Chemical suppression of spininess in Geneva 30 apple rootstocks and its residual effects on nursery tree characteristics

Abstract

A proprietary mixture of butralin + fatty alcohols or naphthaleneacetic acid were applied to reduce or prevent spininess in Geneva 30 apple rootstock. Rootstock liners were foliar treated with butralin + fatty alcohols or naphthaleneacetic acid, or hand-cleared. Spine regrowth responses to both compounds, expressed as spine cumulative length, were rate dependent and decreased as the concentration of the compound increased (P<0.003). Before budding, all rates of butralin + fatty alcohols or naphthaleneacetic acid (except naphthaleneacetic acid at 25 mg/L ), or hand-cleared reduced the number of spines and their cumulative length compared with controls. The rootstocks were budded to apple cv. ‘Jonagold’. None of the treatments caused significant spininess recurrence, or stimulated root suckering. All treatments reduced rootstock stem cross-sectional area, except butralin + fatty alcohols at 250 and 750 mg/L in comparison with control rootstock stem cross-sectional area. Budded rootstocks were transplanted into the nursery and grown for an additional year without chemical treatment. No adverse effects of previous treatments on tree characteristics were found, except a significant reduction in tree height caused by naphthaleneacetic acid at 200 mg/L. No differences in quality characteristics between trees grown on chemically or manually deshooted Geneva 30 rootstocks were found.