Nearly 200 apple growers and industry professionals gathered recently at Washington State University’s Roza and Sunrise research orchards in Prosser and Wenatchee, Wash., to encounter the latest discoveries in growth and management of WSU’s new WA 38 apple variety, better known as Cosmic Crisp®.
WSU Tree Fruit team members Karen Lewis, Stefano Musacchi and Bernardita Sallato, and Ines Hanrahan, executive director of the Washington Tree Fruit Research Commission, discussed WA 38 characteristics and techniques in growth, harvest and storage, and most importantly, disease management.
“Fire blight was a top priority for apple growers this year,” said Sallato, Tree Fruit Extension Specialist for south-central Washington. “High amounts of bacteria from last year’s conditions, combined with a warm, wet spring during bloom, were unfortunately, ideal for significant blight infection this year.”
While WA 38 ranks in the mid-range of susceptibility to fire blight, between the Delicious and Honeycrisp varieties, it’s important that growers understand that the rootstocks that WA 38 scions are grafted to may be more susceptible to the pathogen, Sallato said. Infections can completely kill the tree.
WSU’s Roza demonstration block clearly showed that fire blight will need to be managed by growers, especially when utilizing susceptible rootstocks.
“When growers find rootstock blight infection, we encourage them to follow up on the neighbor trees, as we suspect there could be root-grafting transmission going on,” Sallato said.
Walls of fruit
At Sunrise Orchard, Musacchi, WSU’s Endowed Chair for Tree Fruit Physiology and Management, shared the results of five years of research into tree-training techniques that play to WA 38’s strengths.
“Here, we’re building a fruit wall,” said Musacchi, showing growers grafted trees with two- and three main trunks, known as bi-axis and tri-axis.
“WA 38 is a very vigorous variety,” said Musacchi, and in good soil, it fills out the space efficiently. The two-dimensional approach helps all apples on a tree get more sun, developing a consistent, desirable red color.
However, Musacchi says growers need to choose the training technique that works best for their soils, location, and farming practices and preferences.
When it comes to training techniques, physiology and disease management, “We know a lot about this variety now,” says Musacchi, who reports his discoveries annually to growers at workshops and field days.
Pruning tour
WSU researchers continue to share knowledge about the best ways to grow the new variety at a WA 38 Pruning Tour covering the greater Yakima Valley, Monday, Nov. 5.
The event includes a tour of orchards in Tieton, Seleah, Grandview, and Sunnyside, Wash., demonstrating effective pruning methods for the new apple. Learn more here.
- Learn more about fruit research and economics, the WSU Decision Aid System, WSU Fruit School, and other resources for growers at the WSU Tree Fruit website.
