Investigation of Relative Toxicity of Some Combined Herbicides on Earthworm (Eisenia fetida L.) Biomass

Frequent and widespread use of herbicides has adverse effects on nontarget species, such as earthworms. Several experiments were performed in Mohaghegh Ardabili University on 2019 to evaluate the relative toxicity of metribuzin, halosulfuron, flumioxazin individually and combination of metribuzin:halosulfuron and metribuzin:flumioxazin on Eisenia fetida. The earthworms biomass was investigated by different concentration of herbicides and sampling time (24 and 48h after treatment). LC50 values of individual herbicides demonstrated that metribuzin and halosulfuron had high effect on earthworms biomass at 24 and 48 h after treatment. Flumioxazin was less toxic than the metribuzin and halosulfuron. The results indicated that the (50:50) and (25:75)% mixture ratios of metribuzin:halosulfuron and metribuzin:flumioxain provided  higher toxicity than the other mixture ratios (100:0) and (0:100)%, respectively. Isobologram demonstrated metribuzin:halosulfuron and metribuzin:flumioxazin followed antagonistic effect meaning that the mixtures retracted the herbicides action in the earthworms relative to a Concentration Addition (CA) reference model.