Stub length of renewed apple limbs interacts with cultivar and affects the number and quality of replacement limbs

All branches of single-axis apple trees in high-density orchards are subject to limb renewal. Renewal limb management aims to replace overly vigorous and yield inefficient limbs with weaker, balanced limbs of higher yield potential. Recently, producers have adopted the application of long stubs, i.e., 10 cm, when renewing apple limbs despite a dearth of research on the topic. The current multi-year project evaluated the effect of stub length (between 2.5 to 10 cm in 2.5 cm increments) on the number, length and orientation of replacement limbs. The experiment was conducted on 3 rd and 4 th leaf ‘Honeycrisp’, ‘Gala’ and ‘Fuji’ trees on Budagovsky 9 rootstock, trained to tall spindle. We demonstrate a significant, positive relationship between increasing stub length and limb renewal response (expressed as the number of shoots and total vegetative growth per stub) but observed varying levels of the response in relation to scion vigor. Moreover, stub length did not affect the orientation of replacement limbs nor decrease the length of the longest limb on the stub. The data suggest that different stub lengths should be considered on the basis of cultivar and site vigor and not uniformly applied across cultivars.