Studies on the control of fireblight on pear trees in South-Eastern Romania

Fireblight, produced by the bacteria Erwinia amylovora (Burill.) Winslow, is currently the most serious disease of pome fruits species inducing quantitative and qualitative high crop losses during certain years and in regions favorable to attack. The profilaxy of this disease has a more important role compared with other diseases, due to its great speed propagation and its unusual virulency. Thus, in the framework of the Fruit Research Station Constanta-Romania, a strategic program for control, comprising a series of measures and actions for limiting the spread of disease was elaborated. There should also be included treatments of efficacious products, applicable at the timings when the plant host has the maximum susceptibility of infection. The efficacy of these products in the profilaxy of fireblight was tested in vitro and in vivo. The test in vitro of the 14 products was conducted in petri dishes with nutritive medium, being inoculated with a 24 h culture of Erwinia amylovora. The products which impeded the bacteria development on the surface more than 5 mm around the disk were considered efficacious in the profilaxy of the fireblight. In this category were products with Cu and antibiotics. These products were tested on trees of the Passe - Crassane varieties (known to be very susceptible to attack). The results were reported in terms of frequency and intensity of attack/variant, the last one calculated on the USDA scale. The results showed that the products, which prevent fireblight development, are limited in efficacy and number. Moreover, the efficacy of a product depends not only on its properties but also on the time of application, climatic conditions, application technique, susceptibility of variety, etc.