EFFECTS OF CHAIN SAW GIRDLING AND ROOTPRUNING OF APPLE TREES

The effects on vegetative growth and fruit yield and quality of two modified girdling techniques using a chain saw were investigated in three studies using the vigorous apple cultivars ‘McIntosh’ and ‘Mutsu’. The first technique, termed “ring girdling,” involved cutting two horizontal half-circle rings 2 cm deep into opposite sides of the trunk with a 4- to 6-cm overlap of each half-circle ring. The rings were vertically spaced 20 cm apart on opposite sides of the trunk. The second technique, termed “guillotine girdling,” involved making two deep, horizontal cuts one-third the radius of the trunk on opposite sides of the trunk. The guillotine cuts were also vertically spaced 20 cm apart. Both techniques reduced trunk cross-sectional area, vegetative growth removed during summer pruning, average shoot length and average number of shoots per tree. When compared to root pruning (60 cm from the trunk), the greatest reduction of vegetative growth was obtained with root pruning, followed by ring girdling and guillotine girdling. Root pruning significantly decreased ‘McIntosh’ yield compared to ring girdled or control trees mainly by reducing fruit size. Ringing successfully reduced vegetative growth and increased ‘Mutsu’ yields whether done during the dormant season or at 2 weeks after full bloom. Fruit drop was reduced by ring and guillotine girdling and root pruning.