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

Abstract

were held in the same chambers for an Conlin, K. C., and McCarter, S. M. 1983. Effectiveness of selected chemicals in inhibiting additional 10-12 days to allow symptom Pseudomonas syringae pv. tomato in vitro and in controlling bacterial speck. Plant Disease 67: development. Disease severity was replicates were used. to Pseudomonas syringae pv. tomato (PST) in vitro and significantly reduced severity of bacterial Efficatiof Fous cheatmend speck on foliage and fruit of Chico III tomato plants. These chemicals also reduced epiphytic populations of PST on field-grown plants. Of 30 fungicides tested in vitro, only the organic sulfur involving four bactericides and two compounds, especially those containing manganese ethylenebisdithiocarbamate (Mn EBDC), were fungicides alone and in combination were toxic to PST. In vitro tests suggested a synergistic action between EBDC fungicides and several evaluated (Table 1). The bactericides and copper compounds although combined treatments did not always give better disease control than rates per liter were cupric hydroxide the fixed coppers alone. Mn EBDC compounds (maneb, maneb plus ZnSO4, and mancozeb) alone (Kocide 101, 2.4 and 4.8 g), streptomycin at field rates were highly toxic to PST in vitro. Mancozeb alone significantly reduced lesion counts sulfate (Agri-Mycin 17, 1.2 g), copper in the greenhouse but gave poor control in the field. Our results suggest that both streptomycin and ammonium carbonate (Copper-Count- cupric hydroxide are useful in a preventive control program for bacterial speck on tomato N, 5.0 ml), and sulfur (50%)-copper transplants grown in southern Georgia. (4.4%) (Top Cop, 5.0 ml). The fungicides and rates per liter were mancozeb (Manzate 200, 2.4 g) and chlorothalonil Bacterial speck of tomato (Lycopersicon copper compounds were effective in some (Bravo 6F or Bravo 500, 2.5 ml). The esculentum Mill.) caused by Pseudomonas tests (12,14,26) but not others (4,13). rates used are those recommended for syringae pv. tomato (Okabe) Young et al Because of the limited and conflicting field use. (hereafter referred to as PST) has been a information available on chemical Effect of interval between chemical threat to the southern transplant industry efficacy, we conducted laboratory, application and inoculation on chemical since 1978, when the disease resulted in greenhouse, and field tests from 1979 to efficacy. Cupric hydroxide, cupric rejection of 160 ha of tomato transplants 1982 to evaluate various bactericide and hydroxide plus mancozeb, cupric hydrox- by the Georgia Department of Agriculture. bactericide plus fungicide combinations ide plus chlorothalonil, streptomycin Bacterial speck also occurred widely for their inhibition of PST in vitro and plus mancozeb, and streptomycin plus throughout the eastern and midwestern control of bacterial speck. chlorothalonil at rates used in earlier tomato-producing areas of the United studies were sprayed to cover all surfaces