Stefano Musacchi, Washington State University horticulturist and endowed chair in tree fruit physiology and management, discusses fruit spacing of the Cosmic Crisp in September at the Sunrise research orchard near Wenatchee. (Ross Courtney/Good Fruit Grower)

The first commercial trees were planted this spring of the new apple variety WA 38, following nearly a decade of research into the horticultural traits at four research plantings and the storage behavior of the fruit.

Developed by Washington State University and marketed under the brand name Cosmic Crisp, the WA 38 has unique behavior compared to most scion varieties.

Those of us who’ve worked with the trees in the field have found the variety to be grower friendly, but for those growers who’ve just planted their trees, here are the top five tips for the first year:

—Never forget that WA 38 is a Type 4 tree that produces a lot of blind wood, and growers don’t want to sacrifice productive space to blind wood, particularly in a fruit wall. To avoid blind wood, you should…

—Prune. The variety has the potential to produce feathers, and you should cut them back to four to six buds, cutting the terminal 1 foot from the top of the central leader.

—Never bend the branches below 90 degrees, which both creates blind wood and the potential for the tree to become a biennial producer very quickly. WA 38, in particular, has a huge capacity to produce flowers, and because it’s producing flowers on one-year wood, growers could see an excess of flowers one year, followed by a dramatic reduction the following year.

—Don’t crop in the first year. If you have a wonderful tree, wait until at least the second year to crop.

—And remember, WA 38 usually sets just a single fruit or two fruit per cluster. That means thinning has to be really targeted, on the basis of flower distribution and fruit set.

It’s also important to remember that WA 38 requires a little bit more space, about 10 percent more, compared to other varieties. It’s a vigorous tree and needs adequate light for the bi-color fruit to color, so prune to allow more space to reduce the number of leaves and the amount of shade in the canopy. •

– by Stefano Musacchi, Ph.D., is an associate professor and endowed chair in tree fruit physiology and management at Washington State University in Wenatchee, Washington. He can be reached at stefano.musacchi@wsu.edu