Effect of herbicides on Rhizobacteria density in experimental fields and on Bacterial Strains Survival In-Vitro

We evaluated six selected commercial herbicides commonly used for the control of several weeds in Daloa (Côte d’Ivoire), for their toxicity against density of rhizobacteria in experimental field conditions, and against survival of symbiotic and associative bacteria in vitro. Herbicide applied under dose recommended and reduced to 50 %, decreased the soil bacteria density from 2,83.1010 to 3,7.106 CFUg-1soil, respectively for control soil and spots treated. The loss of rhizobacterial population was estimated to be more than 36 % (5,75.103 CFUg-1soil) after a week and a month of herbicides application. All six herbicides have shown differences concentrations in their toxicities on bacterial strains survival in culture medium. The inhibitory effects with more than 80 % were observed at concentrations within the range of at 13,5-27 µl/ml, 13,5-27 µl/ml, 27-54 µl/ml, 1,7-3,4 µl/ml respectively for Rapid max, Roundup, Bibana and Herbo select. But, Killer and Detru-herb were less toxic (40 %) even at label concentration and were considered suitable for field application.