Written by Bernardita Sallato, Sara Serra, Manoella Mendoza, Kate Evans and Stefano Musacchi, October 2024.
WA 64 is a bicolored apple, the result of a cross between Cripps Pink and Honeycrisp, developed by Washington State University’s apple breeding program in Wenatchee, Washington, by Kate Evans and Bruce Barritt. It was patented by WSU in 2023; trees will become available for Washington growers in 2026. It is characterized by a small to medium size, closer in taste and appearance to its Cripps Pink parent, with outstanding storability (Evans et al., 2023). It is estimated to ripen around the end of September in Eastern Washington conditions, close to Golden Delicious timing, and two weeks before WA 38 (Evans et al., 2023).
In 2022, two pilot orchards were planted to better understand the influence of rootstocks and training systems on WA 64 tree growth and fruit. The rootstocks included were Bud 9 (very dwarfing), G.969 and G.41 (semi-dwarfing), and G.890 (vigorous). This document provides preliminary findings and general recommendations based on the observations from these two sites for the first three growing seasons.
Environmental conditions, including soil type, elevation, temperatures, water quality, etc. and management can significantly influence tree growth, fruit quality, and overall productivity. Thus, describing the site’s conditions and highlighting their differences are relevant to characterize a cultivar-rootstock combination.
a) WSU Sunrise Farm (SRO), Wenatchee
Site conditions: SRO, is located close to Rock Island, WA, USA (47°18’38.6″N, 120°03’52.4″W). The elevation is around 274 m (approximately 900 ft). Soil has a neutral pH (7.3-7.4) and sandy-loam, with the North end of the trial plot having a higher percentage of sand. The mineral composition in the North end has less organic matter (OM 0.9%), is very high in potassium (K) and magnesium (Mg), high in Zinc (Zn), moderate in calcium (Ca), low in phosphorous (P), and extremely low in boron (B) and sulfur (S). The South (loamier) has higher OM (1.1%), is very high K, Mg, and P, elevated in Ca, and low in Zn, B, and S. To stabilize this soil variability, peat moss was supplemented by mulching a 3.2 ft-wide-strip close to the trees.
Trial layout: Due to the soil variability, the research plot was designed in randomized blocks. The trial was planted on May 24, 2022, with four randomized blocks, each including two training systems (spindle and bi-axis) and four rootstocks (Bud 9, G.969, G.41 and G.890). Planting distance was the same for both training systems (11 ft x 3 ft), corresponding to a planting density of 1,320 trees/acre. Snowdrift, Evereste, and Indian Summer pollinizer trees were interplanted every ten WA 64 trees along the rows.
b) WSU Roza Farm, Prosser
Site conditions: Roza is located in the Yakima Valley near Prosser (46°17’31.3’’N, -119°43’54.6’’W). The elevation is around 355 m (approximately 1164 ft). The soil is a Warden silt loam, with an effective depth ranging from 32 to 48 inches, characterized by a layer of calcium carbonate (Caliche) at variable depth. Soil pH is neutral to alkaline with a slow water infiltration rate of 0.5 in/hr. Soil OM is low (0.8%), and nutrient levels are high except for P, B and S, which are generally below adequate ranges in the Yakima valley (Sallato et al., 2019).
Trial layout: the demonstration plot has one 400 ft row established as a V-angled system at 12 ft between rows, and three vertical rows at 10 ft. In the V trellis, trees were planted by rootstocks (not randomized), starting with 25 double-budded trees planted at 1.5 ft apart (forming a Y axis), followed by the single-budded trees (forming a V system). A modification of the system was established in a few trees on G.969 and G.41, training the laterals to the vertical wire in a Tatura style system (Van den Ende et al., 1987). Two of the remaining vertical rows were planted at 3 ft between trees, the first grown as bi-axis and the second as spindle. In the last vertical row, a set of five trees per rootstock were planted at 6 ft, 5 ft and 4 ft apart trained to an Upright Fruiting Offshoot (UFO) training system.
Growth and productive habit
Tree Habit
WA 64 tree growth habit is similar to Braeburn, considered a type III bearer (Lespinasse, 1977 classification), with low-medium vigor, depending on the rootstock. A severe lack of vigor can result in excess spur formation, compromising fruit size. It tends to produce abundant lateral shoots with a wide crotch angle (from 60 o to 90o) (Figure 1). WA 64 tends to produce on spurs and terminal mixed buds of 1-year-old shoots.
The apical bud of the leader, when in vertical position, consistently developed 2-3 uprights, equivalent in size, suggesting it does not have strong apical dominance. It is important to remove the competition during active growth (spring) to promote growth of the leader, during orchard establishment (Figure 2).
WA 64 produces plenty of mixed buds; it is recommended to remove them in the first year to promote growth. Shortening the shoots requires attention in high-vigor conditions, because the internodes can be long, and die-back can occur (Figure 3).
Bearing wood
WA 64 bear fruit on the terminal buds of the shoots (brindilla) or on spurs (Figure 4 and 5).
Bloom
Like its parent Cripps Pink, it blooms early, around Gala timing. In Wenatchee (SRO), during the 2024 season, the king flower opened on April 3 (Figure 6 left), being the earliest cultivar to bloom on site. In Prosser, bloom was 2-3 days after Honeycrisp, around April 18 in 2024 season (Figure 6 right). Bloom density was higher than both Honeycrisp and WA 38. More years of data are needed to better define bloom time and intensity.
Pollinizers
The study of the S-alleles for WA 64 is ongoing; however, given that the parents of WA 64 are Cripps Pink S2/S23 and Honeycrisp S2/S24, most crab apples will work well as pollinizers. Snowdrift (S25/S45b), Indian Summer (S26/S50b) and Evereste (S20/S26, Sheick et al., 2018) were planted as pollinizers in Wenatchee and Prosser sites (Figure 7). At the Roza site, 2024 first bloom was observed on April 12, full bloom on April 15, coinciding with Evereste and Snowdrift bloom.
Thinning and crop load management
WA 64 can be highly productive and preliminary work suggests the need for crop load management strategies. Trees left un-thinned lead to doubles, triples, quadruplets, and sometimes five apples, which will compromise fruit size and color (Figure 8). However, in previous work on Phase 3 trees, approximately 60 – 80% of the clusters naturally thinned to singles and doubles.
A thorough trial will be necessary to establish the thinning procedure for WA 64. No information is available on biennial bearing, due to the age of the orchards. In Wenatchee, 50% of the trees in the trial were de-fruited entirely in the third year. Cropping trees in the third leaf dramatically reduces vegetative growth (Figure 9, G.969 and Figure 10, G.890).
Harvest time
Under Washington growing conditions, the apple requires 150 – 165 days after full bloom, to ripen, equivalent to Golden Delicious timing. In Prosser, harvest has been approximately two weeks before WA 38.
Like other bicolored apples, good light distribution through the canopy is essential for color development. Managing light at least two weeks before harvest with hedging, leaf removal or reflective material, could benefit color development.
Fruit Quality
WA 64 is a bicolor apple, characterized by a small to medium size, closer in taste and appearance to its Cripps Pink parent. One of the most prominent characteristics of this apple variety is firmness retention. Previous research shows that firmness decreases 2 lb. on average after long term storage.
WA 64 is described as an apple with balanced sweet/tart flavor, firm, crisp and juicy. Taste and texture were preferred by consumers when directly compared to Cripps Pink or Honeycrisp in pairwise tests in April/May 2022. There has been no incidence of internal browning or cavities, with watercore found sporadically at harvest. No incidence of bitter pit or superficial scald have been recorded in the breeding program Phase 3 evaluations, while only a few apples with bitter pit were found in Roza orchard.
If left unprotected, fruit is susceptible to sunburn (Figure 11), similar to other bi-color apples, and heat mitigating practices will likely be needed in Washington.
Fruit quality assessment on the apples harvested in the two pilot sites (SRO and Roza) will continue as trees mature.
Rootstocks
Four rootstocks have been evaluated: Bud 9, considered very dwarf, the Geneva 969 and 41, considered semi-dwarfing, and G.890, vigorous. These rootstocks represent a wide range of vigor and provide us with general information relative to vigor influence and its relation to each other.
Some differences regarding vigor level have been noticed between the two locations. This can be related to the different soil conditions between Wenatchee and Roza sites, and management practices. For this reason, we reported the data for both orchards separately.
Sunrise (SRO)
One month after planting in the spindle combinations, the G.969 trunk cross sectional area was smaller and similar to Bud 9, while G.41 was intermediate and G.890 was larger (Figure 12).
The bi-axis trees at planting show a different situation. G.969 consistently had the smaller trunk cross sectional area, while no differences were noticed between G.41 and Bud 9 trees. G.890 showed the larger trunk cross sectional area. In general, the bi-axis trees reduced the vigor compared to the single-axis trees by approximately 25%.
After two growing seasons, the difference in vigor among the rootstocks became evident. Trees grafted on Bud 9 were significantly smaller than the other rootstocks. G.969 and G.41 showed an intermediate vigor and G.890 was the most vigorous. The TCSA in spindle were 51% higher than in bi-axis (Figure 14).
Roza
Trees on Bud 9 are smaller while very fruitful. Given the reduced vigor imposed on the cultivar, it would not be suitable in sandy coarse soils, soils with reduced nutrient and water retention, or stress conditions. If choosing Bud 9, we recommend single leader systems instead of a bi-axis or multi-leader system. For Bud 9 or other very-dwarfing rootstocks, intensive winter pruning will be necessary to promote vigor. Avoid cropping the trees until the leader reaches 70% of the desired height. Crop load management will be necessary to maintain adequate shoot-to-fruit balance and ensure fruit size.
At the Roza site, almost all terminal buds of the shoot were reproductive (Figure 15). Thus, we recommend heading cuts to promote structure (vegetative growth).
The semi-dwarfing G.41. The first year after planting, G.41 at the Roza site grew like G.890 and G.969 (more vigorous rootstocks). However, after the third year, tree growth of G.41 was lower.
The G.890 and G.969 had equivalent height and shoot growth. Given the higher vigor imposed by these rootstocks when planted in fertile soils with high water retention (considered vigorous conditions), consider vigor management strategies. For example, minimize winter pruning, manage nitrogen and water, summer pruning or de-leafing prior to harvest. However, given the susceptibility of WA 64 to sunburn damage, if high temperatures and light intensity conditions are expected before summer pruning or de-leafing, growers will need to implement heat mitigation practices (e.g. protective sprays, shade).
When utilizing vigorous rootstocks in vigorous conditions, training systems that provide vigor control might be more suitable (Bi or multi axis, angled systems [V or Spindle]) at high density to restrict root growth or Tatura at lower density.
At Roza site, tree height was lowest in Bud 9, when compared to all Geneva rootstocks, regardless of the training system (Figure 17). The angled bi-axis system provided greater vigor control compared to all other training systems.
Training System
One of the most important decisions growers make when establishing a new orchard is the training system. In most cases, the selection of the training system will remain unchanged throughout the orchard’s life and determine the block’s cost and productivity. Matching the cultivar-rootstock combination, site, density and grower preference can be challenging. In Washington State, most apple orchards are planted on a high-density trellised system. Thus, we will focus our comparisons among most used systems. High-density systems are intended to manipulate the tree’s natural growth habit to promote precocity and productivity.
WA 64 was established as spindle and bi-axis in SRO, while at the Roza, a plethora of training systems have been set up for demonstration, including spindle, bi-axis, Angle Systems (V-Trellis and Y Trellis), and Upright Fruiting Offshoot (UFO).
Spindle
Spindle trees have a single central leader as a permanent structure and many lateral branches of different lengths; larger laterals at the bottom and smaller at the top (Figure 18). The distance between trees can range between 2 – 3 ft. This system architecture allows for good light interception and distribution. In general, it is not recommended to head-back the leader. At the same time, vigorous limbs need to be removed following the criteria of removing branches with a diameter equal to or higher than 50% of the stem where they are inserted. Dormant pruning in consecutive years consists of removing vigorous, upright-growing shoots, thinning excessive or crowded areas, and stub-cutting all laterals. If trees become too vigorous, spring pruning (June) could promote fruiting wood and prevent excessive shading.
The spindle system is suitable for most rootstocks and conditions. Relative to the other systems described here, it promotes more vigor for the individual trees. When selecting dwarfing rootstocks such as Bud 9, the distance between trees must be reduced (1.5 – 2.0 ft) to fill the allocated space adequately.
Bi-Axis
This system is a nursery innovation that utilizes bi-axis trees pre-formed in the nursery (“Bibaum®”) or headed back in the field after planting (Musacchi, 2008). Trees can be planted vertically (longitudinal Y) or in an angle (Y trellis).
In the longitudinal Y, trees are planted with the double axis oriented toward the row to form a flattened shape and a 2D canopy (Figure 19). Dividing the vigor between two leaders helps control vegetative growth and might reduce the number of trees per acre. The distance between trees will depend on the vigor of the cultivar–rootstock combination, commonly ranging between 3 – 4 ft apart, with each leader at 1.5 – 2 ft from each other.
Once the two main leaders are selected, they should not be headed. The pruning strategy is based on dormant pruning and consists of removing vigorous, upright-growing shoots, thinning excessive or crowded areas, and heading (stub) cutting laterals.
This system is preferred for vigorous growing conditions; loamy soils or sites with high nutrients and water retention, as it provides greater vigor control relative to the spindle. It is suitable for most rootstocks but should be avoided for dwarfing and weak growing conditions (Figure 20).
Angle Systems
In angled systems, trees are bent to form a V or Y shape, generally at a 75 – 80 ° angle from the horizontal (equivalent to 30 – 10 ° opening). Angled systems are generally more productive as they can provide approximately 70% more growing area. However, they are not as well suited for mechanical pruning and harvest. The lower third of the trees can become shaded if not managed appropriately.
- V trellis: Trees are grown as a single leader from single-budded trees. After planting, trees are bent to opposite sides of the trellis (Figure 21). This system can be more vigor-controlling, relative to the spindle, if the distance between leaders remains equal. The planting distance between trees varies between 1.5 and 2 ft apart. This system seems suitable for all rootstocks combinations at Roza.
- Y Trellis: The Y trellis can be obtained utilizing bi-axis trees (described above). Trees are planted in the middle, and each leader is bent to opposite sides of the trellis (Figure 22). This system is more vigor-controlling, relative to the previously described systems. The distance between trees will determine the distance between leaders. Under Roza cultivation conditions, this system is recommended for semi-dwarfing to vigorous rootstocks, such as G.41, G.890, and G.969, with planting distance varying between 1.5 and 3 ft. The Y system is not recommended for very dwarfing rootstocks, such as Bud 9.
Multi leader or Upright Fruiting Offshoot (UFO).
The Upright Fruiting Offshoot (UFO) is a highly productive system intended to create a wall of fruit, easy to manage and prune once fully established. This system can be established with double-budded trees, headed trees or top-grafted orchards. At Roza, leaders in the double-budded trees were crossed, to reduce strain at the bud union, and tied in upright position forming U shape (Figure 23). Bending of the leaders, close to horizontal angle induces new uprights, filling the center of the U. This system provides flexibility regarding number (and distance) between fruiting uprights, as it can be adjusted as the trees fill the space.
This system is suitable for medium to high-vigor conditions and rootstocks. The distance between trees will depend on the vigor of the rootstocks. At Roza, G.969 and G.890 have filled the space adequately when planted at 5 – 6 ft tree spacings, while G.41 can be planted closer (4 – 5 ft). This system is not suitable for very dwarfing rootstocks (Bud 9).
Tatura
The Tatura system can be established as a vertical or angled system (Figure 24). At planting, only laterals near the wires are promoted to grow, while all the laterals between the wires (or windows) are thinned. At the end of the growing season, laterals are tied to the horizontal wire, creating a permanent structure for future fruiting wood. The distance between horizontal wires commonly varies around 18 – 22″ apart. This system requires intensive training during establishment, however, once established, it is easy to prune or harvest. The Tatura system provides great light distribution, which is important for color coverage in WA 64.
This system is more suitable for medium to high vigor conditions and rootstocks. The distance between trees will depend on the rootstocks’ vigor and angle. At the Roza site, a few trees on G.969 and G.41 were trained as Tatura on a V trellis, with single-budded trees, planted at 1.5 ft between trees (3 ft between leaders). This system is not recommended for very dwarfing rootstocks such as Bud 9.
Pruning Techniques
WA 64 has shown good response to heading or stub cuts, leading to re-growth of one or two laterals right below the cut. Renewal cuts should be made each year to promote vigor, renew old or weak wood, and create laterals to fill trellis space.
Even very short stubs (less than one inch) led to re-growth of one or more laterals in vigorous conditions. Thus, when considering thinning cuts (not intended for renewal), to remove excessive or crowded branches, vigorous uprights, or competition, the cut should be made close to the origin.
At the Roza site, Bud 9 trees were pruned more intensively in the winter, heading all laterals to 2 or 5 inches, and thinning laterals to remove excessive branching (Figure 25).
The same strategy was used for all Geneva rootstocks; however, depending on the vigor of the trees, basal laterals in the bottom third of the trees were left to 5 – 8”, leaving a few terminal fruiting buds. All shoots in the upper third of the tree (except for the leader), were headed to remove the mixed buds. Excessive branches were thinned (Figure 26).
In the Roza orchard, unpruned trees on Bud 9 exhibited high crop load and precocity, stunting the tree growth when compared to pruned trees. Similarly, but to a lesser degree, G.41 had an intermediate crop load. While unpruned G.969 and G.890 combinations were relatively less productive, they had excessive long branches and blind wood in shaded areas.
Summer pruning (July – August) on WA 64 can induce fall blooms (Figure 27). However, this response is dependent on timing and environmental conditions; for example, in 2023 summer pruning led mostly to vegetative re-growth. Secondary bloom seems common in WA 64, especially in low vigor conditions.
Overall, WA 64 trees have adequate branching and do not have a strong apical dominance, which provides flexibility in determining the optimal training system. In both test sites, the tree responded well to short stub cuts for wood renewal. As a scion, it has intermediate vigor, thus will perform well in various rootstocks, however we caution utilizing very dwarfing rootstocks (Bud 9) on weak growing conditions. More information on WA 64 will become available as the trees mature and new orchards become available.
References
Evans, K. M., Barritt, B. H., Schonberg, B. S., Brutcher, L. J., Mendoza, M., & Hanrahan, I. (2023). WA 64 Apple. HortScience, 58(10), 1275-1276. https://doi.org/10.21273/HORTSCI17334-23
Lespinasse, J.M., 1977. La conduite du pommier. I-Types de fructification. Incidence sur la conduite de l’arbre. INVUFLEC, Paris, 80 pp.
Musacchi S., 2008. Bibaum®: A new training system for pear orchard. Acta Hort. 800: 763-768. DOI: https://doi.org/10.17660/ActaHortic.2008.800.104
Sallato, B.C., DuPont, S. T., and Granatstein, D. 2019. Tree fruit soil fertility and plant nutrition in cropping orchards in Central Washington. Washington State University Extension 119E. https://hdl.handle.net/2376/16944
Van den Ende, B., Chalmers, D.J., Jerie, P.J. 1987. Latest Developments in Training and Management of Fruit Crops on Tatura Trellis. HortScience 22 (4); 561 – 568
Sheick, R., Serra, S., De Franceschi, P., Dondini, L., Musacchi, S. (2018). Characterization of a novel self-incompatibility allele in Malus and S-genotyping of select crabapple cultivars. Scientia Horticulturae, 240, 186–195.
Contacts
- Bernardita Sallato, email: b.sallato@wsu.edu
- Sara Serra, email: sara.serra@wsu.edu
- Manoella Mendoza, email: manoella@treefruitresearch.com
- Kate Evans, email: kate_evans@wsu.edu
- Stefano Musacchi, email: stefano.musacchi@wsu.edu
Additional Information
WSU Tree Fruit Extension Web page. https://treefruit.wsu.edu/wa-64-resources-2/
Terra Sokol (May 27, 2023). “WSU Tree Fruit Research and Extension Center discover new apple variety”. Wenatchee, Washington: KPQ (AM).
Bill Radke (June 6, 2023). “A new WA apple is on the way”. Seattle: KUOW.
This document will be updated as we learn more about WA 64. New plantings have been planned for 2025, 2026 and 2027, with six rootstocks and different training systems at Sunrise and Roza farm.
Fruit Matters articles may only be republished with prior author permission © Washington State University. Reprint articles with permission must include Originally published by Washington State Tree Fruit Extension Fruit Matters at treefruit.wsu.edu and a link to the original article.
