruit, Vegetable, and Farm Market Expo.
Project Outcomes
Tree fruit growers are facing extremely narrow profit margins, limited labor availability, and decreasing land availability. This project identified several high-density, planar systems which had better estimated yield per acre than our three-dimensional control system. We also identified challenges and advantages of implementing these planar systems with several different growth habits (spreading, upright, and pillar). This provides growers with information that can help them make informed decisions as they design orchard systems for their specific requirements. More efficient orchard systems support sustainable agriculture by decreasing labor and land use and by improving grower profit margins while keeping food prices low.
Through this project, we were able to test our hypotheses about how to limit vegetative vigor in peach for more efficient fruit production. We were also able to collect several additional seasons of field data and gain skills in measuring quality attributes relevant to the market. Finally, we found ways to interact directly with growers to gain feedback. This revealed that the industry has interest in sustainable fruit production through high density plantings, but also has questions about how to implement them and skepticism over whether the initial financial investment can be recovered.
"It was a great experience getting to know and work with Andrea. High density stone fruit has been something I have wanted to learn more about, but didn't want to do so by trial and error. Her research and work with fruiting wall structure showed me it was possible and how to achieve my goal. This spring I planted five acres of high density prunes and peaches on trellis. Without her help this would not have been possible."-Tree Fruit Grower in New York.