Optimal Training of Apple Trees for High Density Plantings - UKREC
Joseph G. Masabni, Gerald R. Brown (Professor Emeritus), and Dwight Wolfe, Department of Horticulture

Introduction

Kentucky apple growers often have a problem with excessive vegetative growth or vigor, which greatly reduces the production that can be achieved from high density apple plantings. Early production and optimal fruit size on vigorous sites are obtained when photosynthates are balanced properly between flower bud initiation and vegetative growth. Pruning and training are possibly the most important operations performed by growers to maintain the proper balance between flower bud initiation and vegetative growth. Identification of effective pruning and training techniques for vigorous sites is required for continued expansion of apple production in Kentucky. The University of Kentucky College of Agriculture (UK) and the Kentucky State Horticultural Society (KSHS) have made long-term commitments to help meet this need and are cooperating in this ongoing research. The purpose of which is to determine the best training and pruning practices needed to obtain early production and optimal fruit size from trees trained to the slender-spindle or the French vertical-axe system.

Materials and Methods

One hundred-sixty trees of Golden Delicious on M.9 rootstocks were planted in May 1997 in a randomized complete block design consisting of five rows and 32 trees per row. At planting, trunk circumference at 12 in above soil surface averaged 2.4 in and did not vary significantly among rootstocks. A trellis was constructed, and trickle irrigation was installed. Trees were spaced 8 ft apart within rows 16.4 ft apart. Orchard floor management was a 6.5 ft herbicide strip with mowed sod alleyways. Trees were fertilized and sprayed according to local recommendations (1, 2). Beginning in 1998, yield, trunk circumference, and maturity indices such as soluble solids and flesh firmness were measured after harvest.

The trees were trained according to detailed treatment protocols presented in Table 1. Trees began to fill their allotted space in 1999, and leader management was modified to maintain leaders at specified heights (Table 1). Limbs of one tree that overlapped or touched those of adjacent trees were headed back into two-year-old wood.

Results and Discussion

No significant differences were observed between the French vertical-axe and the slender spindle training systems for any of the measured variables. Therefore, all data are presented as the combined values for both systems. No differences among the 4 pruning levels were observed for cumulative yield (1998-2002), yield in 2002, fruit weight, and trunk circumference (Table 2).

Pruning time per tree was not analyzed statistically, thus, no LSD values are presented in Table 3. Even though pruning time per tree appears to be the highest for the heavy pruning level, this difference was not significant to the pruning crew. Pruning time when adjusted per lb of fruit did not differ among all 4 treatments (Table 3). Total pruning and training periods were 14 weeks in 1997, 12 weeks in 1998, 18 weeks in 1999, 4 weeks in 2000, 4 weeks in 2001, and 1 week in 2002.

This planting has been regularly used as a demonstration for visiting apple growers, Extension personnel, and research scientists. The data collected in these trials have helped establish baseline economics and production methods for the various orchard system/rootstock combinations that can be utilized by Kentucky fruit growers.

Literature Cited

1. G.R. Brown, R.T. Jones, J.G. Strang, L.A. Lester, J.R. Hartman, D.E. Hershman, R.T. Bessin. 2002 Commercial Tree Fruit Spray Guide. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-98.

2. Midwest Tree Fruit Handbook. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-93.

Table 1. Details of pruning and training treatments of the 1997 apple training study at UKREC, Princeton, KY.