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Stefano Musacchi of Washington State University discusses horticultural practices for the new WSU-bred apple variety, WA 38, to be sold under the brand name Cosmic Crisp, during a field day July 20, 2018. (Shannon Dininny/Good Fruit Grower)

Stefano Musacchi of Washington State University discusses horticultural practices for the new WSU-bred apple variety, WA 38, to be sold under the brand name Cosmic Crisp, during a field day July 20. (Shannon Dininny/Good Fruit Grower)

Researchers have learned plenty about the growing habits of WA 38 over the past decade, but in just their first year, commercial growers are learning a few things of their own about the new apple variety bred by Washington State University.

The highly vigorous variety is already known to be grower friendly, which might be a good thing since a recent WSU field day devoted to the variety showed that growers are forging their own paths when it comes to choosing rootstocks, systems, spacing and trellis.

At the same time, though, growers need to be willing to share their experiences and learn from one another, said Karen Lewis, WSU tree fruit extension specialist. The variety isn’t a club variety, but the industry needs to act like it is. “We need to act like a community with WA 38 for everyone to be successful,” Lewis said.

During a Cosmic Crisp field day July 20, 2018, researchers noted that a commercial block of WA 38 trees near Tieton, Washington, had been planted 2 to 3 inches too deep. Growers should ensure there is space for four fingers between the bottom of the bud seals and the ground, and researchers recommend growers trail string down the row to ensure workers don't plant trees too shallow or too deep. (Shannon Dininny/Good Fruit Grower)

During the field day, researchers noted that a commercial block of WA 38 trees near Tieton, Washington, had been planted 2 to 3 inches too deep. Growers should ensure there is space for four fingers between the bottom of the bud seals and the ground, and researchers recommend growers trail string down the row to ensure workers don’t plant trees too shallow or too deep. (Shannon Dininny/Good Fruit Grower)

Grower Jan Strand Selby buys into that argument. “I’m relatively new to the orchard side of the ag business, so having access to researchers is invaluable,” she said during a stop at her new WA 38 planting west of Yakima near Tieton in Central Washington. Researchers noted in one of her two WA 38 blocks, planted on EMLA 111 rootstocks, trees had been planted 2 to 3 inches too deep, where there should be four fingers between the bottom of the bud seals and the ground.

Strand Selby said she and her orchard manager chose Budagovsky 118 and EMLA 111 rootstocks to give the trees added “oomph” given the site’s higher elevation and less sandy soil than the lower Yakima Valley.

However, noting what they had learned from the researchers, she said later they took 2 inches of dirt from the base of the trees of the latter rootstocks.

Not forgiving

Domestically, the variety, to be sold under the brand name Cosmic Crisp, will be exclusive to Washington growers for at least the first 10 years, and though it’s grower friendly, it doesn’t come without a few challenges.

A highly vigorous, tip-bearing variety, its apical dominance can result in large caliper branches that present significant blind wood.

“Cosmic Crisp is not a forgiving variety. If you stub too short, wood will be blind forever. Leaving three fingers could be nothing,” said Stefano Musacchi, associate professor and endowed chair in tree fruit physiology and management at the Washington State University Tree Fruit Research and Extension Center in Wenatchee.

At Monson Orchards’ Lookout Ranch in Selah, Washington, orchard manager Jerry Mertz talked about steps he’s taken to try to avoid blind wood. The company has planted 120 acres of new, store-bought trees vertically, largely on Geneva 41 and Nic 29 rootstocks, with a smattering of Malling 935, all at 3-by-12 foot spacing. Another 50 acres has been grafted onto what was once a Red Delicious block, believed to be on M.106, with 8-by-14 foot spacing.

The latter is being trained a little differently; Mertz is running a V and running two leaders off each to try to fill the space. He plans to calculate the cost differential over time.

Mertz stubbed limbs that were growing well at 6 to 8 inches to avoid blind wood, and breaks are now growing well.

Musacchi liked the idea. “With a top graft, with two leaders or three leaders, within two years you recover your orchard. The vigor is really amazing,” he said.

However, Musacchi noted that growers are getting to the point they’re past talking about pruning trees; now, they want to talk more about management of the variety. “The industry is focused on growing trees as fast as they can to crop, but I’m scared because this variety can produce a lot of blind wood.”

Horticulturist Tom Auvil, formerly of the Washington Tree Fruit Research Commission and who is working with Mertz on the Monson plantings, advised growers not to worry about exceedingly vigorous or low-vigor trees. “Farm the 80 percent.”

Yakima Fruit and Cold Storage has planted WA 38 two different ways in this block near Zillah, Washington: two-leaders down the row and so that the bi-ax goes to each side of the V system. During a Cosmic Crisp field day on July 20, 2018, WSU's Stefano Musacchi noted that he wants to know he as a stem every food to ensure the same distribution between each leader for a vertical fruiting wall. (Shannon Dininny/Good Fruit Grower)

Yakima Fruit and Cold Storage has planted WA 38 two different ways in this block near Zillah, Washington: two-leaders down the row and so that the bi-ax goes to each side of the
V system. Musacchi noted that he wants to know he has a stem every foot to ensure the same distribution between each leader for a vertical fruiting wall. (Shannon Dininny/Good Fruit Grower)

How many leaders?

Last fall, Yakima Fruit and Cold Storage fumigated a block that had been planted in Bing cherries 20 years ago, then planted Cosmic Crisp this spring on M9.337, with bi-leader trees planted down the row in one area and flipped 90 degrees in another, so that the bi-ax grows to each side of the V trellis rather than all to one side.

Musacchi noted that with a bi-ax, he wants to know that every foot he has a stem. “I want the same distribution between each leader for a vertical fruiting wall,” he said. “I think the bi-ax will work well for this variety because it will halve the vigor.”

Workers planted the block near Zillah, Washington, the second week of March, and as soon as the trellis was up, headed the tree. Next spring, when the trees are 4 to 5 feet tall, the company plans to score them every foot, notching two to three times to ensure there are three to four buds in that spacing, orchard manager Mike Hargrave said during the tour.

A Kershaw Orchards block near Zillah, Washington, on the July 20, 2018, Cosmic Crisp tour had originally been intended to be a two-leader block, but when it came time to decide whether to head back and lose a year, the company decided to go with three leaders instead, field manager Lauren Gonzalez said. Musacchi recommended girdling the main leader to decrease its vigor and removing some shoots on outer leaders to remove competition. (Shannon Dininny/Good Fruit Grower)

A Kershaw Orchards block near Zillah had originally been intended to be a two-leader block, but when it came time to decide whether to head back and lose a year, the company decided to go with three leaders instead. Musacchi recommended girdling the main leader to decrease its vigor and removing some shoots on outer leaders to remove competition. (Shannon Dininny/Good Fruit Grower)

At a Kershaw Orchards block down the road, the original intent was to grow everything two leader and split the vigor, said orchard food safety leader Lauren Gonzalez. The trees are planted on 5-by-10 foot spacing on Geneva 969, 210 and 890 rootstocks, as well as some Nic 29.

On the latter block, Gonzalez said they chose to go with three leaders, rather than head back and lose a year, leaving a lot of non-uniform trees. Musacchi recommended girdling the main central leader to decrease the vigor and remembering to remove some shoots on outer leaders to eliminate competition.

He also said crews will have to be trained to prune inner and outer leaders differently. “You might have to train one person to prune inside and one outside.” •

—by Shannon Dininny