GA and Ethephon Have Limited Effect on Secondary Bloom in ‘Bartlett’ Pear

Abstract

GA₃, GA₄₊₇ + BA or ethephon was applied in the spring or summer 1997, 1998 and 1999 to reduce secondary bloom in ‘Bartlett’ pear (Pyrus communis L.). Reduction of secondary bloom could reduce associated fire blight (Erwinia amylovora [Burrill] Winslow et al.) infections. The number of Type I secondary bloom was reduced by 400 mg·L⁻¹ GA₃, applied between 33 and 97 DAFB, dates which also reduced normal bloom and fruit set. Summer timings of GA₃ at 100 mg·L⁻¹ or GA₄₊₇ + BA at 200 mg·L⁻¹ reduced the number of Type V secondary bloom with no difference between GA₃ and GA₄₊₇. Ethephon applied one month after harvest in 1997 and 1998 reduced Type Vs in 1998 but not in 1999. Ethephon also reduced fruit set in 1999. Use of GAs to reduce Type V secondary bloom in a fire blight management program may be possible.

Key Words:

• Pyrus communis
• rat-tail bloom
• gibberellins
• flowering
• fruit set
• fire blight
• Erwinia amylovora
• GA₄₊₇