Chemical Control of Spininess with Apple Rootstocks

Abstract

Spininess is characteristic of many Malus species, especially American crabapple and Malus baccata L. Spininess often is present on rooted stoolshoots of commercial apple rootstocks (M.9, M.26, MM.111, and MM.106) and some rootstocks from the Geneva Breeding Program. This undesirable characteristic makes liner production costly and laborious. It is estimated that the cost of manual removal of spines amounts to ≈20% to 25% of total production costs. To counteract spininess, the stoolshoots of excessive spiny rootstock selections [74R5M9-760 (T/1), 74R5M9-707 (T/2), and 75R5M9BR-521 (T/3)] were chemically treated while growing at stoolbed. Chemical treatments consisted of single sprays of nontranslocated growth regulators Tamex (a.i. butralin) or Tamex AG (a.i. butralin + fatty alcohols C8- C10), and commercial auxin formulation (Tre-Hold A-112). Tamex AG and A-112 at applied rates brought about some phytotoxicity effects while Tamex did not. On average, Tamex application (1000, 2000, and 4000 ppm) reduced spine number to ≈80%, 68%, and 84% of T/1, T/2, and T/3 control plants, respectively. However, Tamex at 4000 ppm reduced the number of spines to 57% and 60% of control T/2 and T/3 plants, respectively, without any detrimental side effects. A parallel greenhouse experiment is being performed using commercial M.26 and Geneva 30 apple rootstocks.