Effects of captan on the non-parasitic microflora of apple leaves

Abstract

The microflora of leaves from Worcester Pearmain apple trees sprayed with captan according to normal orchard practice, and from unsprayed trees, was examined by shaking, macerating and spore-fall techniques. Serial dilutions of macerates or wash liquids were incubated on selective media and the major groups of micro-organisms enumerated. Bacteria and yeasts were more numerous than moulds. Total numbers of yeasts and moulds were greatly reduced by captan but this effect was not long-lasting so that by the end of the season the numbers, and proportions of the major groups, on leaves from sprayed and unsprayed trees, were similar. The effect of captan sprayed in one season was not carried over to the next season. No conclusive data were obtained on the toxicity of captan to leaf bacteria. The implications of fungicide usage in relation to the balance of saprophytic and parasitic micro-organisms of the phylloplane are discussed.