Ethephon and prohexadione-calcium influence the flowering, early yield, and vegetative growth of young ‘Northern Spy’ apple trees

‘Northern Spy’ apple trees have a relatively long non-fruiting period following planting, which reduces their economic feasibility of production. Previous work supporting the benefits of ethephon (ETH) for enhancing flowering precocity on bearing apple trees was the impetus behind the present study in which ‘Northern Spy’ and ‘Jonagold’ were treated with ETH to determine its effects on flowering, early yield, and vegetative growth. Early summer ETH application significantly increased flowering the year following treatment, with a greater effect from a higher concentration or a second application. Flower clusters per tree on 4th-leaf ‘Northern Spy’/M.9 increased from a mean of 4.0 (1.6 ± 0.4 ln transformed) on control trees to as much as 18.7 (3.0 ± 0.4 ln transformed) following ETH treatment. Increased flowering also translated into significantly greater yield at harvest. Two applications of 1500 mg L−1 ETH applied 5 and 8 weeks after full bloom (WAFB) were particularly effective on three-year-old ‘Northern Spy’/M.9, where fruit yield increased by 2.6 kg tree−1 (1.0 ± 0.4 ln transformed), or ≈2.4 t ha−1. This study supports the use of ETH applications on young ‘Northern Spy’ apple trees in the year prior to expected initial bearing to increase flowering and early fruit production.

► ‘Northern Spy’ apple trees often require 5 years to produce fruit after planting
► We examined the effects of bioregulators on flowering, yield, and vegetative growth
► Two applications of Ethephon increased flowering in a rate responsive manner
► Prohexadione-calcium provided effective control of vegetative shoot growth
► Prohexadione-calcium did not influence flowering or yield components.