This chapter summarizes the results of previous experiments on the effectiveness of different chemicals used against fire blight (Erwinia amylovora). The common and commercial names, dosage, disease type, host of these chemicals categorized into copper compounds, antibiotics, disinfectants and miscellaneous compounds, are also provided. Botanical extracts tested against Erwinia amylovora are tabulated.
The results of experiments on transmission of Corynebacterium michiganense pv. michiganense showed that the spread of the bacterium by artificially infested seeds varies, but it was confirmed that from artificially infested seeds few diseased plants can be grown. The results depend on the environmental conditions during experimentation and the method of assaying the seedlings. High relative humidity favours the spread of the pathogen. The use of selective media helped the detection ofthe pathogen in seemingly healthy plants. It was proved that host can have population of C. michiganense pv. michiganense in a resident phase. It is assumed that when conditions are favorable the pathogen multiplies and cause disease.
The efficacy of various chemicals as alternatives to antibiotics for the control of fireblight (Erwinia amylovora) on pear trees was tested. The chemicals were applied in two ways. In 1999 and 2000, preselected pear twigs (80-90% bloom stage) were sprayed once either preventively 1 day before inoculation or curatively one or three days after artificial inoculation with pathogen concentrations of 10 5 and 10 7 cfu ml -1 . In 2000 and 2001, whole trees were sprayed 2 and 4 days before artificial inoculation of the flowers. From the incidence of diseased flowers it appeared that Bion (50% benzothiadiazole) at 0.2 g litre -1 H 2 O and Aliette (80% fosetyl-Al) at 2.5 g litre -1 H 2 O showed considerable preventive action by eliciting systemic acquired resistance mostly when they were applied in the whole trees. However the best control was achieved with the antibiotic Agrept (20% streptomycin) at 0.5 g litre -1 H 2 O. This showed both preventive and curative action. Kocide (77% copper hydroxide) at 0.9 g litre -1 H 2 O, Dentamet (citric acid in chelate) at 1.5 ml litre -1 H 2 O, Bactosan (an extract from the plant Pongamia pinnata) at 3.0 g litre -1 H 2 O and Bion at 0.1 g litre -1 H 2 O, showed preventive action, but only when the inoculum concentration was low.
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