The effects of some pesticides on root nodule bacteria and subsequent nodulation

Abstract

The effects of four fungicides and five insecticides on nodule bacteria were compared in laboratory and field trials. The fungicides differed in toxicity with in vitro studies according to concentration and strain of Rhiqobim. The order of toxicity was Ceresan> thiram>captan>chloranil. Thiram formed an unusual ring-type inhibition zone on agar plates which was often associated with a bacteriostatic reaction. However, a high degree of compatibility was shown in field trials with soybeans. The order of toxicity of insecticide emulsions with in vitro studies was dimethoate>lindane>isobenaan >endrin>dieldrin. The dried crystals showed lower toxicity. In the field, crown nodulation in Centrosema was slightly reduced but the overall nodulation was unaffected if the seeds were treated with insecticide before inoculating except with dimethoate. Treating inoculated seed with insecticide emulsion reduced overall nodulation with all insecticides.