Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 1995
Publication Date: N/A
Interpretive Summary: Excessive vegetative growth can reduce fruiting and fruit quality in apple trees. Methods to control unwanted growth in high density apple orchards are limited due to the loss of effective plant growth regulating chemicals. Root pruning or trunk scoring have been shown to control growth on apple trees in some fruit producing regions. Studies were initiated to evaluate the effect of root pruning, trunk scoring, and a combined treatment over several years on the growth of young apple trees on semi-dwarf rootstock in a high density planting. The combined treatment of root pruning + trunk scoring was generally most effective in reducing tree growth. However, overall results were inconsistent and discouraging in terms of the extent of growth control achieved under the conditions of this study, especially with root pruning. These findings will be useful to fruit specialists and fruit growers in the Appalachian fruit region.
Technical Abstract: Vigorous 'Smoothee Golden Delicious', 'Jonagold', 'Empire', and 'Gala' apple (Malus domestica Borkh.) cultivars on M.7A rootstock planted at close in-row spacing (2.5 m or 1.8 m) were mechanically root-pruned (RP) and/or trunk-scored (TS) annually for 3 to 5 years beginning in the fourth leaf to control excessive growth. Trees were grown in a deep, well-drained, fertile soil and supplied with trickle irrigation. The effect of RP and TS was inconsistent and generally failed to reduce shoot growth or slow canopy spread. No practical advantage was recognized from this technique for young apple trees growing on a fertile site with trickle irrigation. The combination of RP and TS generally reduced growth, and in one year, increased bloom clusters on 'Smoothee Golden Delicious'. RP reduced yield in 'Gala' and TS reduced yield in 'Empire' in one of two years; fruit size was reduced by RP + TS treatments in 'Gala' and 'Empire' in both years. It is suggested that lack of response to RP was due to edaphic factors, abundant moisture, and localized root growth away from the area of root pruning. Proper selection of a rootstock/scion combination and planting distances remain the best known approaches in solving the problems of canopy crowding and excessive vegetative growth in high density plantings.