Sensitivity of oilseed rape (Brassica napus L.) to soil residues of imazethapyr herbicide

Imazethapyr is one of imidazolinone herbicides that may leave residual activity in the soil for extended periods causing injury and yield reduction of susceptible crops in rotation. An experiment was conducted in order to study the sensitivity of oilseed rape (Brassica napus L.) to imazethapyr soil residues. Experimental type was completely randomized design with three replications. Treatments included Imazethapyr simulated concentrations residuals in soil (0.002, 0.004, 0.008, 0.012, 0.02 and 0.04 mg. kg-1soil). Shoot and root biomass production was measured 30 days after emergence. Oilseed rape responses to imazethapyr residues was fitted with sigmoidal 3 and 4 parametric equations to the root and shoot biomass data as a function of the herbicide residue concentrations and was used to calculate the doses for 50% inhibition of root and shoot growth (ED50). Results showed that the oilseed rape shoot and root dry matter were significantly affected by increasing imazethapyr soil residue (p<0.01). This reduction in root dry matter was severe than shoot dry matter, where root ED50 (0.0019 mg.kg-1soil) was less than shoot dry matter (0.0025 mg.kg-1soil). Considering the high sensitivity of oilseed rape to imazatepara residues, attention is needed to provide oilseed rape cultivation in fields with a history of imazateaper application.