Effects of Thinning Time on Yield, Fruit Size, and Return Bloom of ‘York’ and ‘Golden Delicious’ Apple Trees

Abstract In 1994, heavily flowering ‘York’ apple trees (Malus Xdomestica Borkh.) selected for 80% or more of spurs flowering were hand thinned to a crop density (CD) of approximately 7 fruit/cm2 trunk cross-sectional area (FCSA) at bloom, petal fall, or up to 61 days after bloom. This thinning did not result in an adequate return bloom even for a partial crop in 1995. Heavily flowering ‘Golden Delicious’/M.26 trees were treated similarly in 1994 and responded with more flowering in 1995 than ‘York’/M.26 trees. In 1995, a different group of heavily flowering ‘York’/M.26 trees were hand thinned to a CD of 3 to 5 FCSA at bloom and at 7 day intervals up to 35 days AFB. Thinning at bloom or 7 days after full bloom (4.5 mmfruit diameter) resulted in much greater return bloom in 1996 than any other thinning. In 1995, ‘Golden Delicious’/M.26 trees were treated similarly to ‘York’/M.26 and responded similarly in 1996 with the greatest return bloom resulting from bloom thinning with somewhat less return bloom from thinning 7 or 14 days after full bloom and dramatically reduced return bloom.