Photo by Eran Chesnutt/

The U.S. imported $24.7 million worth of hazelnuts from Turkey and Chile in 2012. That same year, U.S. growers produced 36,000 tons of hazelnuts and exported 25,000 tons, worth approximately $50 million. Oregon’s 600 producers harvested the majority of that crop: $63 million in nuts on 29,000 acres.

Oregon’s dominance in the U.S. market is due, in part, to Oregon State University’s (OSU) aggressive breeding program. In the last 20 years, breeders there have developed 17 varieties resistant to the plant’s most devastating threat nationwide: eastern filbert blight (EFB). First identified in 1874, EFB is a native fungal parasite of the wild American hazelnut.

The native hazelnut is resistant to the parasite, but not totally immune. When native trees are infected, small cankers appear. However, this response is mild and nonthreatening in comparison to the response of European varieties to EFB. Imports from Europe have better nut quality but no resistance to EFB. As EFB attacks European hazelnuts, it first destroys the crop and subsequently destroys the plants themselves.

By 1970, EFB had spread west of the Rocky Mountains and threatened to decimate the nation’s most viable and productive crop of hazelnuts. In fact, EFB had caused so much destruction that U.S. growers ceased planting new hazelnut orchards. OSU’s first EFB-resistant release, ‘Jefferson’, was planted in 2010, and it revived the state’s hazelnut industry.

Wild American hazelnuts are less appealing to consumers because they are tough, fibrous nuts with thick shells, but ‘Jefferson’ is prized for its large, flavorful nuts. The university’s most recent cultivar, ‘Wepster’, released earlier this year, was developed to serve growers who sell to the baking and chocolate industries.

Too soon to celebrate

Although OSU’s new cultivars have benefited Oregon’s hazelnut growers, EFB has not been eradicated there. The state lost 1,600 acres to the blight in the last decade. In the harsher climates of the Northeast and Upper Midwest, the same plants that thrive in Oregon suffer and cannot fend off EFB.

Since the early 1900s, breeders have sought to develop cold-hardy, EFB-immune varieties suitable for growing in the Northeast and Upper Midwest, with little success – until recently.

Under the leadership of Tom Molnar, Rutgers University, new hazelnut breeds are currently being trialed in New Jersey, Pennsylvania, New York, Nebraska and Ontario, Canada. It took several years to get to this point, but many of the trees currently in the ground are nearing the maturity needed to start producing nuts.

It takes about five years from initial planting for a hazelnut tree to produce nuts for evaluation. When breeders find one seedling they like that produces nuts they like, they propagate it asexually through grafting or layering and put the grafted trees into replicated trials. Typically, researchers can select the plants they like after seven or eight years, and then propagate them and get them to trial. After another seven years in trial, the breeder can usually tell which of the experimental plants could work for growers. All told, it takes anywhere between 15 and 17 years from planting the seed to being able to release a cultivar.

At Rutgers, Molnar and his team are still about a year away from beginning yield evaluations. There are 14 experimental plants from the breeding program that Molnar and his team think have the potential to be new cultivars.

To ascertain each plant’s performance at each location, they’ll collect all the nuts from the trees and weigh them to determine how many pounds of nuts grew on each tree. Next they’ll dry the nuts, crack them, look at kernel percent (percentage of total weight), and check for the presence of mold or other defects. By comparing the weight of the nut in the shell to the weight of the nut out of the shell, the researchers will get a percentage of how much of the total weight is actually the kernel. “We’re hoping to get 50 percent,” says Molnar. “When the companies buy the nuts, they’re interested in how many pounds of kernels they can get, so that’s an important trait.”

The ‘Gasaway’ gene, which has been fully mapped and characterized, confers resistance to EFB in breeds like ‘Jefferson’ and ‘Wepster’. That gene does not provide the same level of resistance to EFB in New Jersey as it does in Oregon.

Researchers have been looking at other genes that provide resistance. One gene comes from a cultivar called ‘Grand Traverse’, a hybrid of the ornamental Turkish hazel originating from Michigan. Molnar reports that the ‘Ratoli’ cultivar from Spain also seems to be holding up really well against EFB, although the cultivar blooms too early for the Northeast region to produce a viable crop.

Molnar believes the EFB-resistant gene within ‘Ratoli’ is better suited than the ‘Gasaway’ gene to the local isolates of the EFB fungus in the Northeast and Upper Midwest. The team at Rutgers is also sourcing from the wild American hazelnut, which has a different genetic background than European and Turkish varieties.

Within the 14 selections researchers at Rutgers made, there are four different sources of resistance to EFB. Molnar believes using a diversity of plants will create cultivars that are better adapted to different climates. “We hope that developing widely adaptable plants will address any issues in changing climate pressure. Part of that is testing the plant in warmer and colder locations.”

The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.