SPUR PRUNING ‘DELICIOUS’ APPLE FOR IMPROVED SPUR QUALITY AND YIELD

Mature, spur-type apple trees can become spur-bound, a condition characterized by extensive, multiple-bud spurs and limited extension shoot growth (Ferree and Forshey, 1988; Ferree et al., 1990). Young spur-type cultivars on precocious, dwarfing rootstocks can experience a similar condition called “runting”. In both conditions, trees have limited growth and tend to set a heavy crop load, and the resulting fruit are small and poor quality. Two management systems may be used to correct the spur-bound condition: 1) whole-tree renovation pruning (Barritt and Rom, 1987; Elfving et. al. 1990; Ferree et al., 1990; Robinson and Lakso, 1986), or 2) detailed spur pruning (Ferree and Forshey, 1988; Ferree et al., 1990). Whole-tree pruning improved light distribution within the tree canopy (Robinson and Lakso, 1986) and improved spur quality with increased percentage of large fruit (Barritt and Rom, 1987) in some orchards but had no effect on light penetration or fruit color in other orchards (Elfving et al., 1990).

Detailed spur pruning has been done to limit the number of buds developing on a spur complex, to cause further bourse-shoot development, to result in additional shoot development along a limb, and to rejuvenate spurs. Reducing spur bud number may reduce local competition among flower clusters for assimilates and nutrients. Additional bourse-shoot leaf area and shoot leaf area development may enhance fruit growth. Spur rejuvenation would resut from the removal of the oldest spurs and new spurs forming on shoots developed after pruning. In the last half of the season, shoot leaves are important for continued fruit growth (Rom and Ferree, 1984), and younger spurs are of better quality and produce larger fruit than older spurs (Rom and Barritt, 1990).

The objectives of the studies presented herein were to test methods of spur pruning alone and in combination with other treatments to determine if such treatments have potential to improve spur quality, fruit quality, and yield of mature, spur-bound ‘Delicious’ apple trees.