Cherry Training Systems

Stub or renewal cut

A stub cut is used to renew fruiting wood to keep it young and productive. The term "stub cut" usually describes a heading cut that removes all but a few inches of growth on a branch, although it is possible for a stub of 1 foot or longer to be left. If the wood is relatively young, visible buds below the cut may be stimulated to grow and replace the older branch. When older wood is stubbed back, visible buds may no longer be present. In this case, adventitious buds located beneath the bark may begin to grow and develop into a replacement branch.

Another form of a stub cut can be made when a branch is too upright or is simply becoming too mature. If a lateral branch is present, head the primary branch so that the cut is slightly below the terminal point of the secondary lateral (Figure 1). It is important that the secondary branch terminal (a) be higher than the remaining stub (b). This discourages vigorous vertical wood from growing out of the stub, and it keeps the secondary branch more horizontal and less vigorous.

Making stub cuts late in the dormant season or at bloom will provide a higher percentage of regrowth than during other seasons.

Kym Green Bush (KGB)

The Kym Green Bush (KGB) is the only system covered in this manual that creates a fully pedestrian orchard — one that can be harvested without ladders or platforms. Tree formation is easy and requires minimal labor; mature pruning is simple and follows a repeatable plan. Although most varieties grow and produce well with a KGB system, it is not recommended for non-spur type varieties such as ‘Regina’ and ‘Attika’, which produce a significant proportion of fruit at the base of 1-year-old shoots. This wood is eliminated in the KGB system.
The establishment years of the KGB system are similar to the Spanish Bush (SB); however, once the structure is formed, the two systems diverge significantly. In the SB tree, all upright leaders are permanent and fruit is produced on small laterals that are renewed regularly. This contrasts with the KGB tree, where all vertical leaders eventually are renewed and the only permanent wood is the lower framework of the tree. The KGB utilizes vigorous or semi-vigorous rootstocks, and the number of vertical leaders established should be proportional to tree vigor.

Stage: At planting

Goals

• Promote strong root system establishment in the first growing season.
• Promote moderate growth throughout the establishment period by providing adequate nutrients.
• Begin forming structure.

System development

• Head nursery tree 18 inches above ground (Figure 5).
• Ensure that there are three or four live buds below the cut.
• Expect a minimum of 24 inches of growth on each leader during the first growing season.

Stage: First dormant season

Goals

• Continue forming tree structure.
• Promote uniformity of growth.

System development

• Head all leaders to 2–5 inches in length (Figure 6).
• Head strong leaders to the shorter length and weak leaders to the longer length.
• Remove very strong or very weak leaders to obtain uniformity.
• In areas with high bacterial canker pressure, these cuts can be made at the end of the preceding growing season, i.e., late summer or early autumn when the weather is dry.
• Proper pruning results in a tree with a flat top and strong, upright leaders cut shorter than outside weaker leaders.

Stage: Second growing season

Goals

• Promote moderate growth throughout the establishment period by providing adequate nutrients.
• Continue forming tree structure.
• Promote uniformity of growth.

System development

• Prior to the summer solstice (first day of summer), head all leaders to 2–5 inches in length (Figure 7).
• Head strong leaders shorter than weak leaders.
• Remove very strong or very weak leaders to obtain uniform leader development throughout the tree.
• Proper pruning results in a tree with a flat top and strong, upright leaders cut shorter than outside weaker leaders.

Stage: Second dormant season

Goals

• Promote moderate vigor through leader numbers.
• Continue forming tree structure.

System development

• For trees on full-size rootstocks, repeat the steps described in “First dormant season” section.
• These steps are important for trees on full-size rootstocks in order to obtain a balanced tree without excessive vigor.
• Suggested number of leaders to establish a balanced framework of fruiting units: semi-vigorous rootstocks, 20–25 leaders; vigorous rootstocks, 25–30 leaders.
• Leader numbers may vary depending on soil fertility and other conditions. The target is to achieve annual elongation of 24–36 inches per leader, so leader number should be adjusted higher if annual elongation is greater than the target, or lower if annual elongation is less than the target.
• Trees on semi-vigorous rootstocks should now have enough branches and are not pruned at this time.

Stage: Third dormant season

Goals

• Begin crop load management

System development

• Leaders on moderately or highly productive varieties of semi-vigorous rootstocks and highly productive varieties of full-sized rootstocks must be tipped. Remove a quarter of the new growth to balance the leaf-area-to-fruit ratio and produce high-quality fruit (Figure 8).

Stage: Third and subsequent growing seasons

Goals

• Initial minor fruiting on shoot basal flower buds for trees on semi-vigorous rootstock in the third year.
• First commercial harvest (mixed spur and shoot basal fruiting sites) for trees on semi-vigorous rootstocks in the fourth year.
• Promote light distribution.
• Manage tree vigor.

System development

• The presence of yellow leaves at the bottoms of the leaders indicates excessive shading; two to four strategically placed leaders should be removed from the center of the tree to improve light penetration (Figure 9).
• If leader growth is weak (i.e., less than 24 inches per year), remove additional leaders.
• Suggested number of leaders at maturity to maintain a balanced, productive tree: semi-vigorous rootstocks, 12–16 leaders; vigorous rootstocks, 15-20 leaders.
• Leader numbers may vary depending on soil fertility and other conditions.
• The idea is to produce a tree of moderate vigor with annual leader elongation of 24–36 inches.

Stage: Mature pruning

Goals

• Establish mature height to maintain pedestrian profile.
• Promote light distribution.

System development

• Top the tree at 8 feet. This can be done mechanically or by hand.
• If the tree is not yet 8 feet tall, remove a quarter of the new shoot growth from each leader (Figure 8).
• Remove all easily reached lateral branches. Leaving stubs of approximately 3 inches will allow fruit-bearing axillary buds located at the base of this 1-year-old wood to produce fruit for one season (Figure 10). Non-spur-bearing varieties such as ‘Regina’ can produce significant fruit at this point. These small stubs will die after fruiting and can be removed the following year.

Stage: Dormant or bloom

Goals

• Renew fruiting wood.

System development

• Select the largest leaders for renewal. Renew any leader that cannot be pulled down easily for harvest.
• Renewal is accomplished by removing the selected leaders back to a stub of approximately 10 inches with three to four buds. A replacement leader will grow from this stub to form new fruiting wood (Figure 11).
• Renew all leaders associated with a basal fork. Failure to do so will result in the unheaded leader becoming dominant and only weak regrowth will proceed from the adjacent stubbed leader (Figure 12).
• When multiple renewal leaders grow from the stub, they should be thinned to the one or two strongest. Remove weak leaders as soon as possible to enhance the strength of the renewal leader to keep it vertical as it grows and becomes fruitful (Figure 13).

Summary

Whether trees are grown on vigorous or semi-vigorous rootstocks, the KGB system will produce a true pedestrian orchard. This simple, repeatable pruning process allows the least skilled workers to quickly learn the system, reducing mistakes and the time required to prune.

Spanish Bush (SB)

The Spanish Bush (SB) training system promotes the production of numerous scaffolds and branches that reduce vigor, impart a small tree structure, and permit fast and easy tree maintenance and harvest. A deliberate branch renewal plan produces a steady supply of young fruiting wood. Pruning steps that establish the framework of the tree are very similar to the establishment steps in the KGB system. The SB utilizes vigorous or semi-vigorous rootstocks, and the number of vertical leaders established should be proportional to tree vigor.

Stage: At planting

Goals

• Promote strong root system establishment in the first growing season.
• Promote moderate growth throughout the establishment period by providing adequate nutrients.
• Begin forming structure.

System development

• Head nursery tree 18 inches above the ground (Figure 14).
• Ensure that three or four live buds remain below the cut.
• Expect a minimum of 24 inches of growth on each leader during the first growing season.

Stage: First dormant season

Goals

• Continue forming tree structure.
• Promote uniformity of growth.

System development

• Head all leaders to 2–5 inches in length (Figure 15).
• Head strong leaders to the shorter length and weak leaders to the longer length.
• Remove very strong or very weak leaders to obtain uniformity.
• In areas with high bacterial canker pressure, these cuts can be made at the end of the preceding growing season, i.e., late summer or early autumn when the weather is dry.
• Proper pruning results in a tree with a flat top and strong, upright leaders cut shorter than outside weaker leaders.

Stage: Second growing season

Goals

• Promote moderate growth throughout the establishment period by providing adequate nutrients.
• Continue forming tree structure.
• Promote uniformity of growth.

System development

• Prior to the summer solstice (first day of summer), head all leaders to 2–5 inches in length (Figure 16).
• Head strong leaders shorter than weak leaders.
• Remove very strong or very weak leaders to obtain uniform scaffold development throughout the tree.
• Proper pruning results in a tree with a flat top and strong, upright scaffolds cut shorter than outside weaker leaders.

Second dormant season

Goals

• Promote moderate vigor through leader numbers.
• Encourage branching on trees with semi-vigorous rootstocks.

System development

• For trees on full-size rootstocks, repeat the steps described in “First dormant season” section.
• These steps are important for trees on full-size rootstocks in order to obtain a balanced tree without excessive vigor.
• Suggested number of leaders to establish a balanced framework of fruiting units: semi-vigorous rootstocks, 20–25 leaders; vigorous rootstocks, 25–30 leaders.
• Leader numbers may vary depending on soil fertility and other conditions. The target is to achieve annual elongation of 24–36 inches per leader, so leader number should be adjusted higher if annual elongation is greater than the target, or lower if annual elongation is less than the target.
• Trees on semi-vigorous rootstocks should now have enough branches, and all leaders should be tipped to encourage branching by removing a quarter of the new shoot growth.

Stage: Third dormant season

Goals

• Begin crop load management.

System development

• Leaders on moderately or highly productive varieties of semi-vigorous rootstocks and highly productive varieties of full-sized rootstocks must be tipped. Remove a quarter of the new growth to balance the leaf-area-to-fruit ratio and produce high-quality fruit (Figure 17).

Stage: Third and subsequent growing seasons

Goals

• Initial minor fruiting on shoot basal flower buds for trees on semi-vigorous rootstock in the third year.
• First commercial harvest (mixed spur and shoot basal fruiting sites) for trees on semi-vigorous rootstocks in the fourth year.
• Promote light distribution.
• Manage tree vigor.

System development

• The presence of yellow leaves at the bottoms of the leaders indicates excessive shading; two to four strategically placed leaders should be removed from the center of the tree to improve light penetration (Figure 18).
• If leader growth is weak (i.e., less than 24 inches per year), remove additional leaders.
• Suggested number of leaders at maturity to maintain a balanced, productive tree: semi-vigorous rootstocks, 12–16 leaders; vigorous rootstocks, 15–20 leaders.
• Leader numbers may vary depending on soil fertility and other conditions.
• The idea is to produce a tree of moderate vigor with annual leader elongation of 24–36 inches.

Stage: Mature pruning

Goals

• Establish mature height.
• Renew fruiting wood.
• Continue to monitor and manage tree vigor.

System development

• In the SB system, lateral branches are allowed to develop on each scaffold and fruit for several years before being renewed.

Late summer or early fall

• Top the tree at 8 feet. This can be done mechanically or by hand (Figure 19).
• If the tree is not yet 8 feet tall, remove a quarter of the new shoot growth from each leader. (Figure 17)
• Hedge the sides of the tree each year, mechanically or by hand (Figure 19).

Summary

The Spanish Bush training system produces trees that are a maximum height of 8 feet, making this a semi-pedestrian system that is easy to harvest and maintain. Non-spur type varieties such as ‘Regina’ and ‘Attika’ perform well under Spanish Bush training, since these varieties produce a significant proportion of fruit on the basal buds of 1-year-old shoots.

Steep Leader (SL)

The Steep Leader (SL) training system was developed by growers in Washington State. It consists of three or four vertical leaders emerging from the base of the tree with horizontal scaffold branches to develop a pyramidal shape at maturity. Fruiting occurs on temporary lateral branches that grow from the vertical leaders and horizontal scaffolds. Each leader mimics a one-sided spindle tree.

Stage: First dormant season

Goals

• Select leaders for future development.
• Promote development of permanent bottom lateral scaffolds.

System development

• Select three or four upright growing leaders of uniform vigor. These will form the main leaders and should be allowed to grow vertically.
• If the tree is growing on a semi-vigorous rootstock and one or two very strong leaders developed from the cut made at planting, remove these to keep the tree in balance (Figure 25).
• If the tree is growing on a vigorous rootstock and one or two very strong leaders developed from the cut made at planting, leave these temporary leaders to absorb excess vigor. Removing them during dormancy could invigorate the tree.
• Head all leaders about 24 inches from their base in order to promote branching and establish a permanent bottom whorl of lateral scaffolds (Figure 26).
• Leave other leaders temporarily to moderate tree growth.
• In areas with high bacterial canker pressure, these cuts can be made at the end of the preceding growing season, i.e., late summer or early autumn when the weather is dry.

Stage: Second dormant season

Goals

• Continue developing leaders.
• Select and train scaffold branches for permanent bottom whorl.

System development

• Select one vertically growing shoot per leader to serve as the vertical extension of the leader.
• Head this shoot approximately 24 inches from its previous season point of origin if ultimate tree height is to be less than 12 feet, or at 24–36 inches if tree height will be greater than 12 feet (Figure 27).
• Select one outward-facing lateral shoot to serve as the permanent bottom whorl. Tie this branch down to a horizontal position to establish a wide base. Head this branch 24 inches from its base (Figure 28). Tie downs will be removed at the end of the third growing season.
• Remove any inward-oriented lateral shoots to keep the interior area between leaders open.
• Until fruiting begins, several temporary branches will help control overall tree vigor. These should be headed at about 24 inches. (Figure 29).
• Select smaller and weaker wood as permanent branches for SL trees on vigorous rootstocks. Thin out very strong wood (Figure 30).
• On semi-vigorous rootstocks, leave moderately growing branches and prune out thin, weak branches (Figure 31).

Stage: Dormant pruning until maturity

Goals

• Continue leader and lateral fruiting whorl development.
• Promote fruiting on temporary branches.

System development

• To promote lateral branch development, continue to head leader extension at 24–36 inches from its previous season point of origin as explained in the directions for the second dormant season (Figure 32).
• Head new terminal growth on the horizontal bottom whorl 24 inches from point of origin.
• Allow the temporary branches that were left in the first dormant season to fruit. Once growth begins to slow due to fruiting, remove these to improve light distribution to the tree bottom (Figure 33).
• SL trees of bearing age will have three or four permanent, vertical, well-branched leaders for fruit production.
• The tree base will include one permanent, horizontal, well-branched scaffold per leader.
• Fruit will be produced on small temporary branches emerging from the permanent vertical and horizontal wood.

Stage: Mature pruning

Goals

• Renew fruiting wood.
• Promote light distribution.
• Promote quality fruiting sites.
• Reduce and maintain desired tree height.

System development

Lateral branch (fruiting wood) maintenance and renewal

• Treat each leader as an individual one-sided spindle tree.
• In order to keep shading at a minimum, do not allow lateral branches to grow larger than one-half the diameter of the parent branch. Remove very large branches. Keep in mind the concept of retaining “big, smaller, smallest” wood as the tree is pruned from lower to higher in the canopy (Figure 34).
• Establish a regular fruiting-wood renewal process. Allow lateral branches to fruit several years before renewal (Figure 35). The highest quality fruit develops at the base of 1-year-old shoots and on young spurs.
• At late dormant or bloom, stub back approximately 20 percent of all fruiting wood each year so that spurs are no more than 5 years old.
• Renew branches each year by stubbing them back to a vegetative bud, or, where no vegetative bud is visible, leave a stub approximately 4–6 inches in length. Older branches will not renew as successfully as younger branches.

Maintain light channels

• Remove or cut back large branches that extend beyond the lower branches in order to maintain light channels and fruiting wood throughout the tree (Figure 36).

Weak and pendent wood

• Remove weak or pendent wood, which tends to overset and produce small fruit (Figure 37).

Branch terminals

• Where adjacent branches are the same size, remove one in order to improve light penetration (Figure 38).

Tree top

• As the tree reaches maximum height, prune the top back to one weak lateral, generally in late summer (Figure 39).

General maintenance

• On less productive SL trees, tip and remove up to a third of the new growth of only those lateral branches you can reach while standing on the ground. This will invigorate the bottom of the tree and stimulate new growth in an area otherwise difficult to re-invigorate (Figure 40).

• To balance crop load if the tree is very productive, tip and remove a quarter to a third of the new growth of all lateral branches (Figure 41).

Summary

• The goal of mature tree pruning in the SL training system is to encourage light penetration and good fruit quality throughout the tree by maintaining a pyramidal shape. Branches from bottom to top should follow the pattern of “big, smaller, smallest.”

Super Slender Axe (SSA)

The Super Slender Axe (SSA) was developed as a modification of the spindle to gain greater control of tree growth. The SSA needs dwarfing and precocious rootstocks such as Gisela®5 and Gisela®3. In the case of low vigor sites or self-fertile varieties, it may be possible to use more vigorous precocious rootstocks, such as Gisela®6 or Gisela®12. Varieties with good vigor, upright growth habits, and the ability to produce lateral shoots are preferred. The most important characteristic for a suitable variety is the capacity to produce fruit on basal buds of 1-year-old shoots.

The production habit of this system is significantly different from other systems. Instead of producing fruit on spurs with multiple small flower buds, SSA utilizes the solitary large flower buds at the base of 1-year-old shoots. This results in a favorable fruit/leaf ratio that yields very good fruit size and quality. The low production capacity per tree is compensated by the high planting density.

Stage: First growing season

Goals

• Develop at least 75 percent of the final leader height.
• Develop 10 or more well-distributed lateral branches with relatively uniform moderate vigor, which will provide shoot basal fruiting capacity in the second year.

System development

• When 3–4 inches long, the more upright-growing lateral shoots can be adjusted to horizontal crotch angles by attaching a clothespin at a 90-degree angle to the trunk just above the shoots.
• Clothespins can be removed after 2–3 weeks, or reset to just behind the shoot tip to help keep the shoot from turning upwards.
• Figure 44 illustrates the type of desired lateral shoot activation and growth at the end of first year compared to a tree with no bud activation (Figure 45).
• A high single-wire trellis may be useful for aligning the tops of the SSA trees.

Stage: First dormant season

Goals

• Impose bud-activation techniques to stimulate additional extensive lateral shoot formation on leader.
• Begin “short-pruning” of existing lateral shoots to simultaneously balance leaf area with second-year crop load and renew or initiate new fruiting laterals.

System development

• SSA “short-pruning” is done by removing the majority of the length of each 1-year-old (previous season) shoot, retaining only the basal flower buds plus at least two vegetative buds for new shoot formation (Figure 46a). Lower branches can be left slightly longer than upper branches.
• Short-pruning may be accomplished best during bud swell, when it is easier to differentiate between the rounded flower buds and the more pointed vegetative buds (Figure 46b).
• When leader extension has been moderate, bud activation steps can be taken (as described above) to induce another 10 or more lateral branches on this leader growth, repeating as needed until the full tree height is achieved.

Stage: Second and subsequent growing seasons

Goals

• Achieve final leader height in the second year.
• Complete formation of well-distributed lateral shoots on 75 percent of the leader in the second year and on 100 percent of the leader in the third year.
• Begin cropping in the second year, achieving full production by the fourth and fifth years.
• Maintain permanent canopy height without invigorating the tree top.

System development

• When 3–4 inches in length, the more upright-growing lateral shoots on the leader can be adjusted to a horizontal crotch with clothespins.

• Once the leader has reached its mature height, it should be headed back to a relatively weak lateral shoot just below the preferred mature height, either done at a delayed budbreak timing (4–5 weeks after budbreak) or postharvest (mid-summer) to minimize regrowth.

Stage: Second and subsequent dormant seasons

Goals

• Impose “short-pruning” on all lateral shoots to achieve 100 percent annual renewal of all fruiting laterals.
• Maintain balanced and moderate vigor and fruitfulness throughout canopy.

System development

• Every “fruiting feather” is short-pruned annually, leaving two to three vegetative buds for leaf area renewal plus the basal flower buds for cropping (Figure 48); feather length should decrease slightly from canopy base to apex (Figure 49).
• Short-pruning maintains the production close to the central leader (Figures 50a and 50b).
• When fruiting feathers become too long, they can be removed with a short stub to promote renewal of shoots close to the leader (Figure 51).
• On SSA trees, flowering (Figure 52) and cropping (Figure 53) should occur primarily on basal buds of 1-year-old shoots throughout the life of the orchard.

The TSA is a training system well-suited for dwarfing to semi-vigorous rootstocks, or vigorous rootstocks on weak soils, since growth is comprised primarily of lateral shoots of moderate vigor borne on a single vertical leader.

Stage: First dormant season

Goals

• Impose bud-activation techniques to stimulate additional lateral shoot formation on leader.
• Stimulate secondary lateral-shoot formation and begin managing future cropping capacity.

System development

• If six or more lateral branches were not achieved in the first year, all existing lateral shoots should be restarted by cutting back to the most basal (bottom) vegetative bud.
• If six or more lateral branches were achieved in the first year, these should be headed, preferably just beyond two side-oriented buds, to remove 15–25 percent of the length (less for weaker shoots, more for stronger shoots) (Figure 57).
• Since every shoot that formed in the first year should form flowering spurs in the third year, this heading of laterals is a strategy to not only fill out the canopy, but to also begin balancing the crop load (i.e., leaf-to-fruit ratio) for the third year and beyond.
• The new portion of the leader (which grew in Year 1) should be treated the same as the nursery leader in Year 1 regarding bud removal, selection, and activation (see above).
• Expectations for the Year 2 growing season are to obtain 8 to 12 new lateral shoots well-distributed down the leader growth from Year 1 and a doubling of lateral shoots from those lateral shoots that developed in Year 1.
• If terminal leader growth in Year 1 was excessively vigorous (e.g., 4 feet or more), the leader should be headed back to about 3 to 4 feet of new terminal before sub-terminal bud removal and imposing a bud activation strategy.

Stage: Second and subsequent dormant seasons

Goals

• Stimulate secondary/tertiary lateral shoot formation and manage future cropping capacity.
• Maintain good canopy light distribution by thinning out laterals as needed.
• Begin fruiting branch renewal in Year 5.

System development

• Bud selection and activation on the leader should continue until the tree has reached its mature height (usually by Year 3 at the latest).
• Most lateral shoots should again be headed to remove 15–25 percent of the previous season’s shoot length growth (Figure 59).
• Overlapping shoots, weak shoots, pendent shoots or watersprout-type upright shoots should be removed to maintain good light distribution along all fruit-bearing sites (Figure 60).
• Branches in the lower portion of the canopy can be left longer than in the middle or upper portions, to maintain the Christmas tree-like conical shape.

Stage: Third and subsequent growing seasons

Goals

• First commercial harvest (mixed spur and shoot basal fruiting sites) in Year 3.
• Complete 100 percent of the final leader height in Year 3 Lowest tertiary branches should fill 100 percent of the allotted orchard area per tree in Year 3.
• Continue filling canopy fruiting volume with secondary and tertiary branches in Years 3 and 4.

System development

• Once the leader has reached its mature height, it should be headed back to a relatively weak lateral shoot just below the preferred mature height, either done at a delayed budbreak timing (4 to 6 weeks after budbreak) or postharvest (midsummer) to minimize regrowth (Figure 61).
• As fruiting branches reach 5–6 years old, the largest two or three should be cut back to a basal weak shoot, spur, or bud (if present), or approximately 8-inch stub from the leader, to stimulate fruiting branch replacement (Figures 62–63).

Summary

• The TSA system will produce relatively compact, freestanding trees that fruit precociously with good yields of high-quality fruit that can be picked mostly from the ground.

Upright Fruiting Offshoots (UFO)

The Upright Fruiting Offshoots (UFO) system was developed to:

• Simplify training, pruning, and crop load management.
• Utilize the sweet cherry’s natural upright growth habit and manage vigor by establishing multiple vertical structural fruiting units (number of vertical units should be proportional to tree vigor).
• Optimize input efficiencies (e.g., light, labor, agrochemicals) and achieve high, uniform light distribution to fruiting sites.
• Facilitate the adoption of orchard mechanization and automation technologies.

Stage: At planting

Goals

• Fill the in-row tree space with the horizontal nursery tree leader.
• Promote formation of multiple upright fruiting offshoots (vertical leaders) on trunk.
• Maintain upright growth of the tree terminal growing point.

System development

• Unheaded and unbranched (whip) nursery trees are recommended. This requires close communication with the contracted nursery, since standard commercial practice is to head trees back to about 4 feet for shipping.
• Plant trees at a 45-degree angle pointing the terminal to the south (northern hemisphere) or to the north (southern hemisphere) (Figure 64). This reduces the potential for sunburn on the trunk during establishment. Important: do not plant the trees vertically and bend them to a 45-degree angle.
• Clip/tie the trunk where it intersects the lowest wire (20 inches above ground) to maintain the planting angle. There is a single lowest wire in both the UFO and the UFO-Y trellises.
• Remove any nursery tree feathers with thinning cuts.
• Manually rub off all buds below the first trellis wire.
• Impose bud-activation techniques to upper buds about every 8 inches (UFO) or about every 4 inches (UFO-Y) to stimulate vertical shoot formation.

Stage: First and second dormant seasons

Goals

• Impose bud activation techniques to stimulate lateral shoot formation.
• Promote wide branch angles and an open tree form.

System development

• Head the leader only if its growth during the previous year was greater than 30 inches.
• Treat the leader as in the establishment year. Retain the top two buds and remove the next five to six buds (Figure 72).
• Promote branching by scoring or bud removal as described on page 58.
• Encourage branches to grow throughout the entire length of the trunk in a spiral rather than allowing distinct whorls to develop (Figure 72).
• Promote adequate light penetration by thinning closely spaced branches (Figure 72).

Stage: Second and third growing season, until maturity

Goals

• Initial minor fruiting on leader spurs and shoot basal flower buds in Year 2.
• Develop about 10 more well-distributed primary lateral branches of moderate vigor in Year 2, which will provide shoot basal fruiting capacity in Year 3 and spur fruiting capacity in Year 4.
• Promote wide branch angles and an open tree form.
• First commercial harvest (mixed spur and shoot basal fruiting sites) in Year 3.
• Complete 100 percent of the final leader height in Year 3.
• Lowest tertiary branches should fill 100 percent of the allotted orchard area per tree in Year 3.

System development

• Apply clothespins to emerging shoots as before, through Years 2 and 3.
• Branch angle should be approximately 60 degrees. To maintain this angle as branches grow, they may need to be spread or tied down.
• If necessary, thin new shoots to promote good light distribution throughout the canopy (Figure 73).
• Pinch back vertical shoots growing from primary laterals. Remove vertical shoots completely if they grow within a few inches of the trunk (Figure 73).
• Maintain a dominant terminal on all lateral branches.

Stage: Mature pruning, growing season

Goals

• Reduce and maintain desired tree height.

System development

• Control tree height only when tree growth has begun to slow due to cropping.
• Reduce tree height by cutting the top back to a weak lateral in late summer or early fall (Figure 77). Remove 36–48 inches of height in this way, depending on tree vigor.

Summary

• Due to minimal pruning in the establishment years and the use of scoring to induce branching and limb bending, the VCL system is labor-intensive in the first 2 years. However, the tree responds by producing early, high-quality crops. By maturity, labor input with this system is similar to other systems, such as the KGB and SL. The VCL system is particularly suitable for varieties having lower productivity, such as ‘Regina’, because it does not include branch tipping, which tends to reduce crop load. More productive varieties grown as a central leader tree are better suited to the TSA system which incorporates crop load moderation via pruning.