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

A proprietary mixture of butralin + fatty alcohols or naphthaleneacetic aci d were applied to reduce or prevent spininess in Geneva 30 apple rootstock. Rootstock liners were foliar treated with butralin + fatty alcohols or nap hthaleneacetic acid, or hand-cleared. Spine regrowth responses to both comp ounds, expressed as spine cumulative length, were rate dependent and decrea sed as the concentration of the compound increased (P<0.003). Before buddin g, 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 w ere budded to apple cv. 'Jonagold'. None of the treatments caused significa nt spininess recurrence, or stimulated root suckering. All treatments reduc ed 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 a n additional year without chemical treatment. No adverse effects of previou s treatments on tree characteristics were found, except a significant reduc tion in tree height caused by naphthaleneacetic acid at 200 mg/L. No differ ences in quality characteristics between trees grown on chemically or manua lly deshooted Geneva 30 rootstocks were found.