Oregon State University’s hazelnut breeding program spent decades developing cultivars resistant to eastern filbert blight, a fungus that threatened Oregon’s industry after it took hold in the 1970s. Starting about six years ago, Jeffersons have been widely planted to replace diseased trees and in new orchards, expanding total hazelnut acreage, according to Grant Allen of the Nut Grower’s Society and Hazelnut Industry Office in Aurora.