How to Grow Cosmic Crisp® Brand WA 38 Trees
A research report from Tom Auvil, Dr. Ines Hanrahan, Stefano Musacchi and Dr. Kate Evans.
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. 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.
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.