Rupture Strength of Unions of ‘Golden Delicious9 Apple with Mailing 8, Mailing 9, and Vigorous Rootstocks 1

Abstract

As determined on the test bench, 18-year-old ‘Golden Delicious’/Malling (M) 8 and ‘Golden Delicious’/M 9 graft unions fail at about 1/3 the stress required for failure of unions of ‘Golden Delicious’ and vigorous stocks (Malus domestica Borkh.). The stresses at rupture of these unions are of the same order of magnitude as reported by other workers with much younger graft unions. The average wind velocity that the ‘Golden Delici-ous’/M 8 and ‘Golden Delicious’/M 9 unions can withstand is about 10% less than that for the ‘Golden Delicious’/vigorous union, because the ‘Golden Delicious’/vigorous tree is much larger and encounters the greater wind resistance forces. The weakest unions are able to resist forces of winds over 100 km/hr. The mechanical shaking forces required to remove apples from these trees in the “worst case” situation do not exceed the maximum allowable stresses in the graft union. Failure of graft unions is not expected in normal shake-and-catch harvest.