Effect of pendimethalin and imazethapyr on the development of microorganisms in vitro and at field conditions

Abstract

Abstract The herbicides may have adverse effects on the soil microorganism. The aim of the study was to investigate the effects of herbicides pendimethalin and imazethapyr and mixture thereof on the growth of Rhizobium leguminosarum M-1, Rhizobium leguminosarum LSMR-1 and Strenotrophomonas maltophilia RB-3 in vitro and on soil microflora (bacteria, fungi and actinomycetes) at field conditions. The tolerance of Rhizobium and Stenotrophomonas to pendimethalin at 180–1980 mg/L and imazethapyr at 26–200 mg/L and mixtures thereof in nutrient media was tested. The tolerance for pendimethalin was higher than for imazethapyr. In field experiments with mungbean, the effects of pendimethalin alone as well as in mixture with imazethaypr at 0.45 and 0.75 kg ha−1 (applied as pre-emergence) and imazethapyr at 50 and 75 g ha−1 (applied at 15 and 25 days after sowing) in the rainy and summer season were tested. Pendimethalin and its mixture with imazethapyr did not influence the population of fungi and actinomycetes in rhizosphere (0–10 cm soil depth) at 35 days after sowing and at harvest. Imazethapyr treatments recorded inhibitory effects on bacterial population in rhizosphere at 35 days after sowing but no adverse effect was observed at harvest. Pendimethalin alone and in mixture with imazethapyr were found safe to investigated microorganism groups.