ABSTRACT
The range of plant growth regulating chemicals used by apple producers around the world is unmatched by any other crop. Plant growth regulators are used in the production of nursery trees, to regulate the shape and size of orchard trees, to promote flowering, and to increase and reduce fruit set. The discussion of growth regulator usage in apple and pear production is organized by practice rather than by chemical. There are several reasons for choosing this format, an important one being that some materials are used to achieve very diverse aims. Applied as paint, naphthaleneacetic acid (NAA) prevents the growth of unwanted sprouts and suckers. Producers in many areas use NAA or naphthaleneacetamide, this practice is considered unnecessary in California, the state that produces the most pears in North America. Obviously, it is difficult to generalize about growth regulator practices. The clonal rootstocks so important in modern apple and pear culture are mainly produced by stooling or layering procedures.
