Foliar-applied Boron Increases Fruit Set in ‘Barcelona’ Hazelnut

Abstract Boron (B) sprays applied to ‘Barcelona’ hazelnut orchards induced fruit set increases over controls, averaging 23% in 1984 and 17% in 1985. Leaves from B-sprayed trees had higher B contents than controls throughout the season. Amounts of B in young fruits increased two-fold with B sprays, but, unlike leaf values, differences between treated and control fruits disappeared by mid-summer. In the orchards studied, the B content of developing fruits from unsprayed trees was similar even though leaf B content varied widely. Because fruit set increases were obtained in both seasons with B sprays on trees whose leaf values currently are considered excessive, as well as those considered optimal or deficient, guidelines for B recommendation need revision. Boron content in May fruit from unsprayed trees might be universally low for optimum nut development, indicating that annual B sprays may be required. Foliar sprays in April damaged young leaves and shoot tips; thus, delaying sprays until the 2nd week of May is recommended.