Pre- and post-plant applications of copper-based compounds to control Erwinia soft rot of calla lilies

Abstract

Erwinia carotovora subsp. carotovora is a plant pathogen responsible for producing soft rots in many vegetable and floricultural crops, particularly calla lilies, Zantedeschia spp. In this study, the efficacy of various copper-based compounds, such as Phyton-27, Champ 2, fixed copper, and analytical copper, was compared under laboratory and greenhouse conditions. Copper-based compounds suppressed bacterial growth at various cupric ion concentrations in vitro, but the efficacy of some products was reduced by the presence of phosphate ions in fertilizer solutions used in commercial greenhouses. Under greenhouse conditions, the compounds were applied as a preplant or a postplant treatment to tubers of calla lilies. Postplant applications were made either as an overhead drench or through subirrigation, and the applications were carried out at different stages of plant development. Preplant application of Champ 2 or Phyton-27 did not reduce the number of diseased plants compared with the controls. In contrast, postplanting applications of Champ 2 or fixed copper were effective in reducing soft rot; however, these two compounds also reduced overall plant growth. Poor root development and reduced plant growth occurred when these products were applied during the early stages of plant development and when the products were applied overhead rather than through subirrigation.