Published 9:15 am Thursday, January 25, 2024
Researchers are hunting down the origins and extent of the outbreak of a new Eastern Filbert Blight strain that overcomes the disease resistance bred into Oregon hazelnut trees.
Meanwhile, farmers are scrambling to determine if their orchards are infected and reacquainting themselves with strategies for controlling the pathogen.
“It’s a bit of a shock because people weren’t prepared for this,” said Doug Olsen, a hazelnut producer near Scholls, Ore. “The ones who have dealt with this before are more upbeat than the new ones.”
Though growers are facing a resurgent enemy that until recently seemed all but vanquished, the industry is far better prepared than when the battle initially began.
Decades ago, when blight was originally encountered in the region, farmers didn’t have the management tools they’re armed with today, experts say. Nor did they have a powerful breeding program already tackling the problem.
“It gives us a lot more hope for the future than we had the first time around,” said Rich Birkemeier, a hazelnut grower and nursery tree producer near Canby, Ore.
The newly identified strain can defeat the gene that confers resistance to EFB, originally discovered in the Gasaway cultivar and incorporated into popular hazelnut varieties by Oregon State University. That’s a serious blow to farmers who’ve invested in roughly tripling the state’s hazelnut acreage over the past decade.
“In some regards, we are starting over,” Birkemeier said. “The new strain does not appear to recognize Gasaway in any of the varieties.”
For those young orchards to remain productive, they’ll need to be subjected to a regimen of pruning and fungicide spraying that’s typically associated with older, susceptible blocks of hazelnut trees.
Untreated trees eventually die of blight, but across the industry, the new strain is expected to be more like a chronic ailment rather than a terminal illness.
“It’s nothing to panic over,” said Birkemeier.
Despite being relatively new to hazelnut farming, Carter Clark said he’s not “too worried” about the disease’s threat to his orchard near Aumsville, Ore.
Clark said he’s confident the industry has the available chemistry to keep the strain at bay, though it’s discouraging growers will be burdened with additional production expenses.
“The bad news is more trips across the field,” he said. “It’s another thing to pay attention to and another thing to throw some money at.”
While the pathogen is broadly considered manageable, key questions about the new strain remain unanswered.
Experts from OSU have confirmed the new strain is different from the common form of EFB but don’t yet know the full extent of its spread in the Willamette Valley, the major hazelnut growing area in the U.S.
They’re also still uncertain if the strain came from another region or if the existing pathogen mutated to evade the defenses of disease-resistant trees.
Reports of worrisome symptoms prompted OSU to conduct a test last year that has verified the strain affects otherwise resistant hazelnut cultivars, said Nik Wiman, an OSU Extension horticulture specialist.
Though young trees of resistant varieties are known to exhibit early symptoms of EFB, researchers were alarmed the disease was progressing all the way to spore production, he said. At that stage, the pathogen produces rows of “stromata” that bulge and erupt through the bark to release spores.
“It was unusual to see full reproduction of the disease in the resistant varieties,” Wiman said.
The strain was initially believed to be centered in the vicinity of Woodburn, Ore., but OSU has been receiving reports from other parts of the Willamette Valley, he said. Those suspected infections haven’t yet been validated.
“We’re trying to get growers to self-report when they’re doing their pruning,” Wiman said. “It’s very possible the site we found is not the source of the new strain. It could be more widespread but it appears the worst-hit orchards are in that area.”
Unfortunately, the pathogen is probably more pervasive than symptoms currently indicate. The disease only becomes visible the season following infection, after a 15-month latency period, he said.
“It makes it more difficult to detect in real time,” Wiman said. “It’s always a catch-up game with this disease.”
Within the next month or two, DNA fingerprinting should reveal whether the new strain is homegrown or arrived from elsewhere, he said.
An invader would be preferable to a mutant in this context, as an adaptable pathogen would cast doubt on the ability to maintain stable, long-term resistance to the disease.
“That, to me, is a little more scary,” Wiman said.
Plantings in New Jersey have already shown other types of EFB affect trees resistant to Oregon’s longstanding strain. Unless the new strain is a mutation of the existing pathogen, it’s possible one of those East Coast strains simply hitchhiked over here.
“They’ve had the fungus for thousands and thousands of years on the local American hazel,” while the trees grown in Oregon are European species that hadn’t historically confronted it, said Shawn Mehlenbacher, the OSU hazelnut breeder who developed the resistant varieties.
Years ago, the hazelnut industry realized an outside EFB strain could eventually conquer Gasaway’s genetics, which prompted a search for additional kinds of resistance.
Sources of resistance different from Gasaway’s were discovered in cultivars from Spain and Georgia about three decades ago and have since been incorporated into OSU’s breeding program.
Some of the resulting crosses are nearing the end of the 17-year “pipeline” generally required for a new variety’s release.
Genetic mapping of 120 resistant selections from around the world also identified 35 hazelnut trees with resistant genes on five different chromosomes so far.
“We’ve got a lot of genetic resources and we’re using them,” Mehlenbacher said.
Another 72 specimens have been found to have “quantitative” resistance that’s not tied to a specific gene, but nonetheless give the tree some ability to withstand the disease.
“The hope is that type of resistance is more durable than the single-gene type of resistance,” he said.
While the breeding problem offers the hope genetics will again prevail against the pathogen, farmers with newly susceptible orchards can’t afford to wait for those solutions.
In recent years, many new growers in Oregon have planted hazelnuts, and it’s concerning they apparently lack experience with the disease, Mehlenbacher said.
To brush up on techniques for fighting the pathogen, he suggested they search for OSU’s EFB Help Page online, which offers comprehensive information.
“We need a big educational effort to bring them up to speed. We need to put our knowledge into practice: Scouting, pruning, spraying,” Mehlenbacher said. “It’s not the end of the world. Been there before and survived.”
