Effectiveness of Selected Chemicals in InhibitingPseudomonas syringaepv.tomatoin vitro and in Controlling Bacterial Speck

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Abstract
In laboratory, growth chamber, and field studies, streptomycin sulfate and certain fixed coppers alone and in combination with recommended fungicides (mancozeb and chlorothalonil) were toxic to P. syringae pv. tomato (PST) in vitro and significantly reduced severity of bacterial speck on foliage and fruit of ''Chico II'' tomato [Lycopersicon esculentum] plants. These chemicals also reduced epiphytic populations of PST on field-grown plants. Of 30 fungicides tested in vitro, only the organic S compounds, especially those containing manganese ethylenebisdithiocarbamate (Mn EBDC), were toxic to PST. In vitro tests suggested a synergistic action between EBDC fungicides and several Cu compounds although combined treatments did not always give better disease control than the fixed coppers alone. Mn EBDC compounds (maneb, maneb plus ZnSO4, and mancozeb) alone at field rates were highly toxic to PST in vitro. Mancozeb alone significnatly reduced lesion counts in the greenhouse but gave poor control in the field. Both streptomycin and cupric hydroxide are useful in a preventive control program for bacterial speck on tomato transplants grown in southern Georgia [USA].