Quad V. Photo: Edwin Winzeler, Penn State
At the same time, the ideal system would be easy to teach to laborers, and compatible with mechanization. Current peach production practices are labor-intensive, requiring multiple trips through the orchard to dormant prune, hand thin, hang OFM mating disruption, summer prune, and for multiple (often 3) harvests. The traditional approach to training and pruning peach trees in the eastern U.S. has been the low headed open vase, at low tree densities of 113 to 173 trees per acre (Figure 1). In this system, trees are pruned severely, using bench cuts to spread the scaffolds at a wide angle and keep the canopy within 9 feet of the ground. This allows growers to maintain a pedestrian orchard.
Figure 1. The open center-trained tree has been the industry standard for over 150 years. Photo: Tara Baugher, Penn State
The pedestrian objective of the open vase exerts a heavy toll on economic returns. Low tree density equates to low precocity and production of low yields. The severe pruning required by open vase further reduces early bearing and its vigorous regrowth requires that it must be summer pruned to produce fruits of marketable red color. V-shaped canopies such as Tatura, Kearney V (perpendicular-V), Quad V, and Hex V, have been shown to be more productive and more compatible with the natural growth habit of trees. Severe bench cut pruning is not required, and V trees come into bearing earlier as a result. Even a modest increase in early yield per tree is multiplied 2.5 to 3 times because of the higher planting density.
V systems are simpler to manage, and more compatible with mechanization. The high-to-moderate planting density increases the amount of productive bearing surface of these systems, producing higher yields than open vase. V systems are inherently tall, and require the use of a ladder or platform to access the upper canopy. This adds to the cost of labor, although use of mechanical string thinning and labor platforms lessens the additional expense. Refer to Table 1 for a summary of the comparison of open vase and V-canopy systems.
Table 1. Comparison of relative differences between traditional open vase and higher density V canopy production systems for peach.
|Characteristic||Open Vase||V-shaped canopy|
|Tree density per acre||100 – 172||242 – 544|
|Need for irrigation||Beneficial||Essential|
|Final canopy height||7’ – 10’||12’ - 14’|
|Set crop potential with pruning?||Feasible||Precise|
|Compatibility to mechanization||Low||High|
|Years to full production||8 to 9||5 to 6|
|Yield (bushels per acre)||350 – 450||550 - 670|
|Average fruit size (Loring)||3.5||3.25|
|Average red color (Loring)||50%||70%|
|Relative income||“100% of standard”||“116% - 154% of standard”|
Both vase and V systems have challenges inherent to the natural tree form of the peach tree. Peach bears fruit on 1-year-old wood, so a substantial amount of annual vegetative re-growth is needed to generate a new bearing surface each year. The pattern of growth in peach is acrotonic, meaning most of the new growth occurs in the outer portion of the canopy. This growth pattern is an inherent trait, and it is amplified by the species’ intolerance of shade. Shaded portions of a peach canopy grow weakly, fail to flower, and quickly die off. As a peach tree matures, its bearing canopy migrates up and out of reach from the ground.
Migration of the bearing surface can be slowed, but not eliminated, by pruning with bench cuts in the open vase system. The heavy bench cuts required to keep the trees short result in strong local invigoration of the canopy and increase shading. Early season shading reduces flowering the following year, and late season shading reduces red fruit coloration. The strong regrowth that results from heavy pruning must be counteracted with summer pruning once or twice a season to prevent severe shading effects.
In the taller V systems, the acrotonic growth pattern and shade intolerance of peach makes it challenging to renew new fruiting laterals within reach of workers on the ground. Peach does not readily renew fruiting branches from short stubs as does apple. As a result, short sections of 2-year-old wood (secondary branches are stubbed back to the most proximal fruiting lateral. This increases the complexity of the canopy and of pruning decisions, which is counterproductive to the original intent of the simplified pruning rules of the V systems.
There is not presently an ideal peach production system, as all of them have flaws. Furthermore, our 2007 trial of open vase, perpendicular V, quad V and hex V systems in Pennsylvania showed that, at prices received for fresh market peaches from 2009-2015, all 4 systems were profitable. That doesn’t mean that there isn’t much difference among these systems.
In this trial, V systems came into full production 3 years sooner than open vase, were 50% more productive over the 8 year trial, and produced 20% more red fruit. Depending on planting density V systems were 16% to 54% more profitable. Unlike apples, the most intensive (and expensive) perpendicular V system wasn’t the best. Moderate planting density with quad V training created more bearing surface, and more peaches per acre than the perpendicular, with 29% fewer trees (346 versus 484) per acre.
Low-headed open vase trees still fit in special circumstances. For instance on hillside sites with steep slopes, or in financial circumstances when the enterprise needs to minimize planting costs.
For the present, we recommend a quad V peach training system spaced at approximately 7 ft. between trees and 16-18 ft. between rows. Quad V is productive, precocious, and produces higher packout, with a system that is easily taught and compatible with mechanization. That leaves “pedestrian” as the only pin still standing when the characteristics of the quad V are considered. For information on training trees to quad V see Innovations in Peach Training Systems. This Learn Now video is available in Spanish or English and can be used for employee training.
Figure 2. Hex V in bloom. Photo: Edwin Winzeler, Penn State
What about the future?
In the near term, several dwarfing rootstocks may provide a measure of success with keeping peach trees shorter. In particular, some of the Controller series from UC Davis show promise. Controller 8 has been the best in PA trials, producing a precocious tree that is 70% the size of Lovell, with the same level of productivity as seedling peach trees and great survival. Our results to-date indicate that trees on Controller 8 rootstock are putting more energy into fruit and less into vegetation, which is necessary for more efficient production on dwarfed trees. Another rootstock in this series, Controller 7, also shows promise. If trees with 70% vigor could be managed at 70% shorter canopy height, then the vast majority of fruit will be within reach from the ground.
In the long term, we must continue to study techniques for further reducing labor inputs through mechanization. In the 1980s, a “meadow orchard” system was described and tested. Peach trees were planted at very close density and mechanically harvested, by cutting off the entire tree at harvest, much like combining corn. Even in regions with an extended growing season, [Georgia (US), and Israel], it wasn’t possible to grow annual crops of quality peaches. In Israel it could be accomplished only with early maturing cultivars, and even then, fruit maturity was delayed and fruit quality suffered when the growing of annual crops was attempted.
The meadow orchard system was modified to two scaffolds at 2 ft. x 6 ft., and named the “intensive system”. Initially it looked much like the perpendicular V, except that one of the two scaffolds was pruned to a short stump while dormant, leaving the second to bear fruit the following season, while the other side regenerated. By alternating removal of the 2 scaffolds, the trees maintained enough vigor to produce adequate flowering, fruit set and yield. Since the canopy of an intensive system will never be more than two years old, it follows that the orchard would remain pedestrian. Concerns with the intensive system include lower tree survival, rapid development of mineral nutrient deficiencies, and small fruit size. One limitation of the intensive concept is the lack of small machinery to deal with the very tight spacing. Modifications of this system should be investigated further.