Influence of the Organophosphorus Insecticides Nuvacron and Dipterex on Rhizospherie Microflora of Broad Bean Infested with Wilt and Root Rot Fungi

Abstract

The effect of the organophosphorus insecticide Nuvacron or Dipterex on rhizospherie microflora of broad bean plants infested with Fusarium oxysporum f. fabae or Rhizoctonia solani, wilt and root rot fungi, respectively, was studied. Moreover, influence of these insecticides on wilt and root rot incidence was also included. Soil inoculation with both phytopathogenic fungi proved inhibitory of normal rhizospherie flora. Nuvacron or Dipterex at the two levels applied, initially depressed densities of normal microflora, then counts progressively increased thereafter. The only exception was noted for phosphate dissolvers which showed a vast increase, indicating their activities in the mineralization of these organophosphorus insecticides. Despite the activity of insecticides applied in depressing the densities of Fusarium and Rhizoctonia spp. in rhizosphere only Nuvacron at the levels applied proved being effective in the control of wilt incidence. Unexpectedly, both insecticides significantly increased the spread of root rot disease. It is, therefore, recommended to apply Nuvacron not only for insect control, but also for achieving economic levels of wilt control.

Es wurde der Einfluβ von Nuvacron und Dipterex auf die Mikroflora der Rhizosphäre von Ackerbohne, welche mit Fusarium oxysporum und Rhizoctonia solani infiziert war, untersucht. Diese beiden Krankheitserreger wirkten auf die normale Rhizosphäreflora inhibierend. Insektizidzusatz in zwei Stufen wirkte auf die normale Mikroflora anfänglich depressiv, anschlieβend erhöhten sich die Zahlen. Die Phosphat-lösenden Mikroorganismen zeigten einen starken Anstieg, welcher auf die Mineralisierung der organischen Phosphorverbindungen hinweist. Obwohl die Insektizide auf Fusarium und Rhizoctonia depressiv wirkten, konnten nur mit Nuvacron die Welkeerkrankungen vermindert werden.