A research report from Tom Auvil, Dr. Ines Hanrahan, Stefano Musacchi and Dr. Kate Evans.
[/fusion_builder_column_inner] Since 2008, trees have been grown in four locations across Washington and evaluated for horticultural traits and storage behavior by Washington Tree Fruit Research Commission scientists Tom Auvil and Dr. Ines Hanrahan and WSU apple breeder Dr. Kate Evans, with the help of an industry advisory group.
In addition, WSU tree fruit physiologist Dr. Stefano Musacchi is leading the evaluation of two newly established plantings at the university’s research orchards near Wenatchee and Prosser. WA 38 is a vigorous tip bearer, similar to Granny Smith (see Figure 1). The good side of this double-edged sword is that it does well in replant sites.
The bad news is that Granny Smith is often managed to minimize light exposure to fruit, but fruit from WA 38 is red and needs light to have consistent color. The Granny Smith tree growth habit also develops blind wood.
High vigor, larger caliper branches seem to have much more severe blind wood. This can be mitigated by bending limbs as they grow beyond 12 inches long, or by removing the very large limbs to allow smaller limbs to reestablish.
A pruning stub with a viable bud should be left, which may require a two- to four-inch stub. -Musacchi is working on management strategies to minimize the negative aspects of this growth habit and is already seeing considerable success. Unlike most other varieties, WA 38 produces good quality fruit on spurs and one-year wood. Russet, parrot beaks, and small fruit are common maladies seen on fruit originating from one-year wood on many varieties, but not with WA 38.
The flower clusters typically will slough to a single fruit (see Figure 2). WA 38 has not required as diligent hand thinning as Fuji or Red Delicious. The tree’s susceptibility to mildew is similar to Granny Smith and not as debilitating as Honeycrisp.
Fire blight will catch WA 38. It blooms later than Cripps Pink and Scifresh (Jazz), but does not have as much late bloom as some other varieties. In 2014, in both Prosser and Quincy, we observed secondary bloom of a cluster or single flower as late as May 21 scattered through mature trees and second- or third-leaf grafts (see Figure 3).
This should be a consideration during high to extreme fire blight conditions, such as those of 2014. Early comparisons between WA 38 on Geneva 41 or Malling 9 Nic 29 rootstocks show better canopy development with better branching, shoot extension, and leaf area with G.41 than with M.9 Nic 29. Cumulative yield for the Quincy trial in bins per acre is based on the 38 trees planted in 2008 on M.9 337 rootstock.
The yield per acre is calculated using 1,452 trees per acre and 870 pounds net weight per bin. Data are shown in Figure 4.
WA 38 has not shown high sensitivity to sunburn (compared to Honeycrisp or Gala) nor bitter pit. Storage disorders such as internal browning, lenticel breakdown, soft scald, or superficial scald have not appeared in fruit stored for ten months.
Fruit size is moderate to large (with an average of 65 percent or more in the 64 to 80 size range). WA 38 has been picked at starch clearing of 1.5 to 2.0 (see Figure 5) on the Washington 6-point starch scale, which occurs around September 21 in Mattawa to October 1 in Quincy. This fruit has stored with minimal loss of flavor in long-term CA (controlled atmosphere) storage, even when not treated with MCP (1-methylcyclopropene).
Fruit has also been harvested at 3.5 to 4.0 on the 6-point starch scale and stored well in RA (regular storage) through January and CA until May. Although we have used several pick dates in our trials, we have also strip picked fruit and stored it successfully.
Trials are planned for the 2014 season to better delineate the relationships of harvest maturity (as related to one pick), fruit history (such as bud type), or crop load to flavor in fruit stored for six months or more. WA 38 eating quality is good when fruit is picked early or late.
Consumer taste tests have shown WA 38 apples stored for six months (CA only, no 1-MCP) are preferred over Gala (CA + 1-MCP) in appearance, taste, texture, and flavor.
When WA 38 were presented to consumers for direct comparison with Honeycrisp, consumers liked both cultivars equally in October and December, but in March, WA 38 was preferred by most (see Good Fruit Grower, June 2014).
In addition, in an experiment conducted with fruit from the 2012 crop, WA 38 (CA storage) was preferred by consumers to Gala apples (industry standard treatment of CA + 1-MCP). The late-picked fruit (with advanced starch degradation) may need to be sold relatively early (November to December). Fruit color does vary by climate in central Washington, but eating quality and storability have not been affected significantly by heat.
Cooler, high-elevation sites (or blocks with overhead cooling) can achieve very dense red color, while hot locations may have partial red striped color similar to the better striped strains of Gala or Red Delicious.
Staining, as seen in Figure 6, which is visible in early September, has always colored over and has yet to be an issue in evaluation plots at the time of harvest. WA 38 has been thoroughly evaluated before being introduced to the Washington tree fruit industry.
—Assessment of horticultural traits in nine locations and environments —Food science sensory evaluations —Regular and CA storage trials, both with and -without MCP —Evaluation for internal defects and flavor after 6, 8 and 10-month CA storage (No observed issues in four years of Red Delicious storage protocols) —Commercial packing line runs —Sensory laboratory tests against other varieties (2010, 2011) —Consumer tests (compared to Gala and Honeycrisp) —Grower sampling at Washington State Horticultural Association meetings and Washington Tree Fruit Research Commission reviews It is our conclusion that WA 38 is grower friendly in most (perhaps all) sites in Washington State and that it should present minimal problems in harvesting, storage, packing, or marketing. In addition, it should have good consumer acceptance.
Appended clarification: The new apple variety developed by Washington State University remains known as WA 38. For marketing purposes, the brand name, or trademark, that WSU has selected for use with the WA 38 variety is Cosmic Crisp.