Title: PLANT GROWTH REGULATORS THAT MODIFY TREE AND FRUIT GROWTH
Submitted to: Proceedings of the Apple Plant Growth Regulator Meeting
Publication Type: Proceedings
Publication Acceptance Date: March 8, 1996
Publication Date: N/A
Interpretive Summary: Plant growth regulators (PGRs) are an important cultural management tool for deciduous tree fruit growers. PGRs are used to reduce crop load, affect shoot growth, improve fruit coloration and internal quality (sugar levels), and to reduce skin and surface disorders such as russet and cracking. PGRs improve the quality and appearance of the apple and enhance eits marketability. Background and practical use information is presented on several PGRs including a synthetic auxin, a cytokinin, and a gibberellin. The information is intended for presentation to apple growers at a comprehensive fruit school covering the use of chemical apple thinners and other growth regulators used in apple culture.
Natural plant growth regulators (PGRs), or hormones, produced by the plant's enzyme system, play a significant role in plant growth and development. The use of four groups of hormone-like chemicals (auxins, cytokinins, gibberellins, and ethylene) are discussed with practical information provided for controlling shoot growth and several fruit disorders. The ethyl ester formulation of NAA applied at 5,000 to 10,000 ppm will reduce sprout growth and control rootsuckers. Ethephon, an ethylene generator, at 300 to 600 ppm applied 2 to 4 weeks after bloom will suppress excess vegetative growth and promote flower bud formation. A mixture of 6-benzylamino purine and gibberellin A4/A7 applied as a foliar spray to young, non-bearing apple trees at 125 to 500 ppm will promote lateral branch development, important in the development of young trees. Conditions for optimum response are provided. The same PGR applied at a low rate on bearing trees can improve the shape and weight of certain appl cultivars such as 'Delicious'. PGRs can also be used to reduce the incidence of several physiological disorders including skin russeting and 'Stayman' apple cracking. Timing and concentration of chemical are important to obtaining good response.