Influence of Pruning and Urea Sprays on Growth and Fruiting of Spur-bound ‘Delicious’ Apple Trees

Abstract

Abstract Spur quality and leaf nutritional levels were determined in various canopy sections of mature spur-bound ‘Delicious’-type apple (Malus domestica Borkh.) trees and then various pruning and foliar urea treatments were applied to alter growth and improve fruit size. Fruit size declined from the top to the bottom of the canopy of mature spur-bound ‘Starkrimson Delicious’ trees with a similar pattern in the following criteria: leaf area/spur, spur specific leaf weight, and spur bud diameter. Spur leaf area was higher in the top center and east sections than in the top south. Spur bud diameter in the bottom third of the canopy was highest in the north and east sections, lowest in the central section, and intermediate in the south and west sections. Concentrations of leaf Mn, Zn, B, Al, and Na tended to increase from the top to the bottom of the canopy. Four urea sprays (6 g urea/liter) during the cell division period of fruit growth had little influence on spur quality, but fruit weight was increased 3 successive years. Spur pruning of 25-year-old ‘Starkrimson Delicious’ trees was not sufficient to increase shoot growth or improve spur quality, but heading back into 2-year-old wood plus spur pruning increased shoot number by 38%. Spur and heading-back pruning increased the number of shoots and total shoot leaf area of 13-year-old ‘Red Chief Delicious’ trees, and the combination of both pruning types led to the greatest increase. Heading-back of the younger trees increased leaf area of both shoots and spurs and spur pruning also increased leaf area/spur. Heading-back pruning increased average fruit weight, and the increase was positively correlated with total leaf area, shoot leaf area, and number of shoot leaves/mm of branch circumference.