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Effect of Copper Bactericides on Copper-Resistant and -Sensitive Strains of Pseudomonas syringae pv. syringae

April 1998 , Volume 82 , Number  4
Pages  397 - 406

Heather J. Scheck , Former Graduate Student , and Jay W. Pscheidt , Associate Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902

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Accepted for publication 19 December 1997.

Fourteen formulations of copper-based bactericides were evaluated for their efficacy in reducing populations of copper-resistant and -sensitive strains of Pseudomonas syringae pv. syringae growing on tissue-cultured lilac and of copper-sensitive strains of this pathogen on field-grown lilac. The amount of free cupric ions (Cu2+) in solution was the only predictor of formulation efficacy, but this variable could not be estimated from the metallic copper content of the product. Relative to nontreated controls, all copper-based bactericides reduced the population size of copper-sensitive strains by 50%, but only cupric hydroxide mixed with mancozeb or ferric chloride reduced the population size of copper-resistant strains by an equivalent amount. Several noncopper bactericides, including streptomycin-sulfate, caused only small reductions in bacterial populations on tissue-cultured or field-grown lilacs. In the field, two applications of cupric hydroxide (wettable powder) when plant growth stages were at dormant (mid-February) and delayed dormant (late February) provided better control than either one or no treatments.

© 1998 The American Phytopathological Society