Manchurian crab apple trees (trees with dark leaves dotted throughout this orchard) are widely used as pollinizers in Washington State. (Courtesy Kim Young, Pace International)

The Washington State apple industry doesn’t appear to be any closer to finding a crab apple pollinizer to replace Manchurian than it was a year ago when industry spokespersons identified the need for such research.

During recent winter meeting talks about crab apple diseases causing postharvest rots and international trade issues, Dr. Mike Willett of the Northwest Horticultural Council and Tom Auvil of the Washington Tree Fruit Research Commission called for work to find a replacement pollinizer for Manchurian crab apple.

Manchurian has been widely planted in Pacific Northwest orchards because it blooms early enough to pollinate king blossoms of Red Delicious, grows tall and upright, and works well with other varieties like Fuji, Gala, and Granny Smith.

“The problem is that when we first evaluated crab apples as pollinizers in the late 1970s and ’80s, nobody looked at disease susceptibility,” said Willett. “We’ve created the situation that now we’re rearing high enough levels of inoculum in the orchard that it’s become an economic problem for growers.”

Two crab apple canker diseases commonly found in Northwest orchards—Sphaeropsis rot (Sphaeropsis pyriputrescens) and speck rot (Phacidiopycnis washingtonensis)—were the reasons Chinese officials closed their market to U.S. apples in 2012. The market is still closed to Red and Golden Delicious apples from Washington, although the two countries are near to an agreement defining a new export protocol that would reopen the market.

Auvil said pollinizer research is sorely needed. He noted that Ed Stahly did some of the original crab apple work decades ago at U.S. Department of Agriculture’s research lab in Wenatchee, Washington. Most of Stahly’s work was done on Red Delicious, and some on Granny Smith.

At the time, Manchurian was superior to other crab apples, such as Dolgo, Mt. Evereste, and red-flowered selections, which were biennial bearing, bloomed too late, or weren’t attractive to bees because of blossom color.

“The first step would be to do pollen germination and pollen tube growth studies from candidate crab apple genotypes on several commercial fresh apple cultivars,” Auvil stated in an e-mail message.

Auvil believes pollinizer research needs to consider the following traits:

• bloom time and duration
• pollen viability
• annual bloom habits
• bee attractiveness
• disease susceptibility

One of the largest crab apple breeders is J. Frank Schmidt and Son, an ornamental nursery located in Boring, Oregon, which lists nearly 40 crab apple varieties on its Web site.

Willett believes that apple growers and nurseries should collectively evaluate crab apple selections. “It might be that some of the varieties used in home gardens could be early bloomers and be suitable for commercial orchards,” he said.

Based on a phone conversation Willett had with the director of product development at J. Frank Schmidt, he believes the nursery is willing to work with the industry on pollinizer research and would be a potential collaborator under the right conditions.

Both Auvil and Willett believe a research trial is needed to compare selections alongside the standard Manchurian variety and screen for compatibility with major apple varieties.

But thus far, no research project is under way, nor is any project proposal before the Research Commission. •