Jeff Olsen, horticulture expert at Oregon State University Yamhill Extension office, is urging hazelnut growers hoping to steel crops against Eastern filbert blight to make five-year management plans to remove susceptible trees in 20 percent increments.
“The general encouragement I try to give people is that it’s a situation that is not going away, but should be addressed at your own pace,” he said.
Nut Grower Society President, Sean Denfeld, called EFB a “continuing issue,” but said the disease is well known among growers -- especially those with older susceptible varieties, which are the most likely to be hit by blight.
“Growers need to back fill with new varieties that are blight resistant,” he said. “Jeff’s recommendation is correct.”
Eastern filbert blight was first discovered in the Northwest in the 970s in European Corylus cultivars. Olsen estimates now nearly 90 percent of Oregon’s hazelnut trees are susceptible to EFB fungus. Its spores spread by wind and rain splash and germinate in leaves before moving into a tree’s vascular tissue. Blight visually expresses itself in the form of cankers in the bark and dead or dying branches caused by restricted oxygen and nutrient flow.
“Unless a tree has the resistant gene in it, there’s every likelihood that it may have been affected by EFB,” Olsen said. “Ennis trees are going downhill very fast.”
Hazelnut trees cannot self pollinate, meaning they require another variety such as Ennis or Daviana, to breed with. These varieties are typically planted as “pollinizers” in orchards with primary crops like Barcelona, popular for their robust yields and large fruit.
According to Olsen, Ennis trees are highly susceptible to blight and make up nine to 10 percent of the hazelnut trees in Oregon. He said by replacing Ennis or Daviana with York, a blight resistant variety cultivated at OSU, growers can maintain substantial pollen shed and harvest yield.
“You’re going to get some yield, but not as high as Barcelona,” he said. “You have to put in an inferior variety because you need it as a pollinizer.”
A Specialty Crop Research Initiative grant funded a study completed last year by Olsen, Clark Seavert, an OSU College of Agriculture economics professor, and former student, Matt Miller, to learn grower costs for planting one acre of 108 trees spaced 20 by 20 feet. The team undertook the study in collaboration with researchers at the University of California Davis and the University of Arizona.
The study revealed the total cost for planting and painting one acre, estimating $6.60 per tree, is $836.
Seavert said after a three-year establishing period, 108 trees are estimated to only yield 75 pounds of nuts; however, by year 12, in full production, they can yield as many as 2,800 pounds.
“If a grower has 50 to 60 year old trees, I would probably say stay with those,” Seavert said. “But if it was a younger block, and you felt your chances of blight were reasonable, I’d probably replace them.”
When incrementally replacing trees in an established orchard, Olsen suggested removing the target tree and one additional primary crop tree before placing two new pollinizers in their place.
“Taking a Barcelona out with a Daviana or Ennis will create a bigger light bay for the new pollinizers and generate a pollen-producing canopy faster,” he said. “Putting in twice the number of trees is going to be a faster ramp-up to make it worth the investment.”
Hazelnut varieties should be planted post harvest, in late fall or winter when trees are not fully leafed, Olsen said. Typically, he added, pollinizer varieties make up 10 percent of an orchard.
“The long-term goal is to replace the weakest link for a plant that is more robust,” Olsen said. “This is a systematic way to finish the job.”