INFLUENCE OF CHEMICAL GROWTH REGULATION ON THE HOST SUSCEPTIBILITY OF PEAR TREES FOR FIRE BLIGHT

Host susceptibility of young pear trees for fire blight is largely influenced by the presence of secondary blossoms and by the presence of late regrowth reactions on the trees. These two phenomena are typical for young pear trees between 2 and 10 years old. There is an influence of the pruning system itself on the secondary blossom formation. The use of growth retardants in the post floral period increases the total number of secondary blossoms significantly, as well on Conférence as on Doyenné du Comice. The application of some growth regulators during summer can reduce regrowth tendency but not secondary blossom formation. Some types of secondary blossoms are more influenced by the use of growth regulators than other types. The quantitative results of 4 years of observation are presented for young pear trees of the cultivars Conférence and Doyenné du Comice.