NATURAL OR CHEMICAL GROWTH REGULATION IN PEAR

Since the growth regulator chlormequat chloride (CCC) was removed in 1998, pear growing in intensive training systems has become more difficult and fruit growers are looking for alternative ways to control the vegetative growth of trees.
First of all, adaptations in the training and pruning methods were made; there is a strong preference for single row systems and the training systems mainly concentrate on central leader, trellis or intensive V system. A pruning system which can keep vegetative growth reactions under control becomes important. As long as CCC was available as chemical growth regulator, everybody was able to prune pear trees and all 2-year-old branches were pruned back into the flowerbuds for optimal fruitset. Today the effect of each pruning intervention on vegetative growth reaction of the pear trees should be considered and growth stimulating pruning interventions should be avoided. Some of these growth stimulating pruning measures will be discussed. There is also a change in rootstock choice from the vigorous ‘Quince A’ rootstock to ‘Quince Adams’ and the dwarfing ‘Quince C’ rootstock. Root pruning in different intensities or girdling with a chainsaw are made with the aim to reduce vegetative growth on the trees and to improve crop regularity. The results of these measures are difficult to predict and there can be an important effect on fruit quality at harvest or during storage. In the meantime, there is the development of Prohexadione-Ca (ProCa) as a new growth regulator for apple and pear trees. On pear the growth reduction is different for each cultivar; the growth reduction is strong for ‘Doyenné du Comice’, medium for ‘Conference’ and very weak for ‘Beurré Alexander Lucas’. The general application of this compound on pear is in discussion because there can be a negative influence on the return bloom. This negative effect on flower bud formation is strongly dose dependent. Results of 3 consecutive years of application of ProCa at different doses on the pear cultivars Conference and Doyenné du Comice will be discussed in this paper. It becomes clear that ProCa will never be able to replace CCC as growth regulator and that a better understanding of the natural growth pattern of a pear tree will be more important in the future. Within the guidelines for integrated fruit production (IFP) chemical growth regulation is not allowed and many discussions were held in different European countries recently on this topic. It is clear that preference should be given to natural ways for vegetative growth control and an overall use of chemical growth regulators is not indicated. On the other hand it is necessary to bring a solution for the pear trees that are completely out of balance when the crop is missing. For this reason the exact possibilities of chemical growth regulation should be known.