Reduced vigor and smaller size are features rather than bugs for Oregon State University’s new Thompson hazelnut variety, which is intended specifically for high-density orchards.

The diminutive trees will be available for purchase and planting this winter after OSU recently submitted a plant patent for the new cultivar to federal authorities.

Increases yield

The cultivar is geared toward maximizing yield potential per acre, including in fruiting wall systems harvested with over-the top machinery currently used for blueberries, said Shawn Mehlenbacher, OSU’s hazelnut breeder.

“If you want a harvester to go over the top of the trees, you need to be able to keep the trees short,” Mehlenbacher said. “The overall theme is high density and the increased yield that could result from that.”

Though exact configurations will be determined by individual farmers, Thompson trees can be planted 7 feet apart from each other within rows spaced at about 16 to 20 feet, he said.

“You still need to get in there with your harvester,” Mehlenbacher said.

To compare, Oregon’s traditional Barcelona variety was often planted on a 20-by-20-foot grid, which he said would obviously be inadvisable for the new variety.

“They wouldn’t fill in the space,” he said.

Barcelona trees grow up to 40 feet tall but most of the hazelnuts develop near the top, where sunlight is plentiful and the most flowers appear, Mehlenbacher said.

40% of normal height

New hazelnut varieties released in recent years typically attain about 70% of Barcelona’s size while the Thompson cultivar will only reach about 40%, he said.

Within the same area of tree canopy, however, the Thompson cultivar yielded 22% more than the Jefferson variety and 32% more than the McDonald variety in an OSU trial.

Farmers are already experimenting with fruiting wall-type orchards and using altered blueberry harvesters, which can knock off and scoop up hazelnuts before they touch the ground, Mehlenbacher said.

“There will be more modifications if people get serious about that approach,” he said.

Maintaining naturally smaller trees in such systems will be less burdensome than those which are meant to grow large, Mehlenbacher said.

“They don’t want to stay in that small space,” he said.

Thompson trees could be planted at a higher density even without the fruiting wall approach, which growers are already doing with other varieties.

Currently, every other tree is eventually eliminated so the orchard doesn’t become too crowded, but farmers could skip that labor-intensive step with the new cultivar.

“I think they would design it to stay at high density — no removal,” Mehlenbacher said.

Better spray coverage

Blast sprayers used to apply chemicals will also achieve better coverage with the smaller tree, he said.

“You can spray and control pests and disease a lot easier,” he said. “The pesticide can reach all parts of the canopy.”

Release of the new variety was delayed by about two years because OSU had problems generating enough plant material through the tissue culture process, Mehlenbacher said.

Once the university had enough, it was turned over to two wholesale nurseries — North American Plants of McMinnville, Ore., and Rancho Tissue Technologies of Santa Fe, Calif. — to produce and sell the trees.

Highly resistant to EFB

The new cultivar is meant to produce nuts for the kernel, and the tree is highly resistant to Eastern Filbert Blight, a fungal pathogen that once threatened the hazelnut industry’s existence.

Thompson trees can be pollinated by several other EFB-resistant varieties released by OSU in recent years, including Wepster, York, PollyO, Dorris and Yamhill.

“There’s lots of things that could be investigated,” in terms of orchard configuration, Mehlenbacher said. “We have a lot of creative people in our industry and now they have a new variety to play with.”

Pioneering breeder

The new cultivar was named after Maxine Thompson, the horticulture professor who started OSU’s hazelnut breeding program in 1969, among other botanical ventures, he said.

Thompson died in 2021 at the age of 94.

“She knew a lot of different plants and all the variations within them,” Mehlenbacher said.

Before then, the Oregon hazelnut industry had tried to find European varieties that would be a good fit, he said.

When it became clear none were superior to the staple Barcelona cultivar, the solution was to begin a breeding program.

“Maxine was the person who did that. A big job starting from scratch,” Mehlenbacher said.

From her travels to Europe and elsewhere — including Pakistan, to retrieve walnut and apricot varieties — Thompson was among the first to recognize the future importance of the kernel market, he said.

She was also among the researchers who discovered that Gasaway trees in an orchard north of Vancouver, Wash., were resistant to EFB, Mehlenbacher said. That trait proved crucial to developing the new varieties that saved the industry.

“She did make the first crosses to bring Gasaway resistance to the breeding program,” he said.