Old and new kids on the orchard block: a review of defoliation as a canopy management strategy to improve the red colouration of apples

Retailers demand high-quality apples with vibrant red blush, a trait shaped by tree genetics and environmental factors. Canopy management enables orchardists to optimize the apple microclimate by enhancing exposure to cooler night temperatures and increased ultra-violet and visible light, which promotes red anthocyanin pigment accumulation. While much is known about the role of light and temperature, pre-harvest canopy management strategies require optimization based on location and scion-rootstock combinations. This review compares how summer pruning and fall defoliation via chemical, manual or pneumatic methods, manipulates canopy structure. We discuss optimal timing and application of defoliation treatments, typically in the early fall for maximum fruit exposure. Finally, we highlight research gaps, such as identifying how late season defoliation influences apple storage and bud hardiness, that need to be addressed to help guide the adoption of management strategies by orchardists.