Regulation of flowering and fruit set of European pear

When established in modern orchard systems, highly vigorous pear trees require intensive management to balance canopy growth and fruiting. Application of plant growth bioregulators can have a profound effect on the development and growth of vegetative and reproductive organs. In pear systems, regulation of excessive vegetative vigor is a prerequisite to early flowering. Gibberellin synthesis inhibitors have been shown to markedly reduce vigor but, depending on the cultivar, may adversely affect return bloom and cropping. The ethylene generating compound 2-chloroethylphosphonic acid (ethephon) is highly florigenic and improved flowering of low productive cultivars. Moreover, applications of ethephon to trees treated with GA inhibitors overcame the deleterious effects of those inhibitors on return bloom. Despite increased bloom, flowering precocity does not necessarily equate to greater fruit set. The ethylene inhibitor, aminoethoxyvinylglycine (AVG), when timed to coincide with the natural ethylene production of fruitlets 7 to 14 days after bloom, markedly increased fruit set. In contrast, several precocious cultivars or highly productive rootstock-scion combinations, require crop load management to ensure fruit size and quality. New post-bloom thinning chemistries, ABA and metamitron, reduce photosynthesis and consistently increased fruit abscission. Finally, a brief discussion of decision support models developed to facilitate apple thinning and/or predict thinner efficacy may be transferrable to pear. Use of new compounds to regulate growth and developmental processes opens exciting new opportunities that may facilitate the profitable management of modern pear orchards.